Experimental Study On Prestressed Steel-HSC Composite Box Beams Under Pure Torsion & Combined Bending And Torsion

In order to grasp the behavior of prestressed Steel—HSC(high strength concrete) composite box beams under pure torsion & combined bending and torsion, nine full-scale specimens are first performed, including three specimens under pure torsion, five specimens under combined bending and torsion and one specimen under pure bending.The experimental results of prestressed composite box beams, including deformation, cracking distribution, section strain, failure mode and the mechanism under pure torsion are analyzed in detail. The cracking figures of each specimen are given also. The influence of prestress degree and stirrup spacing on cracking torque, ultimate torsional strength and structure durability of prestressed composite box beams are discussed. The formula about cracking torque and ultimate torsional strength are proposed and show that the predicted results are in good agreement with the test. Based on reasonable assumption and consideration of constitutive relation of concrete, steel beam and bar, series of equations for the ultimate torsional strength and full-course analysis on torsional performance of prestressed composite box beams are derived in the paper by using the equilibrium and deformation compatibility condition. A simplified method of analysis on prestressed composite box beams subjected to torsion is given. And the corresponding program is developed with VB, which provides visual interface for input and output. Comparison between test and predicted results shows that the method proposed in this paper is rational.With different torsion-bending ratio, the experimental results of prestressed composite box beams, including mechanical behavior, section strain, cracking distribution and failure mode under pure torsion are analyzed in detail. The cracking figures of each specimen are given also. The failure mode of prestreesed composite box beams under combined bending and torsion are divided: failure with torsional feature for torsion-predominate and failure with flexural feature for bending-predominate. The reason why its ultimate torsional strength increases when prestressed composite box beams are subjected to torsion-predominate complex loading, are found out. The optimum torsion-bending ratio for promoting the ultimate torsional strength of prestressed composite box beams is between 3 and 4.8. The load capacity improvement can range from 26% to 28%. A formula of calculating the ultimate bending capacity of prestressed composite box beams is derived with account of the stress increase of steel tendons. Finally, the interaction equation of prestressed composite box beams subjected to bending-torsion is put forward.Based on the experimental and theoretical study, many valuable conclusions of prestressed composite beams under pure torsion & combined bending and torsion can be drawn, which can provide scientific bases and reference for engineering design and establishing the standard about torsional design provision in the future.