Seismic performance of reinforced concrete external beam - column joints in ductile frames

Abstract

This report describes the experimental testing of eight reinforced concrete external beam-column joint sub-assemblies designed to the current NZ Concrete Standard (NZS3101:1995). The first four test units incorporated Grade 430 reinforcing in the beam while the later four units used the new Grade 500E reinforcing steel.

The aim of this project was to investigate different ways of detailing the beam bar anchorage within the joint region, especially the requirement that the beam bars should be bent into the joint with 90 degree bends, which must be anchored at a distance no greater than ¼ of the column depth from the outside face of the column. Several test units employed the conventional “standard hook” (90 degree bend and a 12 bar diameter (db tail) while two units used the continuous U-bar detail as a comparison. 

The testing also set out to examine the influence of beam elongation, due to plastic hinging on the performance of beam-column joints at the first floor level of multi-storey frames. One test unit had its beam reinforcing behaviour spread uniformly down the beam section (with horizontal U-bars) so as to compare its seismic behaviour with that of the conventional detailing with concentrated areas of beam steel at the top and bottom of the section.