Comprehensive Evaluation of Fracture Critical Bridges. Final Report: Fid-Bau Portal

Comprehensive Evaluation of Fracture Critical Bridges. Final Report

H Pham / S Doust / A Yakel / A Azizinamini

Two-girder steel bridges are classified as fracture critical bridges based on the definition given in the AASHTO LRFD Bridge Design Specifications. In a fracture critical bridge a failure of a tension member leads to collapse of the bridge. However, a number of such bridges with a partial or full-depth crack in one girder have been reported. The main objective of this research project is to understand the behavior of two-girder steel bridges and evaluate their redundancy level in the event that one member is fractured. This can be achieved by investigating and identifying the factors that control whether a two-girder steel bridge will survive a girder fracture without collapse. Once identified, these factors may be used in the evaluation of existing in-service bridges to reclassify their redundancy level as non-fracture critical and decide whether a mandatory hands-on inspection is necessary every two years. In this research, laboratory testing of full-scale two-girder steel bridges and detailed finite element analyses were carried out. Data from the experimental testing was used to verify and calibrate the non-linear finite element model of these testing specimens. It was observed for the specimens tested that redundancy was dependent upon the level of damage. Fracture of the tension flange alone did not result in immediate collapse and the strength of the intact system could be attained. However, when the initial fracture involved at least half of the web, a reduced capacity was observed and the crack rapidly propagated leading to collapse.