Test And Analysis Of Compatibility Torsion In The Floor System With Monolithic Slab

In reinforced concrete floor system of spandrel beams and floor beams, the spandrel beam is subjected to the compatibility torsion arises from the member twisting to maintain compatibility of deformations; the compatibility torsional moment depends on the ratio of the linear torsional stiffness of the spandrel beam and the linear flexural stiffness of the floor beam, and the anti-torsion action caused by the rigid-plane effect in the monolithic slab. Because of the nonlinear material character of concrete and the drop in torsional and flexural stiffness after cracking, the torsional moment in the spandrel beam is difficult to calculate accurately. Until now, there is no specific provision for compatibility torsion in the Concrete Structure Design Code of China (GB50010-2002).In order to solve this problem, further tests of compatibility torsion in one conventional floor system specimens with monolithic slab have been done in this paper, based on four Long-span P.C. Secondary Beams Floor System specimens of associate Professor Huangyin in Chongqing University. The following conclusions about conventional floor system specimens with monolithic slab can be drawn from these tests and analysis:①The inner force redistribution of compatibility torsion between the spandrel beam and the floor beam is a complex process, influenced to different degree by the cracking of the spandrel beam and the floor beam.②In conventional floor system with monolithic slab, the spandrel beam is always subjected to torsion-bending-shear; the compatibility torsional moment in the spandrel beam can NOT be neglected.③Before cracking, spandrel beams'torsional moment analyzed by the elastic method can be accurate, but the elastic torsional moment is higher than the actual after cracking.④After cracking, the compatibility torsional moment keeps increasing with the load. It is obviously different from the basic supposition of the limit design method proposed by the American Concrete Institute (ACI) Code.⑤In the American Building Code Requirements for Structural Concrete (ACI 318-05), the design value of spandrel beams'compatibility torsional moment is on the low side, and the spandrel beam may be unsafe.⑥As the elastic method, the zero torsional moment design method or the ACI limit design method have a bit different from the actual situation, the reduced elastic torsional stiffness design method can be used in the conventional floor system specimens with monolithic slab.⑦Adopted space frame FEM nonlinear analysis program, the nonlinear entire process simulation of the compatibility torsion in the large-scale specimen has been finished. With the comparison of experimental and analysis'spandrel beams'load-twist curves for the specimen, the torsional stiffness of the spandrel beams after cracking in this paper is only 20 percents to 30 percents of the initial value that before cracking.