SEISMIC DESIGN AND BEHAVIOR OF EXTERNALREINFORCED CONCRETE BEAM-COLUMN JOINTS USING500E GRADE STEEL REINFORCING

摘要

Four external reinforced concrete beam-column sub-assemblages were tested under pseudoseismicrncyclic loading. The approximately 2/3 scale units incorporated the new Grade 500Ernreinforcing steel as the beam bars. Two different forms of beam bar anchorage were tested,rnthe normal 90-degree "standard hook" and the continuous U-bar detail. In all units thernfarthest point of the beam bar anchorage was positioned at the minimum limit prescribed inrnthe NZ Concrete Standard (NZS3101), namely 3/4 of the column depth from the inner columnrnface. All 4 units formed plastic hinges in the beam and joint degradation was minor. Failurernoccurred at drift ratios between 4 and 6% (approximate ductility factors of between 4 and 6)rnpredominantly due to buckling of the beam bars in the plastic hinge zone. The stiffness ofrnthese units was significantly less than similar units reinforced with 300E Grade reinforcing orrnthe recently replaced 430 Mpa reinforcement. The decreased stiffness will cause higherrnlateral drifts during large earthquakes, than those anticipated in current Standards.