The impact of load history on deformation limit states for the displacement-based seismic design of RC moment frame buildings

The main goals of this research were (1) to study the relationships between material strain and deformation parameters such as curvature and drift for reinforced concrete moment frame structures and (2) to identify the load history effects on these relationships. Through the use of moment-curvature analyses, trends between strain and curvature for rectangular reinforced concrete sections were explored. Curvature-strain relationships that depend on axial load ratio and longitudinal steel ratio were developed from the moment-curvature analyses results. The curvature expressions were subsequently used to develop equations to compute interstorey drift based on strain limits for RC moment frames. The resultant equations can be used in performance-based design approaches such as direct displacement-based seismic design to compute target drifts and system displacements for prescribed limit states based on material strains. The interstorey drift equations were correlated against 54 frame building analyses using OpenSees with reasonable accuracy.;To study the load history effects in the relationship between material strains and drift, the research was divided in two phases. The first phase considered RC column members subjected to symmetrical and asymmetrical cyclic reverse loading and seismic acceleration time histories. Column members with 2% and 4% longitudinal steel ratio and axial load ratio of 5% to 20% were analyzed. The second phase considered moment frame buildings subjected to seismic acceleration time histories. A total of five different moment frame models were analyzed. All the results were compared to monotonic (pushover) analyses. It was concluded that monotonic section analyses can be used to describe the envelope of seismic response since the relationship between strains and displacements/drift is minimally affected by different loading histories. It was also determined that a simple addition of the growth steel strain to the flexural tension strain is not correct, as previously thought.