System Safety And Reliability Assessment For Adjacent Precast Concrete Box Beam Bridges

Analyses on catastrophic collapse of some adjacent precast concrete box bean bridges reveal the fact that the function loss of shear keys can result in the formation of the "Single Plate Load Effect"; as a result, loads cannot transfer between adjacent beams and damage to both the structure and vehicles can be triggered on the loaded beam by heave trucks. This leads to the concern that the system safety of adjacent precast concrete beam bridges becomes insufficient when the shear keys deteriorate to a certain degree. To understand the system performance of this type of bridges, this dissertation studied the system performance of a model bridge over the full load range through an experimental investigation and finite element simulation. The results confirmed that the assumption that the robustness of certain adjacent precast concrete beam bridges may be considered safe according to the traditional safely check standards, but may not be sufficient in terms of the system safety criteria. Thus, a system factor is recommended to be applied in the safety check equation of this type of bridges. Even though some codes have already incorporated the criteria for evaluating the system behavior of highway bridges in the design and evaluating procedure, little guidance has been provided on how to determine corresponding redundancy or system factors. On the basis of the experiment findings and theoretical analysis, a simplified framework was proposed to address the particular structural feature and topology of adjacent precast concrete bean bridges, which can reduce the computation complexity compared to existing approaches for redundancy and robustness assessment. Sensitive parameters for system reliability were investigated and system reliability indices were computed using a finite element response surface method. The rationality and calibration of system factors were analyzed. In the end, the procedure for system safety and reliability assessment of adjacent precast concrete box beam bridges was applied on a bridge in service with different transverse connections and damage scenarios. The case study verified the proposed approach and outlined the procedure that can be adopted for routine bridge evaluation practice.