Conventional inspection access methods such as Under Bridge Inspection Units (UBIU) or aerial lifts may have limitations of reaching all required Nonredundant Steel Tension Members (NSTM) on a structure. These limitations could include the structures geometry, location, and/or allowable loading. The Triborough Bridge and Tunnel Authority / MTA Bridges and Tunnels (MTA BT) flagship structure, the Robert F. Kennedy (RFK) Bridge is a major, complex group of bridge and ramp structures that connects the boroughs of the Bronx, Manhattan, and Queens in New York City. Since the 1990s, the RFK Bridge has been inspected by either rigging systems or using ladders on a rigid work platform which was installed between the anchorages and used on numerous rehabilitation contracts. Following completion of the rehabilitation work, the platforms were removed. Then the question of How would the inspection intensity requirements of 100% hands‑on inspection of all NSTMs be met, arose. Following award of the first post platform contract, rope access methods were utilized to inspect the underside of the RFK Bridge suspended spans which span over parks, the East River, and multisport turf fields. In addition to the RFK (Suspension) Bridge, rope access have been used on other of MTA BTs RFK (Lift Span Towers), Verrazzano‑Narrows, Throgs Neck, Bronx‑Whitestone, and Henry Hudson Bridges (Steel Arch). Additionally, SIE and HNTB personnel have used rope access on other long span structures throughout the US East coast including various bridges, suspender ropes, various buildings, and the Walkway Over the Hudson which is the worlds longest elevated pedestrian bridge. Rope access meets and/or exceeds Occupational Safety and health Administration (OSHA) 1926 Subpart M Fall Protection. This paper will summarize the training, methods and procedures associated with rope access methods for various structure types including suspension and cantilever bridges.

Japanese road bridges must be visually inspected at close range in accordance with the Guidelines for Periodic Inspection of Road Bridges issued by the Ministry of Land, Infrastructure, Transport, and Tourism. The same applies to long‑span bridges such as suspension bridges, but these bridges have components such as main cables and suspender ropes that are not found on truss members and box girders, and are located at high elevations over the sea, making many components and points difficult to access. The upper side of the main cables on suspension bridges can be walked on, but the undersides are not visible, so maintenance vehicle for cable (MVC) are installed on the main cables for inspection in the Honshu‑Shikoku bridges. Cable inspection using MVC has the advantage that the entire circumference of the main cable can be inspected safely and reliably. However, the installation of an MVC requires a crane and traffic control on the traffic lanes. These are also required to move between spans, so it is necessary to install and move several times to inspect a single suspension bridge. This costs a lot of money each time. The work also requires traffic control, which is a problem for the safety of the workers and for the traffic. Since the MVC is narrow, the number of passengers is limited, which means that inspections take a long time. To overcome these problems, the development of a prototype of a new inspection system to replace the current close visual inspection was started. The completed prototype is a piece of equipment with cameras that can provide an entire circumference view of the main cable. It is light weight enough to be easily carried and operated by two people. This allows the cables to be fully inspected without the need for cranes or complicated traffic control. The prototype was evaluated by carrying out an in‑situ tests on some suspension bridge to check the performance of the device in terms of man‑powered installation, operation and fall protection. As a result, the prospect of a low‑cost and safe inspection system to replace MVCs has been raised. Future plans include improving on the problems identified during the actual bridge tests and developing a more efficient device for inspecting the outside of the main cables, which are difficult to access at close range.

The Tamar Bridge is a suspension bridge in the south‑west region of the United Kingdom and was opened to traffic in 1961. It forms a vital transport link carrying the A38 trunk road over the River Tamar between the city of Plymouth and the town of Saltash. The bridge was designed and built as a conventional suspension bridge, and has an overall suspended length of 642 metres and main span of 335 metres. The bridge underwent a major rejuvenation between 1999 and 2001 when it was both strengthened and widened while remaining open to live traffic, during which additional cantilever lanes were added, the deck was replaced with an orthotropic steel deck and additional stay cables were added to supplement the original suspension system. The rockers (sometimes called pendles or truss end links) supporting the ends of the steel trusses at the main towers and side towers have, in some specific locations, been exhibiting vertical movement in the articulation pins and showing evidence of fretting corrosion. The observations have been recorded in annual inspections since around 2011 and these movements have gradually been increasing to the point where intervention was deemed necessary. Without intervention it was possible that the wear and movement could increase more quickly, and that the unwanted movement could have an adverse effect on adjacent structural members as well as the expansion joints in the bridge deck. Preliminary investigations into replacement of the affected rockers concluded that it would prove very difficult and very expensive, up to 10M. The scheme would be very complex, requiring significant temporary works, as well as having a significant impact on traffic due to full or partial bridge closures and long term traffic weight restrictions. This paper presents the rockers remedials scheme in detail and explains how the project has developed and evolved over a number of years leading to a very cost effective repair solution that minimized the risks to the bridge structure, reduced the financial impact on the organization, prevented significant delays for bridge users, and associated financial burden on local and regional economy.

When opened in 1981 the Humber Bridge was the worlds longest span suspension bridge, with a main span of 4,626ft. The bridge is owned and operated by the Humber Bridge Board (HBB). The bridge was designed with unusual A‑Frame rocker bearings to support the end of the deck at the towers and anchorages, whilst allowing large movements under traffic, temperature and wind loading. They keep the ends of the deck aligned at the towers to maintain a safe and even road surface across the expansion joint that spans between the main and side span deck boxes. During a special post storm inspection in 2020, the A‑Frames at the south tower were found to have significant crack defects. Acting as both client and contractor, HBB appointed a team of specialists to perform a series of high priority Stage 1 inspections, structural health monitoring, testing, and steelwork repairs. Information generated by the Stage 1 investigation and repairs informed the design of Stage 2 rocker bearing replacement steelwork installed firstly at the south tower, then at the north tower. The deck box shape is complex with sloping webs at the sides, inclined end diaphragms, and longitudinal slope. This made it difficult to devise a solution that could accommodate large longitudinal movement and rotation and be installed with the minimum of strengthening and minimum disruption to traffic. New hatches were also needed to facilitate safe access into the end of the deck box to install the Stage 2 steelwork internal strengthening and improve future access for inspection and maintenance crews. The Stage 2 design allowed installation of all steelwork while traffic continued to use the bridge, which kept the duration of the bridge closure required for load transfer to an absolute minimum. Load transfer to new Stage 2 steelwork was successfully achieved at both towers in less than 4 hours, and involved jacking load into the new steelwork, cutting through the old rocker bearings to take them out of service, and finally bolting anti‑uplift steelwork in place. The project was successfully completed with minimal disruption to bridge users. The Stage 2 replacement steelwork has performed well since 2020 and is soon to be replaced with permanent Stage 3 rocker bearings and wind shoes.

The structural integrity of cable‑supported bridges relies heavily on factors such as cable design, proper tensioning at construction, and ongoing maintenance. Over the past decade, numerous cable‑supported bridges have encountered varying degrees of issues stemming from factors like aging, inadequate tensioning procedures, heavy traffic loads, suboptimal maintenance practices, exposure to accidents or extreme events. Despite these challenges, these structures often manage to endure due to redundancy or alternative load‑bearing pathways integrated into their design. For instance, the 50‑year‑old 1st Bosporus Bridge experienced a loss of hanger cable following strong winds, which was identified through visual inspection. Anomalies in bridge monitoring data can also serve as indicators of such losses. Typically, only specific cables within a cable‑supported bridge monitoring system are actively monitored. This is achieved through a combination of sensors including pin load cells at connections, accelerometers on exposed cables, cameras, thermocouples, and strain gauges. The conditions of non‑monitored cables are usually inferred from the analysis of data from adjacent cable sensors. The primary aim of this study is to establish a methodology for detecting anomalies in structural responses following extreme events by developing a digital twin with help of monitoring system, inspection records and risk analysis of extreme events thru structural analysis. Therefore, it is crucial to distinguish between temporary fluctuations in cable measurements caused by seasonal temperature changes, regular winds, and expected traffic patterns, and permanent changes resulting from extreme events. Additionally, its essential to consider that a permanent offset in measurement may also occur due to sensor loss following an extreme event. The paper will delve into the development of tools to create a filtering system capable of discerning whether a change in measurement is attributable to a genuine extreme event or not. The significance of redundancy in the layout of monitoring sensors will also be examined.

The safety and resiliency of the mobility network heavily depend on the structural health of transport infrastructure, with bridges often being the bottleneck of the network. Current structural health monitoring methods are significantly limited by the lack of seamless integration between infrastructure sensor/monitoring data, structural modeling, and decision‑making. Stand‑alone data‑driven structural modeling of cable supported bridges based on sensor data often falls short as they do not leverage physics‑based predictive modeling to correlate local defects to the global health state of the structure. Furthermore, physics‑based structural modeling such as advanced Finite Element Analysis (FEA) often face challenges in scalability, computational intensity, and adaptability to real‑time scenarios. To address this, we propose a paradigm shift through the adoption of a Structural Digital Twin (SDT) framework, leveraging the cutting‑edge capabilities of Physics‑Informed Neural Networks (PINNs). This cyber‑physical system represents a quantum leap in structural health monitoring, enabling real‑time prediction of structural responses and facilitating a closed‑loop, computationally efficient solution that evolves in tandem with the structure it mirrors. Our proposed SDT framework is built on the harmonious integration of physics‑based models, governed by the differential equations that describe structural behavior, and data‑driven models that are continually refined using sensor data. This pioneering method overcomes the limitations of independent computational models, improving the precision of predictions and the speed of convergence, thereby transforming infrastructure management. The key feature of our methodology is its dynamic adaptability, ensuring that the SDT consistently mirrors the physical structure throughout its lifespan. By merging sensor data, structural modeling, and predictive analytics, the SDT provides infrastructure owners with crucial insight into potential risks arising from various factors such as heavy vehicle traffic, extreme loadings induced by climate changes, or the aging of the infrastructure. In our presentation, we will highlight the transformative potential of the SDT as a cutting‑edge tool for managing cable‑supported bridges. Through various case studies, we will demonstrate the effectiveness of our model in conducting real‑time structural simulations. By integrating sensor data, our model creates a dynamic, continuously updating digital counterpart that not only forecasts potential issues but also guides proactive maintenance strategies.

Data plays a pivotal role throughout the life cycle of infrastructure projects. A pilot study was conducted on a major suspension bridge in Canada to demonstrate the viability and benefits of developing a digital twin and the opportunities of incorporating a range of data enabled approaches successfully deployed on major international cable supported bridges. A Data Exchange platform was developed and deployed that allowed for prototype inspection and maintenance decision support tools, integrating data management and processing and aligned with client and industry data standards. By consolidating site inspection data and asset information, a comprehensive database was established linked to a Building Information Model (BIM) bridge model and web portal facilitating direct model interrogation. The prototype enabled operators to access critical information such as defect impact classes, risk prioritization numbers, and demand values, informing targeted inspections, maintenance schedules, and operational decisions. Spatial analysis facilitated access to load rating and Weighted Average Defect Impact Scores, that could inform the development of future strengthening and rehabilitation works. The paper discusses how to integrate successful features from other cable‑supported bridges the authors have worked on, such as the Queensferry Crossing, Forth Road Bridge, resund Bridge, and Source of the Nile Bridge. For example, leveraging the real‑time monitoring success of the Queensferry Crossing, the system could deploy sensors for continuous data collection. Refined Risk assessment tools could then be used to prioritise investigations, interventions and repair and strengthening works, similar to the approach used for the Forth Road Bridge. Using data enabled inspection methods ensures that data provided by the model reflects the current condition of the bridge as well as informing life cycle cost analysis. Experience is drawn from the resund Bridge to support the service life extension of that bridge that would also greatly enhance the usefulness of a data enabled digital twin for major cable supported bridges.

The Sunshine Skyway Bridge, inaugurated in 1987, was born out of necessity following a tragic vessel collision that destroyed the southbound main span, killing 35 people. Conceived by the accomplished French engineer, Jean M. Mueller, this iconic bridge boasts a 366 m cable‑stayed main span, complemented by a 1,219 m main unit featuring 11 spans employing a combination of cable‑stayed box girder and balanced cantile‑ver post‑tensioned concrete box girder components for the back spans. Acknowledging the significant milestone of the bridge reaching its 37th year, the Florida Department of Transportation is actively engaged in intensive efforts to extend the service life of the bridge. This paper delineates the innovative Data‑Driven Preventive Maintenance and Service Life Extension approach currently being applied to the Sunshine Skyway Bridge. Spearheaded by TYLin, the approach integrates structural monitoring employing nearly 100 sensors, encompassing conventional structural health monitoring (SHM) sensors combined with custom‑built sensors designed to cater specifically to the distinctive monitoring requirements of this structure. Concurrently, a finite element model is under development to precisely represent the as‑built structure. This model will be fine‑tuned with sensor data, culminating in the creation of a comprehensive digital twin of the bridge, which is poised to enhance comprehension of the bridges behavior and furnish crucial data for gauging the remaining service life of critical components such as stay cables and stay cable dampers. In tandem with monitoring and modeling, the data procured from sensors undergoes advanced post‑processing techniques using Big Data analytics. Currently, this data is used to train a machine learning model, enabling real‑time prediction of structural parameters. This capability will facilitate the instantaneous identification of any parameter deviating from the normal range, thereby enhancing the bridges overall safety and performance.

