Modeling Parameters for Reinforced Concrete Beams Subjected to Cyclic Loading
The use of nonlinear analysis for seismic evaluation of existing building is becoming more common in industry practice. In order to achieve some degree of uniformity in results jurisdictions and government entities rely on the ASCE 41 standard for seismic evaluation of existing structures. Modeling parameters in the first edition of the ASCE 41 standard, published in 2006, were adopted from the FEMA 356 prestandard and were based primarily on expert judgment due to the lack of research studies evaluating experimental results. Research studies performed since then have led to significant changes in the modeling parameters and acceptance criteria for reinforced concrete columns, while other elements still retain parameters proposed in FEMA 356. Recent studies performed at UTSA show that the drastic differences that exist between the level of conservatism of modeling parameters for the different type of elements introduce bias in nonlinear analysis, misleading engineers on the elements most likely to be damaged during earthquakes and the most effective retrofit measures to improve the performance of building structures. This thesis addresses that deficiency in the ASCE 41 standard by proposing a new set of modeling parameters based on experimental data compiled by the author. The modeling parameters proposed are based on statistical analyses of critical points of backbone relationships from tests of reinforced concrete beams subjected to load reversals. The regression analysis was used to derive relationships between the different modeling parameters of the envelope curve and the variables that affect them. Comparisons between modeling parameters measured experimentally, modeling parameters in ASCE 41-17, and the proposed expressions are presented. Results show that the provisions in ASCE 41-17 are significantly more conservative than modeling parameters for columns and that changes are necessary to eliminate bias in nonlinear analyses performed in accordance with the provisions in ASCE 41.