Effect of column-to-beam strength ratio on earthquake resistance of RC moment frames using probabilistic performance-based design methodologies

Abstract

This study utilizes performance-based design methodologies to evaluate the performance of reinforced concrete (RC) moment frames under seismic loading, and is meant to serve as a precursor to the implementation of performance-based earthquake engineering for RC structures. Two different RC moment frames (three- and six-stories) are used as study buildings. Three different earthquake intensities (with return periods of 73, 475, and 2475 years) and two different building limit states (immediate occupancy and life safety) are considered. The main objectives are to: (1) define the limit states on the system level in quantifiable terms; (2) establish a method for determining the probability of the buildings exceeding the limit states under earthquake excitation; and (3) discern the effect of the variation of one design parameter on the probability that the buildings will exceed the limit states under the three levels of seismic loading. Column-to-beam flexural strength ratio is the varied parameter in order to complete concurrently a sub-investigation concerning the validity of the ACI code requirements for the minimum allowable strength ratio at the joints in RC frames designed to resist seismic loads. Multiple strength ratios are evaluated by: (1) determining the probabilistic structural demands, in terms of inter-story drift, from each series of ground motions; (2) determining the inter-story drift capacities at which the two limit states are exceeded; and (3) determining the probability of structural demands exceeding capacities.