Research On Hygrothermal Transfer Of Prefabricated Building Joints

Prefabricated building has the advantages of simple construction,short construction period,low environmental impact and reducing manpower,which meets the requirements of sustainable development in China.In recent years,the proportion of prefabricated buildings is increasing with the promotion of policies.Compared with traditional buildings,prefabricated buildings connected by lots of prefabricated components in the construction process,which are easy to form gaps or weak links in the thermal performance of the building envelope.Therefore,the difference of connection joints is an important difference between prefabricated building and normal building thermal performance.In addition,the connection joints are also the key parts which are easy to form thermal defects and building quality problems.In addition to the influence of thermal bridge and humidity on the performance of building envelope can not be ignored.At present,the traditional thermal calculation method can not correctly reflect the thermal characteristics of prefabricated buildings.The study focus on heat and moisture transfer of typical joints of prefabricated buildings,which basic on the construction characteristics of prefabricated buildings,combined with the influence mechanism of heat and moisture transfer of building envelope,puts forward the corresponding influencing factors and verify with computer simulation software,to provide basis for energy-saving design and standards of prefabricated buildings.First of all,through the prefabricated building theory and the whole process of component production,design and construction,the study focuses on the research of the connection joints structure of prefabricated building,Extracted and simplified the Two typical prefabricated building connection joints which including prefabricated concrete building and steel structure building connection joints,combs out the design influencing factors of prefabricated building connection joints,and summarizes the problems easily occurred in the design and construction process of prefabricated building.Secondly,based on the heat and moisture transfer theory and heat transfer mechanism,the heat and moisture transfer process of the typical joints of prefabricated building is analyzed.Considering the heat and moisture transfer process under the joint action of heat,moisture and air,and the change of material physical parameters,based on the energy conservation law,Fick’s law and Darcy’s law,the capillary pressure is used to analyze the heat and moisture transfer process A one-dimensional theoretical model of heat transfer and moisture transfer is established.On this basis,the computer simulation software COMSOL Multiphysics is used as the finite element numerical simulation tool.The PDE module is selected to establish the heat and moisture coupling transfer model.The calculation results of en15206 international standard are compared and analyzed to verify the accuracy of the theoretical model.Taking the typical joints of steel structure as an example,the influence of climate on the heat and moisture transfer of joints is studied.Finally,according to the results of finite element numerical simulation,the optimal design of prefabricated concrete building connection and steel structure building connection joint is carried out,and the simulation verification and comparative analysis are carried out.Taking the typical steel structure node as an example,the internal temperature and humidity distribution under the meteorological conditions of four different climate zones are studied,The results show that the location of moisture accumulation in different areas may be different,which needs specific analysis.In addition,the larger temperature difference also promotes the moisture transfer.Finally,the insulation material,insulation structure and insulation layer thickness are taken as the control variables.The results show that the insulation effect of sandwich insulation is lower than that of external insulation when there are dense materials in the structure to block the moisture transfer.Therefore,the lack of thermal insulation materials in local structure should be avoided in the structural design,which may lead to serious heat flow concentration and humidity It is accumulated.The increasing thickness of thermal insulation material can not bring the same effect of heat preservation and moisture insulation.The above research conclusions can effectively reduce the heat and moisture transfer of prefabricated building joints,so as to improve the thermal defects of prefabricated building joints,and provide theoretical basis for the formulation of energy-saving standards for prefabricated systems.