Study on seismic performance of prestressed composite joint with CESA columns

Several issues persist in the design and construction of conventional prestressed concrete encased steel (CES) frame structures. This includes the need to strengthen the steel flanges and webs during the passage of prestressed tendons and longitudinal reinforcements through the joint, and insufficient compaction of the concrete cast in the joint core. Therefore, a novel type of prestressed CES frame structure was developed using concrete-encased steel angle (CESA) columns to replace the conventional CES columns. To investigate the seismic shear performance of this new type of prestressed composite joints to propose a method for predicting the shear capacity of joint cores, this study performed tests and nonlinear analysis on three prestressed joints and one nonprestressed joint under low cyclic loading. The failure patterns, energy dissipation, stiffness degradation, deformation recovery performance, and ductility properties were examined for these joints. The effects of prestress level, axial compression ratio, web thickness, stirrup ratio, and steel angle ratio are also discussed. Two formulas are proposed to predict the shear capacity of joint cores based on the fitting of tests and finite element analysis. The results revealed that the oblique crushing of concrete occurred in the joint core at the peak load, resulting in shear failure. Increasing the thickness of the steel web effectively enhanced the horizontal peak load to increase the shear capacity in the joint core. However, an increase in the axial compression ratio may reduce ductility. The formulas developed to predict the shear capacity of the joint core exhibited much higher accuracy, where the simplified practical formula can facilitate convenient design implementation. Overall, these findings demonstrate excellent seismic shear behavior for prestressed composite joints while providing technical support for applications in such types of prestressed frame structures.