Analysis of reinforced concrete beams with ferrocement overlay

Abstract

Serviceability of a concrete structure is determined by its deflection, cracking, extent of corrosion of its embedded reinforcement and surface deterioration. A satisfactory performance of reinforced concrete structures over their design life under a combination of various types of loads requires a crack free structure so as to prevent ingress of moisture by diffusion. This ultimately leads to corrosion of steel, carbonation of concrete and leaching of soluble soft lime products. Thus, the life and strength of the structure is reduced. Serviceability of the structure can be greatly improved providing a low permeable cover such as ferrocement overlay to the reinforced concrete elements. If this cover can be used as formwork for the structural elements it may significantly reduce the cost of timber shuttering and forrriwork for those elements. An attempt has been made in this research to study the behavior of reinforced concrete beams with ferrocement overlay. An analytical model has been developed based on the basic assumptions of reinforced concrete and on the idealized stressstrain diagrams of the constituent materials. A linear elastic finite element study was also carried out to observe the serviceability of such beams. The performance of both the analytical and the layered finite element model for the composite beam is validated by comparing these results with some existing experimental results. The proposed analytical model is found to perform quite well within the serviceability limit and fair enough at the ultimate limit state. The analytical method proposed is used to calculate the load-displacement response for three sets of beams with varying ferrocement properties. The serviceability of the beams is found to be significantly improved by increasing the number of mesh layers for a constant ferrocement thickness. The confinement effect of the ferrocement overlay on the concrete core is also investigated using the finite element model. The . resulting flexural stresses in the concrete core were found to be significantly improved compared to its unconfined state under identical loading condition. Obviously, ferrocement overlay improves the ductility of the RC beams which is very important for the structures in seismic regions. The inherent crack arresting capacity of ferrocement is expected to enhance the life of concrete beams and hence the durability.