The use of fiber reinforced polymers (FRPs) for the strengthening and repair of existing concrete structures is a field with tremendous potential. The materials are very durable and hence ideally suited for use as external reinforcement. Although extensive work has been carried out investigating the use of FRPs for flexural strengthening (e.g. Meier et al., 1992) a fairly recent development is the use of these materials for the shear strength enhancement of concrete.The current system investigates the use of post-tensioned non-laminated carbon fiber reinforced polymer (CFRP) straps as external shear reinforcement for concrete. Experiments were carried out on an unstrengthened control beam and beams strengthened with external CFRP straps. It was found that the ultimate load capacity of the strengthened beams was significantly higher than that of the control specimen.Existing design codes and analysis methods were found to underestimate the ultimate resistance of the control specimen and the strengthened beams. Nevertheless, the modified compression field theory provided insight into possible failure mechanisms and the influence of the strap prestress level on the structural behaviour.It is concluded that the use of these novel stressed elements could represent a viable and durable means of strengthening existing concrete infrastructure.
Presented is a finite element analysis for carbon fiber reinforced plastic pin-loaded straps of non-laminated form. The MARC K6.2 code was used. The goal was the determination of tensile strength from a knowledge of the peak stresses in the region where a (multi-layer) strap makes contact with the two steel circular pins. The paper illustrates difficulties other researchers and analysts may encounter if they are to analyze similar composite material problems. Numerical problems were found because of computing resource limitations, the highly orthotropic elastic constants, the geometric non-linearity, the geometric and material discontinuities, and the presence of friction and sliding contact. Their influence on stresses is illustrated by way of a simplified model for a single-layer strap. Peak stresses are shown to change significantly on varying a finite element model parameter that is not physical. Acceptable finite element stresses, away from the region with the peak stresses, are found on comparing them with a classical stress solution and experimental measurement.
Advances in material technology allow for the exploration of new structural forms and systems. In recent years, fibre reinforced polymers (FRPs) have emerged as candidate materials for civil engineering applications and the use of FRPs in construction has been an area of growing interest. Unidirectional high strength FRPs are well-suited for use as tensioning elements but anchorage details present a challenge. An alternative is to self-anchor the FRP tensioning element by winding thin layers of material around supports and then laminating all the layers together (a laminated strap) or by securing only the outermost layer to form a closed outer loop while the inner layers remain non-laminated (a non-laminated strap). Non-laminated FRP straps have been found to have higher efficiencies than equivalent laminated straps which is advantageous in high tension applications. The suitability of non-laminated FRP straps for use as unbonded tension elements provides scope for usage in new construction and for the strengthening of existing structures. A review of non-laminated carbon FRP strap system properties and applications in the context of reinforced concrete, timber and masonry structures is presented.
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