CFRP Composites for Strengthening of Reinforced Concrete Walls with Openings
This paper presents the results of a research work aimed at investigating the potential used of externally bonded Carbon Fiber Reinforced Polymer (CFRP) composite sheets as a strengthening solution for uniaxial rectangular concrete walls with central rectangular in-plane openings. Seventeen of 1/3 scale rectangular concrete walls with and without central rectangular in-plane openings of different sizes (5%, 10%, 20% and 30% of wall areas) are tested. In thickness direction, one central layer of steel fabrics was used to reinforce the concrete walls. The walls were subjected to uniaxial loading aligned with the longest edge of the concrete walls. The loading was applied eccentrically (t/6) with respect to the mid-plane of the walls. Two different patterns were used to fix the CFRP to both surfaces of the walls which are parallel to the midplane of the wall segments. The first pattern consisted of applying four strips of CFRP parallel to the four edges of the opening such that they framed the opening. In the second pattern, CFRP strips were used to reinforce the walls in the vicinity of the opening edges only, i.e. four CFRP strips were applied close to the corners of the openings, in an angle of 45 degrees with both adjacent edges of the opening. From the results of the research work, it was found that CFRP strips applied at an angle of 45 degrees to both adjacent edges of the opening yielded a better compressive strength compared to the CFRP strips that framed the openings. Keywords-Reinforced concrete wall, opening, ultimate load, Carbon Reinforced Polymer, CFRP, stress concentration, strengthening
Experimental results of one-way slabs with openings strengthened with CFRP laminates
2 Disclaimer The contents of this report reflect the views of the author(s), who are responsible for the facts and the accuracy of information presented herein. This document is disseminated under the sponsorship of the Center for Infrastructure Engineering Studies (CIES), University of Missouri-Rolla, in the interest of information exchange. CIES assumes no liability for the contents or use thereof. 3 The mission of CIES is to provide leadership in research and education for solving society's problems affecting the nation's infrastructure systems. CIES is the primary conduit for communication among those on the UMR campus interested in infrastructure studies and provides coordination for collaborative efforts. CIES activities include interdisciplinary research and development with projects tailored to address needs of federal agencies, state agencies, and private industry as well as technology transfer and continuing/distance education to the engineering community and industry. One-way RC slabs are very common as a floor system in US structures. It often happens that structures need to be renovated due to many factors, such as placing new staircases, elevators, additional skylights or (more often) wiring and ducts through the existing floor slabs. In these instances, openings usually need to be created, weakening the existing floor system. Fiber-reinforced polymer (FRP) matrix composites can provide an efficient method for strengthening slabs after installation of cutouts , but it is important to define guidelines for the designer, particularly when the openings are created in the negative moment region. This paper presents the results of an experimental program that investigated the behavior of RC one-way continuous flat slabs with openings in both the positive and negative moment regions, strengthened with externally-bonded CFRP laminates following two different schemes of strengthening. The significance of this work is that instead of testing specimens manufactured in the laboratory, the authors had the possibility of using as a research test bed, an old parking garage scheduled for demolition. Experimental results revealed that externally-bonded CFRP sheets can significantly increase the flexural capacity of the system for those specimens containing an opening in the positive moment region. For specimens with an opening in the negative moment region and strengthened using top-surface CFRP laminates, shear failure occurred at a lower load capacity than the original unstrengthened specimen. This has considerable implications for the design of such negative-moment strengthening schemes, and reasons for this behavior are discussed.
BEHAVIOR OF TWO-WAY RC SLABS EXTERNALLY BONDED WITH STEEL PLATE
Although a great deal of research has been carried out in recent years on the use of plate bonding for strengthening reinforced concrete (RC) structures, so far this work has generally been limited to RC beams and one-way slabs, with little work on two-way slabs. This paper presents the results of a recent study on the behavior and strength of two-way square RC slabs bonded with a steel plate. Experimental load-deflection curves, failure modes, and strengths of plated slabs under a central concentrated load are first reported. These results show that debonding failures are unlikely in these plated slabs, contrary to the case of plated beams, and there are significant strength gains due to the bonded steel plate as a result of a modified yield line pattern. Yield line analyses are then described for these slabs, and the results are found to match experimental results closely. The yield line method is thus suitable for practical use to determine the strength of these plated slabs.