Papers by Mohammed G A M A L Gouda
Current FRP guidelines do not have enough evidence on the torsional performance of beams reinforc... more Current FRP guidelines do not have enough evidence on the torsional performance of beams reinforced with glass fiber-reinforced polymer (GFRP) reinforcement due to the lack of research and complexity of the problem. A review of the past work was presented in the state-of-the-art section to stand on milestone prospective considering the variety and development of GFRP manufacturing. This study examined the rectangular spirals and rectilinear stirrups to reinforce concrete beams in the transverse direction under pure torsion loading. The test parameters included four levels of transverse reinforcement ratio and the type of transverse reinforcement in terms of rectilinear stirrups vs. spirals. The test results demonstrated that rectangular GFRP spirals provided superior tensile resistance required to develop high ultimate torsional moments after cracking and hence can be effectively used. The failure of the tested beams was attributed to the rupture of GFRP rectangular spirals at bent portions. The test results of the spiraled specimens were discussed and compared with predictions from a developed analytical model and based on CSA equations. Two values of failure plane angle and stress levels were considered. The 45-degree inclination angle provided safe predictions with an average experimental-to-practiced result of 1.16 compared to 0.99 using the 37.5-degree. Design equations were proposed and validated for the ACI code for a probable future incorporation. 1. Background Reinforced Concrete (RC) beams in buildings and bridges can be subjected to different levels of torsion, and they should, therefore, have adequate resistance to torsion. Common examples are the act of eccentric loading on the connected cantilever slabs and the continuity of beams on rigid floors. Beams subjected to significant torsion must include enough transverse reinforcement in terms of closed stirrups or continues spiral and longitudinal reinforcement. The principles of equilibrium, compatibility conditions, and materials stress-strain relationships formulated the primary foundation to develop the space truss model and skew-bending theory for torsion problems during the 1990s [1-5]. The design of RC beams reinforced with steel (steel-RC) pertains to the crushing of concrete struts or the yielding of steel reinforcement. Torsion transfers by shear stress on a plane perpendicular to the longitudinal axis of beams. These stresses cause inclined cracks that spiral around the beam at which the torsion reinforcement can provide tensile resisting forces. Design provisions have been well established for tor-sion problems in building codes [6-8] based on the thin-tube space truss model. Early studies showed that steel-RC beams could develop higher levels of torque, after cracking, based on the amount and strength of their tensile longitudinal and transverse reinforcement as well as their compressed concrete struts between inclined cracks [9-12]. The failure mechanism, post-cracking stiffness, and failure plane angle are substantially affected by the longitudinal ρ l and transverse ρ T reinforcement ratios. Beams with high steel reinforcement ratios are called "over-re-inforced" and fail due to the crushing of concrete before the yielding of steel in either direction occurs [13]. Others with low steel reinforcement are called "under-reinforced" and fail in a ductile manner due to the yielding of steel in both the longitudinal and transverse directions. Procedures for constructing the failure boundaries can be approached elsewhere [13]. The relation between the failure plane angle θ, ρ l , and ρ T can be established based on the thin-tube and space truss model, which will be explained later in this paper.
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Engineering Structures, Jan 1, 2011
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Papers by Mohammed G A M A L Gouda