Quasi-static tests on prestressed truss-like UHPC structures obtained from topological design

In order to obtain high-performance structures that can improve seismic capacity for external retrofit, this research makes full use of the excellent mechanical properties of prestressed ultra-high performance concrete (UHPC) structures and material saving convenience of topology optimization. An additional shear wall used to retrofit a 1/1.5-scale single-span and single-story frame was optimized into a truss-like UHPC component by the solid isotropic material with penalization method. The final optimized result with 68.7% of the original volume had suitable truss structure indices greater than 95% and met the requirements for truss applicability. By introducing unbonded post-tensioned (PT) strands, the extracted result was taken into detailed design to obtain the prestressed truss-like UHPC (PSTL-UHPC) structure. Quasi-static tests were conducted on 2 prefabricated PSTL-UHPC specimens with different numbers of PT strands to investigate the seismic performance of them. The hysteretic behaviors, self-centering performance, deformation capacity, energy dissipation and remaining seismic capacity of the optimized specimens were studied in conjunction with the crack distribution, prestress of PT strands, and strain of UHPC. The specimens both exhibited a hybrid flag-shaped hysteresis with small residual story drift ratios within 0.2% after unloading at the peak point, and the story drift ratios did not exceed 2% during the loading process. The strain-hardening characteristic of UHPC and strut-and-tie layout formed by topology optimization give full play to the tensile deformation capacity of the PT strands. Therefore, the increase of PT strands not only controls the residual deformation more effectively, but also improves the ductility of the specimen, which leads to better energy dissipation and remaining seismic capacity.