Reliability-based progressive collapse analysis of highway bridges

• A probabilistic dynamic progressive collapse analysis method is proposed.
• Reliability analysis models of a truss bridge and a box-girder bridge are presented.
• The reliability analysis is performed to evaluate the redundancy of two bridges.
• The effect of different damage scenarios on structural safety is evaluated.
• The reliability analysis results can be used to calibrate incremental analysis.
• The method can be implemented to cover a wide range of bridges and damage scenarios.
• The method can be used to develop progressive collapse bridge design guidelines.

Structural systems optimized to meet member design criteria as specified in current design standards and specifications may not provide sufficient levels of robustness to withstand a possible local failure following an unforeseen extreme event. In fact, the failure of one structural element may result in the failure of another creating a chain reaction that might progress throughout the entire structure or a major portion of it leading to catastrophic collapse. To reduce the chances of such collapses, the U.S. General Services Administration (GSA) established a set of procedures and criteria to evaluate the robustness of buildings using traditional deterministic methods. Although widely accepted and used for the progressive collapse analysis of buildings, the GSA criteria may not be suitable for bridges because of the differences in their structural configurations and in the nature and intensity of their permanent and transient loads. Furthermore, it is not clear how the existing criteria take into consideration the large uncertainties associated with estimating the applied loads and the capacity of structural systems to resist collapse following the initiation of a local failure. Because performing direct probabilistic analyses may be impractical for routine engineering practice, following current code calibration processes, design guidelines and standards can specify incremental progressive collapse analysis criteria that are calibrated based on structural reliability concepts to ensure consistent levels of safety for the pertinent range of applications, load levels and structural types and configurations.The objective of this paper is to describe a methodology for performing probabilistic progressive collapse analyses and calibrating incremental analysis criteria for highway bridges accounting for the uncertainties in the applied loads and the load carrying capacities of the members as well as the system. The reliability analysis methodology is illustrated using models of a steel box girder bridge and a steel truss bridge subjected to different initial damage scenarios. The paper outlines how the results from several reliability analyses can be implemented to develop criteria that would lead to consistent levels of safety and reliability. Such criteria can, in the future, be used to propose progressive collapse analysis guidelines for bridges that are compatible with the principles of Load and Resistance Factor Design (LRFD) methods.