The combined influence of bond-slip and joint-shear in the seismic upgrading via externally-attached BFRP-bar reinforced precast sub-frames

Earthquake causes severe damage to building structures, and seismic upgrading is an important solution to enhance the capacity of existing buildings. In recent years, the externally-attached substructure technique has received broad attention, which upgrades the existing buildings on the system level and proves to be prominently effective in the overall performance. In this paper, the authors develop an externally-attached BFRP-bar reinforced precast concrete sub-frame for seismic upgrading. In the Section 2, the working principles of the novel externally-attached technique are introduced. In the Section 3, the critical issues and simulation strategies of the novel externally-attached technique are proposed (i.e., bond-slip and joint-shear effects). In the Section 4, the generation approach of stochastic nonstationary excitations is given, and in the Section 5, the application examples via three concrete frames are analyzed. In general, the research verifies the effectiveness of the proposed externally-attached BFRP-bar reinforced precast concrete sub-frame for upgrading. The individual influence of bond-slip or joint-shear will apparently increase the drift ratio and lower the upgrading performance. Meanwhile, the combined influence of bond-slip and joint-shear is important in consideration, which will further affect the upgrading performance and enlarge the structural demands. Ignoring the combined influence of the two critical issues in analysis or incorporating only one factor in design will overestimate the structural behaviors and underestimate the potential risks after the externally-attached upgrading. In a sense, the research provides an important reference for the further investigation of the combined influence of bond-slip and joint-shear in the seismic upgrading.