A modified softened strut-and-tie model for non-seismically designed beam-column interior joints strengthened with unsymmetrical chamfers

Abstract

A strengthening strategy for non-seismically designed beam-column joints (BCJs) has been proposed by installing unsymmetrical chamfers on the soffits of beams in a previous study. This practical strengthening strategy has no alteration to building plans and can be easily constructed within hours. Comprehensive experimental studies have shown that performance of non-seismically designed BCJs is effectively upgraded by installing chamfers. In this study, numerical studies were conducted through nonlinear finite element analysis to provide a thorough understanding of load transfer mechanism of BCJs with chamfers. An additional strut is observed in chamfer in addition to diagonal strut within joint area which is the main mechanism of unreinforced BCJs resisting joint shear force. Finite element models were verified by experimental results, including failure modes, stress of reinforcements, load displacement curves and strain in chamfers. Parametric studies were then performed in terms of chamfer size. It was correlated with joint shear strength by two separated linear relationships. The width of diagonal strut is expanded by increasing chamfer size, which effectively improves joint shear strength. Based on the above, a modified softened strut-and-tie model to estimate joint shear strength of joint with chamfers is proposed. Finally, design rules are recommended in practical application of BCJs strengthened with unsymmetrical chamfers.