In order to study torsion behavior of steelencased concrete composite beams

experiments were carried out with eight specimens. The destruction shape

working mechanism and the crack development and distribution were analyzed under pure torsion and combine torsion conditions. And also the relationships were investigated between torque and torsion ratio

load and strain

bending moment and deflection and loadcrack. On the basis of elasticity plastic theory

the formulas of cracking torsion were presented for pure torsion and combined torsion of combined beam. And with spatial truss model of variable angle

formulas for ultimate torsion strength of pure torsion and combined torsion were put forward. The predicted results were in good agreement with measured ones. The proposed formulas provided basis for evaluating safety and stability of the structural.