Although the majority of uncoated weathering steel (UWS) structures are performing well when designed and maintained in accordance with existing recommendations, exceptions to this trend exist. Additionally, the guidance on UWS use is largely qualitative. For these reasons, a data-driven method for assessing deterioration of a large sample of bridges as a function of environment was formulated, piloted, assessed, and validated. Key aspects of the methodology include the development of a database that uses graphical information systems to quantify the climate of hundreds of structures, a statistically driven process for selecting a representative sample of bridges for further evaluation, and a review of bridge performance based on owners' evaluations and independent field evaluations. As a result of applying this methodology to UWS bridges with proximity to the Gulf Coast, environments consistently resulting in satisfactory performance were quantified; a rare combination of severe proximity to the coast, humidity, and atmospheric concentrations of chloride was also quantified and correlated with the small number of bridges with overall inferior corrosion performance in these marine environments.

Because uncoated weathering steel (UWS) bridges have been in use in the United States for nearly 50 years, the long-term performance of these structures can now be assessed. An assessment was completed by surveying the varied experiences of 52 U.S. transportation agencies and analyzing the data on all UWS bridges known within these and other agencies, which totaled nearly 10,000 structures. It was established that the superstructure condition ratings system (based on a standard national rating system) of these structures was a valid means of assessing UWS performance in a quantitative manner on the basis of a comparison of these ratings to qualitative information received from bridge owners in the 52 agencies surveyed. Of the most significant findings from the analysis, first, was that the superstructure condition ratings of the majority of UWS bridges were classified as excellent or very good, on the basis of the national criteria for these qualitative descriptors. Second, a comparison of the ratings of UWS bridges and other steel bridges within representative agencies while accounting for differences in ages of the various populations indicated that UWS displays increased or similar performance relative to other steel. UWS bridges performed quite well in most cases. Considering their economic and environmental benefits, continued or increased use of UWS bridges is regarded as sound engineering practice.

Uncoated weathering steel (UWS) bridges have been in use in the United States for nearly 50 years, now enabling the long-term performance of these structures to be assessed. This was accomplished by surveying the varied experiences of 52 U.S. transportation agencies, along with data analysis on all UWS bridges known within these and other agencies, which total nearly 10,000 structures. Climate and age were key considerations in this data analysis. Contrary to previous, more limited research, this analysis showed that there is not a strong trend in UWS bridge performance as a function of climate. A similar climate analysis for non-UWS bridges also showed a counterintuitive relationship between some climate types and these bridges. This suggests that design and maintenance practices may be more influential to UWS performance than climate, and further research to cultivate current best practices in this regard is recommended. Comparison between the UWS and non-UWS data sets also reveals that UWS bridges generally perform well in relation to non-UWS bridges.

This document is the first version (version 1.0) of the Design Guide for Bridges for Service Life, hereafter referred to as the Guide. The Guide is the main product of the Second Strategic Highway Research Program (SHRP 2) project R19A, entitled “Bridges for Service Life Beyond 100 Years: Innovative Systems, Subsystems and Components.” The Guide provides information and defines procedures to systematically design for service life and durability for both new and existing bridges. The objective of the Guide is to equip the user with knowledge that is needed to develop specific optimal solutions for a bridge under consideration in a systematic manner using a framework that is universal with specifics being different. This objective is achieved through providing 11 chapters, each devoted to a certain part of the bridge or aspects of the service life design process. It is important to read and comprehend Chapter 1 of the Guide before proceeding to the other chapters of the Guide. The general framework for design for service life is described in Chapter 1. Specifics related to each step of the framework are covered in the other chapters. Major topics covered include the following: materials; bridge decks; reinforced concrete bridges; steel bridges; jointless bridges; expansion devices; bridge bearings; and life-cycle cost analysis.

