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Chapter 2 – Findings on Assuring Bridge Safety and Serviceability


New, advanced tools and protocols are available to help bridge engineers better assess and assure safety and serviceability of highway bridges. These tools include an overall, integrated approach to bridge analysis, design, evaluation, and determination of load-carrying capacity (load rating). Present-day design specifications (load and resistance factor design (LR FD)) assure safety by analyzing the effect of heavy, legal trucks throughout the United States and comparing that effect to a protocol calibrated using limited but very reliable Canadian site statistics. However, the calibration did not include serviceability calibration to assure bridge serviceability and performance, and it did not use comprehensive statistics available in the United States because the available weigh-in-motion (WIM) data was deemed unreliable. 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 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 (LR FR) section of the manual is based on reliability theory 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 improves the service life of aging U.S. bridges. Therefore, it is desirable to identify good evaluation (load-carrying assessment) practices, including a quantification of the corresponding level of safety and performance, used in other countries to avoid failures, serviceability concerns, unnecessary expenditures, and traffic restrictions.

In addition, knowledge and software have evolved to enable moving away from line girder, one-dimensional approximate analytical models to a system analysis using refined two-dimensional (2-D) or three-dimensional (3-D) analytical models. However, current U.S. specifications and practice still rely heavily on simplified, approximate analyses to determine the structural effects of vehicular loading on bridge girders. Situations impeding the use of advanced analyses in design and evaluation include lack of adequate software training, lack of guidance material, specifications, complexity, and perceived high cost-to-benefit ratio. A migration to the use of more rigorous design and evaluation approaches in everyday practice for both simple and complex bridges may result in a more economical use of materials, a better understanding of structural reliability, and a better quantification of safety and serviceability.

Scan Team

An 11-member team was formed to study European practices (figure 1). This team consisted of three representatives from the Federal Highway Administration (FHWA), four representatives from State departments of transportation (DOTs), one representative from academia, and three structural engineering design consultants, one who served as the report facilitator (see Appendix B).

The purpose of the team’s study was to identify best practices and processes to assure bridge safety and serviceability for consideration by U.S. engineers. The team generated a comprehensive list of technical and operational process questions, including 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 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.

Specific topics of interest to the team included the following:

Figure 1. Photo of the Scan team members.
Figure 1. Scan team members.

Amplifying Questions

Amplifying questions were developed to help the foreign experts more fully understand the topics of interest to the scan team members. These questions, in Appendix A, were provided to the host countries before the scan. The contacts in each country are in Appendix C, and the scan itinerary is in table 1.

Host Countries

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 panel visited Austria, England, Finland, France, and Germany. These five countries were selected through a desk scan of their advanced activities in assuring bridge safety and serviceability. Details of the team’s meetings are shown in table 1.

Table 1. Scan Itinerary.
Date Location Activities
Monday, June 1, 2009 Helsinki, Finland Meeting at the Finnish Road Administration (Finnra). Heard presentations on Finnra bridge management system, bridge inspections, bridge design and building processes and methods, implementation of Eurocodes, bridge loading tests, bridge monitoring, and bridge bearing capacity calculations.
Tuesday, June 2, 2009 Vienna, Austria Meeting at the Federal Ministry for Transport, Innovation, and Technology. Heard presentations on safety inspection and investigation of bridges, training and certification of bridge inspectors, asset management of bridges, bridge WIM and reliability assessment of existing bridge structures, research on load-carrying capacity of existing bridges, and experiences and research on bridge monitoring.
Wednesday, June 3, 2009 Vienna, Austria Meeting at the Federal Ministry for Transport, Innovation, and Technology. Heard presentations on integrated approach to the evaluation of the capacity of existing bridges, bridge life-cycle costing, new requirements for strengthening bridges with top concrete, state-of-the art design and maintenance of bridges without joints and bearings, and monitoring and numerical simulation of bridges without joints and bearings.
Thursday, June 4, 2009 Graz,Austria Meeting at Graz University of Technology. Heard presentations on an approach for improving safety and serviceability from the design phase through the life cycle using bridge information modeling, investigation of high-speed suitability of existing and new railway bridges, lessons learned on highway bridges in Slovenia, and bridge design using ultra high-performance concrete. Visited the Laboratory for Structural Concrete and the construction site of the Traismauer Bridge across the Danube River.
Friday, June 5, 2009 Cologne, Germany Meeting at the Federal Highway Research Institute (BASt). Heard presentations on bridge inventory and condition, traffic on German highways, heavy goods vehicle (HGV) weights and dimensions, HGV traffic with special permission, traffic load models, calibration, use of WIM data, future developments, Eurocodes for bridges, QA/QC procedures for bridge analysis and design, assessment of bridges, and refined analysis.
Monday, June 8, 2009 Paris, France Meeting at the Center for Technical Studies of Highways and Motorways (Sétra). Heard presentations at the Central Laboratory for Bridges and Highways (LCPC) on Sétra and the Technical Center for Bridges (CTOA), Eurocode principles of safety verification, concrete durability, fatigue assessment of steel bridges, existing methodologies of assessment, and a case study on assessment of the loading resistance of the Pont d’Aquitaine.
Tuesday, June 9, 2009 Paris, France Meeting at LCPC. Received an overview of LCPC research units, including highlights of research activity on bridges. Heard presentations on bridge WIM for load assessment and load effect calculations, CESAR-LCPC finite element code, and reassessment of bridges affected by alkaliaggregate reaction and delayed ettringite reaction. Visited the Large-Scale Structural Testing Laboratory and learned about structural investigation methods and specific techniques for portland cement bridges, dynamic investigation, structure durability and reliability, and risk analysis on multispan post-tensioned girder bridges.
Wednesday, June 10, 2009 London, United Kingdom Meeting at the Institute for Civil Engineers (ICE). Heard presentations by the U.K. Highways Agency (HA) on structure assets, key processes, standards, design and operational framework, inspection and technical approval, design (including innovative structures), loading, operations (including assessment), inspection, information systems, integrated asset management, and maintaining agents. A case study focused on the Midland Links motorway elevated structures.
Thursday, June 11, 2009 Cambridge, United Kingdom Meeting at King’s College at Cambridge University. Heard presentations on U.K. bridge management, findings of an audit of the assessment program and management of substandard structures, probabilistic approaches, advanced assessment and analysis techniques, monitoring and sensor technologies, procurement strategies, and an overview of Eurocodes and new materials for bridges.
Friday, June 12, 2009 London, United Kingdom Meeting at ICE. Heard presentations by software providers on developments and trends in software use for U.K. bridges, HA input on the analysis of bridges through the technical approval process, role of design and analysis software in assuring bridge safety, testing and validation of bridge design and analysis software, and Eurocodes and software applications.
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