Abstract
Twelve mixing steel fibers-reinforced high strength concrete beams were experimentally tested under pure torsion to investigating the concrete member torsional behavior. The first cracking torque, ultimate torsional resistance, crack patterns, effect of steel fiber ratio, effects of shape and size of hollow cross-section, and effect of stirrups reinforcement were discussed. The ratio of mixing steel fiber, different shape and size of hollow cross-section, and ratio of stirrups reinforcement were considers as major parameters. The results are shown that the width of cracks decreases and the cracks number increases with mixing steel fibers ratio increased. The first cracking torque and ultimate torsion load increased with decrease in the hollow cross-section area of high strength concrete members strengthened by steel fibers.
Highlights
Introduction e study of reinforced concrete structural member behavior under pure torsion can be divided into two different parts: (1) before concrete cracking, the concrete behavior is considered as elastic response, which is predicted by the Saint Venant’s torsion theory
(2) After concrete cracking, the material behaves as inelastic, and the theory of elasticity becomes unusable and the interpretation of inelasticity mechanism is required in this part [1]. ere are two very different theories used to design a structural element’s resistance to twisting: the first theory depended on a skew bending theory. e ACI Code [2] was based on this theory in the 1971 through 1989 for the torsion design. is theory assumes in postcracking stage that the concrete contributes in resistance to some of the shear forces and torsion strength and the rest forces resisted by reinforcement of shear and torsion. e failure mode is assumed that the bending skew surface resulting from the torsional spiral cracks consists around three of the member four sides [3]
Research Significance e crack patterns, cracking torsional strength, ultimate torsional strength, cracking, and ultimate twist angle for steel fiber-reinforced high strength concrete beams subjected to pure torsion were studied. e steel fiber ratio and shape and size of hollow cross-section are considered as main parameters. e mixing steel fiber (50% corrugated and 50% end hooked) with approximately same aspect ratio, yield strength, and length was used in this study
Summary
It should be noted that the ancient ACI Codes of practice do not include detailed rules and are specific for design of reinforced concrete beams under torsion [11]. E torsion design methods of solid and hollow sections are based on two theories: thin-walled tube and space truss analogy. E space truss analogy equations of torsional strength relatively to the amount of longitudinal reinforcement are. E basic space truss analogy equation of torsional strength relative to quantity of transverse reinforcement is. E ACI design provisions for torsional concrete cracking strength is specified as follows [6]: . Fc′ ⎛⎝A2cp⎞⎠ Ag for hollow section, 3 Pcp Acp where Tn is the nominal torsional strength under pure torsion, Tcr is the torsional cracking strength under pure torsion, A0 is the gross section area enclosed by perimeter of the wall within the path of shear flow, ACI-Code section 11. Pcp is the outside perimeter of the concrete cross-section and fc′ is the specified compressive strength of concrete
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