U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
U.S. engineers need new, advanced tools and protocols to better assess and assure safety and serviceability of highway bridges. These tools include an overall, integrated approach to bridge analysis, design, evaluation, and load-carrying capacity (load rating). Present-day design specifications (load and resistance factor design (LR FD)) have assured safety by analyzing the effect of heavy, legal trucks throughout the United States and applying calibration protocol using limited Canadian site statistics. However, the calibration did not include serviceability calibration to assure bridge serviceability and performance. Therefore, it is desirable to identify design practices, design truck assessments, and detailed code calibration procedures used in other countries to assure the safety and serviceability of newly designed bridges.
The new American Association of State Highway and Transportation Officials (AASHTO) Manual for Bridge Evaluation was developed to assist bridge owners by establishing inspection, evaluation, load rating, and posting practices and procedures. The load and resistance factor rating (LRFR) section of the manual is based on reliability theories to assure a certain level of safety for members. However, certain serviceability checks were left optional because they are not directly related to bridge safety, but are geared to protecting the long-term serviceability and durability of structures. It is unclear whether making these checks optional has an effect on the service life of aging U.S. bridges. Therefore, it is desirable to identify evaluation (load-carrying assessment) best practices and quantify the required level of safety and performance used in other countries to avoid failures, serviceability concerns, unnecessary expenditures, and traffic restrictions.
Knowledge and software have evolved to enable moving away from line girder approximate procedures to a system approach using advanced finite element analyses. However, current U.S. specifications and practice still, for the most part, rely on simplified, approximate analyses to determine the structural effects of vehicular loading on bridge girders. Situations impeding the use of advanced analysis in design and evaluation include the cost of software, lack of training, lack of guidance materials, modeling complexities, and perceived high cost-to-benefit ratio. A growing number of U.S. bridge owners and engineers seek to expand and mainstream the use of more rigorous design and evaluation approaches in everyday practice to achieve more economical use of materials, a better understanding of the structural system, and a better quantified level of safety and serviceability.
The purpose of the scan was to identify best practices and processes to assure bridge safety and serviceability for implementation in the United States. Specific topics of interest included the following:
The team developed a comprehensive list of technical and operational process questions, including topics on safety and serviceability concerns and the use of refined analysis during the design, construction, and operational phases of a bridge’s life (Appendix A).
An 11-member team was formed to conduct the study. This team consisted of three representatives from the Federal Highway Administration (FHWA), four representatives from State departments of transportation, one representative from academia, and three structural engineering design consultants, one who served as the report facilitator.
The team conducted a series of meetings and site visits with representatives of government agencies and private sector organizations abroad from May 29 to June 14, 2009. The team visited Austria, England, Finland, France, and Germany. These five countries were selected through a desk scan that identified their use of advanced activities in assuring bridge safety and serviceability.
The scan team found that, as in the United States, the European host agencies put a tremendous value on bridge programs not only to ensure highway user safety, but also to ensure that durability and serviceability expectations are met and to enhance capital investment decisions on the existing bridge inventory. They place major emphasis on ensuring that there is no service interruption because of a bridge failure or major repair, and that appropriate sophisticated methods are used to evaluate structural safety. Most of the agencies visited had major programs aimed at assuring accuracy of design and rating of highway structures on their systems.
The scan team also identified many practices and technologies related to the topics of interest. The order in which they are presented in this report is for clarity of presentation and does not reflect the priority recommended by the team.
Based on the above findings, the recommendations of the team are as follows:
The scan team developed a detailed implementation plan for the recommended initiatives and practices. Included in the plan are technical presentations and written papers at national meetings and conferences sponsored by FHWA, ASSHTO, the Transportation research board, and other organizations to disseminate information from the scan. also included in the plan is coordination with AASHTO and FHWA to advance these initiatives and practices and to assist with the development of new FHWA and AASHTO standards and guidelines governing bridge design and analysis. These and other planned activities are discussed in chapter 3.