Chapter 1 – Introduction

Background

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:

• Use of advanced refined methods of analyzing, designing, and assessing highway structures for safety and serviceability during design and construction
• Use of enhanced reliability analysis to assess safety and serviceability during operations
• Quality assurance and quality control (QA/QC)
• Use of performance-based approaches for durable structures
• Use of refined analysis during design, construction, and operations

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.