PERFORMANCE EVALUATION OF RC STRUCTURES UNDER EARTHQUAKE LOADING

Abstract

Existing seismic risk in Pakistan, especially in its Northern Areas, emphasis for a detailed and careful design of RC structures to withstand expected earthquake loads. The seismic performance of RC multistory structures is a complex process. An accurate assessment of seismic behavior of RC structures requires an analysis carried out under time history or parameters of time history of real time recorded earthquakes. In Pakistan, a large data bank of strong motion recorders exists in analog form, and its use in performance assessment of structures is very difficult without digitizing it. The response of a multistory RC building is greatly dependant on performance of its columns especially in inelastic range, which can be improved by providing sufficient confinement. Post earthquake surveys revealed that most of the RC buildings collapsed due to insufficient performance of their columns, which were found deficient in confinement. A limited work has been carried out in Pakistan to study the performance of RC columns under axial and lateral loading. Internationally, the efforts are continued to enhance the performance of RC columns subjected to seismic loads. The objective of this research has three main parts. The first part is to collect, segregate and digitize available analog form of earthquake data, which has been recorded in Pakistan. The second part is to device and test a technique which could enhance strength, ductility and stiffness of RC columns subjected to seismic loads and result in lesser residual deformations. The third part is to carry out seismic analysis of a RC multistory frame, using material behavior studied experimentally, under application of ground motion data of Pakistan. A novel digitizing technique is developed in this study that extracts the trace of recorded acceleration as a whole by saving all points required to draw digitized ground acceleration. The proposed digitizing approach has been compared with the available techniques to assess its efficiency. The confinement technique for RC columns developed in this study utilizes specialized rings of steel strips applied as transverse reinforcement in hinge zone. Eight large scale specimens have been cast and tested to study the performance of proposed technique. The experimental results indicated that proposed confining reinforcement, although with lesser volumetric ratio, improved the performance of RC columns by enhancing their shear resistance, ductility, energy dissipation capacity and reducing residual deformations. iiThe columns confined by proposed technique have been named as Steel Strip Confined (SSC) columns. The observed column behavior has been modeled in Response-2000 and DRAIN-3DX. RC frames are modeled in DRAIN-3DX using material properties calibrated with experimental data. The frames are analyzed under north-south component of El Centro ground motion and east-west component of Kashmir earthquake recorded at Abbottabad. The frames, modeled with properties of SSC columns, showed better performance by reducing the damage. The analysis indicates that Kashmir earthquake is more damaging in nature than El Centro ground motion.