The San Francisco Oakland Bay Bridge, also known simply as the Bay Bridge, is one of the most iconic suspension bridges on the west coast of the United States. Its western spans connect downtown San Francisco to Yerba Buena Island, making it a vital transportation link in the San Francisco Bay Area. Constructed in 1936, this historic structure has undergone significant modifications over its lifetime. Notably, the fixed railway tracks were replaced with a standard roadway on the lower deck in the 1960s. Additionally, a comprehensive seismic rehabilitation was carried out following the 1989 Loma Prieta earthquake, which involved strengthening the truss elements, the deck system, riveted connections, and the addition of utilities and maintenance equipment. In recent years, the need arose to create a pedestrian and cyclist pathway to provide alternative transportation options for users. To meet the requirements set by the Federal Highway Administration (FHWA), an assessment of the load‑bearing capacity of the bridges western span was necessary to evaluate its current condition after 83 years of service. This analysis also aimed to determine the bridges ability to withstand the additional loads from the proposed multifunctional pathway. The evaluation of the load‑bearing capacity for the 3 kilometers of suspended spans was conducted using the Load and Resistance Factor Rating (LRFR) method specified by the American Association of State Highway and Transportation Officials (AASHTO). These complex analyses accounted for the structural modifications made since 1936, including adjustments to live loads and seismic rehabilitation. Thanks to these studies, the engineers of Arup in collaboration with Caltrans BATA were able to ascertain the actual capacity and to design the strengthening required of this unique and essential structure which plays a crucial role in the economy of the San Francisco Bay Area.

This presentation will focus on the comprehensive restoration of the 100‑year old Wurts St. suspension bridge in Kingston, NY. Because of the bridges' age and condition, numerous complex construction operations were required to repair primary steel components of the main cable system, including the installation of a supplemental anchorage system and replacement of all 114 suspender ropes. Innovative methods were employed during the deck replacement operation to monitor dead load removal and the corresponding stresses in the stiffening truss and stability of the suspension system. This project also included the replacement of the hanger links between the continuous stiffening trusses and towers, all 120 bottom chord gusset plates of the stiffening truss, as well as numerous steel repairs to the stiffening truss, floor system and towers. Upgrades were made to the pedestrian and vehicular railing systems to meet accessibility standards and improve safety. Decorative lighting was installed on the cables and towers using state‑of‑the‑art control systems to allow fully remote access and programming. This same control system is being used to allow remote monitoring of the anchorage dehumidification system which was installed to prevent further deterioration of the existing eyebars. The goal of this project is to make the bridge safe for pedestrian and vehicular traffic, while preserving historic features important to the surrounding communities for decades to come.

New long‑span bridges are being built using the design concepts presented in SHRP2 R19A (Bridges for Service Life Beyond 100 Years: Innovative Systems, Subsystems, and Components) and FIB Bulletin 34 (Model Code for Service Life Design) to achieve 100+ year service life. Existing long‑span bridges may not have been built with a specific design service life in mind, but the principles of SHRP2 R19A can be used to maintain and extend the service life of existing bridges. Application of these principles and methods can extend service life by mitigating corrosion of embedded reinforcing steel and structural cables by over 80%. Extending the service life of existing bridges provides many benefits to owners and the traveling public. Direct benefits include cost savings for owners and reductions in disruption and delays to the traveling public. Extending service life also provides many indirect benefits including; reduction in the use of materials, reduction in the generation of demolition waste, reduction of environmental emissions, and the protection of sensitive habitat and existing ecosystems. This paper presents bridge case studies which illustrate how the SHRP2 R19A protocol was used to design durable repairs to extend service life of the structures and the direct and indirect benefits which were provided (achieved). Service life extension of existing long‑span bridges is a sustainable practice and should be encouraged.

This paper presents efforts to extend the service life of the Oresund Link. Service life estimations, supported by digital solutions for structural health monitoring together with sustainability planning for extending the service life of the Oresund Link. The service life estimation focuses on detectability, preventability, and repairability. Key assets are evaluated on long term sustainability, predicted service lifetime, and the related relevance for economic reinvestment. Oresund Link has a vision to become the most sustainable bridge in the world. This vision is illustrated by the business goal of +100 years service life, 100% open for traffic, 100% free from severe accidents and 100% free from CO2. The effort to determine the extended service life is done in cooperation with the Division of Structural Engineering at Lund University in Sweden.

Innoshima Bridge, which was opened to traffic in 1983, is a three‑span, two‑hinged stiffening truss girder suspension bridge with a center span of 770 meters, featuring a double‑deck structure with the upper level for motor vehicles and the lower level for bicycles and pedestrians. The seismic design of the bridge at the time of construction was based on the original seismic design code. However, an inland near‑field earthquake was not considered in this code, and there is a concern that a large‑scale earthquake exceeding the original design seismic force would occur. In response to large‑scale earthquakes, such as the anticipated Tonankai‑Nankai earthquakes in the near future, the bridge is required to have the performance that limits seismic damage to a minimum and enables a swift recovery of its functionality as an important structure with no alternative route. The results of the seismic performance evaluation revealed damage to various members in the bridge such as the main truss, transverse truss, end links, end stoppers, wind tongue, center stay ropes, road girders bearings, and bicycle and pedestrian track girders bearings. Therefore, it is decided to conduct seismic retrofit to the damaged members, such as installation of viscous dampers to reduce the seismic forces, addition and replacement of the structures reinforcement of the members around the wind tongues, and some other reinforcements. Due to the various damage, Innoshima Bridge requires the most extensive seismic reinforcement among the long‑span bridges of the HSBE. This paper presents a report on the seismic performance verification and retrofit design of Innoshima Bridge.

Due to the large‑scale earthquakes that have occurred in recent years, it is more important than ever to ensure smooth emergency and relief operations, transportation of emergency supplies, and emergency transportation, which are indispensable for recovery activities in the event of a disaster; this paper presents an example of seismic retrofit design for a long‑span steel cable‑stayed bridge. The Meiko Chuo Bridge on the Isewangan‑Expressway is a 3‑span continuous steel cable‑stayed bridge with a length of 1,170 meters and a maximum span of 590 meters, constructed in 1998. Initially, the bridge was designed to withstand possible large‑scale earthquakes. However, Seismic performance was verified against the seismic motions expected to occur near Nagoya Port in Nagoya, Aichi Prefecture, Japan, which were calculated based on recent studies. It was found that the main girder, tower, Horizontal force resistance steel bearing, and cable damper exceeded the limit values. The bridge is required to function as an emergency transportation road in the event of a disaster, and it is necessary to consider safety, serviceability, and repairability after the earthquake; the primary target performance was set to allow plasticization of the parts and to allow the resulting damage to be easily repaired. The steel sections of main girder and tower, which are particularly difficult to repair after damage, were set to have a performance that does not allow plasticization and stays within the elastic range. The optimum specifications and layout of vibration control devices for the retrofit study were determined by comparing and examining various vibration control and isolation device combinations. Through these efforts, we developed a seismic retrofit design that satisfies the performance requirements of a large‑scale earthquake that is currently anticipated.

Honshu‑Shikoku Bridge Expressway Company Limited has operated 17 long‑span bridges between Honshu and Shikoku, main islands of Japan. One of them is named Tatara Bridge. The bridge was a cable‑stayed bridge with the longest span (890m) in the world at the time of the completion. It is currently ranked the 8th in the world. The seismic verification considering the existing conditions of the bridge was carried out under the aim to further improve its seismic performance. The results of the seismic analysis for the bridge revealed that the considerable sway‑mode vibration in the longitudinal direction was dominant, and so seismic devices such as viscous dampers and stoppers were found to be necessary to mitigate the vibration of the bridge. Therefore, it was decided to install eight viscous dampers at two main towers, which were the largest ones in Japan, with the stroke of 950mm and the damping resistance force of 2,000kN during the velocity of 0.5m/sec. Before the installation of the dampers, in order to verify the performance and behavior, a dynamic performance test assuming an actual earthquake motion was conducted on one representative damper of the actual scale at a vibration table (its length and width are 20m and 15m, and the maximum displacement is 1,000mm), owned by the National Research Institute for Earth Science and Disaster Resilience. Since the test results showed that the damper had the required performance, it was determined that the performance tests were not necessary for the remaining seven dampers by considering and implementing a method of comparison and verification. This paper reports on the results of the performance test of the actual scale of the damper, which is the largest one in Japan. And the seismic retrofit work for the Tatara Bridge is outlined because the work of the bridge was successfully completed in 2022 by installing the eight dampers.

The Meiko Chuo Bridge on the Isewangan‑Expressway is a 3‑span continuous steelcable‑stayed bridge with a length of 1,170 meters and a maximum span of 590 meters, constructed in 1998. Together with the Meiko Higashi Bridge and the Meiko Nishi Bridge, it is a component of the Meiko Triton. This bridge was built in the east‑west direction near Nagoya Port in Nagoya City, Aichi Prefecture, Japan, and at its initial construction, it was designed to withstand possible large‑scale earthquakes. On the other hand, since 1998, large‑scale earthquakes such as the Great East Japan Earthquake and Kumamoto Earthquake have occurred in Japan, and expressway structures have been damaged each time. Seismic performance of the bridge was verified against the seismic motions expected to occur near the bridge, which were calculated based on recent studies, and it was found that some parts and members exceeded the limit values. Therefore, using the latest vibration control and seismic isolation technologies, the bridge was designed with seismic retrofit to absorb energy and control movement during earthquakes. This paper discusses the details of the seismic retrofit work, which involves significant changes in the structural system with modification of seismic devices to minimize the impact on in‑service heavy traffic and marine traffic and to ensure safety during construction at high elevations and narrow areas.

This study is a case study on practical and simple improvement of bridge disaster response plan using SHMS (Structural Health Monitoring System). SHMS is used for disaster response on bridges through triggering of abnormal signals using thresholds. Abnormal signals include electrical noise in addition to abnormal behavior of the bridge, and bridge managers require manpower in the process of checking and reviewing this. To solve this problem, triggering methods have recently been improved by utilizing various research results such as sensor‑specific correlation analysis and AI pattern analysis. However, this method requires research and analysis of the measurement data of each bridge, which incurs additional costs. This study is an example of applying Multiple Threshold Triggering as a way to improve the method of setting a threshold for each sensor and triggering when data is exceeded. Multiple Threshold Triggering is a system that triggers when the threshold is exceeded in multiple sensors. To apply the system, it is necessary to set the number of triggering sensors N and time T. In this case, N = 2, T = 60s were set and applied considering the physical distance among sensors and disaster cases and vibration speed during disasters. As a result of applying and operating this, it was confirmed that the number of abnormal signals occurring due to noise, etc. was reduced by less than half. Since the Multiple Threshold Triggering system is applicable by simply changing the triggering algorithm, it is expected to help maintenance organizations using SHMS reduce manpower without additional costs.

The geometric control of a suspension bridge is an essential element for monitoring it. Traditionally it is carried out periodically at a low frequency (annual periodicity) by surveyors. In order to understand the overall behaviour of the structure and to benefit from structural monitoring indicators, a geometric tracking of the major displacements of the Aquitaine Bridge has been studied. Two technologies meet this need, automatic topometrics and the use of GNSS (Global Navigation Satellite Systems), solution chosen in this case. The turnkey commercial solutions are relevant tools for civil engineering applications. However, these high performance solutions have some drawbacks, mostly being expensive, and sometimes impractical because of their size, power consumption, or software requirements. DGPS (Differential Global Positioning System) offers a potential low‑cost alternative that we studied in lab and on site. Laboratory tests was realized with open source software, different GPS receivers, and antennas shapes made it possible to qualify the performance metrologically. In order to validate our solution, a prototype was set on the main span (394m) Aquitaine suspended Bridge suspended Deployment testing in correlation with traditional sensor have shown the adequacy of this type of system to track small displacements (millimeters). This solution does not measure the dynamic behavior of the bridge, but responds perfectly to follow the thermal effects and trafic loads. Finally, these tests resulted in the implementation of a continuous monitoring of the Aquitaine Bridge with fourteen measurement points spread over the heads of the pylons and on differents positions of the 3 spans. The measuring equipment cost is less than 30.000 euros. The system is now operational since January 2019.

Sixense was selected to provide the structural health monitoring system for the new Ohio River Bridge East End Crossing. The project is a Public Private Partnership with the Indiana Finance Authority (IFA), and has multiple players coming together to build, operate and maintain the structure. As part of the public‑private agreement, IFA required instrumentation be placed on the bridge. The monitoring system complements visual inspections and will prove remaining life at the end of the concession term, when the state will assume full ownership and operation of the bridge. The system is constituted of multiple sensor types including accelerometers, tiltmeters, load cells, and a weather station. While in operation the monitoring system can be used for daily operations and emergency alerts on top of its continuous structural assessments. Sixense has finalized installation of sensors on the bridge in 2016. The presentation would address the selection of sensor types and locations with the bridge contractor, concessionaire, designer, and owner to provide the most actionable data. This included a thorough risk analysis regarding the structural design and project location. The presentation would show unique uses of SHMS including maintenance optimization, design verification, and post‑event anlaysis.

Structural Health Monitoring (SHM) has been used sparingly on cable‑supported bridges over the past 20 years, but is now more widely recognized as a cost‑effective option to enhance bridge management and safely extend service life. SHMs cost‑effectiveness for cable‑supported bridges can vary, depending on monitoring objectives, project implementation, and ongoing amount and utilization of the data generated. As with any engineered solution, careful project planning and diligent execution is essential to achieve long‑term cost‑effectiveness.

Acquisition of an SHM system should always be evaluated using a return‑on‑investment metric. Therefore, bridge owner/operators must develop a clear understanding of how an SHM system is expected to enhance bridge management; what data (otherwise unavailable) SHM systems can provide; consider agency procurement regulations; long‑term operation responsibility; and carefully plan how to efficiently utilize the data an SHM system generates.