The service limit state control of permanent deflection for steel sections in flexure has serious implications for both design and evaluation of steel bridges. These provisions are found in Article 6.10.3 of the American Association State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specification. Load combination Service II of LRFD Table 3.4.1 is the specified combination for this limit state. This uncalibrated limit state load combination governs the design of compact steel sections in flexure, as demonstrated by several published deign examples. Since the vast majority of modern steel sections in positive flexure qualify as compact sections in the LRFD Specifications, the implications of this governing, uncalibrated limit state are significant. The limit state is also suggested in the proposed AASHTO Manual for Condition Evaluation and Load and Resistance Factor Rating of Highway Bridges the review of permit issuance. These provisions were first introduced with Load Factor Design in the 1970's, based upon listed experimental results from the earlier AASHTO test road bridges. Herein, the basis of these provisions is reviewed and discussed, along with the questions that must be answered to calibrate this important limit state for rational use in both design and evaluation of steel bridges.

This Manual covers the relevant issues related to orthotropic steel deck bridge engineering, including analysis, design, detailing, fabrication, testing, inspection, evaluation, and repair. It includes a discussion of some the various applications of orthotropic bridge construction to provide background with case study examples. It also provides basic criteria for the establishment of a cost-effective and serviceable orthotropic bridge cross section with detailing geometry that has been used on recent projects worldwide. The manual covers both the relevant information necessary for the engineering analysis of the orthotropic steel bridge and the requirements for complete design of orthotropic steel bridge superstructures. Additionally, design details such as materials, corrosion protection, minimum proportions, and connection geometry are addressed as well as basic fabrication, welding, and erection procedures. Portions of the manual also cover methods for maintaining and evaluating orthotropic bridges, including inspection and load rating. Wearing surfaces are also covered in depth. The culmination of all the information is demonstrated in two design examples.

The orthotropic steel deck bridge is a structural system that has the potential to provide an extended service life and standardized modular design as compared to more conventional bridge construction. This paper summarizes proposed changes to the fifth edition of the AASHTO LRFD Bridge Design Specifications related to orthotropic deck bridges. The current version of AASHTO-LRFD contains provisions that provide limited guidance to complete the fatigue design. Contained within these proposed changes is a new framework for design verification, which may be based on different levels of design or physical testing. Criteria related to loads, load factors, limit states including fatigue in particular, resistance, and analysis requirements are covered in detail. Designs made according to these new provisions can be expected to perform very well and meet the design service life as per AASHTO-LRFD.

The live load distribution-factor (LLDF) equations in the AASHTO-LRFD specifications were developed under National Cooperative Highway Research Program (NCHRP) Project 12-26. These equations include limited ranges of applicability, and when these ranges are exceeded, a refined analysis must be used. Additionally, the multiple-presence factors, bias, and variability with respect to the rigorous estimates are obscurely embedded. Herein, a simplified LLDF framework is provided. The effects of analysis uncertainty, variability, and multiple presence are separated and distinctly defined. This separation provides specification writers with the opportunity to use different multiple-presence and variability models. LLDFs were calculated using several simplified methods and grillage analyses for over 1,500 bridges. Based on the comparison, two simplified methods were further studied: adjusted uniform distribution and adjusted lever rule methods. Calibration factors were used to their improve accuracy. Seventy-four "test-the-limits" bridges (11 steel) were designed to test wide ranges of girder spacing, relative transverse to longitudinal stiffness, and bridge flexural-to-torsional stiffness. The focus of this paper is on the framework. The procedure and results are similar for other bridge types. DOI:10.1061/(ASCE)BE.1943-5592.0000285. (C) 2011 American Society of Civil Engineers.

Download a PDF of "Recommended Guide Specification for the Design of Externally Bonded FRP Systems for Repair and Strengthening of Concrete Bridge Elements" by the National Academies of Sciences, Engineering, and Medicine for free.

Heavy trucks represent a major load to highway bridges in the transportation infrastructure system. These loads are directly related to the truck weight limits of the jurisdiction, and largely determine the standard loads for bridge design and evaluation. Thus, truck weight limit is one of the major factors affecting bridge deterioration and expenditure for maintenance, repair, and/or replacement. Truck weight in this paper not only refers to the truck gross weight but also to the axle weights and spacings that affect load effects. This paper presents the concepts of a new methodology for estimating cost effects of truck weight limit changes on bridges in a transportation infrastructure network. The methodology can serve as a tool for studying impacts of such changes. The resulting knowledge is needed when examining new truck weight limits, several of which have been and are still being debated at both the state and federal levels in the United States. The development of this estimation method has considered maximizing the use of available data (such as the bridge inventory) at the state infrastructure system level. In application examples completed (but not reported herein), the costs for relatively inadequate strength of existing bridges and for increased design requirement for new bridges were found dominant in the total impact cost.

