强约束轴心受压钢管柱耐火性能试验研究

Experimental study on the fire-resistance of steel tube columns with axial compression and strong constraints

为正确评估强约束钢管柱的耐火性能,利用自行研制的杆系结构构件温度轴力测量装置,采用恒载升温试验方法,设5级初应力水平,6种长细比,对30根Q345钢管柱进行试验研究,揭示轴心受压钢管柱在强约束下的耐火性能。试验结果表明:强约束钢管柱在温升作用下的温度应力相当大,对钢管柱破坏有决定性作用,在耐火设计与评估中必须考虑。钢管柱在高温作用下,破坏前其弹塑性性质较为明显。相同长细比的构件,在较高的初始应力水平作用下,极限承载力大、温度应力小、临界温度低;反之相反。在相同初应力水平下,长细比对强约束钢管柱的极限承载力和温度应力的影响并不敏感,但长细比大的试件为失稳破坏,破坏后变形很大;长细比较小的试件为强度破坏,破坏后变形较小。以试验数据为基础给出两端固定Q345钢管柱的下限临界温度回归计算公式,可用于火灾中约束刚度不变的钢结构耐火设计与评估。

In order to evaluate the fire resistance of steel tube columns with strong constraints, a self-developed thermal internal force measurement device for frame structure members was employed. Test under elevated temperature and constant loading was conducted for 30 steel tube columns of Q345 with 5 grades of initial stress levels and 6 slenderness ratios, to reveal the fire resistance of such columns. The results show that under elevated temperature the thermal stress of the steel tube columns is great, and should be considered in the fire resistance design and evaluation. Under elevated temperature, the steel tube columns exhibite obvious elasto-plastic properties before failure. With identical slenderness ratio, the columns with higher initial stress level hadve larger bearing capability, lower thermal stress and critical temperature, when compared with the columns with lower initial stress levels. Otherwise, the results would be the opposite. Under identical initial stress levels, the bearing insensitive to the slenderness ratio. But the columns with the deformation is larger after failure. On the contrary, capability and thermal stress of the steel tube columns are higher slenderness ratios would undergo buckling failure, and the columns with the lower slenderness ratios would undergo strength failure, and the deformation is smaller after failure. Based on the test data, a lower critical temperature limit regression formula of Q345 steel tube columns fixed at both ends was proposed for fire resistance design and evaluation of the steel structure with constant restraint stiffness under fire.