Seismic response of high-strength steel reinforced concrete frames

Substituting conventional reinforcing steel bars with high-strength steel bars can reduce reinforcement congestion, improve constructability, and lower costs in reinforced concrete construction. Member dimensions remaining the same, high-strength steel reinforced concrete (HSSRC) members have lower post-cracking stiffness compared to conventionally-reinforced members of comparable strength. The subject of this investigation is whether this reduction in post-cracking stiffness results in higher peak drifts in structures containing HSSRC members. Four portal frames with identical member dimensions, but different column longitudinal reinforcement configurations, were tested on a unidirectional earthquake simulator. Two frames (type C) had conventional steel longitudinal reinforcement in the columns. In the other two frames (type H), a reduced ratio of high-strength steel was used as column longitudinal reinforcement to achieve comparable nominal strength. Reinforcing details of the frames were otherwise the same. Each frame was subjected to a series of five ground motions of either increasing or decreasing intensity. Measurements of their response showed that peak drifts of type H frames were comparable to drifts of type C frames. It was also observed that softening caused by damage from previous shaking did not affect peak drift, suggesting that initial period of vibration dominated frame response.