NONLINEAR MODELING OF SOFT STOREY RC FRAME BASED ON CYCLIC TESTING OF COMPONENTS

Abstract

The Performance Based Design of a structure in Earthquake Engineering depends upon non-linear behavior of its structural and non-structural components. In case of moment resisting reinforced concrete frame building the chain of the main structural components through which transfer the lateral and vertical loads takes place during earthquakes is from the floor to beams, beams to columns through beam-columns joints, column to foundation and finally foundation to soil underneath the building. These load resisting elements must be strong and capable to deform for transmitting the load from one component to another component. The evaluation of strength and deformation capacity or ductility of an element(s) is the basic attribute on which the performance of the structure depends. In the present study, the seismic capacity of basic elements of a moment resisting reinforced concrete building has been evaluated under cyclic testing in Quasi-static Test facility at the Department of Earthquake Engineering, IIT Roorkee. The elements under cyclic evaluation are beams, columns, external beam-column joints with and without infill and internal beam-column joints. The number of parametric variation in the construction parameters such as types of reinforcement, effect of confinements, aspect ratio, % of reinforcement in the test program of the specimens have also been considered. Moreover, the uni-axial and cyclic performance of various types of reinforcement such as Thermo Mechanically Treated (TMT) reinforcement and High Yield Strength Deformed Bars (HYSD) popularly known as TOR reinforcement have been evaluated separately to characterize the linear and non-linear properties of reinforcements. The present test program includes the cyclic testing of thirty five beam specimens in two aspects ratio (span/depth) of 6.5 and 10 known as Short Beam Specimens (SBS) and Long Beam Specimens (LBS) under the simply supported condition. Pushover testing of some of the short and long beam specimens has also been made to compare the strength and ductility obtained 111 from cyclic testing. Four specimens of columns with size 275mm x 275mm constructed in TMT type of reinforcement under two grades have been evaluated under un-confined and confined conditions. Cyclic testing of external beam-column joints has also been carried out to study the effect of number of constructional parameters such as type of reinforcement, effect of confinement etc. In total, cyclic performance of 31 specimens of external beam-column joints have been evaluated since the performance of the joints is the most critical region of the buildings. The effect of the infill on the cyclic performance of beam-columns joints have also been studied separately. Three specimens of internal beam-column joints constructed on the philosophy of strong column-weak beam concept have also been tested. The cyclic test results of the different specimens of various components of moment resisting reinforcement concrete frame building have been used to describe the non-linear modeling parameters in the form of force-rotation relationship as per ASCE 41-06. The force-rotation relationships of each test components have been evaluated on the basis of ASCE 41-06 to characterize the plastic hinge properties of each element. These relationships of each element have been updated by a number of parameters as defined earlier. Cyclic testing of Vi scale (G+2) soft storey RC frame building model of two prototype G+2 soft storey RC frame buildings have been constructed and tested in quasi-static test facility. The first soft storey RCframe building (Ml) is designed and detailed only for gravity loading as per IS 456: 2000 entitled "Plain and Reinforced Concrete - Code of Practice". The second soft storey RC frame building (M2) is designed for both gravity and earthquake forces as per IS: 1893 (Part 1): 2002 entitled "Criteria for Earthquake Resistant Design of Structures - Part 1: General Provisions and Buildings (fifth edition)" and detailed as per IS: 13920: 1993 entitled "Ductile Detailing of Reinforced Concrete Structures subjected to Seismic Forces". The complete hysteresis behavior in the form of load - deformation curves of both the cyclic tested models has been presented and compared. The envelopes of hysteresis curves of both the IV models along with the bi-linear idealization are presented. Cumulative energy dissipation, equivalent viscous damping ratio, strength & stiffness degradation and storey profile have also been plotted against the roof drift ratio (%) for comparison. Free vibration testing of both building models has also been carried out before the cyclic testing as well as at various intermittent stages of damage in models during cyclic testing. The non-linear analytical modeling of the tested V* scale of (G+2) soft storey RC frame building models have been carried out in SAP 2000. The present study is focused to update the non-linear analytical model developed on the basis of ASCE 41-06 so that the nonlinear capacity of the structure during earthquake could be predicted with sufficient accuracy. This nonlinear analytical models of have been updated at three stages i.e. linear range, nonlinear range and finally at failure stage. Nonlinear capacities of similar but of full scale soft storey RC frame buildings through analytical non-linear models of prototype soft storey building frame, under the different controlling actions/ mode of failures of beam and column, as mentioned in ASCE 41-06 along with updated properties from component tests based on type of reinforcement, have been used to evaluate the performance. The effects of ductile types of reinforcement on the performance evaluation of frame building under flexure mode of failure have also been emphasized. The purpose of this study is to create a source of resource for the updating of non-linear modeling of soft storey RC frame building for the performance based design. The qualitative and quantitative assessments of different strength and ductility parameters of tested building components including the different types of reinforcing steel are presented. The cyclic performance of tested G+2 soft storey RC frame building of V* scale has been evaluated and the component test results have been applied successfully for performance evaluation of prototype soft storey RCframe buildings under different modes of failure.