ACI 445.1R-12 - Report on Torsion in Structural Concrete by Joint ACI-ASCE Committee 445

By Joint ACI-ASCE Committee 445

Transparent figuring out of the consequences of torsion on concrete individuals is vital to the secure, within your budget layout of bolstered and prestressed concrete participants. This file starts with a quick and systematic precis of the 180-year background of torsion of structural concrete individuals, new and up to date theories and their purposes, and a historic evaluation outlining the advance of study on torsion of structural concrete individuals. old theories and truss types comprise classical theories of Navier, Saint-Venant, and Bredt; the 3-dimensional (3-D) area truss of Rausch; the equilibrium (plasticity) truss version of Nielson in addition to Lampert and Thürlimann; the compression box concept (CFT) through Collins and Mitchell; and the softened truss version (STM) through Hsu and Mo.

This document emphasizes that it really is necessary to the research of torsion in bolstered concrete that contributors should still: 1) fulfill the equilibrium situation (Mohr’s pressure circle); 2) obey the compatibility situation (Mohr’s pressure circle); and three) determine the constitutive relationships of fabrics reminiscent of the “softened” stress-strain courting of concrete and “smeared” stress-strain courting of metal bars. The habit of participants subjected to torsion mixed with bending second, axial load, and shear is mentioned. This document offers with layout concerns, together with compatibility torsion, spandrel beams, torsional restrict layout, open sections, and measurement results.

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The square root factor in Eq. 4a) was labeled the prestressed factor by Hsu (1968b). He showed that this prestressed factor can be derived theoretically from an element subjected to shear and compression, assuming the principal tensile stress reached the tensile strength of concrete. The prestressed factor can also be derived from the skew-bending theory of a beam in pure torsion. To ensure best fit with the test results, the constant 12 in the prestressed factor was reduced to 10, resulting in Eq.

3b. 3a shows that the presence of torsional moment reduces shear strength, especially if the torque is more than 25 percent of pure torsional strength. The amount of transverse reinforcement is considered the main factor affecting the shape of the curve. Based on an experimental testing program, Klus (1968) suggested a bilinear interaction curve as shown in Fig. 3b. The theoretical model and the experimental results of Ewida and McMullen (1981) showed the amount of reinforcement has a considerable effect on the interaction curve.

Rahal and Collins (1995a) confirmed the significant effect the amount of reinforcement has on the interaction curve. They also showed that in completely over-reinforced sections, the addition of shear causes redistribution in the shear stresses and a subsequent slight increase in the torsional strength. ACI 318 adopts a superposition approach in which the reinforcement required to resist T is added to that required to resist V. To control the diagonal cracks and ensure that the stirrups yield before crushing occurs in the concrete, ACI 318 sets an upper limit on the shear stresses due to torsion and shear.

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