Experimental investigation on strengthening of flat plate slab using steel beam

Abstract

This paper reports experimental investigations carried out for seismic retrofitting of RC flat plate using steel beam with different fastening systems. This retrofitting concept is very useful where it is not possible to retrofit the RC structure by inserting strengthening materials in the slab. In this experiment, seven one-third scale flat plate exterior RCC frames were constructed. Three of them were retrofitted by steel beam of Type-I and another three of them were retrofitted by steel beam of Type-II. In Type- I, steel beams were fastened with RCC columns by steel bracket and angle (bracket and angles were connected to columns and beam with the help of bolts) and in Type- II, steel beams were fastened with RCC column using steel channel, angles and brackets (channels were connected to columns with 8mm bars, angles were connected to columns and beam with welding and brackets were connected to column and beam with bolts). In both the types, bolts were connected to column using epoxy. The rest one was kept as control specimen. Then the frames were tested by controlled cyclic horizontal loading with hydraulic jack with a constant axial load on each column. A vertical uniformly distributed load was also applied on the flat plate. Load-deformation behavior of all specimens were measured by three dial gauges and rotational deflection was measured by a video extensometer. Behavior of the strengthened specimens were compared with that of the control specimen considering appearance of first crack, final crack, maximum load, maximum rotation, failure patterns and stiffness. Maximum load carried by the control specimen was 69 kN. By comparing Type-I and Type-II specimens, it was observed that the Type-I specimens carried a maximum load of 83 kN whereas Type-II specimen carried maximum 69 kN. Type-I specimens carried horizontal load about 18% more than Type-II specimens. Reduction of average vertical displacement was 37% in Type-I and 34% in Type-II for maximum vertically applied load. Lateral displacement of retrofitted flat plates was increased up to 38% than control specimen. Flat plate strengthened by steel beam of Type-I exhibits better punching shear resisting capacity than those of flat plate retrofitted by Type-II. So it may be summarized that flat plate retrofitting by steel beam with different fastening systems is effective to resist punching shear under cyclic loading.