Lessons Learned from an Emergency Bridge Replacement Project

The terrorist attack on September 11, 2001, and subsequent potential threats to U.S. transportation systems have presented an urgent need to develop emergency response plans to quickly react to the possible consequences of extreme events. Extreme events include terrorist attack as well as man-made and natural disasters such as explosions, fires, floods, and earthquakes. The objective of this research was to identify strategies and technologies to quickly restore the use of highway bridges, a critical component of the nation’s transportation network, in case they are damaged or destroyed by extreme events. One of the tasks associated with this research was to conduct case studies of previous bridge replacements following extreme events. By studying these cases, the research team sought to identify and expand on lessons learned, address which actions did and did not work well given the circumstances of the incident, and incorporate lessons into the emergency response plan for highway bridges. This paper presents the findings from one of the case studies, the I-40 Webbers Falls Bridge in Oklahoma.     

Rapid Bridge Replacement: Processes, Techniques, and Needs for Improvements

The terrorist attack on September 11, 2001 and subsequent potential threats to the United States transportation systems have presented an urgent need to develop emergency response plans in order to quickly react to the possible consequences of an extreme event. Highway bridges, as critical components of the nation’s transportation network, have received increased attention. To respond to the potential threats on highway bridges, a research project was conducted to identify rapid bridge replacement processes, techniques, and needs for improvements. To achieve the research objectives, the research team studied three cases of previous bridge replacements following extreme events. By studying these cases, the research team first sought to identify and expand on lessons learned and then addressed which actions did and did not work effectively under the incident circumstances. Using the lessons learned government agencies and engineering and construction communities could enhance their emergency response plans for future incidents. Next, the research team identified needed improvements so that the research community could investigate new technologies to advance current practices.     

Best Practices of Bridge System Management—A Synthesis

The paper’s primary purpose is to evaluate current practices in bridge management and inspection procedures in the United States and how State Highway Agencies (SHAs) follow U.S. Department of Transportation guidelines. The efficiency of SHA in utilizing the bridge management systems (BMSs) available to them is analyzed, and the agencies’ readiness to respond to events such as hurricanes, flooding, or earthquakes is evaluated. The paper addresses issues regarding bridges with unknown foundations, interviewing four structural engineers from three SHA regarding these topics. Bridge management officials across the country will benefit from this research by evaluating their agencies’ current practices in comparison with other state agencies. Findings show that state officials attempt to follow very closely the guidelines set by the federal government for bridge inspection and maintenance. However, it was also discovered that, during catastrophic events, agencies rely heavily on managing engineers’ experience and decision-making capabilities because there is no set of response procedures for these extreme conditions. Although powerful BMS tools are available, few SHA utilize these tools to their full capabilities.     

As-Built Information Model for Bridge Maintenance

The transportation infrastructure is key to economic development in the United States. Providing a high level of serviceability through periodic inspection and maintenance is important in keeping the transportation system operational and in avoiding major replacement efforts. Of particular importance is the inventory of bridges in the national transportation infrastructure, due to their high cost and direct impact on public safety. The focus of this paper is on information management in support of bridge maintenance functions. Particularly, the research project discussed in the paper addresses the need for inclusion of construction as-built data in the bridge management database along with the periodic inspection and maintenance data. Attention to this type of data has been lacking. Therefore, the paper promotes bridge as-built data, discusses its role in bridge management, and demonstrates the proper design of an as-built information management model and system that is integrated with existing standard bridge management systems such as Pontis.     

Case-Based Reasoning for Converting Working Stress Design-Based Bridge Ratings to Load Factor Design-Based Ratings

In 1995, the Federal Highway Administration (FHWA) required that all bridges, regardless of the design method used for the original design, be based on the load factor design (LFD) method. In order to comply with the FHWA requirements, state departments of transportation have converted to the LFD method for all new bridge ratings. Further, all existing bridges previously rated using the working stress design (WSD) method must be converted to the LFD method. Consequently, thousands of bridges must be rerated using the LFD method. Steel bridges rated by the WSD method have critical data missing to make the proper conversion to the LFD method. This paper presents a methodology and an intelligent decision support system to help bridge engineers convert a WSD-based bridge rating to the LFD-based rating with little human effort using the artificial intelligence approach of case-base reasoning. The proposed methodology can help bridge engineers create the missing LFD-based data efficiently and quickly with a minimum amount of work. This research demonstrates how bridge engineers can use a novel computing paradigm and modern computer tool to convert an antiquated database to current design.     

