Seismic performance of external reinforced concrete beam-column joints

Abstract

Four external beam-column sub-assemblies were tested to investigate the influence of different details on the performance of the Joint zone. All the details conformed to the current New Zealand structural concrete standard (NZS3101-1995). It is shown that anchoring beam reinforcement in external beam- column joints short of the outer column bars results in a reduction in the flexural strength of the column. In tests premature yielding of the longitudinal bars on the inside of the column occurred when bars were anchored at a distance of 1⁄4 of the column depth from the outside face of the column, as permitted by the structural concrete Standard. This yielding had an adverse effect on the performance of the joint zone. A way of detailing external joint zones to compensate for this loss in strength is described. Elongation of plastic hinges in the beams of ductile frames induces unidirectional plastic hinges in the external columns at the first floor level. While this has a strong influence on the distribution of moments and shears in the columns tests indicated that it does not adversely affect the structural performance of the joint zone. The use of continuous bars bent in the form of a U provides a simple detail that worked very effectively. There was little difference in joint behaviour between beams with main bars uniformly distributed over the beam depth to conventionally reinforced beams with their main bars positioned near the top and bottom edges.