It has been argued that the AASHTO LRFD design code for maximum live loads on highway bridges is overly conservative. In an attempt to determine the level of conservativeness, if any, the writers developed a methodology incorporating real-time visual data collection from traffic cameras coupled with structural strain response of girder bridges. Average daily truck traffic along with frequency of multiple presences (same lane as well as adjacent lanes) and lane-wise truck traffic distribution were estimated for a steel-girder highway bridge on I-95 in Delaware. These data compared well with predictions from a Poisson process based model developed for this study. Statistical properties of girder moments in single and multiple presence conditions were determined as well. In this particular example, the girder design moment on the 24.6 foot approach span according to AASHTO specifications was found to be about 3.5 times higher than that estimated from the in-service data.

Although AASHTO LRFD specifications provide moment capacity equations as an approximate design method and recommend an orthotropic plate model as the refined method for the analysis of filled grid decks, no guidelines are provided for the determination of the flexural rigidities associated with the plate analysis. This technical note briefly reviews orthotropic thin plate theory, discusses the determination of the flexural rigidities using Huber's assumption, and applies the theory to concrete-filled steel grid decks. The accuracy of the orthotropic plate analysis is assessed by comparing it to results of an earlier finite-element analysis.

The life cycle of grid decks has come full circle from their introduction in the 1920s and 1930s through their maturity in 1950s and 1960s to their reintroduction in the 1980s. Many of these decks have been performing satisfactorily over 50 or more years of service. Filled grid decks offer a lightweight and high strength deck alternative to reinforced concrete decks. Despite the good performance history of grid decks, some bridge owners are hesitant to utilize them. With a better understanding of grid deck behavior, the manufacturing process can be optimized, and design method improved. Hence, poor details can be avoided and design efficiency can be achieved. This paper presents results of research conducted with the goal of providing a better understanding of filled steel grid deck behavior through experimental testing and numerical analyses. Three full-scale filled grid decks were tested to experimentally quantify their structural behavior. Threedimensional finite element (FE) models were developed for the grid decks and calibrated using the experimental results. Finally, parametric studies were conducted and used to quantify the effect of variations in the significant design parameters. The results of the parametric studies can be applied to optimize future grid deck designs. It should be noted that crack width and ductility are important serviceability parameters in the performance of filled steel grid bridge decks. However, the work described in this paper is limited to strength issues and does not include evaluation of serviceability parameters.

Two slab-on-girder bridge superstructures are analyzed using grillage models. Different live load placement configurations are investigated to determine the sensitivity of live load shear and moment to vehicle spacing. Results from both bridges show that the distribution factors are relatively insensitive to vehicle spacing. Therefore significant computational speedups are available when applying vehicle loads on an influence surface with a fixed spacing.

This paper reviews the evolution of live load design models for bridges and associated design specification provisions before, during and after the Interstate era, taken as the last 80 years. The types of vehicles on the roads are evaluated and comparisons are made to force effects generated by standard American Association of State Highway and Transportation Officials (AASHTO) design loadings. The introduction of the Federal Bridge Formula is reviewed and a comparison is made to the standard AASHTO HS20 design vehicle used throughout most of the Interstate period. The change in legal loads as well as extra legal loads are reviewed and the implication of the exclusion to the legal load limit made in various states are reviewed and compared to the HS20 loading. The basis for periodic changes to the live load design models, load distribution, and impact is also reviewed. Finally, a brief summary of the development of the post-interstate era live load model, the HL93 loading in the AASHTO Load and Resistance Factor Design (LRFD) Specifications, is also presented.

A significant crack was recently discovered on an I-95 bridge over the Brandywine River in Delaware. The steel girder bridge carries six lanes of traffic just north of downtown Wilmington. The crack was located on the fascia girder at midspan of the bridge's main span. The entire bottom flange was found to be fractured, with the crack extending upwards to within 0.3 meters of the upper flange. This paper will review the circumstances leading up to the crack, discuss the cause of the crack, review the repair strategy, and summarize the results of load tests performed prior to and during the repair.