Study On The Torsional Performances Of Reinforced Concrete Specially Shaped Column Under Combined Forces

When the structure with specially shaped columns is under horizontal load,the specially shaped columns in the structure will actually in the state ofcombined axial force, bending moment, shear force and torque due to theeffect of asymmetry, accidental eccentric load, etc. Research about thetorsional performances of specially shaped columns under combined axialforce, bending moment, shear force and torque has not been reported inliterature at present. The torsional design methods for the specially shapedcolumns were not given in the national standard “Code for Design of ConcreteStructures (GB50010-2010)” and the industry standard “TechnicalSpecification for Concrete Structures with Specially Shaped Columns(JGJ149-2006)”. With the popularization and application of the structure withspecially shaped columns, research about the torsional performances ofspecially shaped columns under combined condition is necessary.The experimental study of the torsional performances for specially shapedRC columns has been conducted in this paper with six specially shaped RCcolumns, including one L-shaped RC column, four T-shaped RC columns, andone cross-shaped RC column. The influence of axial load ratio, torsion-shearratio and cross sectional shape on the torsional performances of speciallyshaped columns was analyzed. Torsion-shear ratio is the ratio of the torqueand the product of shear force and thickness of column leg. The test resultsshow that:(1) the torsional performances of T-shaped RC columns undercombined axial force, bending moment, shear force and torque have beenimproved with the increasing of axial load ratio. Comparing with T-shapedcolumn with an axial load ratio of0.114, the ultimate torque and the ultimatetorsion angle of the one with an axial load ratio of0.314is increased by203.8%and41.7%.(2) the torsional performances of T-shaped RC columnshave been improved with the increasing of torsion-shear ratio under equal axial load ratio. Comparing with T-shaped column with a torsion-shear ratioof1.71, the cracking torque, the ultimate torque and the ultimate torsion angleof the one with a torsion-shear ratio of4.02is increased by85.7%,62.9%and112.5%.(3) the effect of cross sectional shape on the cracking torque and theultimate torque of specially shaped RC columns is complicated. The crackingtorque decreased in the following order: cross-shaped column>L-shapedcolumn>T-shaped column, the ultimate torque decreased in the followingorder: cross-shaped column>T-shaped column> L-shaped column.Numerical models for the torsional behavior of reinforced concrete columnswith special-shaped cross sections under the actions of axial force and torqueand the actions of axial force, bending moment, shear force and torque isestablished by finite element software ANSYS. Some key finite elementmodel parameters for the torsional behavior analysis of specially shapedcolumns under the actions of axial force and torque and the actions of axialforce, bending moment, shear force and torque were suggested by comparingwith the experimental results and through repeated trial numerical analysis.The results of numerical simulation show that the cracking torque, theultimate torque and the torque-torsion angle ascent curves of specially shapedcolumns under the actions of axial force and torque the actions of axial force,bending moment, shear force and torque is well predicted by using the finiteelement models proposed in this paper, however the predicting for the fullprocess curves of torque-torsion angle (especially the descent curves) is stillneeded to be further improved.The influence of axial load ratio, reinforcement ratio, sectional dimensionand stirrup spacing on the torsional behavior of specially shaped columnsunder combined axial force and torque was systematically analyzed based onthe numerical simulation results. The simplified calculation methods for thesection modulus of torsion and the equivalent polar moment of speciallyshaped columns were established.360conditions, including8kinds ofsectional dimension,5kinds of axial load ratio,3kinds of reinforcement ratioand3kinds of stirrup spacing, were calculated by using the finite element numerical model. The regression of the results of360conditions wasconducted by using the statistical analyze software SPSS. A practicalcalculation formula of the ultimate torque of L-shaped columns undercombined axial force and torque was given.