Cryogenic fatigue behaviour of steel-concrete composite structures

Aiming to the application of steel-concrete composite structures in extremely cold zones, a special cryogenic test equipment was developed to simulate the temperature environment along Qinghai-Tibet railway, and cryogenic fatigue tests were carried out on 10 specimens composed of 14MnNbq steel, Φ22 studs and C50 concrete. Taking temperature variation and steel rolling direction into consideration, fatigue failure mode and fatigue behaviour of the composite structures under low-temperature were well studied. Test results were compared with that under normal temperature. Results showed that composite structures performed better cryogenic fatigue performance with temperature ranging from 0 deg. C to -50 deg. C, the lower the temperature is, the longer the fatigue life tends to be. This is due to the excellent cryogenic fatigue performance of 14MnNbq steel. Steel rolling direction has important influence on the fatigue behaviour of composite structures, specimens with along rolling steel girders showed longer fatigue life than those with transverse rolling steel girders. Welding Φ22 studs on 14MnNbq steel girders showed no influence on the material quality of 14MnNbq steel. For safety purpose, fatigue bearing capacity of Φ22 studs in Qinghai-Tibet railway composite bridges was suggested to be 80% of that under normal temperature.