Identification of Environmental Categories for Markovian Deterioration Models of Bridge Decks

In general, state-of-the-art bridge management systems have adopted Markov-chain models to predict the future condition of bridge elements and networks in different environments when various maintenance actions are implemented. However, the categories used to describe the various possible environments for a bridge element are neither accurately defined nor explicitly linked to the external factors affecting the element deterioration. In this paper, a new approach is proposed to provide transportation agencies with an effective decision support tool to identify the categories that best define the environmental and operational conditions specific to their bridge structures. This approach is based on genetic algorithms to determine the combinations of deterioration parameters that best fit each environmental category. The proposed approach is applied to develop Markovian deterioration models for concrete bridge decks using actual data obtained from the Ministére des Transports du Québec. This application illustrates the ability of the proposed approach to correlate the definition of environmental categories to parameters, such as highway class, region, average daily traffic, and percentage of truck traffic, in an accurate and efficient manner.     

Transverse Cracking of Concrete Bridge Decks: Effects of Design Factors

Early transverse cracking is one of the dominant forms of bridge deck defects experienced by a large number of transportation agencies. These cracks often initiate soon after the bridge deck is constructed, and they are caused by restrained shrinkage of concrete. Transverse cracks increase the maintenance cost of a bridge structure and reduce its life span. Most of the past efforts addressing transverse bridge deck cracking have focused on changes over the years in concrete material properties and construction practices. However, recent studies have shown the importance of design factors on transverse bridge deck cracking. This paper presents results of a comprehensive finite-element (FE) study of deck and girder bridge systems to understand and evaluate crack patterns, stress histories, as well as the relative effect of different design factors such as structural stiffness on transverse deck cracking. The results of this study demonstrate the development of transverse deck cracking and emphasize the importance of these design factors. They also recommend preventive measures that can be adopted during the design stage in order to minimize the probability of transverse deck cracking.     

Risk Management and Design of Critical Bridges for Terrorist Attacks

In the aftermath of the September 11th tragedies, the vulnerability of the United States' transportation infrastructure to terrorist attack has gained national attention. In light of this vulnerability, various governmental agencies are looking into ways to improve the design of structures to better withstand extreme loadings. Until recently, little attention has been given to bridges which are critical to our economy and transportation network. This paper summarizes the results of ongoing research to investigate economical, unobtrusive, and effective methods to mitigate the risk of terrorist attacks against critical bridges. It outlines a recommended plan to reduce these threats through proven risk management techniques, lists possible cost-effective security measures, discusses blast effects on bridges, and provides structural design and retrofit guidelines. It also discusses ongoing research oriented towards the development of a performance-based design methodology. In using proper risk management techniques, transportation managers and bridge engineers can mitigate the risk of terrorist attacks against critical bridges to an acceptable level, while ensuring efficient use of limited resources.     

Statistical Significance of Less Common Load Combinations

The purpose of this work is to provide a simple, rational basis for combining bridge loads in the extreme event limit state. Classic methods are used to evaluate the probabilities of traffic, seismic, and storm-related bridge loads occurring simultaneously and in various intensities. The loads are modeled using a Poisson distribution, which circumvents problems encountered when using normal- or log-normal distributions. The hazard level is evaluated directly using a negative exponential function in the time domain. An acceptable hazard level for combined events is subjectively based on that deemed acceptable for the strength limit state and extreme events occurring individually, as well as fiscal prudence. It is shown that (1) application of seismic loads to a structure already subjected to the combined effects of degradation, local pier scour, and contraction of the waterway is not justifiable; (2) live loads reduced from the anticipated 75-year maximum to a 2-week maximum are appropriate when designing a bridge in its 100-year “scoured-out” storm configuration; and (3) vehicular live loads are likely to be on a bridge during a seismic event, but other issues need to be considered.     

Scour Vulnerability of River Bridge Piers

A simple procedure is proposed to assess the vulnerability of bridge piers in rivers, taking into account the phenomena governing fluvial dynamics during flood events. The procedure requires an estimation of the maximum scour depth of the soil surrounding both the pier and the foundation as well as an analysis of the bearing capacity of the pier–foundation–soil geotechnical system. The scour depth is determined in terms of the physical and mechanical properties of the streambed soil, the shape of the pier foundation and the destabilizing effects induced by hydrodynamic forces. The coupling of both the hydraulic and geotechnical analyses enables to identify the most significant factors characterizing scour depth and affecting pier vulnerability. Two levels (low, medium) of allowable vulnerability, bounded by an extreme condition of high vulnerability, are defined and analytically determined in function of the maximum scour depth and the foundation depth. Specific diagrams corresponding to each category of foreseen actions allow a quick evaluation of the vulnerability of a bridge pier.     

