Investigation of the Plastic Drift Capacity of RC Frames with Beam-Column Joint Failure

Abstract

MBIE/NZSEE guidelines have various methods to assess existing buildings, of which Displacement Based Assessment (DBA) is one. This paper reports on the application of DBA to reinforced concrete (RC) frames where beam-column joint shear failure governs. In the current guidelines, direct rotation method is recommended to estimate the probable drift capacity if plain round reinforcement is used. But the guidance is limited to beams, columns, and walls. This paper investigates the plastic drift capacity of RC frames possessing plain round bars and unreinforced exterior beam-column joints. A mechanics-based approach is proposed to estimate the plastic drift capacity of joints post-cracking. This approach suggests that the exterior beam-column joint can deform up to 1% after reaching shear strength without losing its gravity load bearing capacity. For verification purposes, the results of experimental tests are reviewed from the literature. The median plastic drift at a near-collapse limit state is found to be 1.3% with a dispersion of 0.8. Comparison has shown that the predicted plastic drift tends to be underestimated, and the uncertainties in the predictions require further research. Overall, the proposed joint mechanism provides an estimation of plastic drift capacity for RC frames that fail in joint shear. Experimental testing results suggest that the joint shear deformation values in the current C5 guidelines are overly conservative and that the newly proposed approach is more accurate and should be considered as part of future research.