Benchmarking Linear Analysis Procedures for Reinforced Concrete Moment Frames in ASCE 41
Linear analysis procedures in ASCE 41 are based on a hybrid displacement/force approach with equations calibrated using SDOF oscillators. This work focuses on the validation of displacement estimates calculated using linear analysis procedures currently implemented in ASCE 41. Emphasis was given to global metrics of deformation, specifically lateral drift and drift ratio. A parametric study was performed with reinforced concrete moment resisting notional frames. The following parameters were varied in the study: Quality of detailing, intensity of shaking, frame configuration, and effective stiffness.
This validation is important because a true assessment of a building performance for a given seismic hazard requires accurate estimates of the displacement of MDOF nonlinear systems using linear numerical models.
It was found that if the mean drift ratio calculated with the linear model exceeded 2%, estimates of deformation became less accurate as lateral deformation increased and quality of detailing decreased. The discrepancy between the deformation of linear and nonlinear systems was caused by the propensity of flexible frames and frames with poor detailing developing story collapse mechanisms.
Performance assessments using linear procures in ASCE 41 were evaluated. Forces calculated using MDOF linear models were reduced using element m-factors and compared with element capacities. m-factors are predicated on the concept that the ratio of elastic element force to yield force is similar to the ratio of inelastic deformation to yield deformation. These two ratios were compared in beams and columns to evaluate the accuracy of this assumption. A comparison between expected level of performance calculated using linear and nonlinear procedures is also presented.
A parametric study was performed with reinforced concrete moment resisting notional frames. The following parameters were varied in the study: Quality of detailing, intensity of shaking, frame configuration, effective stiffness.
This study showed that in beams, for all hazards, the conservatism of LSP and LDP with respect to NDP increased as the quality of detailing decreased. In columns, both linear procedures provided a more conservative assessment than NDP. In addition, LSP and LDP resulted in nearly similar performance assessments for columns for all hazards and detailing levels.