Experimental and analytical study on the seismic performance of prestressed and non-prestressed steel-reinforced UHPC frames

Steel-reinforced ultra-high-performance concrete (UHPC) combined with prestressing offers a promising construction material system for earthquake-resistant and damage-controllable frame structures. In this study, one prestressed steel-reinforced UHPC frame and one non-prestressed counterpart were designed, fabricated and tested under low-cycle reversed loading to clarify the influence of beam prestressing on the cyclic response, damage evolution and energy dissipation of this composite material system. The UHPC matrix had a cube compressive strength of 133.0 MPa, an axial compressive strength of 117.2 MPa and an axial tensile strength of 10.5 MPa, with 2.5% steel fibers incorporated to enhance tensile resistance and crack control. The experimental results showed that both specimens developed full and stable hysteretic loops, with damage mainly concentrated in the beam-end plastic hinge regions and no obvious cracking in the joint core. Compared with SR-UHPCF, PSR-UHPCF exhibited a 7.26% higher peak lateral resistance, whereas its average nominal ultimate displacement and displacement ductility coefficient were 11.57% and 14.63% lower, respectively. The equivalent viscous damping coefficients of both specimens exceeded 0.25, demonstrating satisfactory energy dissipation. A validated OpenSees model was then developed, with mean experimental-to-numerical ratios of 0.98 for peak load and 0.90 for initial stiffness. Parametric analyses indicated that column slenderness ratio, axial compression ratio and prestress level are the governing factors controlling the cyclic behavior. Finally, a simplified restoring-force model was developed for preliminary nonlinear analysis within the investigated parameter domain. These findings indicate that the investigated prestressed SR-UHPC configuration has the potential to improve lateral load resistance and crack control in seismic applications. However, the prestress level should be appropriately selected by balancing these benefits against the required post-peak deformation, ductility, and energy-dissipation capacity.