Experimental Study On The Axial Compression Performance Of Steel Confined Timber Columns

According to the "Thirteenth Five-Year Plan" of the Ministry of Housing and Construction,it is proposed to establish the technical system and key technologies of assembled buildings and promote the development and application of "steel-hybrid","steel-timber" and "timber-hybrid"composite structures."By applying preload on the connecting angles,the outer clad angles can effectively confine the timber,ensuring good integrity between them and providing good loadbearing performance.Based on the completion of relevant material properties tests,axial compression tests,finite element analysis and theoretical analysis were carried out on the steel confined timber column,and the main research contents and conclusions are as follows.(1)Carry out the relevant material properties tests of timber and steel.The compressive and shear properties of the timber used were tested to obtain the compressive strength of the timber in the smooth grain,the compressive strength of the timber in the cross grain and the shear strength,and the reduction was carried out according to the relevant provisions of the Timber Structure Design Manual;the tensile properties of the steel were tested to obtain the yield strength,ultimate tensile strength and modulus of elasticity of the steel used.(2)Conducted axial compression tests on steel-restrained timberen columns.The effect of preload on the ultimate bearing capacity,stiffness and ductility of the composite column was studied through the axial compression test,and the mechanism of the effect was analyzed.The test results show that with the increase of preload,the circumferential restraint of the timber column in the core area is enhanced,which improves the bearing capacity of the timber column part,but the increase of preload makes the residual stress on the angle steel column also increase,which makes the angle steel enter the buckling state in advance and reduces the bearing capacity of the angle steel column part.(3)ABAQUS software is used for finite element analysis of the SCTC,and the accuracy and validity of the finite element model is verified by comparing with the load displacement curve obtained from the test,and parametric analysis of the SCTC is carried out on this basis to further study the influence of various influencing factors on the mechanical properties of the SCTC.The effect of the number of timber plies on the angle column is mainly to affect its buckling development rate.Meanwhile,through the analysis of the peak bearing capacity of the combined column,steel column and timber column,it is determined that the mechanical performance of the steel restrained timber column with 7 layers of timber plies is better than that of 4 and 10 layers when the outer angle is ∠90×140,the combined section is 200×300and the spacing between the connected angles is 250 mm.The width-thickness ratio of the flange increases with the increase of the limb length,which makes the rate of buckling development increase,then the rate of decrease of the angle bearing capacity increases,which eventually leads to the reduction of the bearing capacity reduction factor of the SCTC.The distance between connecting angles is the main influencing factor to the bearing capacity of SCTC,and the arrangement of connecting angles at the end or not has little influence on the peak bearing capacity of the composite column and angles.In maintaining the connecting angle spacing250 mm,when the column length is below 1000 mm,the angle steel into yielding can still maintain a good restraint effect on the timber laminate;when the combined column column length increases to 1500 mm,the angle steel buckling rate becomes faster,and once the angle steel into yielding,the restraint of the core timber column is failed,the timber ples begin to appear buckling damage.(4)The mechanism of the axial compression of the SCTC was studied.Considering the strengthening effect under the three-dimension compression of the timber column in the core area,the angle utilization coefficient of the profile under the lateral support of the core timber column and the influence of the connecting angle to the effective length of the combined column,refer to the results of the test and finite element analysis and the two constitutive model of the timber under restraint conditions proposed by the existing research,the calculation method for the axial compression bearing capacity of the SCTC was proposed.It is found that both method I and method II can effectively calculate the peak load bearing capacity of the SCTC.For the reason of safety,it is recommended to use method II for the calculation.