Mechanical Properties And Design Methods Of Steel Concrete Columns Under Combined Torsion

With the increasing of high-rise,large span and heavy load structure,the application of steel concrete structure is becoming more and more extensive.Engineering applications,the steel reinforced concrete column under the effect of compound torque inevitable.At present our country combination structure design codes in the lack of the bearing capacity of composite steel reinforced concrete columns under the action of torque calculation method,theoretical research is relatively lagging behind the engineering application.Therefore,it is urgent to carry out in-depth and systematic research on the complex torsion problem.Based on bending shear composite twisted steel reinforced concrete columns as the research object,through 40 steel reinforced concrete column subjected to low-cyclic loading test,combined with the research methods such as numerical simulation and theoretical analysis,reveal the compound torsion failure mechanism of steel reinforced concrete column,analysis the influence law of parameter change on the seismic performance,put forward under the complex stress state effectively improve torsion properties and the seismic performance of structural measures,and establish a theoretical analysis model and the restoring force model,its bearing capacity calculation formula is put forward.The main research results are as follows:(1)Through a self-developed loading setups,quasistatic cyclic pattern loading tests were performed on 20 SRC specimens with different steel form subjected to compression,bending,shearing and torsion.The failure process and patterns of the SRC column subjected to compression-bending-shear reciprocating torsion were observed and the hysteretic loops of torsion-twist angle and load-displacement were obtained.The state of strain and corresponding variability in steel and reinforcing bar were acquired during the test.Respectively,displacement ductility,story drift,energy dissipation,strength and stiffness degradation of specimens as the seismic performance value were analyzed.The hysteresis characteristics and torsion resistance mechanism of SRC column under combined torsion were revealed initially.The experimental results show that the load-displacement hysteresis curve is full and the torquetorsion Angle hysteresis curve is obvious.With the increase of the torsion ratio,the flexural capacity is reduced and the displacement ductility becomes worse,which indicates that the existence of section torques has an adverse effect on the seismic performance of the specimens.(2)Contrast analysis of the steel reinforced concrete with different steel form in a composite torque under the action of seismic performance,the analysis results show that the bending under torsional shear compound,solid web steel reinforced concrete column torsion bearing capacity of a solid web steel reinforced concrete is poor,but the shear bearing capacity of the hollow steel reinforced concrete high,deformation and ductility performance better.The seismic performance of composite reinforced concrete column is superior to that of empty stomach.(3)Quasistatic cyclic pattern loading tests were performed on 20 SRC specimens with different enhancement torsion-resistant constructional measure under compress-flexure-shear-torsion combined cyclic action.The enhancement torsion-resistant constructional measure such as cross-section,steel ratio,longitudinal reinforcement ratio,stirrup reinforcement ratio(web member),thickness of concrete cover,and welding torsion(shear)bolts were investigated for the effect of failure mode and hysteretic behavior on SRC Columns under combined compression-bending-shear-torsion.Respectively from the bearing capacity,stiffness,ductility,energy dissipation capacity performance and interlayer displacement Angle and so on,which can effectively improve the steel reinforced concrete column are analyzed the influence factors of torsion performance,the results show that increasing the cross section size,increase steel steel content,increase the volume,stirrup ratio and welding stud can effectively improve composite by twisting the seismic performance of steel reinforced concrete column.(4)Based on the torsional effect and the influence of bond slip,a numerical model for compress-bending-shear-torsion combined action was established,which were verified to be feasible.Through the model,the important parameters of torsion-bending ratio and axial compression ratio were extended to in established the database of the performance indicators under composite torsion.The calculation results show that the composite under the action of torque,twisted than less than 0.5,the impact is not big,the shearing torque against when twisted is greater than 0.5,has obvious effect,the shearing torque confrontation and the greater the torque,the lower bearing capacity;When the axial compression ratio is less than 0.6,the bearing capacity increases with the increase of axial compression ratio.When the axial compression ratio is greater than 0.6,the bearing capacity decreases with the increase of axial compression ratio.According to the results of numerical calculation,the torsion and shear calculation methods of the concrete columns are presented.(5)The influence of the important parameters of the steel in SRC column such as torsion-bending ratio,axial compression ratio,shear-span ratio,section steel ratio and section size were studied and analysis on the bearing capacity of SRC columns.The influence law of the horizontal bearing capacity were revealed.Considering the torsion effect is proposed through theoretical derivation formula of shear bearing capacity of steel reinforced concrete column,and puts forward the practical calculation method is helpful for engineering design applications.The results show that the practical calculation method and the average error of the experimental results are less than 2%,which has high accuracy.Research analyses the force under the action of bending shear and composite twisted ratio,axial compression ratio,shear span ratio,section steel,section size and other important parameters to affect the shear strength of steel reinforced concrete column,reveals the shear mechanism of the torque for different failure pattern,and considering the torsion effect is proposed through theoretical derivation formula of shear bearing capacity of steel reinforced concrete column,and puts forward the practical calculation method is helpful for engineering design applications.(6)By revealing the bending shear composite by twisting the twisting mechanism of steel reinforced concrete column,based on the variable Angle space truss theory model,using superposition theory,unified computation theory,experience and theory model,and fitting of the domestic and foreign representative compound torsion test data,get the composite stress under the action of shear force against a weakening the influence coefficient of the bearing capacity of torsion is put forward of steel reinforced concrete columns under the action of bending shear and torsion bearing capacity calculation,and then according to the test results,considering the interaction of steel and concrete and the influence of the stud,practical torsion bearing capacity calculation formula are put forward.The results show that the error of the practical calculation formula and the test result is within 5%,the anastomosing degree is good,and has certain safety reserve.(7)From the test results of 40 steel reinforced concrete columns under compress-bending-shear-torsion,the P-Δ hysteresis and T-θ hysteresis were extracted.According to the result,the trilinear skeleton curve model of the steel reinforced concrete columns was presented,characterized by the yield point,the peak point and failure point.After investigating the degradation law of the maximum,the unloading stiffness and the reloading stiffness,the P-Δ restoring force model and T-θ restoring force model of steel reinforced concrete columns under compress-bending-shear-torsion were established.The validity of the proposed restoring force model was verified the validity compared to the test results.The results show that the reconstructed model is in good agreement with the measured results and has high precision.