预应力简支钢梁高温性能试验研究

Experimental Study on Performance of Simply Supported Prestressed Steel Beams at High Temperature

为研究简支预应力钢梁在火灾高温下的耐火性能,基于实际的升温曲线,进行了2根预应力钢梁及1根非预应力钢梁的耐火性能试验,3根试验梁的截面尺寸、跨度及材料均相同。预应力拉索考虑了直线和折线2种布置方式;钢梁顶面绝热、其余3面受火、承受跨中集中荷载。最后分析了钢梁温度-时间、拉索张力-温度、挠度-温度关系。结果表明:随着炉内温度升高,预应力钢梁截面温度逐渐升高,在火灾初期,预应力钢梁跨中挠度随温度升高缓慢增加,在火灾后期挠度急剧发展;升温初期,预应力拉索张力略有降低,随着温度持续升高,拉索张力迅速降低,在临界状态时拉索完全松弛,在恢复至常温时,拉索张力也不能恢复;高温作用下预应力钢梁失效与预应力拉索张力松弛有关,在拉索张力完全消失后钢梁很快达到临界状态;高温作用下预应力钢梁的横向刚度与拉索张力存在关联,拉索一旦完全松弛,预应力钢梁挠度急剧增大并很快进入临界状态;确定拉索初始预应力对临界温度的影响时,需要综合考虑预应力拉索布置方式的影响,不同布索方式对预应力钢梁耐火性能有较大影响,其他条件相同时折线形布索的预应力钢梁比直线形布索的预应力钢梁临界温度高。

To investigate the fire resistance behavior of prestressed steel beams at high temperature in fire disasters, fire resistance tests were carried out on two prestressed steel beams and one conventional steel beam based on actual heating curve. The three beams had the same size of cross section, span and same material. The prestressed steel beams were prestressed by two arrangement forms, namely, the linear and the folded pattern. During the tests, the three adjacent sides of the cross-sections of these steel beams were exposed to fire and top side was under ambient temperature and constant point load was applied to the three beams at the mid-span. The variation curves of temperature with time, tension force in the cable strands and deflection of the beams were analyzed. The results show that the temperature of the steel beam cross section increases gradually with rising of temperature inside furnace. The deflection in the mid-span increases gradually with elevating temperature in the initial stage and develops abruptly in the final stage. The tension force in the cable strands falls slightly in the initial heating stage, reduces rapidly with the constant rising temperature and becomes totally slack at the critical state. This slack tension force cannot be restored when the tested beams are cooled to room temperature. The failure of prestressed steel beams is relevant to tension force in the cable strands at high temperature. The steel beams quickly reach critical state when the tension force disappears in the cable strands. Also, transverse stiffness of the steel beams is relevant to tension force in the cable strands at high temperature. Once the strands become totally slack, the deflections of the prestressed steel beams increase rapidly and the beams quickly enter the critical state. In addition, geometric shape of prestressed cable strands must be comprehensively taken into account when the effect of initial prestress level on the critical temperature is investigated. The configuration of cable strands has great influence on the fire resistance behavior of the prestressed steel beams. The prestressed steel beam with folded-pattern cable strands has higher critical temperature than that with line cable strands when other conditions are identical.