Effect of superstructure modeling assumptions on earthquake response of a reinforced concrete building retrofitted with seismic isolation

In this study, the change in seismic demands of an older-type reinforced concrete building retrofitted with seismic isolation, is investigated depending on the supserstructure modeling assumptions considered in the numerical models. Hence, an 8 story reinforced concrete residental building, with the characteristics of existing Turkish building stock is designed in accordance with the provisions of Turkish Earthquake Code (1998). The designed reinforced concrete residential building is then retrofitted by a base isolation system consisting of lead rubber bearings. The numerical models of the reinforced concrete residental building, retrofitted with seismic base isolation are developed in two different forms by considering linear and nonlinear modeling approaches for structural elements. In the nonlinear numerical model, the amount of transverse reinforcement in the confinement zone of structural elements is also considered as a variable. In all numerical models, the strength deterioration of lead rubber bearings due to the temperature increase in lead core is considered. Eleven pairs of ground motion acceleration records with near field characteristics are selected from the PEER strong ground motion database to be used in the nonlinear dynamic analysis. The selected ground motion acceleration records are scaled in accordance with the target design spectrum to get compatible with the provisions of Turkish Earthquake Code (2018). In the dynamic analysis, the scaled ground motion records are applied simultaneously in both horizontal directions of the numerical models. The average maximum inter-story drift ratio, average maximum story shear force and average maximum floor acceleration demands of the numerical models are examined comparatively depending on the varying modeling approaches. In the first part of the study, a parametric study is conducted to investigate the effect of building characteristics and modeling approaches on the seismic demands of a seismically isolated reinforced concrete residential building. In the parametric study, firstly, new building models are developed by changing the material and geometric properties of the reinforced concrete residental building designed. Then, different modeling approaches for the superstructure elements are considered in the linear and nonlinear numerical models. The seismic demands of the superstructure obtained from the nonlinear dynamic analysis of the numerical models are evaluated separately for each of the parameters considered in the study. In the second part of the study, the change of seismic demands in case of corrosion of steel reinforcement in the reinforced concrete residential building retrofitted with seismic isolation is investigated. Hence, the nonlinear numerical models of the reinforced concrete residental building retrofitted with lead rubber bearings are developed for four different corrosion scenarios and four different corrosion levels. The seismic demands of the superstructure obtained from the nonlinear dynamic analysis of the numerical models are compared with the demands of the numerical model where corrosion effects are not considered. In the third part of the study, the change in seismic demands of the reinforced concrete residential building with seismic isolation due to beam-column joint deformations is investigated. Accordingly, two numerical models of reinforced concrete residential building (i) with consideration of beam-column joint deformations and (ii) without consideration of beam-colum joint deformations are developed. The seismic demands of the superstructure obtained from the nonlinear dynamic analysis of the numerical models are evaluated comparatively. Also, moment-rotation demands of beam-column joints are examined.