Research On Torsional Properties Of Concrete Beam Reinforced With Rectangular Spiral Stirrup

In order to study the mechanical behavior of rectangular spiral stirrup concrete beam in pure torsion, this experiment used stirrup spacing, stirrup winding form and strength grades of concrete as main parameters, determined the number of specimens according to the L9(34)orthogonal table, designed and made 9 rectangular spiral stirrup beams and 1 ordinary stirrup concrete reference beam. The experiment designed a device which was suitable for the experiment’s loading mode, a jack which was used to apply concentrated force on the steel distributive girder, then the steel distributive girder allocated force to both ends of the specimen, so that the specimen was twisted. The contents of direct measurement contained the strain of concrete a nd steel bar, the width of cracks, the deformation of specimens. The contents of indirect measurement contained the craze torque and the ultimate torque of specimens. The recorded contents contained the experimental phenome na, the distribution and the development of cracks. Through the study o n the experiment, the paper described the failure process and failure model of rectangular spiral stirrup beams under torque, analysed the strain of concrete and reinforcing steel bar, analysed the deformation of specimens, and discussed the effects of three parameters on the experimental results according to the analysis of orthogonal test.The experimental results were as follows: The benefition of the rectangular spiral stirrup to resist crack was limited, it was feasible to calculate the craze torque moment of rectangular spiral stirrup concrete beam according to the ordinary stirrups concrete member. The rectangular spiral stirrup remarkably increased the torsional bearing capacity of the beam and improved the torsional stiffness after cracking, and remarkably improved the beam’s ductility performance. The stirrup spacing, stirrup winding form and strength grades of concrete all had significant effects on the experimental results, the stirrup winding form produced the greatest influence, the influence of stirrup spacing was the second and the influence of concrete strength grades was the minimal. Decreasing the stirrup spacing, winding the stirrup multilaterally and increasing the strength grades of concrete could significantly improve the torsional bearing capacity of rectangular spiral stirrup concrete beam.This paper also introduced the calculation formula of the China code, the United States code, the Europe code on the craze torque and ultimate torque of reinforced concrete member in pure torsion. The paper studied and discussed the calculation formula of ultimate torque of each code, and the physical meaning of relevant para-meters.At last, based on the theory of variable angle space truss model, this paper derived the calculation formula of bearing capacity of the rectangular spiral stirrup concrete beam in torsion. The calculation formula contained the bearing capacity of concrete and the bearing capacity of steel bar. The calculation formula considered the angle of the rectangular spiral stirrup α, and put forward the increase coefficient of β to consider the rectangular spiral stirrups’ contribution to the increase of the bearing capacity of concrete section. The formula for the calculation results were close to the experimental results. It can better reflect the bearing capacity of the rectangular spiral stirrup concrete beam bacically. It’s physical significance was clear, and it’s application was convenient. It can be used as a reference of related code, and be used in actual engineering. Moreover, it is also be the basis of in-depth study.