Research on the Working Principle and Failure Mechanism of a Temporary Cable System Based on External Steel Anchor Boxes
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摘要: 临时索系统的锚固有效性是基于外置钢锚箱换索工艺安全应用的关键。以某大跨度混凝土斜拉桥换索工程为背景,提出了一种利用对拉螺杆作为外置钢锚箱锚固系统的换索系统,设计制作了其全尺及主梁节段模型,通过对拉螺杆预紧试验、4种接触条件下的单向拉伸静力试验,探究了该换索系统的工作原理和失效机制,并基于数值分析进行仿真验证。结果表明:外置钢锚箱与素混凝土垫块之间的界面摩擦和对拉螺杆的弯-剪强度决定了该系统的锚固性能;采用对角线预紧的工艺能够使对拉螺杆的受力更为均匀,且设计时应考虑逐个螺杆失效的影响;钢-素混凝土垫块干接触的等效摩擦系数较大;素混凝土垫块发生破坏前后,对拉螺杆从受剪为主转变为受弯为主,超高性能混凝土(UHPC)材料可用于该类换索系统中。Abstract: The effectiveness of the temporary anchorage system is crucial for the safe application of the external steel anchor box cable replacement process. Taking the cable replacement project of a long-span concrete cable-stayed bridge as the background, a cable replacement system that uses pull-bolts as the anchoring system for the external steel anchor box is proposed. A full-scale model and a main beam segment model were designed and manufactured. The working principle and failure mechanism of this cable replacement system were explored through pull-bolt pretension tests and uniaxial static tensile tests under four contact conditions, and validated by numerical simulation. The results indicated that the anchoring performance of the system was determined by the interface friction between the external steel anchor box and the plain concrete pad as well as the bending-shear strength of the pull-bolts. The diagonal pre-tightening process ensured more uniform force distribution among the pull-bolts, and the design should consider the impact of individual bolt failure. The equivalent friction coefficient of dry contact between steel and plain concrete pads was relatively large. Before and after the failure of the plain concrete pad, the pull-bolts transitioned from being primarily in shear to being primarily in bending. Ultra-high performance concrete (UHPC) could be used in this type of cable replacement system.
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