Study On The Main Cable Temperature Field And Fire-resistant Design Of The Suspension Bridge In A Fire Disaster

China has a large number of rivers,lakes and bays.With the rapid development of traffic construction,construction of the long-span bridge structure is still in the ascendant.Once the fire accident happens to the oil tank trucks,heavy-duty truck and other fuel vehicles,it will pose a great threat to the safety of the bridge structure.At present,the research and evaluation indexes of fire resistance of bridge at home and abroad are mostly used for reference from the fire resistance design criteria of building structures.Suspension bridges are common to see in long-span bridge structures,most of which fall under the category of major engineering projects,and pay special attention to design,construction,management and maintenance.So far,research into fire resistance and prevention of suspension bridges is still lacking.As a key component of suspension bridges,the main cable composed of the high-strength steel wire has a poor fire-resistant performance.Once the main cable is destroyed by the fire disaster,catastrophic consequences might be caused.Taking the main cable of suspension bridge as the research object,the author carried out the research on the temperature field and fire resistance of the main cable under high temperature in fire.The main research contents are as follows:（1）Research findings of mechanical properties of high-strength steel wires under the high temperature and after the high temperature,respectively,are summarized.The least square method is used for polynomial fitting of mechanical parameters of the high-strength steel wire under the high temperature.Through deduction and fitting of polynomial function for mechanical parameters of the high-strength steel wire under the high temperature,the error of the value of mechanical parameters changing with the temperature is minimized;（2）Based on basic theories of the heat transfer theory and the law of conservation of energy,considering the contact heat transfer and interspace radiative transfer between steel wires of the cable,this thesis uses the cross-section radial thermal-conduction resistance and the theoretical calculation formula of fire temperature rise of the steel member without fire protection to propose the theoretical formula to compute the steel cable cross-section temperature rise.Results show that this formula can accurately obtain the distribution characteristics of the real temperature field in the section of the steel cable evenly wrapped by heat flow;（3）Based on the ABAQUS numerical analysis platform,and with the single steel wire as the minimum unit,the main cable cross-section fine numerical heat transmission model is established to simulate the contact heat transfer and interspace radiative transfer between steel wires.After a comparative analysis with the temperature field of the commonly-used round steel numerical heat transfer model,it is observed that the temperature field of the steel cable cross-section with certain void ratio demonstrates more significantly uneven distribution.In terms of the practical suspension bridge’s main cable cross-section,the round steel model commonly used by the fire-resistant research can underestimate the temperature gradient of the main cable cross-section.The equivalent numerical computing model that can replace the main cable’s fine numerical heat transfer model can be given by the numerical experiment of the main cable’s thermophysical parameters（heat conduction coefficientλ,specific heat capacity c and densityρ）,which can better accommodate to the computing precision and efficiency;（4）Temperature field analysis is carried out on the main cable with the typical cross-section dimensions under the temperature rise curve of the oil tank truck’s burning of HC_inc.Based on the mechanical properties of the high-strength steel wires that change with the temperature,the stress redistribution of steel wires at different layers is analyzed.In other words,as the temperature keeps on increasing,the steel wire stress of the outer layer gradually decreases,while the steel wire stress of the internal layer gradually increases.Analysis of the main cable’s high-temperature mechanical property impairment,obtains the damage time of the main cable when the flame directly radiates to the surface of the main cable and the radiation convection of the fire source is uniform around the main cable,and the fire-resistant steel wire temperature control indexes of the main cable are proposed.Finite element heat analysis is conducted on the main cable whose fire-resistant layer is made up of different layers and of different thickness.Based on the analysis results,suggestions for settings of the fire-resistant layer are made.