Seismic Performance of Compliant and Noncompliant Special Moment-Resisting Reinforced Concrete Frames

Shake-table tests were conducted on reinforced concrete frames designed to UBC-97 and detailed as per ACI318. The frames were built complying with the code requirements and having construction defects: low-strength concrete, lacking ties in joints, stirrups being provided at larger spacing, practicing reduced longitudinal reinforcements, along with non-seismic hooks. Five 1:3-scale, two-story representative models were subjected to a linearly scaled accelerogram of the 1994 Northridge earthquake. The observed damage mechanism and lateral force-deformation behavior of tested frames were obtained. The response modification factor calculated for the code-complaint frame is approximately 7.50, which is reduced by 40 to 60% for models with construction defects. One of the major findings reveals the minimum ACI 318 requirement for exterior column depth of 15 times the diameter of longitudinal steel bars is inadequate to avoid joint panel damage, specifically for structures built with low-strength concrete and/or joint panels lacking confining ties under design-level earthquake.