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
The effects of CFRP orientation on the strengthening of reinforced concrete structures
In recent years, the strengthening and retrofitting of structural members using externally bonded carbon fibre reinforced polymer (CFRP) materials has gained a great deal of attention. This has eventuated from the superior properties of composite materials, including high elastic modulus, higher strengths and lighter weights. This paper presents a finite element analysis that has been validated against laboratory tests of two reinforced concrete (RC) beams, two columns, two slabs and six walls. The main focus is on the ultimate failure load of these members as they have different CFRP orientations to the loading direction. The analysis result shows a sound agreement with the experimental data regarding the ultimate failure load of RC samples, except for the RC wall. In fact, the RC wall, while under eccentric axial load, confirmed that the CFRP orientation was parallel to the loading direction, and it proved to be an insignificant contribution in the ultimate failure load of the samples. This finding demonstrates that more experiments should be considered when investigating the influence of CFRP on the ultimate strength of strengthened RC walls. Copyright © 2016 John Wiley & Sons, Ltd.
Design against cracking at openings in reinforced concrete beams strengthened with composite sheets
Web openings in beams and girders occur quite often in practice to provide a convenient passage for utility ducts. Accommodating the environmental services in such a manner eliminates a significant amount of dead space and results in a more compact and, often, more economical design. However, introducing an opening into the web of a reinforced concrete beam causes local cracking around the opening leading to reduction in stiffness and capacity of the beam. In this paper the use of fibre reinforced polymer (FRP) sheets to strengthen the opening region is presented. Several design parameters are varied including opening width and depth, and amount and configuration of the FRP sheets in the vicinity of the opening. The experimental program included testing of 10 reinforced concrete beams, five of which were strengthened with FRP sheets around the opening, four were tested without strengthening, and the remaining beam was solid without opening considered as a control beam. The effect of this strengthening technique on deflection, strain, cracking, and ultimate load is investigated.