An SHM system can provide objective, timely and highly accurate data that cannot be obtained from visual inspection, e.g. member strain, modal response, displacements, crack propagation, and/or inclination of various elements. The data captured could be short term (a few weeks) or long‑term (a decade or more) as necessary to enhance bridge management. Captured data can be utilized to diagnose the severity of specific structural distress, assess if a repair is necessary, or provide a structural engineer with the data necessary to determine overall structural integrity.

Most importantly, the information gleaned from an SHM system is highly useful to determine if major repairs are essential or can be safely deferred without compromising user safety. In this sense, SHM systems provide the technical support necessary to make financial decisions; either promptly implementing repairs, safely deferring repairs, or starting a full replacement project.

This paper will review the benefits derived from four distinct SHM systems ‑ both manual and automatic ‑ provided to owner/operators by LifeSpan Technologies for cable supported bridges. The bridges discussed include the Mackinac Bridge in Michigan; the Bear Mountain Bridge in New York; the Ravenel Bridge in South Carolina and the Throgs Neck Bridge in New York City.

Each of these four SHM systems had unique data capture objectives that justified the use of sensors, since visual inspection (routine or specialized) could not provide the accurate, timely and specific data to inform owner/operators about structural integrity or repair urgency. For each of these SHM systems, the information returned was highly useful for enhancing bridge management and minimizing the cost of operation.

The high strength steel wire of bridge cables is strong and resilient; however, it is vulnerable to cracking and embrittlement. The high load carrying capacity is obtained by cold drawing of a steel rod of about 13‑14mm in diameter.The rod has lower strength and higher ductility than that of the wire itself. The successive cold drawing process results in the 5‑mm wire, with much higher strength and lower ductility than the original rod. The wire deterioration starts at a micro deficiency on the surface of wire. With exposure to the combined effects of moisture and loading,the microdeficiency grows in depth until it forms a well‑developed crack. Under fatigue loads,the crack eventually reaches a critical depth causing break of the wire. This crack growth is aggravated by the penetration of atomic hydrogen through microdeficiencies on the surface of the wire into the metal lattice. The underlying causes for degradation of the highly stressed cable wire are moisture,coupled with hydrogen‑induced cracking under fatigue loadings. One of the main sources of hydrogen is the chemical reaction that takes place between the wire material and the atmospheric pollutants. The effort of preservation of bridge cables involves evaluation of cable strength, gauging its resilience overtime and assessment of safe service life. This presentation summarizes recent investigations of main suspension cables, utilizing a probabilistic‑ based methodology that accounts for wire breaks, crack growth, and reduction in wire strength and ductility.

This presentation will discuss the outcome of research performed under NCHRP Project 12‑115 to develop new guidelines for the risk‑based inspection and strength evaluation of suspension bridge main cable systems. These guidelines will be adopted as an AASHTO document to replace the current guidelines contained in NCHRP Report 534 (originally published in 2004). The guidelines introduce a new analysis method to evaluate cable strength which accounts for the variation of wire strength along the length of the wire (based on the Random Field method), an important characteristic for a ductile material like steel. The guidelines also outline a risk‑based method for determining inspection intervals for various elements comprising the main cable system based on the specific attributes of individual bridges. The presentation will highlight the differences between the current NCHRP Report 534 guidelines and the proposed AASHTO guidelines which are anticipated to be released in 2024.

The Forth Road Bridge, across the Firth of the Forth, near Edinburgh, Scotland, was opened to traffic, alongside the iconic Forth Rail Bridge, on September 4, 1964, with a main span of 1006m. Since 2004, the main suspension cables have undergone several internal inspections and strength evaluation. In the fourth internal inspection, Transport Scotland required two application of two different methods for the evaluation of the remaining strength of the main suspension cable. Under this investigation, wire specimens were subject to tensile, fatigue and hydrogen content tests. This paper will provide a discussion of the management and preservation strategies for the main suspension cable, with details of the ongoing analysis of test results.

NCHRP project 12‑115 – Guidelines for Risk‑Based Inspection and Strength Evaluation of Suspension Bridge Main Cable Systems by AASHTO was instituted to update the guidance available to owners for the inspection of the main cable systems on suspension bridges, and to convert the guidance into a document that could be adopted by AASHTO as the national standard for cable inspection. These new Guidelines, developed as a result of NCHRP Project 12‑115, are based on the previous NCHRP sponsored work, in particular NCHRP Report 534 – Guidelines for Inspection and Strength Evaluation of Suspension Bridge Parallel‑Wire Cables. Much of the methodology of inspection and material testing remains unchanged from that previous work, as it has withstood the test of time and has proven to be practical and effective. The methodology of determining an estimated cable strength presented in these Guidelines and based on the work of NCHRP 12‑115 is based on the Random Field method. Additionally, risk‑based procedures for determining inspection frequencies have been developed. This paper will examine the effects the new methodology has on cable strength evaluation, inspection frequencies and number of locations or panels that require to be opened and the frequency of inspections. The authors consider that there are several drawbacks in the methodology that should be addressed, and these are highlighted in this paper. Worked examples using inspection results from two bridges are set out to compare results from NCHRP 12‑115 and NCHRP 534. The effects on main cable preservation strategies, in particular, main cable dehumidification, will also be reviewed.

Existing infrastructure plays a critical role in supporting economic growth and social well‑being, while keeping environmental impact to a minimum. However, it is unknown if structures predating AASHTO Vessel Collision provisions (first published in 1991) are at unacceptable risk. The Francis Scott Key Bridge collapse due to a ship collision proves that it is essential to assess the current state of infrastructure comprehensively. Ship impact is one of the components in verifying structural safety. This requires insight into both the structural resistance of the infrastructure and the impact loads. This study focuses on the latter. Ship collision has always been a global problem and is even more relevant today. Assessment methods often are based on conservative deterministic approaches and fail to account for probabilistic factors. Arup has developed a probabilistic ship collision analysis tool named, Sirene for structures in, besides and over inland waterways in the Netherlands. Sirene is a geometric and graphical Monte Carlo simulation model to derive ship impact energies, that was built based on Eurocode principles. Its theory and method are applicable for other countries and could be adapted to other codes. To test this hypothesis, Sirene has been calibrated to the AASHTO Method II framework and applied to a theoretical ship impact analysis. First, a theoretical ship impact analysis is performed to demonstrate if Sirene is capable of meeting the AASHTO Method II standard. Here the input parameters are chosen for a single site in such a manner that the methods align. Second, parameters are modified and applied to different sites in order to show the added value of this probabilistic approach. Here it is discussed how using Sirene could add economic value and quantify the (unidentified) risk of existing structures. The end result is a verified method and discussion of the benefits of Sirene over the prescribed AASHTO Method II approach.

The AASHTO LRFD Bridge Design Specifications have codified into general practice a fully detailed probabilistic vessel collision methodology which was developed in the 1980s and extrapolates research conducted into ship to ship collisions in the 1970s.

Meanwhile the world has moved on. We have Ultra Large Container Ships, Automatic Identification Systems, Vessel Transit Services, GPS and advanced finite element analysis, not to mention artificial intelligence and progressive social values. What does any of this mean for bridge engineers in the coming years when the United States is likely to be undergoing a program of tightening its navigational practices and strengthening its bridges to catch up with, and keep ahead of, the risks of growth in marine traffic?

This paper makes five specific recommendations to improve vessel‑bridge collision practice in the US which are built around a proposal of identifying and focusing on the most strategically important bridges.

The recent collapse of the Baltimore Key Bridge due to ship collision underlines the need for bridge owners to ensure that the structural safety of existing as well as new cable supported bridges is at an acceptable level. Ramboll has during many years applied ship collision risk analyses as a basis for reviewing the safety of existing bridges and as a basis for designing new bridges. The present paper goes through the main principles of the risk analysis divided into five main steps; 1. Mapping of existing ship traffic in the area and forecasting of future traffic traffic volume, distribution of ship types and sizes, distribution of ship speeds. The mapping is based on detailed analyses of AIS data containing registrations of ships with respect to location, speed, course over ground, and ship particulars (type, length, width, draught, air draught etc.). Additional data is obtained for relevant ships in ship databases such as the SeaWeb IHS Maritime Portal. Ship traffic data (AIS and additional data) is very detailed and easy accessible and hence forms a sound basis for the risk modelling. 2. Modelling of physical boundaries in the area (bathymetry, coastline, physical obstacles, bridge geometry and alignment, etc.) 3. Geometric modelling of shipping routes and distribution of the ship traffic on the routes. The route modelling also account for the bridge passages and typical passage patterns of different bridge types as e.g. the cable supported bridges. 4. Modelling of accident scenarios related to human failures and technical failures, e.g., electronic black out, engine failures, rudder failures etc. 5. Assessment of collision frequencies for individual structural elements, piers, and girders. The collisions are divided into various types; head‑on, sideways, transverse, longitudinal etc. The resulting ship collision frequencies for the structural elements form a basis for the bridge owner to decide on the need for a required capacity of structural elements for new bridges, and to decide if the capacity of existing bridges is sufficient to withstand the estimated impacts from ship collisions or if retrofitting or the need for additional protective structures is required. In the present paper the principles and basic elements in a risk analysis is described, and examples are given in relation to design review of the existing resund Cable Stayed Bridge (DK/SE), the new Bjrnafjord cable stayed/pontoon supported Bridge (NO) as well as protection arrangements for the existing Sallingsund Bridge (DK).

This contribution presents two recent approaches to ship impact risk management on major bridges in Denmark. In both cases, a detailed analysis of the maritime traffic at the site, based on internationally available AIS traffic data, provided a specification of various representative design ships. The first example covers the New Storstrm Bridge which is currently under construction and was designed by Ramboll. The bridge carries both road and high‑speed rail traffic, is 2.4 miles long and has two cable‑supported navigational spans. In this case, the mitigation of risks due to ship impact were decisive for the foundations near the main spans. The risk picture was dominated by two effects, being global structural failure and derailment of trains passing during ship collision. Global failure was defined as a 400mm displacement limit at seabed level and numerous simulations of ship impact collisions were performed to optimize the foundations against this criteria. Train derailment was critical due to a combination of high naval and rail traffic intensities, and detailed simulations of ship/bridge/train interaction were performed to document that only very extreme cases would lead to wheel unloading. This information was included in a probabilistic risk assessment which demonstrated a satisfactory safety level without the need for e.g. foundation size increases or protective structures such as dolphins or artificial islands. The second example covers the Sallingsund bridge which is a 1.1 miles long concrete road bridge. The bridge opened in 1978 and since then the naval traffic has intensified, both in terms of ship frequency and size, leading to an unacceptable probability of bridge collapse in case of collision. In 2016 Ramboll delivered a full solution to the Danish Road Directorate for increasing the safety class of the bridge, integrating probabilistic risk assessments with the design of two dolphins for protection of the bridge piers. The dolphins consisted of concrete caps on 18 180ft‑deep steel piles and were installed in 2017 at a construction cost of USD 11 million.

Maintaining and operating long‑span bridges presents unique safety challenges, particularly during short‑term activities like component rehabilitation, condition surveys, and inventory verification. The limited number of these bridges in a region and the varied approaches used during these activities create a data gap, hindering objective risk assessment. Consequently, current practices often lack differentiation, assigning similar risk scores to different activities for different long‑span bridges. This paper introduces a methodology for assigning monetary values to these risks. This allows for a comparison of risks associated with various activities and specific long‑span bridges based on their approaches, accessibility, and overall profile. To quantify risk, the paper proposes evaluating the probability of injury (P) and its severity (S). Fuzzy logic, a mathematical framework for dealing with uncertainty, is used to compute relative probabilities of different injury types associated with a specific activity and bridge. The severity of the injury can be assessed using the KABCO scale, a scale commonly used by law enforcement, and then converted to monetary values using the MAIS conversion system. The risk (R) is then calculated as R = (P) (S) in monetary terms. The paper concludes by offering an example that delineates a step‑by‑step methodology for computing risk using the proposed approach. This is demonstrated by calculating the risk associated with the inspection of two bridges owned and operated by the New York State Bridge Authority, the Walkway Over The Hudson (WOTH), and the Newburgh‑Beacon Bridge (North Span).

Thousands of long span bridges rely on grouted post‑tension (PT) tendons and stay cables. Problems with grouting techniques and grout materials has resulted in tendons and cables with grout voids, and defective grout. This has resulted in corrosion and failure of PT tendons, some within 6 to 17 years of service. The Florida Department of Transportation (FDOT) has spent more than $55 million (USD) repairing 11 post‑tensioned bridges to date. A cost‑effective corrosion mitigation technique has been developed to minimize the corrosion of grouted PT tendons and extend the service life of bridges which have grouted tendons and cables. This paper describes the collaborative development and implementation of this technique on compromised grouted PT tendons in segmental bridges, including the Ringling Bridge (Sarasota, FL), the I‑95 / I‑295 Interchange, and Wonderwood Bridge (Jacksonville, FL) and the I‑4 Connector (Tampa, FL) as well as verification testing of the corrosion protection performance of the system. Results from projects completed for CalTrans, Virginia DOT, Canada, Korea, and UK will also be discussed.

