Test And Analysis Of Compatibility Torsion In The Long-span P.C. Secondary Beams Floor System

In a monolithic concrete frame, the spandrel beam is subjected to the compatibilitytorsion arises from the member twisting to maintain compatibility of deformations; thecompatibility torsional moment depends on the ratio of the linear torsional stiffness of thespandrel beam and the linear flexural stiffness of the floor beam, and the anti-torsionaction caused by the rigid-plane effect in the monolithic slab. Because of the nonlinearmaterial character of concrete and the drop in torsional and flexural stiffness aftercracking, it is difficult to calculate accurately the torsional moment in the spandrel beam.Until now, there is no specific provision for compatibility torsion in the ConcreteStructure Design Code of China (GB50010-2002). In the floor system makes up of R.C. spandrel beams and long-span P.C. secondarybeams, different from the conventional floor system, the ratio of the linear torsionalstiffness of the spandrel beam and the linear flexuralstiffness of the floor beam is larger,which makes the compatibility torsional moment in the spandrel beam much larger. As aresult ofthe lack of design method for the compatibilitytorsion,the development and thepopularizationof the Long-span P.C. Secondary Beams Floor Systemwere prevented. In this paper, in order to solve this problem, the tests of compatibilitytorsionin fourfloor system specimens have been done. Each of these specimens is made up of spandrelbeams which are restrained at both ends and long-span P.C. secondary beams between thespandrel beams. The plan size of these specimens is 6 meters multiplied by8 meters, twoof them with monolithic slab and the other two without. With the meticulous designedconstraint condition at the ends of the spandrel beams, the whole course of redistributionof internal forces between the spandrel beams and the P.C. secondary beams is tested, andthe effect of the monolithic slab to the compatibility torsion in the spandrel beams hasbeen identified. With author's space frame FEM nonlinear analysis program, thenonlinear simulationof the compatibilitytorsion in these large-scale specimens has beenfinished, in which the depreciation law of torsional stiffness after cracking has beeninputted to simulate the bending-torsion effect. The simulation accords with theexperiment test result. At the same time, the check computations have been accomplishedwith the solid model in the ANSYS. Based on the tests of these large-scale specimens andthe research results relative to this problem, the design method based on the torsionalstiffness is prompted in this paper, which is different from the zero torsional momentdesign method, the ACI limit design method, or the reduced elastic torsional momentdesign method, and the value of the spandrel beams'torsional stiffness with or withoutthe monolithic slab has been suggested. The productionof this paper can fill up the gapof the national design code. The following conclusions can be drawn from the tests and analysis: 1. In the Long-span P.C. Secondary Beams Floor System, the spandrel beam isalways subjected to torsion-bending-shear; the compatibility torsional moment in thespandrel beam can NOT be neglected. 2. Before cracking, the structure can be analyzed by the elastic method, and thetorsional stiffness of the spandrel beam is 0.64 of the elastic value of the split piecessection, the effective overhanging flange width in torsion can be assumed three times theflange thickness, as the GB50010-2002 Code recommend. 3. The torsion-shearing cooperation should be considered when the cracking checkcomputation is carried out. The formula, T/Tcr0+V/Vcr0=1, can be adopted as thecrackingcriterion of the spandrel beam, where the Tcr0 is the cracking torque under puretorsion, Vcr0 is the cracking shear under bending-shear. 4. The cracking of the spandrel beam will weaken its torsional stiffness, and thecracking of the floor beam will reduce its flexural stiffness. All these cracking at themidspan...