STUDY ON SHEAR BEHAVIOUR OF EXTERIOR REINFORCED CONCRETE BEAM-COLUMN JOINTS BASED ON MODIFIED SOFTENED STRUT AND TIE MODEL

Based on the softened strut and tie model, a more precise equation for calculating the angle of diagonal concrete strut inclination is suggested based on the strain distribution of exterior beam column joints, and an empirical softened constitutive model of concrete is given on the basis of experimental data from 44 exterior RC beam column joints. Thus the modified softened strut and tie model is derived. The shear strength of 91 exterior joints (joint shear failure occurred on 56 of them) and shear stress-strain curves of 26 exterior joints are calculated by SSTM, diagonal compression strut model (DCSM) and MSSTM, respectively. The results indicate that MSSTM is more accurate on predicting the shear strength and the shear stress-strain curves compared with SSTM and DCSM. The average ratios of calculated to measured shear strength of SSTM, DCSM and MSSTM are 1.028, 1.203 and 0.995 respectively, and the coefficient of variation are 0.230, 0.273 and 0.164 respectively. The accuracy of MSSTM prediction is better and the variability is significantly reduced. Also, MSSTM can predict the key points of shear stress-strain curves well, particularly in terms of peak shear stress and initial stiffness. The average ratios of calculated to measured peak shear stress and initial stiffness are 1.14 and 1.02 respectively.