Shake table investigations on code non-compliant reinforced concrete frames

Abstract

Shake-table tests were performed on a code conforming and four non-compliant 1:3 reduced scale two-story RC frames. The models were subjected to 1994 Northridge earthquake acceleration time history, linearly scaled to multiple levels for studying the progressive damages. The code conforming model was observed with plastic hinges at the beam-ends and base of columns on ground story. This frame incurred only slight cracks in the joint panels under extreme shaking. The code-conforming model resisted input excitation with peak horizontal acceleration of 1.0 g before attaining the incipient collapse state. The non-compliant models were observed with plastic hinges in beam/column members, and incurred extensive damages in beam-column joints under extreme shaking. The fully non-compliant frame resisted peak horizontal acceleration of 0.50 g before attaining the incipient collapse state. The response modification factor of code-conforming model is 7.54 that reduced to 2.90 in case of fully non-compliant frame, which was due to the non-compliance of constructions. This was partly due to the reduction in the overstrength of frame (which was about 20%) and partly due to the reduction in ductility of frame (which was about 50%), in comparison to the seismic response parameters given in the seismic code. The less redundant structural system and joint shear hinging are the main reasons resulting in the reduction of overstrength and ductility, respectively. Static force based performance assessment in various seismic zones revealed that the code-conforming frame performance is “OK” while non-complaint frames performance is “NG” in both seismic zone 3 and zone 4. The present research suggests a reliability/redundancy factor to take in to account in proposing response modification factor for seismic design of structure. This will take care of the construction deficiencies found in the region. This factor can vary from 1.0 (in case of fully compliant structure) to 0.40 (in case of fully non-compliant structure). Keywords: Shake table test, SMRF, ACI-318, Damage scale, Response modification factor, Beam-column joints