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The use of carbon fiber reinforced polymer (CFRP) anchors can improve the performance of reinforced concrete (RC) beams strengthened in flexure with CFRP sheets. This improvement results from delaying or controlling the debonding of FRP sheets at failure. In this research, six full-scale T beams and six full-scale rectangular beams are prepared and tested as two separate series. All the specimens are strengthened identically using three layers of unidirectional CFRP sheets and one layer of bidirectional CFRP sheet. The first strengthened beam in each series is anchored with side GFRP bars inserted longitudinally to both sides of the beam. The second strengthened beam in each series is anchored with GFRP patches applied to both sides of the beam. CFRP spike anchors are utilized for the other beams in the two series. The third beam in each series is secured with CFRP spike anchors of 16 mm diameter at 140 mm spacing along the shear span. The fourth strengthened beam in each series is anchored with CFRP spike anchors of 19 mm diameter at 203 mm spacing along the shear span. Four CFRP anchors are applied to each shear span of the fifth beam in each series with 16 mm- diameter (spaced at 406 mm) to secure the flexural CFRP sheets. An end CFRP anchorage technique is considered for the last beam in each series, which includes installing one CFRP spike anchor placed at 76 mm from the free edge of CFRP sheets. The beams were tested under four-point bending until failure and the results for each series are evaluated. In addition, the outcome is compared with other anchorage techniques that have been examined by some researchers utilizing the same beam geometry and properties. The experimental testing and nonlinear analysis showed improvement in the flexural performance of anchored beams compared with those strengthened beams without anchorage. By attaining debonding or rupture failure modes for the T beams and concrete crushing failure mode for the rectangular specimens, the ultimate sectional force capacity is achieved. Accordingly, the results prove that the anchors offer an effective solution against premature debonding failure.
This research presents an analytical and experimental investigation for the use of flexural CFRP sheets as a strengthening technique to improve the shear capacity of reinforced concrete deep beams. The analytical work presents a new analysis method that is developed to predict the response of reinforced concrete deep beams with and without flexural CFRP strengthening. The method utilizes the truss analogy approach that is extended from the Strut-and-Tie Model (STM) for unstrengthened beams. In contrary to STM, the new method is used to capture the full structural response of unstrengthened beams by modeling a single truss. On the other hand, the new method is used to predict the entire response of strengthened beams by assuming the beam to be composed of two parallel compatible trusses. The first truss has its lower chord member composed of the steel bars while the second truss has its lower chord member composed of the flexural CFPR sheets. By imposing the compatibility condition of a statically indeterminate truss, the contribution of each truss is realized. The experimental work was conducted on three deep beam specimens with identical rectangular cross-sectional area. The first beam was tested as a control beam, and the other two beams were strengthened in flexure with four layers of flexural CFRP sheets anchored by two different flexural anchorage devices. The first strengthened beam was anchored with GFRP patches applied to both sides of the beam. The second strengthened beam was anchored with side GFRP bars inserted longitudinally to both sides of the beam. The comparison between the analytical and experimental results showed reasonable agreement and asserted the validity of the analytical approach and methodology developed in this study.
Structural elements such as beams, slabs and columns may require strengthening during their service life period. The need for strengthening may arise due to one or a combination of several factors including construction or design defects, increased load carrying demands, change in use of structure, seismic upgrade, or meeting new code requirements. Studies have shown that Fiber Reinforced Polymer (FRP) composites, in the form of sheets, have emerged as a viable, cost-effective alternative to steel plates or other techniques in strengthening RC members. The principal advantages of FRP sheets over steel plates include high strength-to-weight ratio, corrosion resistance and flexibility in its use. Another significant advantage of this repair technique is that overall repair cost in terms of labor, material and equipment is low and can offset the high material cost. However, the long-term durability and performance of FRP sheet strengthened RC members is a concern in civil engineering community. This work study involves experimental and theoretical investigations of the behavior of flexural debonding carbon fiber reinforced polymer (CFRP) laminates with steel anchorages.
Many studies conducted on the use of Fibre Reinforced Polymer (FRP) sheets for shear strengthening have been completed on beams that are small in relation to the effective bond length of the FRP. This study focuses on the use of FRP sheets for large-scale concrete members. Two series of large scale concrete beams were strengthened in shear to develop a better understanding of the behaviour of FRP shear strengthening on large specimens and to develop a means of predicting the shear capacity for all sizes of members. The first series of three specimens were obtained from a full sized I-section prestressed concrete bridge girder. One of these specimens was tested as a control, with the remaining two strengthened for shear with different configurations of Carbon Fibre Reinforced Polymer (CFRP) sheets. To develop a better understanding of bond behaviour of large-scale specimens, three reinforced concrete T-section beams were fabricated with a web height that was larger than those found in the literature. One of these beams was strengthened in shear using Glass Fibre Reinforced Polymer (GFRP) sheets and two others were strengthened using CFRP sheets. These beams were tested under static loading conditions. (Abstract shortened by UMI.).