后张拉预应力成形鞍形网壳竖向极限承载力试验研究

Experimental study on vertical ultimate load capacity of post-tensioned and shaped hypar space truss

通过对一个静置于地面的单弦杆网架进行预应力后张拉,得到马鞍形网壳.对鞍形网壳模型进行了竖向加载试验,静载施加于上弦节点,分级加载.测试了各级荷载作用下的杆件应变和上弦节点挠度,得到荷载-挠度曲线,从而得出该结构模型的竖向极限承载力.试验结果表明,轴力是杆件主要内力形式;杆件破坏现象较少,仅支座附近腹杆发生了轻微屈曲;在成形阶段部分上弦节点即进入塑性,节点承载力降低,在加载过程中易发生断裂破坏,进而引起结构刚度下降,削弱了结构竖向承载能力;由荷载-位移曲线看出该结构的主要破坏形式不是整体失稳.最后给出改进结构的指导思想是在不降低节点铰接特点的同时,设法提高其承载能力.

Initially assembled on the ground level, the single chord space truss, which is composed of a single layer of chords, together with out of plane web members, was deformed into saddle shape by posttensioning method. Vertical ultimate load test was carried out on hypar space truss model. Top joints were applied by concentrated load step by step. Stresses and vertical deflections were measureded in the test. According to the load deflection curve, actual vertical ultimate load were gained. The test result showed that axial force was the main internal force, and structural components seldom failed except that several webs around supports buckled slightly. Some top joints in plasticity during shape formation lead to low load capacity and fractured under vertical load, which declined the overall vertical stiffness and ultimate capacity. The load-displacement curve indicted that structural failure mode was not overall instability. Finally, some improved measurs were proposed to increase the load capacity of top joints with pin comection maintained.