the same as those of T1 and T2. One 100 t hydraulic jack was added to apply an axial compressive force. Two 10 t hydraulic jacks were used to apply torsion to the beam in the same manner as in the experiments for T1 and T2. First, an axial compressive force of 588 kN was applied. Then, a torsion load was applied and increased.

The first crack of beam NT1 was observed considerably later than those of T1 and T2. After the concrete cracked, the internal stress was transferred to the reinforcement. The torsion-rotation curve illustrates that the rotation of NT1 began increasing rapidly when the torsion reached 26 kN•m, indicating the yielding of the reinforcement. The critical inclined crack of NT1 appeared on the bottom, and the inclinationof RC members changes due to changes in combined loads. The experimental results conform to common sense and can serve as a benchmark for theoretical analysis.

2.  Torsion can reduce the ultimate capacity of beams under combined loading, and the axial compressive force could affect the ultimate strength of beams. An appropriate compressive force can increase the ultimate strength of the beam and the shear strength of the concrete. However, a high compressive axial force may decrease the ultimate strength of the beam.

3.  The crack inclination angles change with changes in combined load. The critical cracks constitute the twist failure surface of the beams, which affects the ultimate strength of the beams. When a compressive axial force is applied, the axial force changes the direction of the