Probabilistic approach for correlating stiffness and strength irregularities in RC buildings under earthquake shaking

Abstract

Stiffness irregularity in buildings is commonly associated with strength irregularity. Recent research has primarily focused on examining these irregularities independently, with comparatively less emphasis on the correlation to the presence of both irregularities. Two sets of 2-D reinforced concrete (RC) moment frame buildings with varying configurations and locations of irregularity are analyzed to examine the limitations of current research and building code provisions. Based on elastic behavior, interstorey drift is identified as a more reliable indicator for determining stiffness irregularity, while lateral storey strength proves to be a more effective parameter for evaluating strength irregularity. Updated provisions and new limits are proposed to address the shortcomings, with the evaluation considering three stories at both the upper and lower levels as the ratio for accurately assessing irregularities at higher and lower stories. A storey may exhibit stiffness irregularity without the presence of strength irregularity. Inelastic results show that shifting the irregular storey to higher levels increases building strength from the ground storey to the roof storey, while probabilistic analysis reveals that the probability of exceeding the yielding state decreases from 95 % to 24 %. However, irregularity due to column removal, even at the ground storey, can result in higher strength than a regular configuration, with less probability ∼36 % of exceeding any yielding state, suggesting it to be more stable. This observation underscores the need for improved evaluation methods, particularly through nonlinear analysis, to more accurately identify and design irregular buildings.