大长细比约束圆钢管杆件高温承载力试验研究

Experimental study on fire resistance of axially restrained steel chords with large slenderness ratio at elevated temperature

受局部火灾作用的网架结构杆件呈现显著的约束构件特性,其中圆钢管是网架结构最常见的杆件类型。为研究网架结构中的约束杆件在火灾下的受力性能,设计了为圆钢管提供恒定轴向约束的组合弹簧装置,开展了多参数影响的大长细比约束圆钢管构件的受火试验。结果表明：荷载比增大100%,试件的屈曲温度降低90℃,屈曲承载力增大18%,屈曲后强度略有增大;轴向约束刚度比增大77%,试件的屈曲温度降低90℃,屈曲承载力增大7%,屈曲时轴力突变量及受火后残余变形明显减小;长细比增大29.3%,试件的屈曲温度降低124℃,屈曲承载力减小40%,屈曲后强度略有增大;初始弯曲增大,试件的屈曲温度升高,屈曲承载力略有减小。轴向约束圆钢管构件受火试验得到的轴力曲线与理论分析结果吻合较好,从而验证了所提出的理论分析方法的正确性,明确了理论分析得出的轴力在屈曲时的突变现象具有近似性。

Restrained member characteristics of elements in grid structures were shown obviously when they were exposed to localized fires. Steel chords are the most common type of members in grid structures. In order to study the mechanical behaviors of restrained steel chords in grid structures under fire, a spring sets was designed to provide the constant axial restraint to the pin supports of the chords. And then, a series of fire tests of restrained steel chords with large slenderness ratios were conducted under multiple parameters. The results show that as the load ratio is doubled, the buckling temperature of the specimen drops 90 ℃, and the resistance at buckling stage increases by 18%, and the resistance at post-buckling stage increases to some degree. With the increase of axially restrained stiffness ratio by 77%, the buckling temperature drops 90 ℃, and the resistance at buckling stage increases by 7%, and the axial force jumping at buckling stage and the residual deformation after fire decreases obviously. With the increase of slenderness ratio by 29.3%, the buckling temperature drops 124 ~C, and the resistance at buckling stage decreases by 40%, and the resistance at post-buckling stage increases to some degree. With the increase of initial imperfection, the buckling temperature increases and the resistance at buckling stage decreases slightly. The axial force curves in fire tests fit well with analytical solutions of axially restrained steel chords under fire. The tests results verify the analytical method effectively and specified that the jumping phenomenon of axial force in analytical solutions has proximity.