Detection of Common Defects in Concrete Bridge Decks Using Nondestructive Evaluation Techniques

The transportation infrastructure in the United States is deteriorating and will require significant improvements. Consequently, innovations in the area of transportation infrastructure maintenance and rehabilitation are keys to the health and wellness of this valuable national asset. A major component of maintenance and rehabilitation is the ability to accurately assess the condition of the transportation infrastructure. This can be accomplished in part by using nondestructive evaluation techniques. Several nondestructive techniques have been used on concrete bridge decks and have proven to be efficient and effective. This paper aims at studying the different nondestructive evaluation techniques used in the assessment of concrete bridge deck conditions. An experimental investigation to evaluate the ability of infrared thermography, impact echo, and ground penetrating radar to detect common flaws in concrete bridge decks is developed and discussed. Results from this study showed the ability of these methods to detect defects with varying precision. Capabilities of the methods were verified and comparisons among the methods were made.     

Analysis of Edge-Detection Techniques for Crack Identification in Bridges

Bridge monitoring and maintenance is an expensive yet essential task in maintaining a safe national transportation infrastructure. Traditional monitoring methods use visual inspection of bridges on a regular basis and often require inspectors to travel to the bridge of concern and determine the deterioration level of the bridge. Automation of this process may result in great monetary savings and can lead to more frequent inspection cycles. One aspect of this automation is the detection of cracks and deterioration of a bridge. This paper provides a comparison of the effectiveness of four crack-detection techniques: fast Haar transform (FHT), fast Fourier transform, Sobel, and Canny. These imaging edge-detection algorithms were implemented in MatLab and simulated using a sample of 50 concrete bridge images (25 with cracks and 25 without). The results show that the FHT was significantly more reliable than the other three edge-detection techniques in identifying cracks.     

Light-Weight Fiber-Reinforced Polymer Composite Deck Panels for Extreme Applications

Currently within the military there is a need for a universal light-weight bridge deck system capable of supporting extreme loads over a wide temperature range. This research presents the development, testing, and analysis of five different fiber-reinforced polymer (FRP) webbed core deck panels. The performance of the FRP webbed decks are compared with an existing aluminum deck and with a baseline balsa core system, which has previously been tested as part of the development of the composite army bridge for the US Army. The study shows that for one-way bending, the FRP webbed core can exceed the shear strength of the baseline balsa core by a factor of 3.2 at a core’s density, which is 28% lighter than the balsa baseline. In addition, weight savings in excess of 30% are shown for using FRP decking in place of conventional aluminum decking. Based on test results and finite-element analysis, the failure modes of the different FRP webbed cores are discussed and design recommendations for FRP webbed core decks are provided.     

Evaluation of Seismic Damage to Memphis Bridges and Highway Systems

This paper presents a procedure for the evaluation of the expected seismic damage to bridges and highway systems in Memphis and Shelby County, Tenn. Data pertinent to 452 bridges and major arterial routes were collected and implemented as a geographic information system database. The bridges were classified into several bridge types using a bridge classification system modified from the NBIS∕Federal Highway Administration coding guidelines. The bridge damage states considered are no∕minor damage, repairable damage, and significant damage. The fragility curves corresponding to these damage states were established for various bridge types. Given an earthquake with a moment magnitude of 7.0 occurring at Marked Tree, Ark., the intensity of ground shaking and liquefaction-induced permanent ground deformation in Memphis and Shelby County were estimated, and then the expected damage to bridges and highway systems was determined. The results can be used to prioritize bridges for retrofitting, to prepare a pre-earthquake preparedness plan, to develop a postearthquake emergency response plan, and to assess the regional economic impact from the damage to highway transportation systems.     

Using Soft Computing to Analyze Inspection Results for Bridge Evaluation and Management

The national bridge inventory (NBI) system, a database of visual inspection records that tallies the condition of bridge elements, is used by transportation agencies to manage the rehabilitation of the aging U.S. highway infrastructure. However, further use of the database to forecast degradation, and thus improve maintenance strategies, is limited due to its complexity, nonlinear relationship, unbalanced inspection records, subjectivity, and missing data. In this study, soft computing methods were applied to develop damage prediction models for bridge abutment walls using the NBI database. The methods were multilayer perceptron network, radial basis function network, support vector machine, supervised self-organizing map, fuzzy neural network, and ensembles of neural networks. An ensemble of neural networks with a novel data organization scheme and voting process was the most efficient model, identifying damage with an accuracy of 86%. Bridge deterioration curves were derived using the prediction models and compared with inspection data. The results show that well developed damage prediction models can be an asset for efficient rehabilitation management of existing bridges as well as for the design of new ones.     

