Torsional experiment and analysis on composite steel-concrete beams

In order to study the torsional behavior of composite steelconcrete beams,experiments were conducted on four specimens with varied stirrup ratios subjected to pure torsion.Then,the torsional deformation and stress distribution of composite beams in elastic range are analyzed using structure analysis software with spatial finite elements of 8 joints.Test and analysis results showed that the torsional carrying capacity of composite steel-concrete beams are undertaken mainly by concrete flange,and the section dimensions of flange are the main effect factors.Moreover,the flange thickness is the most important one.The ultimate torque for composite beams will arrive at maximum under otherwise equal conditions when the stirrup ratio is about 0.54 percent.The formulae about elastic torsion stiffness and cracking torque are presented.Finally,by using spatial truss model with variable angle,a formula for ultimate torsional strength is proposed in which test results are taken into account.The predicted results are in good agreement with the measured ones.