Abstract
Present approaches for assessing bridge redundancy are mainly based on nonlinear finite element (FE) analysis. Unfortunately, the real behavior of bridges in the nonlinear range is difficult to evaluate and a sound basis for the nonlinear FE analysis is not available. In addition, a nonlinear FE analysis is not feasible for practitioners to use. To tackle this problem, a new simplified approach based on linear FE analysis and field load testing is introduced in this paper to address the particular structural feature and topology of adjacent precast concrete box-beam bridges for the assessment of structural redundancy. The approach was first experimentally analyzed on a model bridge and then validated by a case study. The approach agrees well with the existing recognized method while reducing the computation complexity and improving the reliability. The analysis reveals that the level of redundancy of the bridge in the case study does not meet the recommended standard, indicating that the system factor recommended by the current bridge evaluation code for this bridge is inappropriate if considering the field condition. Further research on the redundancy level of this type of bridges is consequently recommended.
Highlights
Adjacent precast concrete box-beam bridges have been a popular solution for small and medium span bridges worldwide. e bridges are built by placing precast concrete box-beams side-by-side in parallel, which are connected laterally by shear keys longitudinally grouted in between the beams and covered with a concrete deck. e shear keys and the concrete deck provide the transverse connection between the concrete box beams
E system performance of adjacent precast concrete box-beam bridges is presently reflected by the design lateral load distribution factors (LLDFs), which are determined based on the assumption that the points of contact in two adjacent beams deform [1]. is assumption does not reflect the actual joint condition between adjacent beams when there are cracks in the joints
RFcomp is normally higher than 1.0 and can be neglected. e system-level redundancy can be evaluated by the ratio of the design LLDF to measured deflection distribution factor (DDF). e LLDF and DDF are equal for bridges in service, which are generally in the elastic range. e design load distribution factor can be calculated with the method provided in a design code or through a linear analysis. e measured DDF is computed using equation (1), and the data used in equation (1) can be obtained through a field load testing or an finite element (FE) simulation. e approach is demonstrated in the following case study
Summary
Adjacent precast concrete box-beam bridges have been a popular solution for small and medium span bridges worldwide. e bridges are built by placing precast concrete box-beams side-by-side in parallel, which are connected laterally by shear keys (hinge joints) longitudinally grouted in between the beams and covered with a concrete deck. e shear keys and the concrete deck provide the transverse connection between the concrete box beams. E system performance of adjacent precast concrete box-beam bridges is presently reflected by the design lateral load distribution factors (LLDFs), which are determined based on the assumption that the points of contact in two adjacent beams deform [1]. Us, the redundancy level of adjacent precast concrete boxbeam bridges in service should be evaluated according to the actual conditions of the shear keys and box beams, and the current safety evaluation procedure for this type of bridges should be revisited. It was found that the three most sensitive parameters are all associated with the properties of shear keys, indicating that the behavior of shear keys plays a dominant role in the performance of adjacent precast concrete box-beam bridges. A method is proposed based on a linear FE analysis and field deflection measurement, which is able to address the particular structural feature and topology of adjacent precast concrete box-beam bridges. It is verified that the level of redundancy of the bridge in the case study does not meet the recommended code standard
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