Hydrodynamic Investigation of Coastal Bridge Collapse during Hurricane Katrina

A number of U.S. coastal bridges have been destroyed by hurricanes, including three highway bridges in Mississippi and Louisiana during Hurricane Katrina (2005). This paper addresses three fundamental questions on the coastal bridge failures: (1) what were the hydrodynamic conditions near the failed bridge during the hurricane; (2) what was the cause of the bridge collapse; and (3) what was the magnitude of the hydrodynamic loading on the bridge under the extreme hurricane conditions. Guided by field observations of winds, waves, and water levels, two numerical models for storm surges and water waves are coupled to hindcast the hydrodynamic conditions. Fairly good agreement between the modeled and measured high watermarks and offshore wave heights is found, allowing an estimate of the surge and wave conditions near the bridges in nested domains with higher resolutions. The output of the coupled wave-surge models is utilized to determine the static buoyant force and wave forces on the bridge superstructure based on empirical equations derived from small-scale hydraulic tests for elevated decks used in the coastal and offshore industry. It is inferred that the bridge failure was caused by the wind waves accompanied by the storm surge, which raised the water level to an elevation where surface waves generated by strong winds over a relatively short fetch were able to strike the bridge superstructure. The storm waves produced both an uplift force and a horizontal force on the bridge decks. The magnitude of wave uplift force from individual waves exceeded the weight of the simple span bridge decks and the horizontal force overcame the resistance provided by the connections of the bridge decks to the pilings. The methodology for determining the hydrodynamic forcing on bridge decks can be used to produce a preliminary assessment of the vulnerability of existing coastal bridges in hurricane-prone areas.     

Design of Cotton Duck Bridge Bearing Pads

Bearings are used to support loads and accommodate movements in bridges. Cotton duck bearing pads (CDP) offer a versatile and economical solution for bearing design. The CDPs have closely spaced layers of elastomer and fabric which result in large compressive strength and strain capacities. However, the engineering response of CDP has not been well understood and CDP design provisions are incomplete because of this limited knowledge. To better establish the engineering response and develop improved design provisions, an extensive experimental research study was conducted. The experimental program modeled loads and deformations induced on a bridge bearing and included both static and dynamic loading regimes in compression, shear, and rotation. The primary study parameters included pad geometry, pad manufacturer, and stress and strain levels. The results indicate that CDPs have significant compressive stress and deformation capacities. Using the experimental results, design limits to control pad damage and quality assurance provisions are proposed to ensure adequate service during the lifetime of the bridge. Delamination of the top pad layers occurs after many cycles of repeated load or deformation and limits on the maximum stress, stress range, and uplift are proposed to limit this type of damage. Diagonal fracture occurs when a CDP is subjected to large strains. Strict maximum strain limits are proposed to prevent this failure mode. Finally, quality control provisions are proposed to ensure adequate engineering performance of the pads.     

Analysis of Recent Bridge Failures in the United States

Over 500 failures of bridge structures in the United States between 1989 and 2000 were studied. The age of the failed bridges ranged from 1 year (during construction) to 157 years, with an average of 52.5 years. The most frequent causes of bridge failures were attributed to floods and collisions. Flood and scour, with the major flood disaster in 1993, contributed to the frequency peak of bridge failures (almost 53% of all failures). Bridge overload and lateral impact forces from trucks, barges/ships, and trains constitute 20% of the total bridge failures. Other frequent principal causes are design, detailing, construction, material, and maintenance. Comparison made among three periods of similar studies (1977–1981, 1982–1988, and 1989–2000) revealed almost similar trends, with most failures occurring during the bridge’s service life. Also, human-induced external events occurred frequently in all three periods, but were most dominant in the first and third periods. Technological advances in information systems have a great impact on data collection and analysis.     

Experimental and Analytical Studies of a Horizontally Curved Steel I-Girder Bridge during Erection

A series of studies on an experimental, full-scale curved steel bridge structure during erection are discussed. The work was part of the Federal Highway Administration’s curved steel bridge research project (CSBRP). The CSBRP is intended to improve the understanding of curved bridge behavior and to develop more rational design guidelines. The main purpose of the studies reported herein was to assess the capability of analytical tools for predicting response during erection. Nine erection studies, examining six different framing plans, are presented. The framing plans are not necessarily representative of curved bridge subassemblies as they would be erected in the field; however, they represent a variety of conditions that would test the robustness of analysis tools and assess the importance of erection sequence on initial stresses in a curved girder bridge. The simply supported, three I-girder system used for the tests is described and methods for reducing and examining the data are discussed. Comparisons between experimental and analytical results demonstrate that analysis tools can predict loads and deformations during construction. Comparison to the V-load method indicates that it predicts stresses in exterior girders well, but can underpredict them for interior girders.