BEHAVIOUR OF COMPOSITE SLABS WITH LOST FORMWORK

Abstract

In a composite slab there are two materials structurally integrated with the help of some shear transferring devices and the lower material serves both as a formwork during the construction stage and reinforcement for the concrete placed Over them during the service stage. It is widely used in buildings where the main framing is either steel or composite construction. In the present study the behaviour of eight composite slabs has been investigated,four of the concrete composite slabs had C.G.I sheets as lost formwork and the other four of corrugated ferrocement sheet. Out of the four in each type two specimens had a span of 3.0 metre and the other two 1.5 metre. For shear transfer in the former type, 6 mm 0 mild steel bars have been welded to the C.G.I. sheet at a spacing of 30 cm. The ferrocement sheet were made to have the same profile as that of the C.G.I. sheet and it was having two layers of 20 gauge mesh with 6 mm 0 mild steel bars as skeletal reinforcement. The rough surface of the ferrocement in one side adjacent to the form was purposefully utilised for the required bond between the concrete and the ferrocement. After giving the required shrinkage and temperature reinforcement in the direction transverse to the corrugations, concrete was cast upto the required thickness of the slab. All the eight specimens were tested by applying two symmetrically placed line loads and the failure mode investigated. In the former type of slab, shear bond failure is the mode of failure and in the latter flexural failure is the failure mode. From a comparison of the behaviour of the two types of slabs, it has been found that the concrete ferrocement composite slabswere having more number of cracks of smaller crack width and it ;thsnrhed more energy so it performed better than the concrete C.G.I. composite slabs