Strength of Beam-column Joint in Soft First Story of RC Buildings Part 2: Design Equations

Part-1 of this study presents the experimental results of beam-column joints in soft-first story buildings, in which the first-story column depth is twice that of the upper stories. In Part-2, strut-and-tie models (STMs) are developed for the specimens. The flow of internal forces shown by the developed strut-and-tie models agreed with the observed cracks. The developed models for the joints are different from those for the usual joint: the main difference is that, in the specimens large struts were extended into the wall panel. STMs are also developed for the total frame to understand the overall equilibrium. Based on the STMs, new design equations are proposed, where the joint strength is evaluated as the sum of the flexural strengths of the beam and the second-story column. In I-type joint, the effect of the wall panel and beam stirrups is also considered. In O-type joint, the effect of the hoops in the joint is also considered.