Thermal-mechanical Coupling Effects And Optimal Design Of Hydronic Snow Melting Airport Pavement

Hydronic heating system is an effective method for the airport pavement snow melting due to its advantages as high efficiency,stability,energy saving,environment friendliness,and controllability.The snow-melting performance and influencing factors of the hydronic airport pavement have been theoretical and experimental analyzed.However,the pavement thermal stress distribution during the heating process has not been addressed.Particularly,the mechanical response of pavement under combined action of thermal stress and load stress has not been studied.These phenomena make the security of airport pavement in practical application has been questioned.To solve the above problems,this paper developed an outdoor full-scale hydronic snow-melting airport pavement system and a three-dimensional transient thermo-mechanical coupling effect of hydronic pavement.The pavement thermal stress distribution characteristics has been analyzed.The position and appearing time of the pavement maximum thermal stress has been determined.The coupling relationship between thermal stress and impact load stress of aircraft has been clarified.We determined the reasonable design parameters and operation strategy of hydronic pavement system by considering snow melting effect and mechanical characteristics.The research results were applied to the hydronical airfield pavement engineering of Beijing Daxing International Airport.The contents and results are shown as follow:Considering the actual structure and heat source distribution of airport pavement,an outdoor full-scale test system and a monitoring system were built after the indoor mechanical tests.The distribution characteristics of pavement thermal strain during heating process have been experimental analyzed.The difference of thermal strain distribution between hydronic pavement and common pavement was analyzed.The relationship between pavement temperature and thermal strain was clarified.The results show that the hydronical pavement thermal strain increased with the operating time.The thermal strain diffused circularly from the pipe wall along the radius to the outside.Considering the relationship between pavement thermal strain and stress,a numerical model of transient hydronic pavement thermal stress was established,based on the principles of heat transfer and elasticity.The model was validated by the measured data.The distributions of pavement thermal stress were investigated.The time and location of the maximum stress of the pavement were clarified.The influence of heat flow on pavement thermal strain was clarified.The effects of temperature rise characteristics of fluids,meteorological conditions and pipe layout parameters on pavement thermal strain were investigated.The critical operating conditions of hydronic pavement was determined.The results show that the maximum thermal compressive stress on the pavement surface occurs at the pipe wall,and the maximum thermal tension stress occurs at the position between the pipes.The pavement thermal stress increased first,then decreased and then stabilized with time.The maximum thermal stress occurs at the initial heating stage.Considering the combined action of aircraft load and thermal load,a 3D transient thermal-mechanical coupling numerical model was bulit.The model was validated by the measured data in the full-scale system.The coupled stress distribution characteristic of thermal stress and load stress in pavement were clarified.Comparing the difference of mechanical response of static load,dynamic load,and impact load on hydronic pavement.Defining the most disadvantageous load type and position.The results show that the thermal stress was higher than the aircraft stress.The maximum compressive and tensile stress increased after consider the aircraft load.The most disadvantageous combination of temperature load and aircraft load is that temperature load is coupled with impact load of B737 aircraft for plate angle position.Considering the pavement mechanical properties and snow melting performance,and the weighting ratio by decision makers,A mathematical model of doubleobjective optimization was bulit and solved by the genetic algorithm.The nomogram of hydronic pavement pipe layout parameters and fluid temperature were summarized to determined the reasonable design parameters and operation strategy.Hydronic airport pavement pipe layout parameters and operating parameters of Beijing Daxing international airport was determinedBased on the test and numerical simulation,the distribution characteristics of pavement thermal stress during the operation of the fluid heating pavement system were revealed,and the variation law of maximum stress on the pavement under the coupling effect of thermal load and aircraft load was clarified.Based on the dual objectives of the performance and mechanical properties of the hydronic pavement,the optimization of the design and operation of the hydronic pavement snow melting system is proposed.The method provides theoretical basis and reference for practical engineering application of hydronic pavement.