The accurate prediction of shear strength and flexibility of beam-column joints without transverse reinforcement is essential to assess the seismic performance of nonductile reinforced concrete (RC) buildings characterized by having such unreinforced beam-column joints. In this study, a multilinear backbone curve to represent the moment-rotation relationship of an unreinforced corner beam-column joint is proposed. The modeling parameters of the backbone curve are estimated based on experimental results of four corner joint specimens recently tested by the authors. Furthermore, the proposed backbone curve is modified to be applicable to interior and roof beam-column joints. These backbone curves are validated by accurate reproduction of the force-drift responses of the four corner joint specimens and eight other exterior and interior joint specimens from literature. Using these backbone curves, nonlinear dynamic analyses are performed on three hypothetical building frames. The analytical results demonstrate the importance of joint flexibility for seismic assessment of nonductile RC buildings.

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