斜拉桥索塔锚固区预应力精轧螺纹钢筋断裂试验研究及失效分析

Experimental Study and Failure Analysis on Fracture of Prestressed Fine-Rolled Threaded Steel Bars in Anchoring Zone of Cable-stayed Bridge Pylons

摘要:

针对斜拉桥索塔锚固区预应力精轧螺纹钢筋突发断裂的问题，通过构建足尺“Ⅱ”字型张拉试验台座，对28根直径32 mm的精轧螺纹钢筋开展多因素耦合下为期1年的长期监测试验，以弥补现有研究多基于实验室标准试件、缺乏大尺度工程工况长期数据的不足。结果表明：螺纹钢筋张拉锚固后瞬时预应力损失约为4.4%，前3个月增长迅速，长期累计损失趋于30%的稳定水平；1根PSB1200级钢筋在锚固4个月后发生断裂。经失效分析，钢筋断裂模式为脆性过载，裂纹始于螺纹牙底，呈沿晶断裂形貌，揭示了高张拉应力、螺纹牙底应力集中与材料脆性三者耦合作用下的延迟断裂机理。分析结果可为既有桥梁预应力精轧螺纹钢筋断裂的预防和处置提供试验支撑和参考。

Abstract:

To address the issue of sudden fracture of prestressed fine-rolled threaded steel bars in the anchorage zone of cable-stayed bridge pylons, a full-scale “II”-shaped tensioning test rig is constructed to conduct a one-year long-term monitoring test on 28 prestressed fine-rolled threaded steel bars with a diameter of 32 mm under multi-factor coupling conditions in order to address the shortcomings of existing research, which is largely based on laboratory standard specimens and lacks long-term data on large-scale engineering conditions. Results show that the instantaneous prestress loss after tensioning and anchoring of the threaded steel bars is approximately 4.4%, increasing rapidly in the first three months, and then stabilizing at a cumulative loss of 30% over the long term. One PSB1200 grade steel bar fractured after being anchored for four months. Failure analysis reveals that the fracture mode of steel bar is a brittle overload one, with cracks originating at the thread root and exhibiting an intergranular fracture morphology. The analysis result reveals the delayed fracture mechanism under the coupled effects of high tensile stress, thread root stress concentration, and material brittleness, providing experimental support and reference for the prevention and treatment of prestressed fine-rolled threaded steel bar fracture in existing bridges.