Computer vision is rapidly gaining traction across various industries, and its potential use in bridge engineering could revolutionize the monitoring and maintenance of vital infrastructure. Leveraging sophisticated image processing and object tracking algorithms, this technology enables engineers to detect and quantify structural changes with unprecedented accuracy and in real time. This conference presentation details the development of a cutting‑edge software program that utilizes computer vision techniques to monitor and analyze the dynamic movements of bridges under diverse conditions. Three case studies illustrate the robustness and versatility of this method. The first case study demonstrates the softwares capability in long‑distance monitoring by tracking the deflection of the Manhattan Suspension Bridge as subway trains pass, showing how it can manage large‑scale structures remotely. The second study measures the natural frequency and estimates tension in the cable suspenders of notable suspension bridges, including the Manhattan and Walt Whitman Bridges. This method showcases unparalleled cost‑efficiency and significant advantages over traditional modal testing instrumentation techniques, which often involve cumbersome installations and necessitate traffic disruptions. The third study involves measuring excessive wind‑induced vibrations in a truss bridge member using an unstable handheld camera, highlighting the softwares adaptability to different monitoring conditions and its potential for field application. These case studies collectively validate the efficacy of this approach in bridge engineering, presenting a significant advancement in the maintenance and monitoring of critical infrastructure components using computer vision technologies.

Building on decades of work, in 2015 the United Nations launched its 2030 Agenda for Sustainable Development which was adopted by all member nations. Included in this agenda are the 17 Sustainable Development Goals (SDGs) aimed at addressing the many socio‑economic and environmental challenges facing our planet.

At first sight it might appear that these goals have little to do with the design, operation and maintenance of big bridges. Although this may well be the case with some of the SDGs, others are relevant, and it is these specific goals which will be discussed in this paper.

Some SDGs, such as 9: Industry, Innovation and Infrastructure and 11: Sustainable Cities and Communities may be easily seen as being applicable in the big bridge sector. Many of our existing bridges have outgrown their initial objectives and have led to new residential, retail and industrial developments that are now totally reliant on the fixed links our bridges provide. Those communities are now unsustainable without those bridges.

Both SDG 8: Decent Work and Economic Growth and SDG 12: Responsible Consumption and Production also relate to bridges. SDG 8 is an outcome from SDGs 9 and 11 but SDG 12 should be reflected in our choice of sustainable materials and careful disposal or re‑use of construction materials.

Biodiversity responsibilities are highlighted in SDG 14: Life below Water and SDG 15: Life on Land and both are applicable in the way we manage and maintain our structures.

Lastly, SDG 17: Partnerships for the Goals suggests that no‑one should be approaching the goals in isolation. As bridge owners and operators, we should work with and seek mutual support from our stakeholders and neighbours to help meet the challenges we face.

And when we build new major bridges, we must recognise that they will do more than just provide transportation links; and if the concept of the UN SDGs is embraced from the outset then the outcomes from a new bridge will be many and far reaching.

The UN SDGs should not be seen as a bolt‑on extra or an afterthought in our design or maintenance projects; they need to be embedded in all of our responsibilities as we strive to manage our bridges and our planet as efficiently as possible.

Most cable‑supported bridges in developed countries are aging structures that need or will eventually need rehabilitation and strengthening work. Furthermore, more recurrent extreme storms and climate events such as hurricanes and tornadoes will have an impact on the safety of existing cable‑supported bridges. The combined effect of rehabilitation and climate change could modify the conditions of a bridge in comparison to its initial design parameters. It will therefore be required to conduct new wind studies for these aging cable‑supported bridges. For example, an increase in the design wind speed for a suspension bridge because of climate change could require structural strengthening of the stiffening girder. This would change the bridge‑deck cross section and could likely require a verification of the aerodynamic performance using wind tunnel tests. Due to the bluffness of many older cable‑supported bridge decks, it is believed that wind tunnel tests are still the most reliable way to assess wind performance. Of the different types of wind tunnel tests, section model tests are likely the most relevant in the context of bridge rehabilitation due to their cost effectiveness. However, structural nonlinearities are neglected in section model tests. Considering that cable‑supported bridges are nonlinear structures, it appears relevant to account for structural nonlinearities to achieve more accurate predictions using section model tests. Consequently, a research program between the University of Western Ontario and COWI North America led to the development of a wind tunnel test procedure for more realistic section model tests that account for structural nonlinearities. This research mainly focused on suspension bridges and geometric nonlinearities since it appeared to be the most critical combination. At first, the origins of structural nonlinearities in cable‑supported bridges were assessed. These especially include geometric nonlinearities such as the cable sag effect and vertical‑torsional stiffness coupling, which were characterized using nonlinear finite element models of eleven cable‑supported bridges. From the results on structural nonlinearities, the idea of nonlinear section model tests of bridges was elaborated. A theory and test rig were specifically developed. By conducting nonlinear section model tests, it was determined that it is possible to account for the effect of geometric nonlinearities when predicting the aeroelastic performance of cable‑supported bridges. This new test procedure is especially relevant in the assessment of flutter for suspension bridges since they are more nonlinear.

The Robert F. Kennedy Suspension Bridge has 1,380 long main span and two 671‑8 long side spans. The bridge carries eight lanes of traffic and two sidewalks. Currently, pedestrian access is provided by a 6‑wide walkway located along the stiffening truss top chord on the North side; the South side walkway is only accessible to MTA for maintenance purposes.

In 2013, the wind analysis and evaluation of bridge vulnerabilities were performed by MTAs consultants and the sectional model was tested in a wind tunnel.

The stability limit is a wind speed limit (e.g. the critical wind speed for the onset of torsional flutter), above which the bridge becomes unstable. The bridge is usually required to a possess a flutter wind speed higher than the nominal10,000‑year return period for a 10‑minute mean wind speed.

For the established wind design and bridge performance criteria, the results of the wind tunnel testing showed that the bridge behaves satisfactorily under strong winds with regards to serviceability and strength. However, it did not meet the wind speed criteria for aerodynamic stability. The flutter speed of 88 mph was determined and retrofit was necessary to increase the flutter speed to the desired minimum of 105 mph per design criteria.

As the scope of the ensuing RFK Bridge rehabilitation project was being developed, MTA embarked on an Authority wide effort to improve accessibility. Under that strategic plan, the RFK Bridge was required to have new AASHTO compliant Shared Use Paths (SUPs) on the suspension bridge.

From 2020 to 2023, additional studies were conducted by an MTA consultant and additional wind tunnel testing was conducted. Various SUP configurations, types of fencing, open side barriers, wind screen extensions were studied. Various SUP widths and locations at different levels of stiffening truss were studied. Staged construction of the new SUPs will be done while maintaining traffic.

The project includes painting of the superstructure steel. The aerodynamic stability affected by the enclosures during painting of the bridge was also tested and options were presented in the rehabilitation contract documents.

The design‑build project was awarded this year and is expected to be completed in four years.

The paper will describe all aspects of the studies, how various configurations faired, and how the final configuration was chosen.

This study introduces a hyperlocal tool for short‑term extreme wind forecasting, designed to enhance decision‑making and risk mitigation for bridge operations. Bridges, susceptible to the adverse effects of extreme weather, demand reliable forecasts to proactively address potential hazards. These hazards include structural deformations from dynamic loads, foundation erosion from heavy rains, ice‑induced damage from freezing temperatures, and reduced visibility due to fog, all of which could significantly compromise safety and structural integrity. The proposed model integrates advanced machine learning techniques with a blend of hyperlocal and global sensor data, facilitating real‑time, accurate meteorological predictions. The framework functions by integrating real‑time data from both local and global weather stations, alongside historical weather data, to feed a supervised ML algorithm, specifically tailored for hyperlocal meteorological predictions. The system captures real‑time weather conditions using local sensors situated on the target bridge. Concurrently, data from a global weather station augments this localized information, providing a comprehensive view of impending meteorological threats. The ML forecast algorithm processes this data, leveraging historical records to enhance the model’s learning and predictive accuracy. One practical application of this framework is demonstrated through its deployment on bridge infrastructure, where it functions as an early warning system. By predicting extreme wind speeds, it informs the necessary activation of traffic control measures (early warnings), such as traffic lights, to either slow down or halt vehicular passage, thus preempting risks (accidents or vehicle overturning) associated with high winds. The predictive capability of our framework is illustrated through an application on the Great Belt Bridge in Denmark, where it has been trained on a 5 years database, using 360 minutes (6 hours) of past data to forecast wind speeds 180 minutes (3 hours) into the future. The model’s effectiveness in providing actionable insights for bridge management is critically assessed, highlighting its potential to significantly enhance the resilience of transportation networks against disruptions caused by adverse weather conditions. It is acknowledged that the fidelity of these predictions naturally wanes over time, with a decrease in the accuracy of forecasts further into the future. This system not only signifies an advancement in the field of weather prediction but also illustrates a step forward in infrastructural resilience. It embodies a proactive approach to disaster risk reduction, offering a replicable model that can be adapted to various contexts where extreme weather conditions pose a significant threat to safety and continuity of operations.

This paper not only takes a look back at the history of bridge collapses but also looks forward to question whether enough is being done to safely manage deteriorating bridge infrastructure.

The year of 2018 saw a number of high profile and tragic bridge collapses, including the FIU footbridge in Miami, Florida, USA and the Polcevera Viaduct in Genoa, Italy. Although 2018 was possibly an unusual year, an analysis of statistics for the first two decades of this century shows that there have been 123 bridge collapses across the world that have claimed at least one life, with a total death toll of almost 1,000.

This paper examines the underlying causes of bridge failures and demonstrates how bridge engineers have enhanced their understanding of structural behaviour by learning lessons from history. There are just five reasons why a bridge may collapse: through errors in design, in construction, in operation, lack of maintenance or unforeseen environmental factors. Often it is not just a single cause but a combination of two or more.

The need to share knowledge is also emphasised even when that means acknowledging mistakes. This has been the pattern followed since the 19th Century when engineers were pioneering new materials and new structural forms, pushing boundaries in pursuit of elegance and efficiency.

But with the boom in bridge building across the world over the last 70 years, how well are we managing and maintaining our aging bridges as they deteriorate? And how safe is the travelling public who rely totally on the competence of engineers charged with the care of bridges which may be approaching the end of their design life?

The paper reflects on the world‑wide need for investment, not only in new infrastructure but also in maintaining existing. That investment is not simply in terms of money but equally should be in the capacity and capability of the engineering profession. It is not only bridges that are aging but also bridge owners and managers; how do we ensure that the next generations are benefiting from the experience of their older peers?

Although not exclusively focussed on cable supported bridges, the over‑riding principles of bridge management are applicable to all. The paper is both challenging and provocative; unless we commit to investment in people and budgets, the next few decades are likely only to extend the statistics of collapses and fatalities.

In the US, main cable dehumidification systems are now being installed on a number of existing, older bridges. Cable dehumidification projects are a complex mix of structural, mechanical, electrical, and controls engineering. An important part of the design process is determining the blow length which is the maximum length that the dry dehumidified air can be effectively blown along the gaps between the wires to channel the dehumidified air along the cable. The blow length establishes the distance between the injection and exhaust positions. Air flow testing on the cables has been carried out on several bridges prior to designing a cable dehumidification system. Air flow testing allows for physical observations to be made of how far air can be blown through the interstices which exist between the high tensile wires that form the cables. This testing is particularly important in order to establish the blow length for previously oiled or heavily corroded cables. It can also be used to determine the layout of the system and whether or not air can travel over tower saddles. On previously wrapped cables, air flow tests are used to establish if the existing cable wrapping is capable of holding the pressurized air inside the cable. AECOM has now carried out air flow tests on six bridges in the US. These are: William Preston Lane Jr, Memorial Bridge (Eastbound Bridge) in Maryland, South 10th Street Bridge in Pittsburgh, Bronx Whitestone Bridge in NYC, Robert F. Kennedy Bridge in NYC, Verrazzano Narrows Bridge in NYC, and Mount Hope Bridge in Rhode Island. The cables on both the New York bridges and Mount Hope Bridge have previously been oiled. In an innovative change, AECOM have adopted the use og injection and exhaust sleeves to confirm air flow. This paper describes in detail the reasoning behind carrying out these air flow tests; the work in the field and the results obtained from each test. It also covers the development of the testing.

The US has approximately 36 major cable suspension bridges, equating to nearly 25% of the global suspension bridge inventory. The cable protection system traditionally used on these suspension bridges is essentially unchanged from that devised by Roebling for use on Brooklyn Bridge in the 1880s. However, experience from internal cable inspections has shown that this system does not provide the required level of protection with virtually every suspension bridge around the world that is protected in this manner displaying some level of cable deterioration. Water inevitably finds its way into the cable causing corrosion, leading to wire cracks and breaks, in which hydrogen embrittlement is recognized to contribute. Bridge owners have adopted several different methods of trying to slow down the rate of deterioration. These have included different types of paint, with more elastic properties; wedging and oiling the cables, and wrapping the cables in different types of materials. The most recent development is dehumidification, which works by removing moisture from the cables and reducing relative humidity to below 40%. By removing the electrolyte from the electrochemical process to a known threshold then corrosion is reduced to a level where it is considered to have practically ceased. This paper will examine in detail the design, construction, and post construction monitoring and maintenance of the cable (and anchorage) systems now installed on six bridges in the US and three bridges in the UK. They are: the twin bridges of the William Preston Lane Jr. Memorial (Bay) Bridge; the twin bridges of the Delaware Memorial Bridge; South Tenth St Bridge, Anthony Wayne Bridge, Forth Road Bridge, Humber Bridge and Severn Bridge. It will also examine the design and construction of systems on the Benjamin Franklin Bridge due for completion in 2024; the design of the system on the main cables and anchorages of the Mount Hope Bridge and the conceptual design of the cable dehumidification system on the Verrazzano Narrows Bridge. As owners seek to evaluate the benefits of cable dehumidification, this paper will provide an insight into the challenges of retrofitting these systems to existing bridges. It will cover the history, process, and efficacy of cable dehumidification, along with related discussions on recommended project procurement and delivery methods, evaluation of previously oiled cables, applicability of acoustic monitoring systems, and post construction maintenance and monitoring. The paper will also cover the issue of future cable inspections following cable dehumidification installation.

