Experimental Study on Seismic Behavior of Eccentrically Constant-compressed Steel Box Column Under Cyclically Lateral Loading

Pseudo-static experiments on seismic behavior of 16 eccentrically constant-compressed steel box columns under cyclic lateral loading are conducted.The effects of axial compression ratio,width-to-thickness ratio of web plate and bending moment on the seismic behavior of steel box columns are investigated.The experimental results show that the buckling mode of box web plates is influenced by the loading eccentricity of axial compression outside the web plane.If the eccentricity is less than b/8(b is the flange width),the buckling mode of the box web plates is deformed as a half sine-wave,in which the web plates deform outwards from the box and the flanges inwards,and the buckling deformation is almost symmetrical.The plastic deformation of the columns under cyclic load occurs mainly in the fixed end of specimen,and the greatest plastic deformation is generally found at 0.4h or 0.5h away from the fixed end,where h is the width of the web plate.It is also found from the experiments that the width-to-thickness ratio of web plate has the most significant effect on the seismic behavior of the steel box columns.The larger the width-to-thickness ratio is,the less plumpy the hysteresis curve becomes,the faster the skeleton curve declines,and the more severely the load-bearing capacity and stiffness of the column degenerates.The axial compression ratio has more significant effect on the seismic behavior of columns,while the effect of bending moment at the loading joint of the column is little and negligible.Based on the experimental results,a practical criterion to evaluate the applicable seismic grade of steel members and some design suggestions of width-to-thickness ratio of box-section steel column in large span structures are proposed.