TRUSS MODEL FOR TENSION BARS IN REINFORCED-CONCRETE BEAMS - TENSION-TENSION-COMPRESSION REGIONS

A plane truss model for the design of reinforcing bars in negative mom ent regions is presented herein to clarify the effects of diagonal cra cking, stirrup strength, bar embedment length, and beam depth on bond failure load. Understanding these aspects of bond in load transfer hel p to overcome the current empiricism in this area. The truss model is developed for the limit analysis capable of explaining failure modes i nvolving bond strength that cannot be explained by current truss model s. This study finds that the pull-out length over which bond strength fully develops is lower than the whole embedment length in the negativ e moment region of RC beams, and bond failure is combined with diagona l tension failure at support. The model provides a rational design met hodology and a basis for the revision of current design provisions reg arding bar cutoff.