Fire is the greatest and most universal disaster for buildings

especially for steel structural buildings.In the past 100 years

there were many cases that steel structures collapsed in fire.However

steel structures in most cases were not fatally destroyed.These damaged steel structures may be reused after structural inspection

safety appraisal

reinforcement and strengthening.High-strength bolted connections are widely used in steel structures.As a fundamental part of the whole structure

the behavior of high-strength bolted connection is very important for maintaining the integrity and safety of steel structures.Usually

structural behavior of high-strength bolted connection decreases after fire action due to strength loss and initial preload loss of high-strength bolt. Up to now there are only a fewer studies focusing on the mechanical properties of high-strength bolted connections after fire.To obtain the mechanical properties of high-strength bolted connections after fire including slip load capacity

ultimate capacity and load-deformation curve

a series of experiments were carried out in this study.In order to simulate the behaviors of high-strength bolted connections in fire accidents

both natural cooling and water cooling situations were employed in the tests.The results show that when high-strength bolted connections are exposed to a temperature lower than 400°C

the loss of slip load capacity and ultimate capacity after cooling is considerably small

which means the connections can maintain the external design load after fire.When high-strength bolted connections are exposed to a temperature higher than 400°C

slip load capacity and ultimate capacity decease violently.Hence

a deeper inspection of the connections is necessary to check whether the connections are safe.