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The contents of this book have been chosen with the following main aims: to review the present coverage of the major design codes and the CIRIA guide, and to explain the fundamental behaviour of deep beams; to provide information on design topics which are inadequately covered by the current codes and design manuals; and to give authoritative revie
Extensive research has been conducted on strengthening of shear-critical reinforced concrete (RC) beams, particularly using fiber reinforced polymer (FRP) strengthening systems. This previous research has helped to better understand the behaviour of shear strengthening systems and has improved the performance of existing shear strengthening systems. However, there is still a potential to further improve upon the performance of existing shear strengthening systems. A cement-based composite system is an innovative strengthening system that has similar benefits (such as light weight, ease of installation and non-corroding) to FRP systems, but overcomes some of the draw backs (such as poor compatibility with concrete substrate, lack of vapour permeability and fire resistance) of using epoxy as bonding agent in FRP systems. A cement-based composite replaces the epoxy with cementitious mortar and the fiber sheets with fabric or grids. The current study presents the results of an experimental study conducted to investigate the effectiveness of cement-based composite systems in comparison to an existing epoxy-based system (carbon fiber reinforced polymer, CFRP) to strengthen shear-critical RC beams. Two types of cement-based systems were investigated in this study: carbon fiber reinforced polymer (CFRP) grid embedded in mortar (CGM) and carbon fabric reinforced cementitious mortar (CFRCM). The experimental study consisted of two phases. Phase I focused on flexural testing of seven medium-scale shear-critical reinforced concrete (RC) beams. The objective of this phase was to evaluate the potential of FRCM shear strengthening. The test variables included the type of FRCM (carbon FRCM or CFRCM and glass FRCM or GFRCM) and the strengthening scheme (side bonded vs. U-wrapped). Phase II was designed based on results of Phase I study, and it consisted of flexural testing of twenty (20) large-scale shear-critical RC beams strengthened with cement-based systems. The objective of this phase was to evaluate the effectiveness of the two types of cement-based strengthening systems in comparison to the existing epoxy-based FRP system. The test variables included: the shear span to depth ratio (slender and deep beams), amount of internal transverse steel reinforcement and type of strengthening system (CFRCM, CGM and CFRP). The results showed that the cement-based systems (CFRP grid in mortar and CFRCM) performed better compared to the epoxy-based system (CFRP sheet) in terms of the increase in shear capacity relative to the ultimate strength of the strengthening systems. The results also showed that the bond of cement-based system with the concrete substrate was sufficient that u-wrapping may not be required; the studied side-bonded systems did not exhibit signs of premature debonding. This is in contrast to most FRP fabric strengthening systems were u-wrapping is required for adequate bond. In addition, cement-based systems exhibited a better ability to control diagonal (shear) crack widths compared to the epoxy-based system tested, providing a greater reduction in diagonal crack width despite the relative lower ultimate strength and stiffness of the cement-based systems. Shear strengthening resulted in reduced shear strength contribution from stirrups. The strengthened beams with stirrups exhibited steeper shear cracks compared to control unstrengthened beams with stirrups. Similarly, the presence of stirrups reduces the shear strength contribution from strengthening. Again, the addition of stirrups results in steeper shear cracks which intersect fewer fibers tows in the strengthening system which results in a reduced shear strength contribution from strengthening layer. Lastly, the existing models to predict the ultimate load of strengthened shear-critical RC beams were evaluated and modifications to these methods were proposed.
