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

Sefatullah Halim, Susumu Takahashi, Toshikatsu Ichinose, Masaomi Teshigawara, Takashi Kamiya, Hiroshi Fukuyama Journal of Advanced Concrete Technology, 12, 146-157, 2014 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.

This paper together with the first part forms a comprehensive study of strength of beam-column joint in soft first story RC buildings. The authors succeed to present both the experimental and STMs model of the topic. The strength and failure modes predicted by the proposed procedure agreed well with the test results. It is a well written research topic with useful conclusions. (Prof. György L. Balázs) The authors successfully apply the concept of strut-and-tie model to explain behavior and to establish new design equations for beam-column joints of soft first story buildings in their Part 2 of the study, by verifying with the experimental results obtained from their Part 1.  The understandings obtained from this work lead to a future better as well as safer design of the joints.  In fact the contribution of the experimental works done in Part 1 adds the value of the paper in Part 2, which results in this nomination. (Prof. Somnuk Tangtermsirikul)