Over the past 10 years, main cable dehumidification systems have been installed on select suspension bridges across North America. The performance of these systems in achieving the desired objective of maintaining exhaust readings less than 40% Relative Humidity has been inconsistent. As there is presently no code governing the application of dehumidification systems, WSP has compiled observations through involvement in the design, installation, operation, and/or maintenance of 10 suspension bridges. By comparing dehumidification system performance in different bridges, considering variables such as air flow resistance in cables, performance of mechanical equipment, and performance of control and monitoring systems, WSP has developed a series of improvements for inclusion in new DH systems and potential inclusion in existing systems through retrofits. The most critical improvement to main cable dehumidification system layout is the volume of air flow through cables, which is predicated based on the volume of air the cable will receive at injection locations and the distance between injection and exhaust locations. Setting a target volume of air circulating through the main cable of 3.5 Air‑Changes‑per‑Hour (ACH) is a critical improvement, assuming reasonable Loss of Flow along the cable length and Cable Void Ratios, will overcome the non‑homogeneous conditions and effectively preserve the cable. Following the initial dry‑out period, in which the exhaust relative humidities demonstrate falling from ambient or higher to below 40%, the injection pressure (for parallel wire cables) may be reduced from 12 w.c. to 10 or 8 w.c. to maintain an average daily relative humidity below 40%. Thus, should exhaust conditions indicate that increased moisture may be present in the cables in subsequent years, the pressure may be increased back to 12 w.c. and the corresponding flow from the original dry‑out period will remove the additional moisture. The performance of the mechanical equipment in delivering air with reduced moisture content, and eliminating potential for moisture infiltration, is also critical to the effective performance of a cable dehumidification system, as the absolute humidity of the air will effect the capacity of the air to absorb and remove moisture. Additional improvements including use of exhaust location gate values to maintain nominal positive pressure within the cables after the dry‑out period, pipe configurations to improve sensor accuracy, locations of exhaust sensors to avoid outside interference from wind, purge valves at low points of dry air piping and the use of gate valves for balancing will be discussed.

The risk of loosen a hanger either by reason of corrosion, fatigue, or accidentally truck fires have made Sund Baelt consider the importance of having a procedure ready to replace any given hanger at the Great Belt Bridge. In November 2020, a truck fire arose just next to our fifth longest hanger and only due to luck with the wind direction, the hanger was not damaged. Therefore, we started up making a Technical Procedure and a set of 5 technical Instructions how to replace any given hanger. The longest hanger is 177 meters, and the weight is approximately 11 tonnes. The length and the weight made is necessary to produce lifting table and other tools to be installed on the cable clamps. The advantage of having a complete set of each different type of hangers in our stock, in order not to run in to long delivery time and hereby long period with restricted traffic on the bridge. The size of the hanger cables and different types of the sockets complicated the replacement procedure and made it necessary to have more sets of special tools to be invented, for the different positions on the bridge. Eddy current tests have been added into the scope of inspection in the lower area of the hangers. The estimated lifetime and special needs for damping devices have been made for the longest hangers after evaluation on accelerometer measurements. A new setup with Digital Image Correlation on four hangers has been started to verify the lifetime predictions and to calculate the total cost of ownership. The DIC installation has the advantage and the possibility to have visually documentation for the actual movements.

The A. Murray MacKay Bridge is a major suspension bridge opened in 1970 and carries four lanes of traffic across the Halifax Harbour in Nova Scotia. The suspension bridge has a main span of 1400 ft (426.7 m) and two side spans of 513.83 ft (156.6 m). The bridge carries four lanes of traffic and is tolled in both directions. Approximately 65,000 vehicles cross the bridge on an average workday. The A. Murray MacKay Bridge and the nearby Angus L. Macdonald Bridge are operated and maintained by Halifax Harbour Bridges. The MacKay Bridge requires significant maintenance in the years leading up to 2040 and major rehabilitation (or replacement) work is currently planned to be complete by 2040. HHB is currently engaged in the planning stage for this work. This paper describes the inspection, preservation, and replacement work being carried out on specific suspension bridge elements in order to ensure that there is no loss of service provided by the bridge during the planning stage of the major rehabilitation or replacement work. The main cables are constructed of helical strands and this paper describes some of the challenges in carrying out the inspection and strength evaluation of helical strand cables. The loss of strength in the cables determined from internal cable inspections, and some laboratory testing, resulted in a preliminary design of a main cable and anchorage dehumidification system being carried out in 2022. Further internal cable inspections will be carried out and the strength of the cable re‑evaluated. An assessment of the potential of the cable bands to slip was carried out. The loss of tension in the cable band bolts; the frictional resistance of the cable bands and the loads in the suspenders being the significant metrics to be determined. The estimated loss of tension in the cable band bolts will be checked against the loss of tension found in a sample of bolts. HHB has observed the deterioration in the condition of the bolts on the four cable bent saddles and there were concerns about the capacity of the saddle bolts and nuts due to the corrosion observed and potential loss of section. These saddles bolts exert a suitable clamping action to avoid cable slippage through the cable bent saddles. An evaluation of the resistance to slippage was carried out and a replacement bolt design developed to enable the safe replacement of the existing bolts with new bolts.

The iconic Waco suspension bridge was originally constructed in 1869 to provide a reliable way for cattle drivers to get their herds across the Brazos River as they followed the Chisholm Trail. The original construction was a hybrid suspension and cable stayed structure with a wooden stiffening truss and brick towers. In 1914 the bridge was significantly reworked, by providing concrete encasement of the towers, strengthening the anchorages, replacing the hybrid cable system with a suspension‑only cable system, and replacing the wooden stiffening trusses with steel trusses. The structure carried vehicular traffic until 1971, at which time it was limited to pedestrian traffic and an occasional celebratory cattle drive.

In 2018, the City of Waco, who owns the bridge, undertook a project to ensure serviceability of the bridge for future generations. Rehabilitation plans were developed by Sparks Engineering Inc, of San Antonio Texas. The rehabilitation plans called for complete replacement of the suspension cables, replacement of all suspenders, strengthening of the anchorages, replacement of the deck, as well as various other repairs. Construction of the project was carried out by prime contractor Gibson and Associates of Balch Springs Texas, who sub‑contracted cable and suspender work to Structural Technologies of Fort Worth Texas. Structural Technologies’ team included Modjeski and Masters Inc. of Mechanicsburg, Pennsylvania who performed final design of the cable system and served as erection engineer, as well as Pfieffer Group of Memmingen Germany, who supplied the suspension cables and suspenders.

This paper will explore several aspects of the recent rehabilitation, including support of the stiffening truss during re‑cabling, the method utilized for de‑tensioning the main cables, steps taken to ensure proper fit and geometry of new components, steps taken for installation of the new suspension system, as well as design and constructability details considered to ensure success of construction activities.

In this study, the cause of the case where a cable‑stayed bridge MS CABLE HDPE DUCT detached from the upper part of the pylon is analyzed using robots and drone inspection, and maintenance strategies such as repair and monitoring methods are presented. The bridge in this paper is a cable‑stayed bridge located in Korea and built in 2012. The MS CABLE of the cable‑stayed bridge has a configuration in which the HDPE DUCT protects the strand, and unlike the PWS CABLE, it is not integrated. If the HDPE duct is separated or damaged where it is fixed, the strand may be exposed to the outside air, causing problems in the safety of the bridge. In January 2021, it was discovered that MS CABEL HDPE DUCT had separated from the upper part of the pylon. We carried out a desk study of details. In addition, robot customized for cable appearance survey and drones were used to investigate the MS CABLE HDPE DUCT located at the upper part of the pylon. Based on investigation, the cause of the separation was believed to be the difference in shrinkage between the HDPE DUCT and the strand during the winter. It was confirmed that the reason for the difference in shrinkage between HDPE Duct and strand was the difference in coefficient of linear expansion. In addition, a meeting was held to safely repair the cable duct separation located at the upper part of the pylon, the cable duct was lifted and inserted using a crane from the bridge pavement. As a result, we are currently checking for HDPE Duct re‑separation according to the regular inspection cycle. This maintenance case study will prevent similar cases in the future and contribute to the continuous development of operational and maintenance processes for the life of the bridge.

MTA Bridges and Tunnels (Triborough Bridge and Tunnel Authority (TBTA)) owns and operates four suspension bridges (Robert F. Kennedy, Bronx‑Whitestone, Throgs Neck and VerrazzanoNarrows) which are all critical links in the New York City Regional transportation system carrying well over 180 million vehicles per year. MTA BT has an overall strategy to extend the service life of the primary load carrying elements which includes a program of perpetual renewal of these critical bridges. The four bridges are pre‑dominantly steel structures and were built in two different eras, the 1930s and the 1960s. They are subject to deterioration due to corrosion, fatigue and in some of the elements, hydrogen embrittlement. The priorities for the Authority in managing these four suspension bridges are: Ensure their long term structural integrity; Minimize risk to public safety; Accommodate the potential for capacity improvements; Minimize and manage potential disruptions to traffic; Ensure that available funding is invested in a planned, systematic, and efficient manner. MTA BT utilizes Risk Based management techniques as part of their long‑term capital planning to ensure coordinated management of these priorities and the reduction of the risk associated with owning and operating these four complex bridges. This ensures that sometimes competing priorities and associated risks are addressed in a systematic and methodical manner with maintenance and capital improvements identified and prioritized based on structural requirements and public safety while minimizing traffic disruption. This paper describes the work carried out on behalf of MTA BT by AECOM along with partners Modjeski and Masters and consultant Bill Moreau, to quantify the criticality and vulnerability of different elements on the bridges owned and operated by MTA BT. Evaluating risk on suspension bridges requires significant input from the bridge owner. A number of MTA BT staff members made a significant contribution to this project including Deputy Chief Engineer, Aris Stathopoulos.

The Triborough Bridge and Tunnel Authority / MTA Bridges and Tunnels (MTA BT) has been using an in‑depth variation of AASHTOs Bridge Element Inspection before it became standard in New York State in 2016. MTA BTs Bridge Inspection group created a Uniform Bridge Element Identification System (UBEIS) in the 1990s, which identifies all elements with generalized coordinates with up to five (5) designations. This method for data collection allows each element in the UBEIS to have its own rating set which includes AASHTO Codes, Condition States, Load Rating, etc In addition to AASHTOs National Bridge Elements (NBE), Bridge Maintenance Elements (BME), New York State DOTs Agency Defined Elements (ADE), MTA BT has their own Defined Elements (TDE) consisting of over 90 various elements including Drainge Systems. MTA BT inspection program combines NBEs, BMEs, ADEs, and TDEs, but its their UBEIS that separates them from others. Generalized coordinates of the UBEIS include identifying elements by Span, Panel, Sub Panels, down to individual components (i.e. diaphragms). After their Biennial Inspections, MTA BT uses the UBEIS for their Asset Inventory and Condition Assessment (AICA) Program which captures this level of detail to help identify deterioration trends, inclusion of elements into existing Capital Programs, or beginning the identification of a new Capital Program. The AICA program identifies grouped elements by bridge section such as type of framing which identifies average condition rating, service life, along an estimating condition ratings based on deterioration trends. Future AICA programs could coordinate inspection findings with BIM models as this would be a way to to optimize the use of data sets and visually identify trends. The ability for filtering data, visualization, along with assigning the most up‑to‑date condition on an individual element level could help to optimize fund allocation and quickly identify problem areas and design details. MTA BT is looking towards the future of engineering and using what theyve been doing for over 30 years combined advanced techology.

Major cable‑supported bridges are enormous investments for society and are vital links for a functional society. It is essential for society that these bridges are open at full capacity as much as possible and that they are managed in an economically optimal manner. Due to their locations, these bridges are often irreplaceable, and it is therefore necessary to prolong their lifetime as long as possible. Each of these cable‑supported bridges is a unique and complex structure, made up of many materials and components and maintenance is therefore a major challenge that requires a great amount of planning. Asset management is carried out in many different manners and with varying levels of detail, depending on national and local requirements, as well as the requirements from each owner/operator. This paper will mainly focus on practice in Denmark and Sweden, including national and bridge‑based operator practices. The basis for asset management is knowledge of the bridge structure coming from the design project, as‑built documentation, risk analysis results, inspection and testing results and carried out maintenance, repair and rehabilitation projects. It is essential that this knowledge base is continuously updated, such that planning can always up to date. The basis for asset management should be a long‑term strategy for the entire structure, encompassing all elements. The time frame should be quite long, typically 40 to 60 years or corresponding to the theoretical remaining lifetime of the bridge. The strategy contains an element system for the bridge and for each element: A description including illustrations and the current condition; expected need for maintenance/repair and in‑depth inspection and/or testing; and determination of the optimal maintenance strategy based on life cycle analysis. The strategy contains all related costs including access, traffic management and user costs related to possible delays. When all the optimal element strategies are determined, they are combined into an overall optimal maintenance strategy for the entire bridge. This optimization focuses on joint use of access and traffic management facilities as well as minimizing traffic disruptions. This results in some works being carried out earlier or later than in the individual element strategies, such that the total cost of maintaining the bridge is minimized.

