METHOD FOR CALCULATING THE TEMPERATURE EFFECT OF STAY CABLE CROSS-SECTION NEAR OPEN-AIR FIRE

To study the fire response of stay cable in open space, a heat transfer calculation method of cable cavity near open-air fire is established, considering the spatial radiation theory of fire source and environmental heat transfer boundary of cable surface, combined with three basic heat transfer theories of internal cavity radiation, contact conduction and interstitial heat conduction. And the accuracy of the numerical analysis model is verified through experimental results. The time-space distribution characteristics of temperature field and stress field, together with the time-varying characteristics of axial force and bending moment, of cross-section in prestressed cable are analysed under different internal heat transfer modes, different wrapping conditions and different wind conditions. The analysis results show that the transient temperature distribution of cable cross-section near open-air fire can be calculated accurately taking into account the complete cavity heat transfer model when analysing fire response of the cable. The temperature and stress distributions of cross-section in cable present anti-symmetric state and exhibit an approximation from quadratic distribution characteristics to linear distribution characteristics with the increase of fire exposure time, and axial force loss and bending moment effect can occur in the cable cross-section. Compared with the complete cavity heat transfer model, the round steel heat transfer model has a uniform cross-section stress distribution, larger axial force loss and much smaller bending moment effect. The cavity radiation model has an overly concentrated cross-section stress distribution, larger bending moment effect and smaller axial force loss. The smoke-wrapped condition can exacerbate loss of axial force and weaken bending moment effect in the cable cross-section. The windward condition can seriously aggravate loss of axial force and bending moment effect in the cable cross-section. The research results can provide a theoretical basis for the fire-resistant design and protection of cable structures.