Experimental study on inelastic lateral torsional buckling strength of H-shaped steel beam-columns under high axial force

在强震作用下，H型梁柱在轴力和双曲率弯矩作用下的吸能能力受到侧向扭转屈曲的限制。以往关于梁柱在塑性范围内的扭转屈曲的研究大多只针对单调弯曲的情况进行。然而，多层框架的梁柱在地震作用下既要承受脉动轴力，又要承受循环弯矩。轴向力的波动是由倾覆力矩和竖向振动引起的。本文通过不同加载条件下的试验，考虑了柱在地震作用下的受力状态，研究了由弯扭屈曲确定的压弯构件的最大强度和吸能能力。试验的加载条件如下：(1)单调水平加载…更多的是在恒轴向力作用下，(2)恒定轴力作用下的水平循环荷载，(3)在波动轴力作用下的水平循环荷载，(4)在随机波动轴力作用下的随机水平荷载作用下，由恒定轴力作用下循环水平荷载作用下的荷载-变形关系得到的骨架曲线与恒定轴力作用下单调水平荷载作用下的荷载-变形关系相比较，骨架曲线的最大强度和最大强度时的变形都小于单调荷载作用下的最大强度和变形。在极限强度由局部屈曲确定的情况下，众所周知，循环试验得到的骨架曲线与单调加载曲线几乎重合。研究发现，当强度受侧向扭转屈曲限制时，最大强度受塑性滞回的影响，不同于强度由局部屈曲决定的情况。这是因为在塑性侧向扭转屈曲的情况下，屈曲变形不仅由于内力的增加和塑性区的扩展而发生，而且由于绕强轴的循环弯曲而导致塑性变形的累积。阐明了脉动轴力和塑性弯曲滞后对屈曲强度和吸能能力的影响。较少

There is a case in which the energy absorption capacity of H-shaped beam-columns subject to axial forces and double curvature bending moment during severe earthquakes is limited by lateral torsional buckling. Most of past studies concerning the lateral torsional buckling of beam-columns in plastic range have been carried out only for cases where monotonic bending is loaded. However, beam-columns of multi-story frames are subjected to both fluctuating axial forces and cyclic bending moment during earthquakes. The fluctuating axial forces are caused by overturning moment and vertical vibrations. In this study, the maximum strength as well as the energy absorption capacity of beam-columns which is determined by lateral torsional buckling was studied by carrying out experiments under various loading conditions with consideration to the states in which columns are subjected to loads during earthquakes.The loading conditions in the experiments are as follows: (1) Monotonic horizontal loading … More under constant axial force, (2) Cyclic horizontal loading under constant axial force, (3) Cyclic horizontal loading under fluctuating axial force, (4) Random cyclic horizontal loading under random fluctuating axial force.When comparing the skeleton curve obtained from the relationship between the load and the deformation for the specimen subject to the cyclic horizontal load under constant axial force to the load-deformation relationship for the specimen subjected to monotonic horizontal loading under constant axial force, it is discernible that the maximum strength and the deformation at the time of maximum strength of the skeleton curve are smaller than those seen for the monotonic loading. In cases where the ultimate strength is determined by local buckling, it is generally known that the skeleton curve obtained from cyclic experiments nearly coincides with the monotonic loading curve. It was found out that the maximum strength is affected by plastic hysteresis when the strength is limited by lateral torsional buckling unlike the case in which the strength is determined by local buckling. This is so because in the case of the plastic lateral torsional buckling the buckling deformation progresses not only due to the increase in internal force as well as the extension of plastic regions but also due to the accumulation of plastic deformation caused by the cyclic bending about a strong axis. The effects of the fluctuating axial force and the plastic bending hysteresis upon the buckling strength and energy absorption capacity were clarified. Less