Studies On Thermal Effects Of Large-span Steel Structures Under Membrane Caused By Solar Radiation

Because of its lightness and beautiful appearance,membrane materials as envelope member are commonly used in large-span steel structure in recent years.However,Due to high solar transmittance of membrane materials,most of solar radiation can pass through the membrane and irradiate on the steel structures below the membrane.The membrane can also reduce the effect of heat convection.So the temperature of steel structures under membrane exposed to solar radiation is high and non-uniform and further induced a significant thermal stress and thermal displacement on steel structures.In some large-span steel structures,the steel members may be set in enclosed space between upper membrane roof and lower membrane ceiling.Therefore,the radiant energy can enter the enclosed space by passing through upper membrane,but do not go out the space due to the low solar transmittance of lower membrane ceiling.For the case referred above,a closed warm box is formed,which induces a more significant and complicated non-uniform temperature field around steel structure under solar radiation.The solar radiation ratio of membrane is the main factor affecting the non-uniform temperature field of its support structures.In this paper,the solar radiation coefficients of ETFE,PTFE,PVDF,TPO and PE membranes with different kind,color,thickness and printing-dot rate were obtained by experiment and calculation.Furthermore,the surface temperatures of the steel plate in experimental models under different membranes with different sealed surrounding condition were also measured in summer.As the result,the temperature of the steel plate under the transparent membrane is high.With the decrease of the membrane's solar transmittance,the temperature of the steel structure under the membrane dropped accordingly.The significant ?incubator effect? formed under the fully sealed condition.With the decrease of sealed degree,the ?incubator effect? diminishes,and the rate of the drop decreases.CFD numerical models were built to simulate the temperature tests of the steel plate under different membrane with different sealed on the basis of ANSYS FLUENT,the results of which match the actual measured data well.The CFD numerical procedure was concluded to simulate temperature field of steel structure under membrane with the coupling multi-physics among radiation,heat flow and fluid under solar radiation.FEM numerical models were built to simulate the thermal effects of the cable dome under different membrane roof caused by solar radiation.As the result,the solar radiation can induce a significant non-uniform temperature field and thermal effect around the cable dome.The temperature increment of the cable dome caused a significant prestressing loss.The solar transmittance of membrane roof is the main factor affecting the non-uniform temperature field and thermal effect of the cable dome below.