Test analysis on prestressed concrete composite beams with steel boxes subjected to torsion and combined flexure and torsion

While modern prestressed techniques have improved the torsion properties of high-strength concrete (HSC) composite beams with prestressed steel (PS) boxes, no research has been reported in either the national or international literature on the anti-torque and composite torque properties of this type of beam. With the aim of understanding the torque properties of these beams, this paper presents results of ten comprehensive tests; three of these were based on stirrup spacings and prestressing levels as the main parameters, while the other seven were based on torsional rates. The torsion tests were conducted on the results which established several key parameters, including curves of constant torsion, strain curves of steel torsion, strain distribution of steel beams and concrete, curves of bending-moment and mid-span deflection, as well as cross strain distribution. The prestressing impact-factor method was adopted to deduce semiempirical equations for cracking torque in such composite beams. Furthermore, this involves the use of the equation of ultimate torque based on truss-model-theory of the distortion angle, the calculated results show good agreement with the measured values. In summary, this paper offers theoretical analysis for future applications of HSC composite beams with PS boxes, and provides both validation of the methods employed and a reference point for on-going research on composite beams and related anti-torque studies.