The busiest bridge in the world, George Washington Bridge (GWB) had some major additions and rehabilitations over the 92+ years of history, ranging from the addition of lower‑level decks to the current $2 billion Restore the George program. This paper provides an overview of major redevelopment (addition) and rehabilitation programs in the history of GWB. With over 104 million vehicles crossing the Hudson River over the 14 traffic lanes on both eastbound and westbound, effect of the construction activities on the traffic on the bridge span and the approach roadways were carefully analyzed and planned out to minimize the negative impact to the regional traffic.

This presentation will review the construction history of the four suspension bridges owned and operated by MTA BT, along with a detailed discussion of the many past and ongoing structural modifications/upgrades to the suspended spans to improve resiliency, reduce load on the main cables, and in general extend the service life of these critical and iconic structures. The four bridges are the Verrazzano‑Narrows bridge, the Robert F. Kennedy Bridge (formerly know as the Tri borough Bridge), the Bronx‑Whitestone bridge and the Throgs Neck Bridge.

Halifax Harbour Bridges (HHB) recently rehabilitated the Angus L. Macdonald Bridge in Halifax, Nova Scotia in a project known as "The Big Lift." The toll bridge is a vitally important element of the Halifax transportation network. The Contractor completely replaced the suspended spans segment‑by‑segment while keeping the bridge open during peak traffic periods. Bridge owners can reasonably ask: What process did HHB undertake to determine that the bridge could be renovated successfully, and is "my" bridge a suitable candidate? This paper will discuss the engineering examination that HHB undertook to determine if carrying out a complete suspended spans replacement made sense from the perspectives of capital expenditure, construction effects on traffic and long‑term Operation and Maintenance. Structural capacities of key elements such as the main cables and the main towers were carried out to ensure that they had sufficient strength and remaining life to justify the costs of replacing the suspended spans.

The paper will highlight special "add‑ons" that HHB commissioned, such as main cable dehumidification (a first for a Canadian bridge).

The goal of the presentation will be to provide ICSBOA members with the criteria that they can apply to their bridges to determine if they are candidates for the kind of suspended spans replacement carried out on the Macdonald Bridge.

The east span of the San Francisco‑Oakland Bay Bridge (SFOBB) was opened to traffic in September 2013. Located in the seismically active zone in Northern California, this landmark 3.7‑kilometer‑long strucutre crosses the San Francisco Bay between Yerba Buena Island and Oakland. With daily traffic of 270,000 vehicles, the strucure is required to be a lifeline bridge and must remain operational for emergency vehicles shortly after an earthquake. The design life of the SFOBB is 150 years. A comprehensive approach to designing and maintaining the signature structure was employed to ensure its longevity. Key components in this approach included proper fatigue detailing; designing element replacement after a major seismic event; cable and tower anchorage zone dehumidification; design of an under‑bridge traveler for maintenance accessibility and an operation and maintenance plan. This paper discusses how these elements were integrated into the overall bridge design to ensure durability, while overcoming the technical challenge involved with design and construction.

The Hakucho‑Ohashi bridge is the only long span suspension bridge in Hokkaido Prefecture, in the cold region of Japan. The bridge has a total length of 1380 m and a main span of 720 m. The bridge has been in use for more than 25 years. Recently, fatigue cracks were observed in some lighting poles which are located along both sides of the bridge. The bridge is under the wind environment in which the wind from the north‑west direction is dominant and has a high ratio of the strong winds faster than the velocity of 15 m/s. In order to better maintain and manage the lighting poles, it is necessary to appropriately evaluate the fatigue strength of the pole subjected to the strong wind load. From this point of view, in this study, the dynamic response strains of the poles were measured and it is tried to estimate the accumulated fatigue degree of the poles in the current situation using the response strains. The results obtained from this study are as follows: 1) the poles may be in the state of high accumulated fatigue degree; and 2) the poles suffered from the damage due to the fatigue cracks may tend to increase as time proceeds.

As traffic carried across large suspension bridges such as the Great Belt Bridge intensifies, the risk of a truck fire increases. A fire on the New Little Belt Bridge in 2013 showed that a truck fire on a suspension bridge could lead to main cable failure or reduced strength of the cable. The reason is that a truck fire may lead to temperatures equivalent to a hydrocarbon fire. This may cause a permanent reduction in the load carrying capacity or the need for extensive repairs to the main cable, all involving substantial costs for society. In terms of the design, comprehensive studies were carried out to ensure adequate protection against fire exposure and to ensure concept integrity throughout the duration of a vehicle fire. This comprised the simulation of heat penetration into the main cable following a fire, assessment of the resulting strength reduction and experimental verification of the concept. The developed concept included a combination of the use of insulation materials and intumescent fire coating. Plans for the fire protection work were drawn up in collaboration with COWI. Three fire tests were conducted on a five‑meter long steel pipe using different insulating materials. The results were applied for updating the design and choosing the optimum design configuration for the protection of the Great Belt Bridges main cables. DBI (Danish Institute of Fire and Security Technology) carried out the tests. This paper also describes the planning of the installation work. The execution of the project took into account, for example, the design for supporting a fast installation, the concept for fitting to the as built cable, fine‑tuning the concept in aesthetic terms, and providing access systems for the works. Finally, the logistical planning of the installation with traffic continuing to operate on the bridge was also taken into consideration.

This paper presents an approach for fire protecting suspension and cable stay bridges vehicle fires. Over the last 10‑20 years, a number of accidents have resulted in severe truck fires on bridges. Examples can be mentioned from UK, Denmark, Turkey and more. In Denmark, a severe truck fire occurred in 2013 on the New Little Belt Bridge causing extensive damages. The awareness of fire risk to transportation infrastructure is now global. Experiences from fires in lorries/trucks carrying normal but flammable goods show that such fires may have a temperature development equivalent to a hydrocarbon fire with temperatures up to 1100‑1200 C. Depending on the vulnerability of the cable system, this may pose a risk both regarding the bearing capacity during a fire but also regarding the bearing capacity after a fire. The fire risk is particularly large for cable borne bridge where cable elements are vital for the structural integrity. A positive cost‑benefit has been demonstrated for suspension bridge main cables whereas the cost‑benefit of protection suspenders and cable stays will depend on the cable system vulnerability to a vehicle fire. The recognition of the concern was the reason for carrying out fire protection of the main cables on the New Little Belt Bridge in 2016‑2017 and in 2018‑2020 for the Great Belt Bridge and similar studies are approaching a completion in UK, Sweden and France for major cable suspended bridges. For these bridges, fire risk has been assessed through fire simulation of cable cross sections and clam interface with suspenders. Based on the need for fire protection, an innovative concept was developed using a combined numerical and experimental methodology approach for verification. The application of the concept was combined with the use of intumescent paint. The fire protection approach was fully verified by large scale fire furnace testing and RD projects carried out. The installation works on the bridge showed that the concept was very efficient to install with minimum consequences regarding traffic, and also future inspection and maintenance.

Ice shedding from bridge cables and pylons poses a significant risk to traffic flow, potentially resulting in property damage and injuries. Timely detection and tracking of ice shedding are crucial for developing effective early warning systems, aimed at preventing the aforementioned risks. Moreover, the integration of early warning systems can be used to trigger autonomous robots for timely and efficient ice removal on bridge cables, further enhancing the safety measures and reducing the risk of ice‑related incidents. In this context, a new technology for the ice shedding detection to be included in an integrated approach to enhance safety on bridges during icing conditions is proposed. To achieve this goal, machine learning (ML) and computer vision (CV) technologies hold great promise when working in concert as a non‑contact solution. The primary objective of the presented research is to harness advanced CV technologies for precise tracking of ice shedding on bridge cables and pylons, thereby significantly reducing bridge operational risks. Current research and applications within this domain remain limited, and a notable challenge arises from the scarcity of training data available for ML models if applying tracking‑by‑detection multi‑object tracking methods to track ice shedding. Correlation Filter based methods are considered as our preferred option. Transforming Model Prediction for Tracking (ToMP) is one of the best because it utilized the advanced Transformer framework, but usually it cannot work alone, because the information and position of the interested target in the initial frame must input to the tracker before it works. Frame differencing (FD) is used to support ToMP because it can obtain the information and position of possible moving targets. The integration of ToMP and FD enables real‑time and accurate tracking of ice shedding events, contributing to the enhancement of bridge safety through early warning systems. The proposed method can efficiently identify and monitor instances of ice shedding on bridge cables, enabling authorities to take proactive measures to prevent potential hazards and ensure timely maintenance of critical infrastructure.

The Benjamin Franklin Bridge (BFB) was opened to traffic in 1926 and supports 7 lanes of vehicular traffic and two PATCO train tracks. The BFB is a heavily traveled bridge with a total Average Daily Traffic (ADT) of vehicles more than 100,000 and about 200 PATCO trains per day. Therefore, one overarching goal for all construction projects on the BFB is minimizing impact to traffic. After being in service for over ninety years, many major components in the suspended spans require replacement or strengthening. DRPA, the owner, has embarked a major rehabilitation project, which has a total cost about $219 million dollars. The construction project was awarded to Skanska USA Civil, who in turn hired CHI Consulting Engineers to design various jacking frames and temporary supports for the Major Steel Repairs. The scope included the removal and replacement of ninety‑six (96) end sections of bottom lateral bracing in the suspended spans; four (4) wind tongues at both towers; eight (8) rocker links at both towers; two (2) wind pins, four (4) end laterals and four (4) rocker links at both anchorages. The designs of jacking frames and temporary supports need to be robust: capable of supporting all vertical and lateral loads while causing minimal impacts to the traffic, especially the PATCO train service; and easy to construct, adjust, and operate. Many innovative designs have been developed to achieve the project goals and keep the traffic moving on the BFB. The temporary supports, i.e. alternative load paths, for the major steel repairs in the suspended spans, at the towers and inside the anchorages can be installed before removal of any existing members and can resist the full design loads without the existing members, therefore they have ensured the safety of the bridge and minimized the disruption to the train and vehicular traffic throughout the duration of these intensive repairs. The related construction work has been successfully completed, and these high load jacking frames and supports met or exceeded the expectations from both Skanska and DRPA. The project earned 9th place at the 2023 Roads Bridges Top 10 Award, and a Gold Award at the 2024 ACEC NY Engineering Excellence Awards.

The Strmsund Cable‑Stayed Bridge is located in the town of Strmsund, Sweden. The bridge operator is Trafikverket (Swedish Transport Administration). The bridge opened in 1956 and with a main span of 182.6 m it was the first major cable‑stayed bridge in the world, the earlier record span was just 80 m. The bridge has 2 towers and 16 stay‑cables, 8 on each side. Each stay‑cable is composed of 4 locked‑coil cables with diameters from 66 mm to 88 mm. A paper entitled Strmsund Cable‑Stayed Bridge: Cable Corrosion and Replacement, was presented by the author at the 2016 ICSBOC. A brief summary of this paper will be included in the current paper. Hence, the paper will include the entire history from the discovery of cable corrosion and broken wires to the replacement of all the stay‑cables and installation of supplementary dampers over a period of ten years. The current paper covers the period of 2017 to 2023, during which follow‑up measures were carried out and all the remaining original stay cables were replaced. Continuous monthly inspections were carried out and in 2019 signs of wire breakage were observed on stay‑cables 5S and 7N. This prompted the elaboration of tender design for replacement, which was carried out in 2020. The works were successfully carried out in 2021‑2022. Stay cables 5S and 7N were replaced first, as they had the most critical condition. The replacement works were carried out in pairs, working on two corresponding stay cables on each side of a tower at a time. Temporary strengthening cables were installed for these two cable‑stays and 2 cable strands were replaced at a time during one weekend per pair. Hence, the complete replacement of 2 stay‑cables was carried out over 4 weekends. During the construction works, traffic loads were generally restricted to ensure the necessary safety level. During the replacement works in the weekends, the bridge was completely closed for traffic. During construction, the contractor observed that the new cables were more susceptible to wind induced vibrations than the original cables. The new cables are encased in HDPE, which is smoother than the original bare locked‑coil cables. This resulted in mild wake buffeting and wake galloping. This was solved by installing two simple dampers on each stay‑cable.

The Sherman Minton Bridge includes two 800ft arch spans that carry Interstate 64 across the Ohio River between Louisville, Kentucky, and New Albany, Indiana. Completed in 1962, it features an iconic design with its double decks and twin arches, and remains an essential link in the interstate highway system. The bridge is currently undergoing a major rehabilitation project, including the replacement of all hangers. The Kokosing Construction Companys (KCC) DB team included Modjeski and Masters (MM) (as a design subconsultant to Jacobs Engineering) to perform the hanger replacement design, including temporary works. For the hanger replacement task, continuous support of the tie‑girder is required, because the tie‑girder between floorframes is not very stiff. However, MM proposed an Alternative Technical Concept (ATC), which eliminated the need for a separate temporary support system; instead, the new hangers were relocated to the outside of the gusset plates, supported by cantilevered brackets. This permitted the load to be transferred directly from the existing hangers to the permanent hangers without the need for temporary suspenders. This presentation will focus on the cost and schedule benefits of the ATC, as well as its design. The Ambassador Bridge is an 1850 ft main span suspension bridge between Detroit, MI and Windsor, ON, which opened in 1929. Over the past 20 years, the owners have been investing in significant rehabilitation projects, which now includes the replacement of all remaining original suspenders. MM developed the contract plans for the replacement, and Structural Technologies is performing the work. Due to the heavy truck traffic and the questionable condition of adjacent suspenders, it was decided that continuous support of the stiffening truss was needed. Strand jacks were used to support a jacking beam that bore on the underside of the floorbeam, with the strands hung from a temporary saddle at the main cable. The long strands themselves permitted use at the longest and shortest suspender locations. This presentation will focus on the methods used to measure suspender lengths, establish shim heights and permitted jacking loads, allow for adjustability, and to accommodate significant variances in live loading.

