This paper discusses on R/C interior step beam-column joints with headed anchor for beam longitudinal bars, developed to streamline the works of reinforcing for R/C interior step joints. In general, beam longitudinal bars of step beam column joints are applied 90°-degree hook in step beam-column joints. In R/C buildings, step beam column joints are sometimes planed for architectural planning reasons. Nevertheless, interior step beam-column joints reinforcements are congested and 90°-degree hook of the left and right beams may be the case these hooks are overlap. In order to consider interior step beam-column joints design method, four specimens with beam-column strength ratio approximately 1.0 and 1.5 were tested. Regarding step beam-column joints, from the crack behavior, the stress transfer mechanism depends on positive and negative loading and is considered to consist of two struts which are formed by the balancing of the compressive forces concentrated at the ends of the column and beam and the balancing of the headed anchorage reaction forces. The stress transfer mechanism consisting of these two struts was modelled and proposed as a “double strut model”. A design method of R/C step interior beam-column joints based on the double strut model is also proposed. It provides sufficient satisfaction as to the interior step beam-column joints experimental test results.
