Single Column Test - Test#4 - Cyclic with Symmetric Loading Histories Without Trailing Cycles

An experimental program that consists of six quasi-static and two hybrid tests was conducted to study and quantify the inelastic behavior of deep steel wide flange column sections up to collapse. The tests were performed on 1:8 scaled W36X652 column sections. Two monotonic and four cyclic quasi-static tests were carried out. The monotonic loading protocols consist of interstory drift ratio, rotation, as well as constant and variable compression axial load histories. The cyclic loading protocols consist of symmetric and unsymmetric histories of interstory drift ratio, rotation at the tip of the column, and levels of axial load that vary between tension and compression. These protocols are meant to simulate the demands experienced by first-story corner columns in tall steel moment-resisting frame structures.

A three-actuator test setup at NEES@ Buffalo lab was utilized for this experiment. For the quasi-static tests, a displacement-controlled horizontal actuator was used to impose the lateral displacement at the tip of the column. Two vertical actuators were used to impose both axial force and rotation demands. One of the vertical actuators was forced-controlled and the other one displacement-controlled.

In the current experiment, a symmetric cyclic lateral displacement and rotation were imposed at the tip of the specimen simultaneously with a variable axial load. In addition, pairs of increasing amplitude cycles were interrupted by a pair of smaller amplitude trailing cycles.

In the current experiment, intersory drift ratios and rotation loading histories were applied in phase with increasing amplitudes. Cyclic axial loads were also applied with a mean value of 15% of the axial yield load carrying capacity of the column (22 kips). Increasing levels of axial force (fluctuating between tension and compression) were applied until the yield drift value of the column was achieved. From that point on, the axial load cycled between constant levels of tension (27%, 47 kips) and compression (57%, 83 kips). The axial force was applied out-of-phase with the drift demand at the tip of the column.

为研究并量化深型钢宽翼缘柱截面直至倒塌的非弹性行为，开展了包含6项拟静力试验（quasi-static test）与2项混合试验（hybrid test）的试验项目。试验采用1:8缩尺比例的W36X652柱截面试件进行。共开展了2项单调拟静力试验与4项循环拟静力试验。单调加载方案包含层间位移角（interstory drift ratio）、转角、恒定及变压缩轴向荷载历程；循环加载方案包含层间位移角、柱端转角的对称与非对称历程，以及在拉压之间变化的轴向荷载等级。这些方案旨在模拟高层钢框架抗侧力结构中一层角柱所承受的荷载需求。试验采用NEES@Buffalo实验室的三作动器试验装置进行。在拟静力试验中，采用位移控制的水平作动器施加柱端的侧向位移；采用两个竖向作动器施加轴向力与转角需求，其中一个为 力控制（force-controlled）作动器，另一个为位移控制（displacement-controlled）作动器。本试验中，在试件柱端同步施加对称循环侧向位移、转角及变轴向荷载。此外，增幅循环对会被小幅值后续循环对中断。本试验中，层间位移角与转角加载历程采用同相增幅方式施加。循环轴向荷载的均值为柱轴向屈服承载力的15%（22千磅）。施加逐级增大的轴向力（在拉压之间波动）直至达到柱的屈服位移角（yield drift value）。此后，轴向荷载在恒定拉力水平（27%，47千磅）与恒定压力水平（57%，83千磅）之间循环变化。轴向力的施加与柱端位移需求呈异相（out-of-phase）关系。