索桁架结构耐火性能试验研究及分析

EXPERIMENTAL STUDY AND THEORETICAL ANALYSIS ON THE FIRE RESISTANCE OF CABLE TRUSS STRUCTURES

  • 摘要: 索结构常用于较大跨度的工程结构,索结构耐火性能研究可为其抗火设计提供实用方法。索由多根钢丝组成,其传热机理较为复杂,而传热计算是索结构抗火设计的基础。进行涂覆薄涂型防火涂料的多种直径索试件的温度场试验,对索中温度场的分布和发展规律进行试验研究。基于试验结果,提出了考虑空腔辐射传热的索结构温度场计算模型,计算结果与试验结果基本吻合。针对典型的索桁架整体结构,对其高温下的力学性能和破坏形态开展研究。研究结果表明:由于钢丝之间存在热阻,索试件中心测点升温比周围测点滞后,而且随索直径增加,这种滞后作用越明显。高温作用下,索桁架结构的稳定索首先松弛,应力降至零,承重索最后拉断,索桁架发生破坏。荷载增加,索桁架结构的耐火极限降低。稳定索的预应力增加,索桁架结构的耐火极限不变,但索桁架结构保持较好工作状态的时间增加。

     

    Abstract: Cable structures are widely used in larger span structures. The study of fire resistance of cable structures can provide practical methods for their fire resistance design. Cable structures are composed of multiple steel wires, and their heat transfer mechanism is relatively complicated. Heat transfer calculation is the basis of the fire resistance design of cable structures. In this study, temperature field tests were firstly conducted on various diameter cable specimens with intumescent coatings, based on which the temperature distribution and development of cable structures were investigated. Based on the test results, a finite element analysis model for the temperature filed of cable structures considering cavity radiation heat transfer was proposed, and the calculated results agree well with the test results. A fire resistance analysis model of cable truss structures was proposed and the mechanical properties and failure modes under high temperature were studied with the model. The results show that due to the thermal resistance between steel wires, the temperature rise at the central test points lags behind that in the peripheral, and this lag effect become more obvious with the increase of cable diameter. When subjected to fire, the stable cable first slacks and the stress decreases quickly to zero, and finally the bearing cables broke, resulting in the failure of the cable truss structure. As the load increases, the fire resistance of the cable structure decreases. When the prestress of the stable cable increases, the fire resistance of the cable truss structure remains unchanged, while the time for the cable truss structure to maintain a good working condition increases.

     

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