Mixed Torsion Analysis of Reinforced Concrete Channel Beams - A Fourier Series Approach

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Title: Mixed Torsion Analysis of Reinforced Concrete Channel Beams - A Fourier Series Approach

Author(s): Ching- Sheng Hwang and Thomas T.C. Hsu

Publication: Journal Proceedings

Volume: 80

Issue: 5

Appears on pages(s): 377-386

Keywords: angle of twist; beams (supports); channel beams; cracking (fracturing);girders; guideways; prestressed concrete;rapid transit railways; reinforced concrete; ridgity; structural analysis;torsion; torsion tests; warpage.

Date: 9/1/1983

Abstract:
Prestressed concrete double-T-girders, 80 ft (24.4 m) long, 12 ft (3.66 m) wide, 5 ft (1.52 m) deep, and 93 tons (85.3 metric tons), were adapted for the 21 mile (33.8 km) aerial guideway of the Dade County Rapid Transit System. These girders are subjected to large torsional moments caused by wind loads and the nosing/lurching action of vehicles. For the torsional design of these girders, a general method of mixed torsional analysis of channel-type, thin-wall open reinforced concrete sections was developed. This method was based on a mathematical approach using a Fourier Series. In a thin-wail open section subjected to torsion, warping torsional resistance must be considered in addition to the well-known St. Venant torsional resistance. The elastic mixed torsional analysis developed by V. Z. Vlasov is applicable only to reinforced concrete thin-walled sections before cracking. The Fourier Series method proposed is applicable to both the pre-cracking and the post-cracking analysis of such beams. o understand post-cracking mixed torsional behavior, both the post-cracking St. Venant torsional rigidity and the post-cracking warping torsional rigidity must be evaluated. Methods to evaluate post-cracking St. Venant torsional rigidity have been developed in recent years; however, methods to evaluate post-cracking warping torsional rigidity are still unavailable. A bi-material model to determine the post-cracking warping torsional rigidity is proposed.