In the recent years, a trend to equip bridge structures with Structural Health Monitoring Systems (SHMS) has developed. Owners want to achieve a high lifetime whilst being certain about the safe operation of their bridge structures, as well as using sensors during the installation process to confirm and optimize installation procedures. Not only new structures, but existing structures are equipped with sensor‑based monitoring solutions to provide continuous data associated with physical structural properties. Lifespan management for bridge structures typically consists of: Bridge Inspection; Structural Health Monitoring; and Bridge Maintenance. Typically, main inspections, e.g. suggested in fib Bulleting 86 Chapter 6, are to be performed every 6 years. Sensor‑based monitoring solutions overcome the limitations of traditional visual inspections and Non‑Destructive Testing (NDT) methods which are limited to the point of inspection at a discrete time. Structural Heath Monitoring will provide information about the lifetime performance the whole structure. This paper will discuss bridge structures where SHMS have been applied recently and how the gathered data was used to assess the impact of e.g. loading and environmental condition changes. For a comprehensive assessment of bridge structures, a substantial sensor combination to acquire stressors such as strain, displacement, or acceleration is required. The wide array of sensors available on the market is often not optimized or applicable for bridge structures and requires experts to integrate. Therefore, a close cooperation between the designer and the SHMS specialists is required to provide owners with well processed and presented data e.g. in form of an automated reporting. Correct sensor technology choice, sensor accuracy, and sensor location are crucial. Also, an adequate data acquisition system as well as representation on a corresponding platform is required. Data can be used for dynamic short term data analysis resulting in a real time threshold‑based alerting. Typical examples are real time cable forces of stay cable bridges checked against design values as well as a long‑term trend detection e.g. settlement / drift based on displacement data or uncovering hidden dependencies such as wind induced cable vibrations of temperature dependent deck movements. This paper will focus on providing information and education to the bridge industry for a better and more sustainable integration and utilization of SHMS applied to bridge structures enabling a better cooperation between the key civil engineering professionals and electrical engineers as well as computer science specialists.

A novel fiber optic (FO) Acoustic and strain sensing technology is proving successful in its deployment across multiple bridges, marking a significant advancement in civil infrastructure monitoring. While fiber optic sensors have long dominated industries like Aerospace and Petro‑chem, their application in Civil Infrastructure is relatively recent. Unlike traditional electrical‑based sensors, which are likely to corrode and have electrical shorts, FO sensors offer extreme durability and reliability. These sensors need to last for decades, and FO sensors and cables have a life expectancy of more than 20 to 50 years. This FO strain sensing technology has successfully been applied to steel bridges to measure deflection and twist on bridge spans, and efforts are underway to integrate this technology into suspension cable bridges for approach spans and main spans. For suspension cables, acoustic monitoring cannot detect previous wire breaks, thus a pilot installation project is underway to explore the effectiveness of FO strain sensors to enhance safety and reliability. If successful, the use of this technology for older suspension cables would be invaluable in locating bad panels. In 2020, validation testing of the FO strain sensor was performed in a laboratory, showing an exact correlation. Afterward, a pilot study conducted on an NYC bridge showed the effectiveness of FO strain sensors in detecting degradation on reinforced concrete spans. Another large SHM project involved the redesign of 260 traditional electrical point‑strain gauges and multiple systems. The new design used one system and one FO strain cable. This innovation provides strain readings every 4 inches, for the entire bridge. With a single FO strain system capable of monitoring an entire bridge, the cost benefits and asset health intelligence capability are substantial. Electrical‑based Acoustic sensors have been used on many bridges for wire break detection, but cables and sensors typically require replacement in <10 years. For decades, FO acoustic sensors have been used in extreme environments and have undergone accelerated life testing for vibration and water submersion. Additionally, FO Acoustic sensor technology was tested by VDOT as being more sensitive when compared to a piezoelectric AE sensor. Most importantly, a new software dashboard has been developed to intelligently manage and analyze the vast amounts of data collected, incorporating alarms for real‑time notifications to stakeholders. The adoption of FO sensing technology represents a comprehensive and efficient solution for supplementing inspections, non‑destructive testing, and providing confidence in the structural integrity and long‑term preservation of bridges.

The Hakucho‑Ohashi bridge is the only long span suspension bridge in Hokkaido Prefecture, in the cold region of Japan. The bridge has a total length of 1380 m and a main span of 720 m. The bridge has been in use for more than 25 years. In Japan, the visual inspection for all bridges must be done at once during five years by law. Even though the short‑ and medium‑span bridges can be easily inspected visually and structurally, the long‑span bridges cannot be easily done with danger. Therefore, new technologies for inspecting the long‑span bridges safely, precisely, and economically should be introduced. From this point of view, in this paper, in order to effectively inspect structural healthy state of the Hakucho‑Ohashi bridge, proposing usage of a measuring system of the optical‑fiber sensor with IoT technology, an applicability of the system to the maintenance management of the bridge was investigated to measure the dynamic responses of the bridge, in which the fiber sensors were set at the upper and lower fibers of the most outer stiffening girders. From this study, following results were obtained: 1) natural vibration frequencies of the bridge at current state can be easily estimated by using measured strain waves and the healthy state of the bridge can be inspected; 2) the strain waves can be surely measured at the strong wind blowing and/or the severe earthquake occurred; and 3) since the waves can be measured with long term stability, the proposed system may be applicable for monitoring the Hakucho‑Ohashi bridge.

The Texas Department of Transportation has undertaken in‑depth condition assessments on the Fred Hartman Bridge in the Houston District and the Veterans Memorial Bridge in the Beaumont District. Both bridges are long span cable stay structures of complicated nature and were both built in the early 1990s. The in‑depth structural assessments were performed to establish base‑line conditions of the bridges. Both of these bridges exhibited notable vibration of their cables early in their lives that necessitated a retrofit consisting of a damper system. Near the time that the cable dampers were installed, an acoustic monitoring system was also installed as a structural health monitoring system. The acoustic monitoring system essentially consisted of microphones at each cable end calibrated to identify the sound of a wire break and estimate the location of the wire break. Once a sound signal was identified, an alert would be triggered that a possible wire break had occurred within a tendon of over a hundred wires. Using indicators based on Acoustic Monitoring, locations can be selected to further determine the presence of deterioration in stay cable strand wires. No known reliable means of NDT exists to perform examination of stay cable free lengths and anchorages to definitively identify the presence of section loss, cracks, damage, or wire breaks. Therefore, an exploratory procedure which uses the exposed strand tail ends at the anchors was developed to gain understanding of the condition of the individual strands. The detectable test sample size is limited to the length of strand in the anchorage zone, which is the region of the stay cable most likely to suffer deterioration and experience a wire break. The wires of strands within stay cable superstructure anchorages, which are sensitive to corrosion, wind‑ and traffic‑induced axial/bending fatigue loading, and premature deterioration, have failed at or near cable anchorages on several occasions both in laboratory qualification testing and in service, making this a critical section of cable to inspect. This procedure uses Ultrasonic Testing (UT) to determine defects. UT uses high frequency sound energy to transmit acoustic waves into the strand where they travel at a constant speed until they encounter a discontinuity. At discontinuities, reflected and transmitted waves provide information about the size of the reflector, or material discontinuity. Defect locations are determined by the wave travel time. This presentation will discuss using the above methods to determine stay cable deterioration locations in stay cable bridges.

The Seaway International Bridge consists of two distinct bridges, the South Channel Bridge (SCB) and the North Channel Bridge (NCB), that link the Akwesasne Mohawk Territory to the Messena, New York, United States and Cornwall, Ontario, Canada across the St. Lawrence River. Both the bridges are maintained by Seaway International Bridge Corporation (SIBC). The Federal Bridge Corporation (FBCL) and the Great Lakes Saint Lawrence Seaway Development Corporation (GLS) are the owners of SCB. The South Channel Bridge first opened in 1958 and is a suspension bridge with a total length of 1061 metres and a roadway width of 8.2 metres. The stiffening truss of the bridge deck is connected to the towers by eight rocker arms. The rocker arms have pin‑ended connections and therefore are expected to primarily be subjected to axial loads. One of the rocker arms developed fatigue cracks and fractured in 2015 causing the deck to descend 150 mm at the expansion joint. The entire rocker arm assembly was replaced. By 2021 there were concerns about the other seven rocker arms. The basic question we were asked to answer is: should the other 7 rocker arms be replaced, and if so, when? The strategy in this case was to install 32 vibrating wire strain gauges on the original and replaced rocker arms. Through a collaboration with university researchers, a protocol for accessing and analysing the data was established. The paper will describe the installation of the sensors, the data logging equipment and placement, and management of the data files. The paper will also describe the method used to zero the gauges, and to establish a feasible recording rate for the data logger. The processing of the data using a Rainflow analysis, and standard fatigue stress‑life curves, allowed us to quickly identify the most critical rocker arms. We were able to track changes in fatigue damage week‑by‑week for each of the rocker arms. Having the replaced rocker arm instrumented was critical because it provided a baseline for fatigue for comparison with the original arms. The rocker arms were monitored for approximately 8 months, at which point the bridge owners decided that replacement of all the original rocker arms was necessary. Although this is a relatively short monitoring period, we were able to make some observations on the effect of temperature on the rocker arm response.

This contribution demonstrates how operation and maintenance of one of the largest suspension bridges worldwide have significantly benefitted from a structural health monitoring (SHM) setup with +400 sensors developed in a unique collaboration between consultants at Ramboll, contractors, and the owners from Sund Belt. The Great Belt Fixed Link in Denmark opened in 1998 and consists of an 18 km road and railway link composed of a tunnel, a continuous multi‑span beam‑type bridge, and a suspension road bridge with a main span of 1624m, the current 6th longest worldwide. The aim of the tailormade SHM setup is to provide knowledge of structural performance, deterioration and remaining lifetime to the asset managers that can accordingly plan maintenance and actions for mitigation of undesirable structural performance to ensure economical and sustainable asset management and safe operation. The contribution provides an overview of the SHM system followed by case studies showing SHM outputs and how these are used data‑driven decisions in the operation and maintenance. Specifically, it is presented how the SHM provides insight into the vibration phenomena and fatigue lifetime of the hangers, insight into fatigue lifetime of the main girder including influences of operational and environmental parameters, and insight into wear and lifetime of the bearings. It is revealed how this valuable information are used in decision making of the operation and maintenance of the suspension bridge. Lastly, further improvements of the monitoring system and subsequent analyses are discussed with respect to the further value it brings for the asset managers.

Bridge asset owners need a well functioning structural health monitoring (SHM) system to generally manage and operate bridge assets safely and efficiently. Such a system is also necessary to extend the service life of a bridge and thereby meet sustainable goals which are becoming more important for a growing number of public and private bridge asset owners. Finally, the purpose of having SHMand risk management framework is to provide rapid access to SHM data and enable informed decision‑making for bridge owner in relation to risk. Sund Baelt is an owner of the Great Belt fixed link which is an 18 kilometres long multi‑element crossing the Great Belt strait between the Danish islands of Zealand and Funen. It consists of a road suspension bridge, a railway tunnel and a box‑girder bridge for both road and rail traffic. Great Belt Bridge SHM system has been developed over the years to enable collection of data from various sensors that in combination with maintenance and digital asset management strategy led to extension of service life by 100 years. This paper shows the next step in development of the SHM system, namely the integration of cutting‑edge camera‑based monitoring system into the overall cloud‑based asset management platform. The existing computer vision system is one of the first of its kind in the worldand involves digital image correlation (DIC) analysis to monitor wind‑induced hanger vibrations and traffic‑induced deck deflections in real‑time through continuous video recordings. The integration allowed for rapid access to vibration and displacement data, plotting of results and quality assurance of measured hanger vibrations by the acceleration system. One of the benefits of DIC is that it provides direct displacement data in mm from +100 m with no traffic disruption (f.x. vibrations of the hanger center point, while the accelerometers measure accelerations near the bridge deck). Moreover, saving DIC video recordings of large bridge displacement incidents provides previously unavailable insights to the bridge owner. The use of computer vision and DIC technology gives asset owners affordable and accurate analysis of real structural performance and is a huge step forward in improved bridge asset management. It has the potential to give engineers clear data on how the structure is performing in service, regardless of complexity or hidden load paths and helps validate information from models or other instruments.

Serious corrosion problems with main cables on suspension bridges were discovered on a number of suspension bridges in the US in the 1960s. This led to worldwide investigations of main cables and similar results were found on bridges around the world. Even cables that had been well maintained on the surface and showed no outer signs of problems were found to have serious corrosion when opened for inspection. All this evidence proved that a traditional system for corrosion protection was generally not sufficient and that a new improved method was necessary. In the late 1980s and the 1990s suspension bridge owners and consultants were researching methods for improved corrosion protection. Corrosion protection by means of dehumidification already had a long track record on bridges at that time, starting with dehumidification of the steel box girder and the splay chambers (exposed strands) of the Little Belt Suspension Bridge in Denmark in the 1960s. It was however, not yet applied to suspension bridge main cables. A partial application to main cables was applied to the Humber Bridge in the UK in 1995, where dry air was injected into the tower saddles. In the 1990s the Honshu‑Shikoku Bridge Expressway Company carried out research concerning main cable dehumidification and applied a system to the Akashi Kaikyo Bridge, which was completed in 1998. In the late 1990s to 2002 similar research was also carried out in Denmark, which led to the dehumidification of the main cables of the Little Belt Bridge in 2003. Since then the application of dehumidification to main cables has spread to the rest of the world and is generally accepted as a worldwide best practice. Whereas earlier papers on main cable dehumidification have generally concentrated on the design of systems and case stories, this paper focuses mainly on operation and maintenance of systems in service as well as opportunities for further optimization of existing systems. Experience from inspections and analysis of data from monitoring systems of several main cable dehumidification systems that have been in service up to 16 years will be presented. Recommendations for follow‑up and maintenance based on this experience will also be presented. Further, possibilities for optimization of existing systems according to current knowledge will be described and illustrated with case stories.

