Damage Detection of Masonry Infilled RC Frame Structure

Abstract

Masonry infills in a building frame are normally considered as architectural elements, and their presence is often ignored by design engineers. Existence of the infill walls basically provides higher stiffness and strength for the frames, but their detrimental effect on the structural performance is ignored due to a lack of adequate information about the frame. It has been observed through studies on 2D brick infilled frames that these non-structural elements had a significant effect on the seismic lateral capacity of the buildings but at the cost of ductility. However, very little work has been reported on 3D brick infilled RC framed structures. Secondly study on 3D frame will gave actual and accurate results of the behaviour of structure. It is therefore, very important to study the performance of brick infilled 3D RC framed structure under lateral load. Most of the structures continually accumulate damage during their service life. The damages observed in buildings and other structure during an earthquake initiates the need of exploring the possible new techniques for retrofitting and strengthening the structures. Generally retrofitting of these types of buildings include addition of new members such as shear wall and bracing or strengthening of existing members by Fibre Reinforced Polymer (FRP) like Glass Fibre Reinforced Polymer (GFRP), Carbon Fibre Reinforced Polymer (CFRP), steel or RC jacketing etc. Strengthening of infill can also be done using Engineered Cementitious Composites (also known as ECC Concrete) has been contributing to safer, more durable, and sustainable concrete infra-structure which is cost-effective. In this research effort the load deflection behavior and the change in dynamic characteristics of brick infilled RC frame with increasing lateral loads is studied. A brick infilled RC frame model (1/3 scaled) has been constructed in the laboratory and subjected to increasing lateral loads. The load deflection behavior has been studied till failure. The damaged frame has been retrofitted by using two prominent techniques –wrapping using GFRP/CFRP laminates at failure locations and by using ECC after replacing the damaged steel in the soft storey. The effects of GFRP/CFRP retrofitting and ECC strengthening have been reported. The change in the dynamic characteristics using impact hammer excitation has been studied for increasing loading and subsequent damage. These include natural frequency, damping coefficient, and FRF magnitude for the three-storey RC frame model. Change in dynamic characteristics has been studied after subjecting control and retrofitted RC infilled frames to different levels of damage. Nonlinear analysis using Finite Elements (FE) has been performed to model the control and FRP retrofitted frames. Results of retrofitted frame show that the use of GFRP/CFRP wrap for retrofitting provided significant lateral load capacity, as compared to the control frame. The ECC strengthened frame shows higher load carrying capacity than the control and FRP retrofitted frame and possess better post yield behaviour. The damage indexes of FRP retrofitted and ECC strengthened frame have been reduced, indicating better performance as compared to the control frame. Damage indices based on deformation and change in stiffness showed a much more acceptable accuracy correlation with dynamic damage indices in general.The ECC strengthened frame showed significant reduction in FRF magnitude with progressive damage. On the other hand, the damping ratio showed a significant increase as compared to the control frame and FRP retrofitted frame.The ultimate loads of the nonlinear FE models showed good agreement with the data obtained from the experimental tests. Crack patterns at the final state in the FE model corresponded quite well with the failure modes of the experimental frames.