Field testing of RC slabs with openings strengthened with CFRP

Abstract

Introducing openings in existing reinforced concrete (RC) slabs can severely weaken the slabs due to the cut out of both concrete and reinforcing steel. There are several traditional approaches to strengthen RC slabs with openings; however these approaches can be cumbersome, expensive, and may require significant usable floor area. This paper reports field tests on the use of Carbon Fiber Reinforced Polymers (CFRP) strengthening alternatives to restore the flexural capacity of the RC slab after having large openings cut out in the positive moment region. The uniqueness of this study is that the tests were performed on an existing multi-storey RC structure that was scheduled for demolition. Testing a real structure allowed incorporating factors and boundary conditions that typically cannot be simulated in the laboratory. Five tests on five different slabs were conducted to evaluate the ability of the CFRP strengthening alternatives to restore the flexural capacity of the slab after introducing the openings. Three different strengthening techniques were investigated to determine the most effective system for strengthening. The three different strengthening techniques are the use of externally bonded (EB) CFRP laminates, EB CFRP laminates with CFRP anchors, and Near Surface Mounted (NSM) CFRP strips. Test results showed that the three strengthening techniques enhanced the load-carrying capacities of the slabs with openings with the NSM technique more effective than the EB technique. Use of CFRP anchors with EB laminates prevented complete detachment, and hence enabled the slab to restore its full flexural capacity.