Product Development And Thermal Perform-ance Research Of Sandwich Thermal Insulation Composite Floor Slabs

Under the research upsurge of building assembly,few people pay attention to the thermal insulation performance requirements of individual floor slabs,and the research work on the thermal performance of floor slabs is very scarce.In the full-text mandatory codes issued by the state and the local codes issued by Zhejiang Province,it is expressly stipulated that the thermal transmittance of floor slabs in hot summer and cold winter areas should not be greater than 1.8 W/(m~2·K).However,the thermal transmittance of traditional reinforced concrete floor slabs is generally above 2.5 W/(m~2·K),so it is inevitable to explore ways to improve the thermal performance of floor slabs.In this paper,a new type of sandwich thermal insulation composite floor slabs is proposed,in which the thermal insulation layer is placed between the precast bottom plate and the cast-in-place top plate of reinforced concrete composite floor slabs.Although the stiffness and bearing capacity of the slabs can be improved with the increase of the cross-section height,the thermal bridges between the top plate and the bottom plate will be formed by the truss bars,which will affect the thermal insulation performance of the slabs to some extent.Finite element models of steady-state heat transfer analysis considering the thermal bridge effect of truss bars are established for this sandwich thermal insulation composite floor slabs.Based on 648 sample models,the effects of 7 parameters,such as the spacing between the truss bars(S),the thickness(δ_s)and the thermal conductivity(λ_s)of the sandwich layer,on the thermal transmittance of the sandwich thermal insulation composite floor slabs are investigated.The results show that,when sandwich layer is made of the conventional flow plastic materials for construction,its thickness should exceed 20 mm,and the thermal conductivity of the material should be less than 0.15 W/(m·K)to meet the heat transfer requirements of the specification.The thermal bridge effect of the sandwich thermal insulation composite floor slabs is obvious,with an impact on the thermal transmittance of the structure up to13.5%.With the improvement of insulation effect of sandwich layer,the proportion of thermal resistance variation caused by the change of truss spacing to the overall thermal resistance gradually increases,but its proportion to the total influence of truss bars decreases.A new formula for calculating the thermal transmittance with high accuracy is obtained through the regression analysis of the sample model data,which can quickly evaluate the thermal insulation performance of this new type of composite floor slabs.Finally,the design formula of sandwich structure is obtained by deforming and simplifying the calculation formula of thermal transmittance,which can guide the design of sandwich structure of sandwich thermal insulation composite floor slabs in terms of thermal performance.