Since the main cables of suspension bridges are the most important components that are difficult to replace, reliable corrosion prevention systems are essential. As a corrosion prevention method, the Honshu‑Shikoku Bridge Expressway Group, have developed a dry air injection system (DAIS) for main cables and installed it to the Akashi‑Kaikyo Bridge for the first time in the world. After that, it was installed to nine other suspension bridges of the Honshu‑Shikoku bridges in sequence. To ensure reliable operation of the DAIS, temperature and humidity data are collected from several sensors installed in each span of the suspension bridges main cables and used to monitor operating status, detect problems early, and carry out scheduled repairs. However, current monitoring systems are unable to collect real‑time information, require time‑consuming data collection and have other problems. In addition, each sensor and hub is wired together, which requires a lot of money and effort to replace the monitoring system every approximately ten years. This paper describes a response to these challenges and the potential future applications of the newly developed system. A system consisting of two types of devices (temperature/humidity/air‑pressure sensors and data repeaters) and software has been developed. The repeaters have a low power wide area network (LPWA) and a solar panel. The software provides access to temperature, humidity, sensor, and repeater information by accessing a cloud server, eliminating the need for cables on the bridge and allowing real‑time data to be collected anywhere on any device. It also makes replacement work safer and less costly, and the number of sensors can be increased, making maintenance more efficient. Furthermore, since heavy machinery work is not nessesary during installation, it is also possible to significantly reduce carbon dioxide emissions. A prototype of this system was temporarily installed on the Kurushima Kaikyo Bridges in 2024. The effectiveness of the system was generally confirmed, despite some challenges. In the future, the temperature, humidity, and air‑pressure sensors in this system can be replaced with accelerometers and anemometers to create a wireless structural health monitoring system, or with a high‑sensitivity microphone to create a machine abnormality detection system.

The Delaware River and Bay Authority (DRBA) recently rehabilitated the entire deck of the two‑mile‑long northbound Delaware Memorial Bridge using ultra‑high performance concrete (UHPC). The top two inches of the concrete deck were replaced with UHPC, in an application often simply called a UHPC overlay, which strengthened, stiffened, and water‑proofed the 55‑year‑old deck. The UHPC is expected to extend the deck service life for another 40 years. This is the first cable‑supported bridge with a complete UHPC overlay in North America. Construction was carried out in three phases beginning in September 2022 and ending in November 2023, rehabilitating over 550,000 square feet of deck. The project was preceded by a detailed lifecycle cost analysis, followed by a small pilot project which helped guide project decision‑making. The lifecycle cost analysis showed a clear economic advantage to performing a UHPC overlay versus deck replacement or placing other overlay products. Revisiting the comparative analysis from a sustainability perspective shows that the UHPC overlay is also the most sustainable solution. The presentation will provide an overview of the entire deck rehabilitation process, from the 2018 deck evaluation study through the pilot project, and then present the construction of the full UHPC deck rehabilitation. Recommendations will also be presented on how to improve the work of placing UHPC overlays, especially on large bridges, for the benefit of owners and designers looking to implement this cost‑effective and sustainable method of extending bridge deck service life on other projects.

The Verrazzano‑Narrows Bridge (VNB) includes a mile‑long suspension bridge with both an upper and a lower level. MTA Bridges Tunnels (TBTA), along with HNTB, investigated alternatives to improve public safety by restricting access to the bridges suspended span structure beyond the roadway footprint and following several prototype solutions prepared a preliminary design for a cable supported stainless steel mesh system. The fence system had to be as unobtrusive as possible and architecturally appropriate given the iconic status of the VNB. Additionally, the impacts of the proposed fence on long span bridge wind behavior were evaluated in the wind tunnel during the conceptual phase. Under a design build contract, El Sol Contracting and Dewberry Engineers Inc. provided the final design, fabrication, and installation of a 9 high safety fence placed on a 3‑6 barrier on the upper level and a 8‑9 fence on a 3‑2 barrier on the lower level. The fence is designed for wind and ice loads as well the ability to resist a 250‑pound concentrated load in any direction applied to any location of the fence. In order to a allow for an under bridge inspection unit to access the underside of the lower level for inspection and maintenance, the upper portion of the fence was designed with a hinge so that it could be easily lowered. The design had to accommodate the large movements at the towers, and many protrusions, such as fire standpipes, electrical boxes and access points for maintenance throughout the upper and lower levels as well as emergency stairways between the upper and lower levels that had to be protected but kept open. The upper level fence also had to accommodate a wind barrier system to mitigate the effects of high wind forces on trucks. The project from inception to completion took approximately 3 years and has proved to be highly effective.

The $211 million Golden Gate Bridge Physical Suicide Deterrent System (SDS) Project consists of two key components: 1) the addition of approximately 385,000 square feet of specialty net that will be installed along both sides of the entire length of the approximately 1.7‑mile‑long bridge structure and 2) the replacement of the existing 8 maintenance travelers on the Suspension Bridge with 16 new travelers due to interference between the existing travelers and the new SDS supports.The suicide deterrent net system is made from marine grade stainless steel wire mesh, which is connected to galvanized HSS net support brackets, spaced typically at every 50 feet and painted to match the existing International Orange color of the Golden Gate Bridge. The net will be stretched across the support struts located 20 feet below the bridge sidewalk and extending out 20 feet. Prior to the permanent installation on the Bridge, a mock‑up of the net system must be constructed to verify certain key measurements of the net system. The existing maintenance travelers will be replaced with four sets of new Interior, Bottom, West, and East Side Travelers. These new maintenance travelers are battery powered steel travelers with variable frequency drive (VFD) controller driven wheeled trolley system. Each traveler also consists of programmable logic controller (PLC) electronic control system, battery management system including battery power supply and battery charging system. Other supporting infrastructure include replacement of the existing Maintenance Traveler Rails, installation of new Traveler Charging Platforms and Electrical Power supply. This presentation will focus on the SDS net system and provide updates to the construction of the project, highlighting the challenges of designing and constructing this system on one of the most iconic bridges in the world.

The New Samuel De Champlain Bridge in Montreal, Quebec, was opened to traffic on July 1, 2019. As one of the busiest bridges in North America more than $20 billion (CDN) of cross‑border goods traverse the bridge annually, it plays a vital role in Canada's international trade partnerships. Three structures comprise the 3.4‑kilometer (km)‑long bridge across the St. Lawrence River: a 529‑meter (m) signature span featuring an asymmetric cable‑stayed bridge with a main span of 240 m; a 762‑m east approach with a maximum span of 109 m; and a 2,044‑m west approach with a typical span of 80.4 m. The new bridge has highway corridors carrying up to four lanes of traffic in each direction, a two‑lane transit corridor accommodating a planned light‑rail system, and a multiuse path for pedestrians and cyclists. The bridges superstructure, pier caps, pier legs, and tower are constructed of concrete and steel elements. The superstructure is constructed of composite steel box girders with precast deck panels. The aesthetically designed, W‑shaped pier caps are prefabricated in steel. The pier legs are precast concrete, hollow sections made continuous by post‑tensioning. The 170‑m‑high concrete pylon of the cable‑stayed bridge portion comprises twin masts, forming a tuning‑fork configuration with its inclined tower legs echoing the shapes of the pier legs throughout the approach spans. The stay cables are arranged in a harp shape and are anchored to the tower using specially designed link beams. Due to its geographical location, this lifeline structure faces unique hazards, including extreme cold, ice abrasion, deicing salt attacks, wind, vessel collision, scour, and seismic issues, and must meet a design life of 125 years. This paper describes the holistic approach taken to fulfill the durability requirements to ensure that all structures and components maintain levels of serviceability during their design lives. Comprehensive durability plans were developed jointly by both the design and construction teams to address material selection, design detailing, the corrosion protection system, construction quality and inspection, structural monitoring systems, and an access and maintenance plan employing a variety of equipment, including an under‑bridge inspection vehicle and electric superstructure shuttle/vehicle.

The Robert F. Kennedy (RFK) Bridge, originally known as the Triborough Bridge, was constructed between 1929 and 1936 and opened on July 11, 1936. The RFK Bridge Facility consists of three bridges, 14 miles of elevated viaducts and approaches, ramps, and one interchange connecting three boroughs of New York City. It provides access to vehicular, bus transit, and pedestrian traffic. The East River Suspended Spans (ERSS) are the longest spans of the RFK Facility consisting of a 1,380 long main span and 671‑8 long side spans. The spans connect the Queens Viaduct in Astoria, Queens with the Randalls Island Viaduct on Wards Island. The ERSS carries eight lanes of traffic, four in each direction with no shoulders and a deck width of 92‑8. Pedestrian access is provided by a walkway located along the stiffening truss top chord on the North side; the south side walkway is only accessible to MTA for maintenance purposes. The paper discussess the history of the main cables since the original construction. The effect of environmental degradation, maintenance work performed over the years, and the cable assessment investigations performed will be briefly discussed. The paper will discuss how the conflicting objectives of keeping the dead load on the cables controlled versus demands of the emerging operational needs are managed. Two main cable investigations and subsequent strength determinations were performed; in 2001 and in 2021. In 2004, the original deck was replaced with a lighter steel orthotropic deck. The very recent initiative of providing AASHTO compliant Shared Use Paths (SUPs) across the entire RFK Bridge Facility required studying how that can be accomplished on the suspension bridge portion as well. Various options were studied for functionality, aerodynamic behavior, etc. before selecting locations and configuration. The effect of these additional dead loads and corresponding live loads will be discussed. The paper will discuss the original bridge live loads used in the design, and contemporary live loads including non‑permitted overweight trucks and their effect on the cables. The paper will also discuss the planned main cable dehumidification. The paper will demonstrate how the changes to the bridge over decades affect the loads on the cables and the corresponding load carrying capacity and how with strategic planning and measures, the owners can preserve and maintain the load carrying capacity of the main cables of a suspension bridge.

A six‑lane motorway bypass is planned to alleviate overcrowding and congestion in the Osaka‑Kobe metropolitan area in Japan. The plan includes a four‑tower continuous cable‑stayed bridge over the sea, which will have a maximum span length of 653m, making it one of the worlds largest spans for a continuous cable‑stayed bridge when it will be built. The bridge must withstand natural phenomena, such as earthquakes and wind, as well as heavy traffic by truck. This is because it is connected to an international trading port and industrial area. In continuous cable‑stayed bridges, the cable‑stay effect does not reach the central span because there is no anchor cable. This makes the central span more susceptible to deflection than in general two‑tower cable‑stayed bridges. As a result, fatigue characteristics may be significantly different from those of general two‑tower cable‑stayed bridges. This paper investigates the features of fatigue characteristics of continuous cable‑stayed bridges under heavy traffic conditions from a design perspective. A six‑lane congested loading model was created based on the results of a survey of the actual conditions on the motorway connecting the bridge location. The fatigue characteristics of continuous cable‑stayed bridges were investigated using live load simulation with this model. The studys main findings were as follows. First, the cumulative damage which cause damage, was not measured in any of the main girders, cables, or main towers during the 100‑year service period. Therefore, the continuous cable‑stayed bridge used in the study was found to be a safe structure against fatigue. Furthermore, the alternating positive and negative influence lines in some of the main girders resulted in a reduction of stress increase caused by continuous vehicle loading. This effect was more significant compared to that of two‑tower cable‑stayed bridges. The cumulative damage of the main girder resulting from the live load simulation is analyzed using the factors of influence line, based on the above findings. Consequently, a simplified fatigue verification method for main girders of continuously cable‑stayed bridges is proposed. This method is based on the fatigue damage verification method using influence line loading of single‑axle vehicle weight applied to general bridges. In addition, comparison of the results of live‑load simulation and live‑load influence line loading also confirms that the incremental response values due to impact on continuous cable‑stayed bridges are smaller than on small and medium‑sized bridges. This trend is similar to that for two‑tower cable‑stayed bridges.

Suspension bridges of all sizes and uses are elegant accents across our transportation landscape. As longstanding engineering marvels, these ornate structures have a unique set of maintenance aspects. This discussion will be on the construction, monitoring/inspection, rehabilitation, and lessons learned on suspension bridges of all types and sizes. Recent rehabilitation projects discussed will include (original construction): Ambassador Bridge (1929; 1850 ft main span), Waco Suspension Bridge (1870; 475 ft main span), Missouri River Pipeline Suspension Bridge (1956; 457 ft span), Leo Frigo Memorial Bridge (1981; 450 ft span), and Jefferson Barracks Bridge (1983, 1992; 909 ft span). The discussion will involve suspended bridges spanning over 100 years of construction, touching on technologies used to monitor them through their service life, as well as rehabilitate the structures for increased demands while maintaining their historical significance. Monitoring and inspection technologies will include non‑destructive (e.g. magnetic main flux method (MMFM)) and destructive (e.g. load capacity testing) test methods. Rehabilitation aspects to be discussed will include the replacement of the entire suspension system and will primarily focus on the suspender cables. While the basic structural design aspect of these bridges from throughout history is the same, there are particular similarities and differences between these suspension bridges of different sizes and transportation requirements that will be highlighted. Structural Technologies/VSLs experience in suspended spans provides the background, pictures and methods for this discussion.