Strengthening Design of Reinforced Concrete with FRP establishes the art and science of strengthening design of reinforced concrete with fiber-reinforced polymer (FRP) beyond the abstract nature of the design guidelines from Canada (ISIS Canada 2001), Europe (FIB Task Group 9.3 2001), and the United States (ACI 440.2R-08). Evolved from thorough cla
Erstmals in einem Band werden Werkstoffe hier (in zwei getrennten Systemen) sowohl nach ihrer technischen Anwendung als auch nach ihren Eigenschaften geordnet. - Benutzer können deshalb zunächst nach der Gruppe von Materialen suchen, die für eine spezielle Anwendung geeignet sind, und anschließend Details über jedes einzelne Material finden - Suchkriterien sind Eigenschaften wie Wärmeleitfähigkeit, optisches Reflexionsvermögen, Elastizität usw. und Anwendungsgebiete wie Bauwesen, Biomedizin, Fahrzeugbau, Luftfahrttechnik, Elektrotechnik usw. - berücksichtigt werden sowohl herkömmliche Werkstoffe (Eisen- und Nichteisenmetalle, Kunststoffe, Klebstoffe) als auch Kompositwerkstoffe und synthetische Materialen wie Laminate, Fasern und Keramiken
TRB's National Cooperative Highway Research Program (NCHRP) Report 678: Design of FRP Systems for Strengthening Concrete Girders in Shear offers suggested design guidelines for concrete girders strengthened in shear using externally bonded Fiber-Reinforced Polymer (FRP) systems. The guidelines address the strengthening schemes and application of the FRP systems and their contribution to shear capacity of reinforced and prestressed concrete girders. The guidelines are supplemented by design examples to illustrate their use for concrete beams strengthened with different FRP systems. Appendix A of NCHRP Report 678, which contains the research agency's final report, provides further elaboration on the work performed in this project. Appendix A: Research Description and Findings, is only available online.
The objective of this research is the evaluation of shear behavior of full-scale reinforced concrete T-beams strengthened with carbon fiber reinforced polymer (CFRP) sheets and CFRP anchors. Although the CRFP material has high tensile strength, premature failure due to debonding CFRP sheets prevents utilizing that strength. The use of CFRP anchors prevents this failure, so the CFRP sheets are able to reach ultimate strain. The current shear design is based on plasticity, which assumes that all steel (ductile material) stirrups, across the critical section yield at ultimate. However the strain in the CFRP (brittle material), is essential to estimate the shear contribution of CFRP. To evaluate the validity of CFRP strengthening for shear, 24 tests were conducted with several parameters including shear-span-to-depth ratio, depth of beams, different transverse reinforcement ratios, and the layout of CFRP strips. In addition, a simple shear behavior model was developed to explain the differences between ductile and brittle material. From test observation, the use of CFRP anchors resulted in U-wrap application to perform like continuous wrapping which implies that a CFRP strip reached rupture strain because the anchors prevented debonding failure. However, all FRP strips did not rupture simultaneously because the strain distribution across a critical crack was not uniform. The average strain across the critical crack was about 0.005. Therefore a conservative value of effective strain (0.004) was selected for design purposes. In addition, when a beam is strengthened with CFRP, interactions between the contributions of the CFRP, steel or concrete must be taken into account. Factors ka, ks, and kf were introduced in the proposed shear design equations. Factor ka reflects the change in the material contributions as the shear span to depth ratio (a/d ratio) changes in deep beams. Factors ks and kf account for the change in steel or CFRP shear contribution due to the change in the critical crack angle as well as the interactions between the steel and FRP transverse reinforcement. As the amount of either steel or FRP material increase, the efficiency of the other material decreases.
Studies have shown that fiber-reinforced polymer (FRP) wraps can improve the capacity of rectangular beam sections. This technology has potential application to highway bridges that may have less shear capacity than flexural capacity or require added load capacity to handle current traffic demands. Compared with steel repair materials FRP offers several benefits, such as corrosion resistance and field-workability. Several studies have investigated the use of externally bonded FRP sheets to improve strength and stiffness of reinforced concrete (R/C) beams, but most have addressed flexural strength, not shear. The objective of the current study was to test the effectiveness of FRP wraps in repairing full-scale prestressed high-strength concrete joists fabricated with insufficient shear reinforcement. Four prestressed high-strength concrete tee-beams (joists) with integral web openings were tested. Two of the joists were repaired or upgraded with FRP wraps to improve shear performance and two were used as control specimens. Performance criteria were specified, and standard structural engineering practice for shear design was employed to determine wrap thickness. The results of the tests indicate that significant increases in the shear strength of R/C beams with insufficient shear capacity can be achieved by proper application of FRP wraps.
Fibre-reinforced polymer (FRP) composites are used to strengthen reinforced concrete (RC) structures. A large amount of research now exists on this. This book brings together all existing research into one volume.