Experimental Study On Eccentric Compression Behavior Of High Strength Concrete Short Columns Of Spatial Steel Frame

Spatial steel frame is a kind of spatial light steel structure,which is welded by angle steel(chord)and transverse(oblique)batten(web).It has a certain spatial stiffness and bearing capacity.The confinement effect of spatial steel frame on core concrete can improve the bearing capacity and deformation behavior of columns under axial load.It can be used in practical engineering and has a wide application prospect.In order to explore the confinement mechanism of spatial steel frame on core concrete under unidirectional eccentric load and the eccentric compression behavior of spatial steel frame concrete column,the effects of various parameters,i.e.,eccentricity,angle steel limb length and battens spacing,were considered respectively.The static test of 7 specimens of spatial steel frame concrete column under eccentric load and 1 specimen of spatial steel frame concrete column under axial load were carried out.The failure modes,load and deformation curve and bearing capacity of spatial steel frame concrete eccentric compression column were analyzed.The test results show that the average strain of section is basically in accordance with the plane section assumption,other conditions are the same,the compressive bearing capacity of spatial steel frame concrete column decreases gradually with the increase of eccentricity or battens spacing,and the axial deformation increases at peak load,the compressive bearing capacity of spatial steel frame concrete columns increases with the increase of angular steel limb length,and the axial deformation changes little during peak load.Based on the test,the finite element analysis software ABAQUS is used to simulate the eight specimens in this paper.The simulation results are in good agreement with the experimental values,which verifies the rationality of the finite element modeling.In order to make up for the limitation of the test,based on the reasonable modeling method,37 finite element models were established with the parameters of volume stirrup ratio,concrete strength grade,eccentricity and reinforcement ratio.The simulation results show that with the increase of volume stirrup ratio,the increase of concrete strength grade and the decrease of eccentricity,the restraint effect of the spatial steel frame on the concrete in the core area is better,and the bearing capacity of the specimen is higher.When the eccentricity increases from 0 to the limit failure,the peak load and bending moment of the specimen conform to the correlation curve of small bias failure,and when the eccentricity increases to infinity,it conforms to the correlation curve of large bias failure.The whole process meets N_m-M_mcorrelation curve.With the increase of volume stirrup ratio and reinforcement ratio,the peak load and bending moment increase at each eccentricity.According to the simulated N_m-M_mmm correlation curve,the simplified N_m-M_m curve formula is establishedBased on the experimental research,the mechanism of spatial steel frame constrained concrete under eccentric compression and formula for calculating compressive strength of constrained concrete are put forward.Considering the constraint effect of spatial steel frame on concrete in compression zone,a formula for calculating the normal section bearing capacity of spatial steel frame concrete columns under eccentric load is established,the calculated value is in good agreement with the test value,which provide technical support for the engineering application of spatial steel frame concrete columns.