预应力拉索锚头抗火性能试验

预应力拉索在大跨径桥梁结构中应用广泛,其火灾安全却面临严峻挑战。拉索锚头是拉索遭遇火灾高温时最薄弱的环节,若无专门的防火设计将造成极大的安全隐患,为此,以中国工程中广泛应用的热铸锚、冷铸锚和Wirelock锚三大类锚固系统为研究对象,采用平行钢丝束拉索足尺试件对其抗火性能进行研究。通过6个拉索锚头试件在有应力状态下的火灾试验(试验参数包括拉索锚固类型和应力水平),研究其温度场分布及锚固性能退化规律。试验结果表明:锚具内部温度分布不均匀,底端温度最高,前端最低;拉索锚固系统在高温下的滑移过程大致分为无滑移、滑移稳定增长和破坏3个阶段,其中热铸锚的无滑移段持续时间最长,约为60min,冷铸锚和Wirelock锚的无滑移段持续时间都在20min以内;3类试件的破坏时间即耐火极限相近;当构件破坏时,热铸锚、冷铸锚、Wirelock锚的临界温度分别为420℃~443℃、440℃~450℃、279℃~284℃;当拉索预应力水平从0.3增加到0.4时,拉索锚头耐火性能下降。

Fire Tests on Prestressed Cable Sockets

Prestressed cables are widely used in large-span bridge structures, and fire is a major threat to their service life. Cable sockets are the weakest link in cable structures under fire conditions, which poses a tremendous safety risk if no specific fire protection design has been implemented. In this study, the fire resistance of three types of anchoring systems, namely, hot cast, cold cast, and Wirelock, were selected based on engineering application in China, and full-scale tests were conducted on them. Six parallel wire strand specimens were heated under axial tension to investigate the temperature field distribution and degradation law of anchoring performance. The test parameters included the anchorage type and stress level. Experimental results show that the temperature distribution inside the anchors is non-uniform. In particular, the lowest and highest temperatures exist in the front and bottom parts of the anchors, respectively. The slip process consists of three stages:non-slip, stable growth, and failure. For hot cast anchors, the slip does not occur until 60 min after ignition. For cold cast and Wirelock anchors, the slip occurs approximately 20 min after ignition. Six specimens share a similar failure time. The critical temperatures for the hot cast, cold cast, and Wirelock anchors are 420℃-443℃, 440℃-450℃, and 279℃-284℃, respectively. The fire resistance of the cable sockets decreases when the cable stress level increases from 0.3 to 0.4.