Mechanism and control of preload force loss of precast structural joint bolts under freeze–Thaw environments

Abstract

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-t-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.