In June 2009, a team of U.S. engineers visited several European countries to review their policies and procedures to assure safety and serviceability of their highway bridges.
The itinerary for the two-week scan of technology included Helsinki, Finland; Vienna, Austria; Graz, Austria; Cologne, Germany; Paris; and London. These five countries were selected through a desk scan that identified their use of advanced practices in assuring bridge safety and serviceability.
The scan team was led by Firas Sheikh Ibrahim of the Federal Highway Administration (FHWA) and Susan Hida of the California Department of Transportation. The remainder of the team included Gregory Bailey of the West Virginia Department of Transportation; Ian Friedland of the FHWA; Jugesh Kapur of the Washington State Department of Transportation; Barney Martin Jr. of Modjeski & Masters Inc.; Dennis Mertz of the University of Delaware; Gregory Perfetti of the North Carolina Department of Transportation; Thomas Saad of the FHWA; and Bala Sivkumar of HNTB Corp. Harry Capers Jr. of Arora and Associates P.C. was the contracted report facilitator. The team was sponsored by the FHWA, the American Association of State Highway & Transportation Officials (AASHTO) and the National Cooperative Highway Research Program (NCHRP).
A comprehensive list of technical and operational process questions was generated by the team and included topics on safety and serviceability concerns and the use of refined analysis during the design, construction and operational phases of a bridge’s life. (Refined analysis is defined herein as analysis beyond one-dimensional structural analysis using lateral live-load distribution factors.) These questions were forwarded to the hosts for their use in preparing for the team’s visit.
The scan team conducted a series of meetings and site visits with representatives of government agencies and private-sector organizations in the five countries. Specific topics of interest to the team included:
- Widespread use of advanced refined methods of analyzing, designing and assessing highway structures’ safety and serviceability;
- The use of enhanced reliability analysis to assess safety; and
- The use of performance-based approaches being used to provide durable structures.
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To-do list Based on the findings of the scan team, their general recommendations are as follows: Develop a nationally accepted strategy for promoting and increasing practicing bridge engineers’ use of refined analysis. The strategic plan should address training, perhaps by developing a National Highway Institute training course to provide background on grillage and finite-element modeling methods available for analysis of highway bridges. The strategic plan also might entail developing standardized curricula that can be adopted by universities and offered as graduate-level and continuing education courses throughout the U.S. The strategy also must include partnering with the software industry to ensure supporting tools become available with integration of CADD for both rating and design. States should be encouraged to utilize refined analysis (properly checked and verified) and reliability assessment as a measure to avoid posting, rehabilitating or replacing bridge structures that affect commerce, schools and the traveling public. The AASHTO MBE should introduce levels of structural safety assessment where each additional level of assessment introduces increasing sophistication with the objective of assessing the safety of a bridge more accurately, commensurate with risk and the need to verify adequate capacity. The AASHTO Subcommittee on Bridges and Structures (SCOBS) should consider adopting the concept of annual probability of failure (exceedance) as the quantification of safety in their probability-based design and rating specifications rather than the reliability index for a 75-year design life. Probability of failure is a more intuitive measure of safety than the reliability index. Further, annual probability of failure, instead of the probability of failure during the 75-year design life, would put the risk due to the strength limit state force effects in a format comparable to the extreme-event-limit states, which are typically quantified in terms of annual probability of failure. In other words, the reference period in the table would be one year. The specification of a one-year reference period, or annual probability of failure, is standard practice in other probability-based specifications such as the Eurocode. A synthesis project should be initiated to develop the basis to systematically introduce increasing levels of sophistication into the analysis, load models and reliability assessments with the objective of assessing the bridge more accurately. Owners should periodically and routinely reassess traffic highway loading to ensure that the AASHTO LRFD Bridge Design Specification design-load model adequately provides for bridge safety and serviceability for a 75-year service life or greater. The AASHTO SCOBS should consider requiring that states develop an overweight permit design vehicle for the Strength II load combination, particularly in high-load corridors. Develop and maintain a database of bridge failures domestically and internationally, which provides detailed information and data on the cause(s) of failure. A protocol should be established to initiate necessary actions to be taken by owners and code-writing bodies to ensure that bridge design guidance addresses these failures. Continued efforts to develop guidelines and training for proper use of NDE techniques to detect corrosion and breakage of cables of cable-supported bridges should occur. Identify or develop new NDE technologies to actually quantify the amount and severity of corrosion and breakage in hidden elements (prestressing strands, ducted cables, mild steel reinforcement, etc.). “Independent Check Engineering” and “Check Engineer Certification” should be explored for the purpose of augmenting QA/QC processes and practices already in place for bridge designs and analyses. Initiate the investigation and possible technology transfer of selected best practices and emerging technologies identified during the scan. Potential candidates include:
- Development of an integrated asset management process from planning through decommissioning/demolition;
- Development of guidance on the use of waterproofing membranes and asphalt overlays;
- Expansion of the use of cast-in-place concrete box girders with external post-tensioning for new bridges and retrofit/repair of existing structures using external post-tensioning. This technology has already been implemented in the states and is sometimes used in segmental concrete bridges; and
- The use of drag plates in the design of integral-abutment bridges as practiced in Austria.
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Entering the mainstream In summary, the scan team found many similarities, as well as significant differences, in practices between the U.S. and the host countries with respect to bridge design and analysis practices and bridge management and operating procedures. Several key findings were identified that the team considered best practices and were outlined in their final report. The team believes that the best practices should be mainstreamed into practice in the U.S. The strategies for championing these best practices are currently being refined but, in general, involve obtaining more information about the technologies from the host countries, making the information available on websites, seeking demonstration or pilot projects and holding workshops in association with the pilot projects. In addition, the scan team has planned numerous papers and presentations at national and local meetings and conferences over the next several years. The purpose of the papers and presentations is to describe the overall results of the scanning study and details of specific technologies for participants to consider implementing in their states. The results of this scan will support ongoing activities by the FHWA, the AASHTO Subcommittee on Highway Bridges and Structures and TRB/NCHRP to improve U.S. bridge design and analysis codes and specifications. This scan team has developed a report and implementation plan which contains many detailed findings that will increase current U.S. understanding of bridge design safety and serviceability and will lead to pursuit of further practices that will improve bridge design, analysis and operations nationwide. The scan team is convinced that implementing the key findings of this study will improve the design and operational safety standards in the U.S. Bridges will provide longer service life with less maintenance. Changes to the bridge design and analysis codes will provide operational improvements that will increase mobility and help preserve the nation’s highways. For more information on this scan, or to download a copy of the team’s final report, go to www.international?.fhwa?.dot?.gov.
