| BHT dam is located in the area of strong solar radiation in China..The measured temperature data at the construction site show that: Under the influence of strong solar radiation heat,In summer,the temperature in the valley is high in daytime and low in night,and the temperature difference between day and night is over 10℃.This large temperature difference between day and night caused by strong solar radiant heat tends to make the internal temperature of the concrete higher than the surface temperature,resulting in a certain tensile stress on the concrete surface.Due to the low tensile strength of the early age concrete,surface cracks are easily generated.According to statistics,80% of the cracks in the project occur at the age of 3～15d.Therefore,accurately grasp the surface temperature distribution of concrete blocks under the action of solar radiant heat,and study the influence of solar radiant heat on the temperature of early age concrete.And to analyze the temperature control effect of different surface protection measures,and propose a more targeted high temperature season concrete block surface temperature control measures,it is of great significance.This paper mainly carries out the following research work:(1)The surface temperature monitoring test of BHT dam concrete block is carried out.Distributed optical fibers are used to monitor the temperature of concrete at 10 cm,20 cm,40 cm and 60 cm away from the surface of concrete.The effects of water cooling,solar radiation heat and air temperature on the temperature of concrete within 60 cm away from the top surface are analyzed.(2)In order to improve the calculation accuracy of solar radiant heat,temperature field and stress field,this paper firstly uses BP neural network to invert the concrete thermal parameters of BHT dam,then,based on the thermal parameters and measured temperature data,the actual value of solar radiation heat absorbed by surface concrete is calculated.On this basis,the actual value of solar radiant heat is converted into temperature increment,applied to the boundary condition of finite element model,and the finite element calculation model of concrete block considering solar radiant heat is established.The reliability of the simulation calculation model is verified by combining the concrete temperature data.(3)Based on the finite element calculation model of the BHT dam concrete block considering solar radiant heat.The temperature field and stress field of concrete when the top surface of the concrete block covers the polyethylene sheet with different thicknesses is calculate.The temperature field and stress field of the concrete block when water curing at different water temperatures is calculate The influence of the above two temperature control measures on the surface temperature effect of concrete block and its temperature control effect is analyze.According to the calculation results of tensile strength and stress field allowed on the top surface of concrete block,the suggestions for temperature control and crack prevention measures for the top surface of concrete block in high temperature season are proposed.The results show that:(1)The temperature of concrete block surface is mainly affected by solar radiant heat and temperature,and the influence depth is about 40 cm away from the top surface of the concrete block.Among them,the temperature of the concrete within 20 cm from the top surface is most affected.The monitoring data show that,in the 2d age period,the temperature is above 30°C under the influence of solar radiant heat,and the maximum temperature difference of concrete at 10 cm and 60 cm from the top surface is 8.4°C.(2)On the top surface,covering 4～5cm polyethylene sheet and water curing at 18～24°C during the day can effectively reduce the effect of solar radiant heat on the surface temperature of concrete.When the top surface of concrete covers 4 or 5cm polyethylene sheet,the maximum tensile stress of the top surface is reduced from 0.81 MPa to 0.41 MPa and 0.35 MPa respectively.During the day,the concrete is cured with water of 18～24°C.When the top surface is covered with 4cm polyethylene sheet at night,the maximum tensile stress of the top surface is controlled within 0.15 MPa.The maximum tensile stress does not exceed the allowable tensile strength of the corresponding age.Considering the economic practicability and the water temperature range of the river,it is suggested that 4cm polyethylene sheet and 22～24℃ water temperature should be the preferred temperature control measures. |
PDF Full Text Request