Research On Temperature Stress Analysis And Crack Control Of Mass Concrete Raft Foundation

With the development of modern construction industry,mass concrete structure is widely used in engineering,however,during the construction of mass concrete structure,the hydration of cement,fly ash and other cementitious materials will produce heat,which will cause the temperature change and volume expansion of concrete.In the large volume concrete bridge,foundation and other structures,the hydration of cementitious materials generates more heat.Generally,the mass concrete structure is equipped with fewer or no stressed steel bars,which only relies on the tensile strength of the concrete itself to resist the tensile stress.At the same time,concrete,as a material with poor thermal conductivity,has poor heat dissipation capacity.Under the influence of the external environment,the heat dissipation speed of concrete surface and interior is different,which easily causes the concrete to have a larger temperature difference,thereby generating a large temperature stress,causing concrete cracking,and affecting the durability of the mass concrete.Therefore,while making full use of the advantages of mass concrete structure,the main problem of easy cracking should be prevented.Based on the raft foundation construction of Hubei province JINGKONG Building,this paper introduces the main influencing factors of temperature stress of mass concrete raft foundation.The temperature field of raft foundation is simulated by Midas FEA finite element software.According to the calculation results,a series of temperature control schemes and crack prevention measures are formulated.The temperature change of raft foundation is measured after the raft foundation is poured.Combined with the final calculation results of finite element software,the temperature field,stress field and foundation cracking of raft foundation are analyzed and studied.Finally,relying on the winter construction of the concrete beam of Qingdao International Academician Park 1#Building,the effectiveness of the selected warm shed method for thermal insulation construction is analyzed.The main research contents are as follows:(1)The main influencing factors of temperature field and temperature stress of mass concrete raft foundation are summarized.According to the main influencing factors of the concrete temperature field,several common concrete temperature control and crack prevention and control measures are summarized.The influence of cement content,mold temperature,insulation measures and construction season factors on the temperature field of mass concrete is systematically analyzed,and the analysis results are compared to select economic and effective crack prevention and control measures for this project.(2)This paper introduces the basic situation of the raft foundation of Jinkong Building,and in view of the key and difficult points in the process of concrete organization and transportation,elevator shaft formwork erection and foundation pouring,formulates the practical and effective solutions,and puts forward the measures for controlling temperature and preventing cracks combined with the key and difficult points of crack control.The hydration heat analysis model of the mass concrete raft foundation was established by using the Midas FEA finite element software,and the temperature field of the raft foundation was calculated and analyzed.According to the analysis results of the raft foundation temperature field,a set of economical,reasonable and feasible raft foundation temperature monitoring scheme is proposed.(3)By comparing the calculated results of hydration heat analysis with Midas FEA finite element software and the measured temperature data of each measuring point on site,the accuracy of finite element software calculation is verified,and the temperature field of raft foundation and the temperature change of each measuring point are analyzed.Based on the calculation results of simulation solid model,the temperature stress of the raft foundation and the raft cracking situation are further studied.(3)With reference to the warm shed method heat preservation measures adopted in the winter construction of concrete beams of Qingdao International Academician Park 1#Building,the construction technology and basis of the warm shed heat preservation are introduced.By embedding temperature measuring point,the temperature change of side beam and frame beam after construction is monitored,and the temperature change rule of concrete beam during winter construction is analyzed after adopting thermal insulation measures of warm house,so as to control the temperature change within a reasonable range to ensure that it is not subjected to freezing damage.