Analysis And Research On Temperature Control Of Bottom Concrete Of Jiepai Pumping Station During Construction Period

With the development of national economy,pumping station,as an important hydraulic structure in water conservancy and hydropower engineering,has been widely used.Most of its large-volume concrete structure,such as pier and bottom plate,would produce large amount of heat due to cement hydration during the construction period.The internal temperature of the concrete structure is greatly increased due to factors such as poor thermal conductivity of concrete,and often leads to large internal and external temperature differences.Eventually,the concrete will have surface cracks and even penetrating cracks,which will affect the integrity and stability of the concrete structure and affect the safe operation of the project.Many researches have been carried out at home and abroad on the cracking phenomenon of concrete during the construction period,and some reasonable temperature-control and crack-proof measures have been taken to effectively avoid harmful cracks.The article focuses on the problem of temperature control and crack prevention during the concrete construction period of the pumping station.Based on the pumping station of Jiepai pivot,the finite element software is used to simulate the temperature field and stress field of the pouring project during the construction period of the concrete floor.At the same time,by calculating and comparative analysis of different temperature control measures,formulate economic and feasible construction scheme is obtained.The main research work of this article is as follows:(1)On the basis of consulting a large number of domestic and foreign literatures,the background of preventing and curing temperature cracks in concrete during construction period is introduced and the previous finite element simulation studies on temperature field and stress field of concrete,the research work on temperature control and cracking prevention measures are summarized.The relevant thermal properties of concrete are introduced,and the basic theory of temperature field,stress field of concrete and finite element calculation,calculation methods related to temperature control and crack prevention such as water pipe cooling and surface heat insulation are explained.(3)Under the guidance of the theoretical calculation principle,taking the bottom plate of the pumping station as the research object,the three-dimensional finite element grid models of the base plate and foundation of the pumping station are established,different construction pouring schemes are simulated by the finite element software MIDAS according its relevant thermodynamic parameters.(4)The temperature field and stress field distribution of the concrete floor of the simulation scheme 1 are calculated.According to the calculation results,the possibility and cause of concrete cracking are analyzed.The early concrete surface will crack,because the early stress of local concrete surface is larger than the allowable tensile strength at that time.(5)The temperature control measures of scheme 2,3,4 are calculated respectively,then different pouring temperature,cooling water pipes under different parameters and different heat preservation material of the surface heat preservation of three kinds of temperature control scheme are studied.The temperature field and stress field are compared and analyzed to judge the quality control effect of each scheme.Some reasonable temperature-control and crack-proof measures have been taken to effectively avoid harmful cracks.The early stress of concrete surface can be reduced by scheme 2,scheme 3 and scheme 4,however,the local surface tensile stress is still greater than the allowable tensile strength,which does not meet the requirements.Finally,the early stress on the concrete surface meet the requirements of anti-cracking safety performance by the comprehensive scheme.