The Mechanical Performance And Numerical Simulation Of SRC Column Under Combined Torsion

Steel-reinforced concrete structure,also known as SRC,is a kind of steel-concrete composite structure.The SRC structure provides higher load and anti-deforming capacity.Compared to common reinforced concrete structure,the SRC component has higher load capacity while maintains the section size at the same level because that section steel exceeds the limitation of reinforcement ratio,which is quite suitable for high-rise buildings.While compared to steel structure,the SRC component is prone to better resistance to fire and corrosion,in addition,larger section size effectively avoids instability which can make the most use of steel material.As the SRC has such advantages,it becomes a hot spot in research across the whole world.Considering that domestic research on SRC initializes later than foreign research,moreover,many foreign experience and standards were referred at the very beginning.Although China has issued relative national standard for SRC structure,it still needs perfection.For instance,method for calculating load capacity under torsion is not listed in current standards.However,in many engineering instances,columns may suffer combined-torsion consisting of serval different types of loads.So,research on this scenario is quite urgent.In order to research how the performance of steel-reinforced concrete column is affected under combined torsion.A research is conducted from 2 aspects,which are mechanical experiment and numerical simulation.Starting from mechanical experiment,15SRC columns with embedded section steel are designed which set axial compression ratio,bending-torsion ratio,stirrup ratio,with or without stud,section steel type and loading method as control variables.Then experiment consisting of axial force,bending moment and torque is conducted.According to the results,increasing axial compression ratio from 0.1 to0.3 has little impact on ultimate torque while weakens ductility by 12.3%～20.2%.Increasing bending-torsion ratio both enhances ultimate torque and ductility by 3.8%～23.2%and12.5%～67.8%respectively.Lowering stirrup spacing from 100 mm to 50 mm significantly increases ultimate torque by 24.6%～28.4%while lowers ductility by 24.1%～40.4%.Enabling stud exerts little influence on ultimate torque but weakens ductility by24.4%～26.4%.Cyclic load both lowers ultimate torque and ductility by 24.3%and 34.1%on average while suffers less impact from different variables.Cross-type section steel slightly increases ultimate torque by 8.2%while significantly increases ductility by 46%.According to the computing mechanism of ABAQUS CDP model and stress atlas during numerical simulation,it is found that there exists a flaw which is the unit stress is relevant to strain,however,the CDP model is unable to simulate the actual process of suppressing crack development.This will cause tensile strength descending rapidly due to rapidly ascending cracking strain.When it comes to the simulation of combined torsion,the flaw will result an error that the shearing-compression superposition zone fails quickly after tensile cracking and impairs the compressive strength,which finally cause the loading capacity extremely lower than that from mechanical experiment.In comparison,the crack development is suppressed after tensile cracking,which means the loading capacity can still ascend.To address this issue,thought that intercepting tensile constitutive curve at proper position to neutralize the fast failure of shearing-compression superposition zone after tensile cracking is proposed.In addition,it is found that intercepting at0.5 f_t makes the results from experiment and simulation matching.To validate the thought above,12 of SRC columns above are picked for numerical simulation.The comparison shows that the torque-torsion-ratio curves from experiment and simulation agree with each other well.The deviation of peak and ultimate torque is limited by 4%for monotonic load specimens and by 7%for cyclic load specimens.Moreover,the hysteretic curve also shrinks to a certain degree.In a word,the modeling method proposed is suitable for simulating SRC columns under combined torsion.