Finite element modelling of reinforced concrete slabs

Abstract

Strengthening of reinforced concrete (RC) structures is frequently required due to inadequate maintenance, excessive loading, change in use or in code of practice and exposure to adverse environmental conditions. Several strengthening techniques have been developed in the past and used with some popularity including steel plate bonding, external pre-stressing, section enlargement whereas now-a-days a new strengthening systems, such as fibre reinforced polymers (FRPs), that have the potential for extending the service lives of RC structures and reducing maintenance costs is used. Structural rehabilitat ion needs, strengthening and retrofitting of concrete structural parts has now-a-days become the major growth research area for the researchers. External wrapping with fiber-reinforced polymer (FRP) is a promising solution for retrofitting due to various advantages such as high strength-weight ratio, corrosion resistance, ease of application, low labour costs, and no significant increase in member size over other strengthening techniques. In particular, the flexural strength of a slab can be significantly increased by application of FRP sheets adhesively bonded to the tension face of the slab. It was difficult to model the complex behaviour of reinforced concrete structures analytically in its non-linear zone. This 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. Nowadays, for structural design and assessment of reinforced concrete members, the nonlinear finite element (FE) analysis has become an important analyt ical tool. But a very limited work is done on the use of FEM to analyze retrofitted RC slabs. The finite element method accounts for non-linear response. The finite element method allows complex analysis of non-linear response of RC structures to be carried out in a simpler way. The finite element method (FEM) also helps in investigating the behaviour of the structure under different loading conditions, the load deflection behaviour of the structure and the cracks pattern. The present study deals with the finite element modelling of control RC slab, retrofitted slab and stressed retrofitted slabs with the help of ATENA. ATENA is software that is based on FE method in which modelling of RC structures is done. In this thesis, a control slab was modelled and the results were analyzed and then retrofitted and stressed retrofitted slabs were modelled and analyzed. The results of the control and retrofitted slabs were compared with the experimental results and the results of the stressed retrofitted slabs were compared with that of IV the control slab. Four simply supported full scale slabs were modelled and area load was applied on the top surface of the slab, surface of the slab, out of which one slab was taken as control slab, one slab as retrofitted slab and rest two slabs were stressed at 75% and 90% and they are then retrofitted by using the GFRP sheet. In the first phase, the control slab was modelled and analyzed. Then the retrofitted slab was modelled and analyzed and then the ultimate load carrying capacity, load-deflection behaviour, crack propagation and crack pattern were noted at different steps. After that the retrofitted slabs were modelled and were stressed to their respective loads, then retrofitted with GFRP layer and results of stressed retrofitted slabs were analyzed and compared with the control slab. In the second phase, the results of all the RC slabs were compared. The results of both control and retrofitted slabs were compared with the experimental results and the results of stressed retrofitted slabs were compared with the results of control slab. From the results it was seen that ultimate load carrying capacity of the stressed retrofitted slabs was higher than the control slab. A close agreement of analytical results was seen with the experimental results.