Experimental study of high-strength steel fiber concrete exterior beam-column joints with high-strength steel reinforcements

This study aims to evaluate the seismic performance of exterior beam-column joints (BCJs) having high-strength steel (HSS) reinforcements in beams and columns coupled with high-strength steel fiber reinforced concrete (HSSFRC). Eight full-scale exterior BCJs with various reinforcement detailing were designed for a moment-resisting frame and subjected to reversed cyclic loading. The parameters in the test include reinforcement strength, concreting pattern in different regions and shear compressive ratio. The amounts of HSS reinforcements in beams, with a yield strength of 600 MPa, were reduced by 22.6% for specimens SEJH1 and EJH1 with 9% higher flexural strength and by 33.3% for the other specimens with 6% lower flexural strength, respectively, due to the enhancement in yield strength. The joints reinforced with HSS reinforcement showed similar failure modes, energy dissipation and secant stiffness as the specimens using 400 MPa reinforcement. Substitution of 400 MPa bars with a smaller amount of 600 MPa as beam longitudinal reinforcements was favorable to seismic performance and could resolve reinforcement congestion. While using HSSFRC effectively enhanced the ductility, decreased slippage of beam longitudinal reinforcements, improved concrete crushing and decreased shear deformation in the joint core due to improved bond degradation of HSS bars; but the peak load and secant stiffness were not significantly affected. The analytical results of design codes in GB50010 were agreed with the experimental results.