Exterior beam column joints – Shear strength model and design formula

• A model for prediction of exterior RC beam–column joint shear strength is proposed.
• The contributions of two concrete struts and steel reinforcements are considered.
• Concrete struts give the main resisting mechanism up to 65 degree angle of ST1 strut.
• Joint stirrups are more effective in providing shear strength than vertical bars.
• Bond deterioration of beam bars is taken into account.

A new model to determine the shear strength of exterior reinforced concrete (RC) beam–column joints under seismic actions is proposed in this paper. An explicit formula that considers the shear strength contributions provided by the strut-and-tie mechanism due to two diagonal concrete struts, as well as the horizontal hoops and the intermediate vertical bars of the column, is derived. The coefficients of each contribution are calibrated using 61 test data sets available in the literature, most of them from cyclic tests. This paper compares the shear strength predictions using the proposed expression, the model of Hwang and Lee, and the model of Park and Mosalam, the last of which is valid for unreinforced joints only. A design formula is also proposed and its predictions are compared to those of Eurocode 8 and ACI Code.