Finite Element Modeling of a Multi-Storeyed Retrofitted Reinforced Concrete Frame

Abstract

In the present study, the non-linear response of RC frame using FE modeling under the incremental loading has been carried out in the first phase of analysis to study the response and load-carrying capacity of a four storeyed RC frame using non-linear finite element analysis. In the second phase of study an analysis model for retrofitted RC frame using finite element method using software ATENA is presented. The results obtained from FE analysis in both cases are compared with the experimental data for four storeyed RC frame tested by BARC at CPRI. The results from finite element analysis were calculated at the same location as used in experimental test. The accuracy of the finite element model is assessed by the comparison with experimental results which are to be in good agreement. The base shear/ displacement curves from finite element analysis agree well with the experimental results in linear range. The maximum difference in base shear is observed to be 7.9%. I. Introduction In order to evaluate the margin of safety of RC structures against failure an accurate estimation of the ultimate load is very important and the project of the load-deformation behavior of the structure throughout the range of elastic and inelastic response is desirable.There are various factors which are accountable for these deteriorations, such as increasing load, corrosion of steel, earthquake, environmental effects and accidental impacts on the structure. The increase in scale of modern structures is closely related to the extent and impact of disaster in terms of human and economical loss in the happening of structural failure (1). As a result, careful and detailed structural safety analysis becomes more and more crucial. The purpose of such an analysis is the investigation of the behavior of the structure under all probable loading conditions, both, monotonic and cyclic The static pushover analysis is becoming a common tool for seismic performance assessment of existing and new structures. The pushover analysis provides adequate information on seismic demands imposed by the design ground motion on the structural system and its components. The purpose of pushover analysis is to evaluate the projected performance of structural systems by estimating performance of a structural system by estimating its strength and deformation demands in design earthquakes by means of static inelastic analysis, and comparing these demands to available capacities at the performance levels of interest. The inelastic static pushover analysis can be viewed as a method for predicting seismic force and deformation demands, which accounts in an approximate manner for the redistribution of internal forces that no longer can be resisted within the elastic range of structural behavior (2). Up-gradation of reinforced concrete structures is required for many different reasons. The concrete may have become structurally inadequate for example, due to deterioration of materials, poor initial design and/or construction, lack of maintenance, upgrading of design loads or accidental events such as earthquakes. That's why repair and rehabilitation has become an increasingly important challenge for the reinforced cement concrete structures in recent years. The major goals of the retrofitting are to strengthening the retrofitted structures for life safety and the protection of the structures. The existing deficient structures are retrofitted to improve their performance in the event of any natural disaster and to avoid large scale damage to life and property. Evaluation of behaviour of structures after retrofitting is more important. 1.1 Importance and Historical Background of Finite Element Modeling The complicated analytical modeling of the complex behaviour of reinforced concrete in its non-linear zone has led engineers in the past to rely heavily on empirical formulas which were derived from numerous experiments for the design of reinforced concrete structures. The finite element method makes it achievable to take into account the non-linear response. Finite element method of analysis has become a powerful computational tool with the introduction of digital computers, which allows complex analyses of the nonlinear response of RC structures to be carried out in a regular mode. Though FEM is useful for obtaining the load