Cyclic performance of middle partially encased composite braces

The utilization of reinforced concrete to fill the middle section of the H-shaped steel in middle partially encased composite brace (MPECB) effectively restrains the buckling deformation of the steel plates, mitigates compression instability, and enhances the compressive stiffness and bearing capacity of the brace component. To investigate the hysteresis performance and energy dissipation capacity of MPECBs, axial hysteresis tests were conducted on four MPECBs and one comparative H-shaped steel brace. The experimental results revealed that the failure mode of MPECBs involved warping deformation of flange plate and separation from the concrete. Compared to steel brace, MPECBs exhibited significantly improved energy dissipation capacity in the early loading stage, as well as enhanced compressive capacity, while showing minor change in tensile capacity. Additionally, finite element models (FEMs) were developed, and parameter analysis was performed. The FE analysis confirmed that the variations in reinforcing bars and stirrup spacing had a minor influence on the bearing capacity of MPECBs in comparison to modifications in the cross-sectional dimensions of H-shaped steel. However, reducing the stirrup spacing can enhance the utilization of the concrete in MPECB, allowing for its performance to be more effectively harnessed. Furthermore, the formula for calculating the tensile capacity of MPECB was proposed, and the design process for MPECB was summarized based on the calculation method.