冷成型钢开口截面短柱高温后力学性能试验研究

EXPERIMENTAL RESEARCH ON MECHANICAL PROPERTIES OF COLD-FORMED STEEL STUB COLUMNS WITH OPEN SECTIONS AFTER A FIRE

为了研究冷成型钢轴压构件的高温后力学行为,对45根开口截面短柱加热至预定温度,冷却后再进行轴压测试。试验设定7种加热温度和两种保温时间,探究温度场参数与构件承载力之间的关系。考察不同加劲模式下,三种开口截面构件的抗火性能和局部稳定性。试验结果表明:1)加热温度和保温时间均可显著影响构件承载力;2)不可把构件承载力的下降简单等同于材性的衰减;3)纵向加劲可以改善开口截面构件的局部稳定性,且腹板加劲的作用更明显。同时利用试验结果评估直接强度法的适用性,可以发现:承载力计算时,对经历温度在700℃以上的试件必须考虑温度引起的构件质量损失;考虑高温效应的修正直接强度法能够提供比较精确和可靠的开口截面高温后承载力计算值。

A series of compression tests were conducted at ambient temperature to investigate the mechanical properties of cold-formed steel stub columns after a fire. The test specimens, including three types of 45 stub columns with open sections, were heated to the pre-selected temperature and then the compression tests were conducted on the specimens after cooling. Seven specified temperatures and two duration times were adopted in the test program to study the relations between the bearing capacity of components and the parameters of temperature field. The effects of longitudinal stiffeners on the local stability and fire resistance of open sections were also evaluated. The test results showed that: 1) the heating temperature and duration time greatly affected the bearing capacity of stub columns;2) the deterioration of material properties was not the only attribute that the stub columns lost their bearing capacity after being exposed to fire;3) longitudinal stiffeners could improve the local stability of open sections, and web stiffeners performed better. The test results were also used to evaluate the appropriateness of the direst strength method(DSM). This evaluation showed that the mass loss of specimens should be taken into account in the design calculation when the heating temperature was above 700℃. It was also shown that the modified DSM, with consideration of the high-temperature effect, was accurate and reliable for calculating the bearing capacity of cold-formed steel stub columns with open sections.