By Joint ACI-ASCE Committee 445
Transparent figuring out of the consequences of torsion on concrete individuals is key to the secure, not pricey layout of strengthened and prestressed concrete contributors. This file starts with a quick and systematic precis of the 180-year background of torsion of structural concrete contributors, new and up-to-date theories and their purposes, and a historic evaluate outlining the improvement of analysis on torsion of structural concrete individuals. old theories and truss versions comprise classical theories of Navier, Saint-Venant, and Bredt; the three-d (3-D) house truss of Rausch; the equilibrium (plasticity) truss version of Nielson in addition to Lampert and Thürlimann; the compression box idea (CFT) by way of Collins and Mitchell; and the softened truss version (STM) via Hsu and Mo.
This record emphasizes that it really is necessary to the research of torsion in strengthened concrete that contributors may still: 1) fulfill the equilibrium (Mohr’s pressure circle); 2) obey the compatibility (Mohr’s pressure circle); and three) identify the constitutive relationships of fabrics equivalent to the “softened” stress-strain courting of concrete and “smeared” stress-strain courting of metal bars. The habit of contributors subjected to torsion mixed with bending second, axial load, and shear is mentioned. This document bargains with layout concerns, together with compatibility torsion, spandrel beams, torsional restrict layout, open sections, and measurement results.
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Additional resources for ACI 445.1R-12 - Report on Torsion in Structural Concrete
The column (location of maximum torsion in the elastic analysis) would reduce the torsion affecting the spandrel beam. 2 Design benefits from torsion redistribution—Plastic hinges and moment redistribution permit full strength use of the strength of the flexural member’s cross section. With torsion, elastic analysis typically results in high torsional moments, which in turn require both stirrups and longitudinal reinforcement beyond minimum requirements. Torsion redistribution can reduce design torsional moments, allowing for more economical designs.
Fig. 2—Normalized T-M interaction curves for members without transverse reinforcement. 2 Members without transverse reinforcement—The T-M interaction in members containing only longitudinal reinforcement has limited practical importance, attracting a significant amount of experimental research, mainly due to its importance in understanding the behavior of members with transverse reinforcement. Behavior and ultimate strength of these members is significantly influenced by the shape of the beam cross section, the amount and distribution of the longitudinal reinforcement, and the T-M ratio (Zia 1970).
Based on the same experimental study (Onsongo 1978), it appears that a small axial compressive force substantially increases post-cracking stiffness of a torsionally cracked member with strength also enhanced. This is because the compressive axial load counteracts the widening of spiral cracks. This point may be particularly relevant in the case of structures under seismically-induced torsion. 31 Fig. 3c—Torque-twist relationships at various T/M ratios for sections with unsymmetrical longitudinal reinforcement (Onsongo 1978).
ACI 445.1R-12 - Report on Torsion in Structural Concrete by Joint ACI-ASCE Committee 445