Estimation of the drift capacity of reinforced concrete columns subjected to displacement reversals

A correlation exists between maximum forces at the critical zone of reinforced concrete (RC) columns and their lateral deformation capacity. Evidence of this correlation is found in experimental results. Based on the observed evidence this correlation can be expressed in terms of initial properties of the column. Thus, the drift capacity of RC rectangular columns can be estimated from initial geometric properties, initial material properties, applied axial load and the quantification of the effect of different displacement histories. A parametric study of RC columns using the found equation shows that calculations of the effects of varying the axial load, transverse reinforcement ratio, area of longitudinal reinforcement and shear span length agree with findings from experiments. The shear span, transverse reinforcement ratio and longitudinal reinforcement ratio significantly affect the changes of the drift capacity. Tests of RC columns, however, shows that drift capacity depends on the severity of applied displacement history as a function of drift amplitude and number of cycles. Therefore, correlation between actual drift demands from earthquakes and experimental drift demands is sought by means of nonlinear dynamic analyses of RC frame building models. According to the analyses, drift demands in buildings are significantly less severe than those used in laboratory tests. Drift-ratio excursions are dominated by low drift-ratio amplitudes regardless of the initial period. The number of cycles in column tests is only comparable for calculated drift demands of structures with periods less than 0.3 sec. No more than 3 cycles at drift ratios larger than 2% should occur in columns of structures with larger periods. Thus, the effects of different displacement histories and drift reversals on drift capacity can be lower. The calculated drift demands are not affected by changes in the base shear strength of buildings