Behaviour of Reinforced Concrete Structures Resting on Soil Classes C and D under Repeated Earthquakes

Abstract

This paper presents a thorough study of inelastic displacement ratios (IDR) of single degree of freedom (SDOF) systems under repeated earthquake loading by accounting for soil–structure interaction (SSI) and system’s degradation. Even though, there have been much research on impact of degradation for structures; presently, no seismic code provisions are used for structural design accounting for repeated earthquakes or degradation. Most of the SSI consideration address rather simple soil models that assume soil foundation system to remain elastic; moreover, fixed-base foundation assumption is still favorable when designing simple structures. Thus, the goal of this study is to analyze the impact of the following key parameters on designing structures: SSI, foundation aspect ratio, strength reduction factor (R), repeated earthquakes, and degradation by means of IDR values. In this paper, a fixed-base model has been taken as a reference to compare SSI-accounted-equivalent fixed-base models, which have been analyzed for variations of soil classes (Soil C and Soil D). The analysis has been computed by using 104 actual earthquake records which have been scaled to the same hazard level and performed on PEER experimentally verified reinforced concrete (RC) columns. The analysis has been conducted by using an in-house program that includes the modified Clough model that takes degradation into account. Effective periods and effective damping ratios have been calculated for varying soil classes. A single earthquake model and two different artificially simulated repeated earthquake models have been applied on SDOF systems for which the period ranges from 0.2 to 1.4 s. Finally, the significant impact of SSI and repeated earthquake phenomena combination on IDR have been addressed. The overall findings demonstrate how structural response changes due to degradation, SSI, aspect ratio, soil class, and different repeated earthquake models in the form of IDR spectra. The effect of aspect ratio has a threshold at period of around 0.6 s and is more apparent for SSI-accounted structures. Similarly, higher values of R have a strong influence on the IDRs of soil–structure systems than those of fixed-base structures. The results also confirm that the IDR values are higher for soil class D than those of soil class C. Conclusively, it has been found that repeated earthquakes, studied in two different models, make the structure reach the collapse failure sooner than the single earthquake case.