Shear Strength Estimation of Nonseismically Designed Exterior Beam-Column Joints Strengthened with Unsymmetrical Chamfers

A practical strengthening strategy for nonseismically designed exterior beam-column joints (BCJs) has been proposed by installing an unsymmetrical chamfer on the soffit of the beam. Its feasibility and effectiveness have been validated by extensive experimental studies. In this study, the load transfer mechanism of an exterior BCJ with chamfer is further analyzed to establish an analytical model for joint shear strength. An additional strut is identified in the chamfer based on finite element analysis results, which serves as the secondary load transfer path in addition to the diagonal strut within the joint area. Furthermore, a parametric study was performed to correlate chamfer size with joint shear strength of a strengthened joint. Width of the diagonal strut is enlarged with increasing chamfer size, whereas the effective width of compression zone in the chamfer is limited. With identified load path of BCJ with chamfer, an analytical model is established based on softened strut-and-tie model (STM) which provides clear load transfer mechanism for rational conception design and reasonable join shear estimation, especially for unreinforced BCJs. Width of the diagonal strut, which is the main parameter in a STM, is redefined accounting for contribution of chamfer. Finally, design procedures and recommendations are provided for application of the strengthening strategy in practice.