The Study On Torsion Behavior And Strength Calculation Methods Of Steel Reinforced Concrete Beams

In order to study the torsional properties of SRC beams,34 specimens are designed in this paper,among which 8 are inverted L-shaped SRC beams under pure torsional condition,and the other specimens are respectively 14 flexural-torsional composite beams and 12 SRC beams under flexure-shear-torsion.Through the design and loading of the specimen,the main test data were obtained,and then the failure pattern of the specimens was described and the main influencing factors were analyzed.Finally,the strength formulas of the cracking torque and ultimate torque of ASRCB and SSRCB are proposed.The main experimental results of this paper are as follows:For（38）SSRCB specimens,increasing the reinforcement ratio of the specimens significantly improves the torsional strength and torsional stiffness of SRC beams under pure torsion.Increasing the flange reinforcement ratio has a great influence on the elastic-plastic stage and the failure stage of the specimen under the action of pure torsion.For the flexural-torsional specimens,the entire process of load-bearing in all specimens under bending and torsion can be divided into three stages which are elastic,elasto-plastic and failure stages.The smaller torsion-bending ratio are,the earlier the cracks appeared in the solid-web steel reinforced concrete beams.Stirrup ratio has no significant effect on the increase of cracking torque.The failure patterns of angle steel truss reinforced concrete beams have two types: failure with flexural feature and failure with torsional feature.Before cracking,the torsional resistance performance of the specimens under bending and torsion depends not only on the tensile strength of the concrete,but also on the torsional rigidity of the steel.The damage degree of specimens also presents three stage features,and the damage degree of reinforced concrete beams is larger than that of steel reinforced concrete beams.The influence of concrete strength on the later damage of the specimen is very small.With the increase of the Ι-steel model,the constraint on the surrounding concrete become smaller and more unfavorable to torsion.For flexure-shear-torsion specimens,the angle steel truss reinforced concrete beams（ASRCB）crack later than solid-web steel reinforced concrete beams（SSRCB）,cracking torque is greater,and the crack width increase more after cracking.The failure patterns of angle steel truss reinforced concrete beams have two types: failure with torsional feature and failure with shear-torsion feature.The internal steel section has great influence on the improvement of torsional capacity.The angle steel truss reinforced concrete beams have higher torsional capacity under flexure-shear-torsion,and torsion-shear ratio has great influence on torsional properties.The enhancement of concrete strength grade promotes the improvement of torsional properties of specimens in later period.Based on the experiment results,linear regression analysis and strength overlap theory are used,and the strength formulas of torsional capacity of ASRCB and SSRCB are proposed.Calculated results coincide with the test results.These results may provide reference for further research on steel concrete composite structures.