Bolt-connected precast buildings are increasingly prevalent, especially due to their efficient force transfer and accelerated construction processes. However, in cold climates, special attention must be directed towards the effects of freeze-thaw (F-T) damage on concrete at bolt connection sites. This study conducted an accelerated F-test to investigate how concrete F-T damage influences the preload force of the connection bolts. The changes in bolt preload forces across F-T cycles were monitored using advanced fiber optic sensing technology. To mitigate preload force loss, silicone rubber sleeves were introduced into the bolts. Results indicate a correlation between initial preload force and subsequent preload loss, with lower initial preloads leading to greater losses. Additionally, the concrete's frost resistance significantly affects preload force loss, with less resistant specimens showing marked preload decreases. A notable risk of brittle damage arises after 3 to 6 F-T cycles if a 4 mm gap between the bolt and concrete exists, attributed to water freezing and expansion within the gap. Concrete specimens subjected to our proposed mitigation strategies effectively withstand over 140 F-T cycles, substantially lowering crack damage risks.

中文翻译：

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冻融环境下预制结构节点螺栓预紧力损失机理及控制

螺栓连接的预制建筑越来越普遍，特别是由于其有效的力传递和加速的施工过程。然而，在寒冷气候下，必须特别注意冻融 (FT) 损坏对螺栓连接部位混凝土的影响。本研究进行了加速 F 测试，以研究混凝土 FT 损伤如何影响连接螺栓的预紧力。使用先进的光纤传感技术监测 FT 周期内螺栓预紧力的变化。为了减轻预紧力损失，在螺栓中引入了硅橡胶套管。结果表明初始预紧力与随后的预紧力损失之间存在相关性，初始预紧力越低，损失越大。此外，混凝土的抗冻性显着影响预紧力损失，抗力较小的样本显示预紧力明显下降。如果螺栓和混凝土之间存在 4 毫米的间隙，则由于间隙内的水结冰和膨胀，在 3 至 6 FT 循环后会出现明显的脆性损坏风险。采用我们提出的缓解策略的混凝土试件可有效承受超过 140 次 FT 循环，显着降低裂缝损坏风险。