高温(火灾)对无粘结部分预应力混凝土梁抗弯性能的影响

Effect of Fire on Flexural Performance of Unbonded Partial Prestressing RC Beams

对预加载的无粘结部分预应力混凝土梁的高温(火灾)性能进行了试验研究,受热温度分别为250,450和650℃,加载试验分别在高温下和冷却后进行。研究结果表明,高温将使无粘结部分预应力混凝土梁的预应力发生改变。在升温的初始阶段,预应力筋的预应力有少量增长,当温度达到一定水平时,预应力才开始下降;高温使得无粘结部分预应力混凝土梁刚度下降,但冷却会使无粘结部分预应力混凝土梁的挠度得到一定程度的恢复;随着温度的升高,无粘结部分预应力混凝土梁的极限预应力和极限挠度增量的变小,高温后加载的试验梁的极限应力增量和极限挠度增量比高温下加载的试验梁要大;随着温度的升高,无粘结部分预应力混凝土梁的开裂荷载和极限荷载呈下降趋势,但高温中梁的开裂荷载、极限荷载值均低于高温后的梁。

The performances of the preloaded unhonded partial prestressing RC simply supported beams at different elevated temperatures were researched. The elevated temperatures were 250 ℃, 450 ℃ and 650 ℃ respectively, and the loading experiments were performed under the high temperature and after cooling. The study shows that the high temperature would change prestressing force of the unbonded partial prestressing RC beam, and at the early stage of heat-up. The prestressing force of the partial prestressing steel enhanced a little, and after the temperature arrived a certain level, the prestressing force descended. The high temperature made the stiffness of the unbonded partial prestressing RC beams descend, and cooling could make the deflection of the unbonded partial prestressing RC beams recovered to some degree. With the temperature ascending, the ultimate prestressing force increment and the ultimate deflection increment of the unbonded partial prestressing RC beams diminished. The ultimate prestressing force increment and the ultimate deflection increment of the beams loaded after high temperature are larger than those of the beams loaded under the high temperature. With the temperature ascending, the cracking load and the ultimate load of the unbonded partial prestressing RC beams tended to descend. However, the cracking load and the ultimate load under the high temperature were lower than those after the high temperature.