Failure mechanism and bearing capacity analysis of the underpinning structure with relative displacement

Abstract

The failure mechanism of the underpinning structure in a leaning building jacking-up rectification was investigated for examining the relative displacement between the underpinning joints (UJ). The experimental specimen of underpinning structure included two UJs connected by girders (CG). A spring support was adopted for one joint, and a roller support for another joint, to simulate the relative displacement between the two joints. Three specimens were designed with different heights of the connection girders between the two UJs. It was found that diagonal cracks appeared on both joints and shear failure of the underpinning joint on the spring support occurred. The connection girder was in a tension state close to the roller support, and in a compression state close to the spring support. The bearing capacity of the underpinning structure was higher with connection girder higher. However, the bearing capacity was 14.1–21.5% lower than the single joint under the condition of relative displacement. Further, a germane finite element simulation was carried out to capture more details about the stress distribution. The derived displacements, strains, cracks, and the bearing capacity were compared with the experimental ones and found in good agreement. Furthermore, it was observed that the angle of the compression zone of the failure beam became smaller than the single underpinning joint due to the constraint of the connection girder. Finally, various relative displacements were studied,and it was found that as the relative displacement became smaller, the bearing capacity became higher. Thus, it was concluded that it is not safe to make design decisions in jacking-up rectification based on the method of the single joint; the relative displacement should also be considered in the design.