SEISMIC EXPERIMENTAL STUDY ON A UHPC PRECAST MONOLITHIC CONCRETE BEAM-COLUMN CONNECTION

To avoid problems such as high required-precision and undetectable quality of grouting sleeve connections and to improve the seismic performance of beam-column connections, we studied the failure modes, hysteretic characteristics, skeleton curves, and energy dissipation capacities through the quasi-static tests of six precast concrete beam-column connections and a monolithic beam-column connection. The results indicate that it is feasible to connect the columns and beams by lap-splice with UHPC (LS-UHPC) with straight bars with a lap length of 15d_b or with 90° hooked bars with a lap length of 11d_b. No significant slippage occurred because of the high bond strength of UHPC and the specimens exhibited good ductility, although the anchorage lengths of 16.7d_b and 13.6d_b for the upper longitudinal bars in the beams did not meet the requirements of 20d_b specified in the GB 50010−2010. The shear capacity of the joint was significantly improved because of the use of UHPC. It exhibited a better performance than that of ordinary cast-in-place concrete joints, even if no stirrup was provided. The increase of stirrup and steel fiber content in the joint delayed the formation of the main diagonal crack in the joint, improved the damage-resistance capacity of the joint, and improved the ultimate displacement, ductility coefficient and energy consumption capacity of beam-column connection. The stirrups can further improve the damage resistance of the joint. The equations in GB 50010−2010 underestimate the shear contribution of UHPC and overestimate the shear contribution of stirrups, while those in ACI 318-19 overestimate the shear contribution of UHPC in the joint. According to the relationship between compressive and tensile strengths, the equations in GB 50010−2010 and ACI 318-19 are modified. The modified ACI 318-19 equation is more accurate while remains conservative.