Date of Award
Anil Kumar Agrawal
Structural Robustness; Progressive Collapse; Cable-stayed Bridge; Tied-arch Bridge; Redundancy; Reliability; Cable Loss; Dynamic Behavior
As a critical part of the current infrastructure system, long-span bridges are directly exposed to adverse environments, such as floods, scours, hurricanes, etc., and dynamic loads such as earthquakes and vehicular impacts. Additionally, recent long-span cable-supported collapse examples show that many bridges suffered progressive collapse when local damage occurred, and they are highly vulnerable to severe damages in the event of a localized failure. However, the traditional design approaches are unable to provide explicit measures of residual safety of bridges, especially after an abnormal event. Currently available redundancy and robustness evaluation approaches, which were developed mainly for short-span bridges, are inappropriate for long-span cable-supported bridges. Therefore, a new performance-based approach has been developed in this dissertation to quantitatively evaluate the redundancy and robustness of long-span cable-supported bridges subjected to different damage initiating hazards. The ultimate behavior of long-span cable-supported bridges subject to single or multiple member failure has also been investigated.
First, two different types of cable-supported bridges, cable-stayed and suspended tied-arch, were selected as example bridges for structural robustness analysis and progressive collapse behavior investigation. Detailed finite element models of these bridges, including explicit models in the LS-DYNA as well as implicit models in other software such as Midas Civil and SAP 2000, were developed. Behavior of these bridges under different single member loss scenarios has been investigated based on the explicit LS-DYNA models. Four indexes, demand capacity ratio (DCR), dynamic increase factor (DIF), static increase factor (SIF) and dynamic amplification factor (DAF), have been introduced. The progressive collapse behavior of these bridges was studied by successively removing members until system failure occurred. The bridge behavior subjected to overloading was examined through pushdown analysis for these bridges in intact and as well as damaged states with single cable loss to identify critical limit states. Subsequently, a new performance-based robustness evaluation method and robustness indexes for bridges, especially for long-span bridges, has been proposed. This method has also been verified for short-span bridges. Both reliability and robustness of the two long-span bridges were quantitatively evaluated using this approach for the limit states identified through the pushdown analysis. The result show that: (1) the effect of various scenarios of single cable loss on each bridge can be captured explicitly, demonstrating the applicability of the robustness evaluation method and the proposed robustness index, especially for long-span bridges, and (2) in spite of the adverse effect of single cable loss, there was no significant reduction on the reliability and robustness in both the two long-span bridges, i.e., they are very robust against any single cable loss scenario.
Chen, Qian, "Structural Robustness of Long-span Cable-Supported Bridges" (2021). CUNY Academic Works.