Study On Early Temperature Stress Of Basement Exterior Wall And Crack Control

This paper mainly studies the early temperature stress and crack control of basement exterior wall,and the results show that the environmental temperature,the heat of cement hydration,the shrinkage and creep of concrete and other factors have significant influence on the early temperature stress of concrete.Firstly,the heat conduction equation of concrete is derived and the early temperature stress of concrete is analyzed theoretically.Then the temperature effect of the wall under different conditions was calculated and analyzed by the finite element analysis software ABAQUS,and the main factors affecting the wall cracking were further studied.The following conclusions are drawn through simulation:1.The temperature difference is an important factor leading to the cracking of the basement outer wall.The temperature stress of the wall increases with the increase of temperature difference,so the temperature difference must be controlled.2.The change of wall length has little influence on its temperature stress,so the design of super-long seamless concrete wall will become possible,among which the control of temperature difference is very important in the design of super-long wall.3.When the wall thickness is less than 250 mm,the wall thickness has an inverse relationship with the temperature stress,that is,the temperature stress increases with the decrease of the wall thickness.When the thickness of the wall is greater than 250 mm,the maximum temperature stress of the wall and the temperature stress in the middle of the wall tend to be stable with the increase of the wall thickness.It can be seen from the height analysis that the thinner the wall,the greater the stress range of its upper end.4.The higher the height of the wall,the greater the temperature stress value of the wall,but the increasing range gradually decreases.5.When the outer wall of the basement is poured together with the roof,the constraint on the wall will obviously increase,making the temperature stress amplitude of the wall larger as a whole.Therefore,in the construction process,the wall part should be poured first and the roof part should be poured later.6.Reduce the longitudinal bar spacing,that is,increase the ratio of longitudinal bar reinforcement,has a certain inhibitory effect on the emergence of wall cracks,the steel bar spacing and the temperature stress in the concrete and the temperature stress in the steel skeleton is roughly linear increasing relationship.7.Under the condition that the reinforcement ratio is approximately the same,the use of steel bars with different diameters results in an obvious change in the temperature stress of the wall.In other words,the use of steel bars with smaller diameters leads to a smaller temperature stress of concrete than that of thicker steel bars.On-site observation of wall temperature,the purpose is due to the shrinkage of concrete is obtained by actual measured data and the surrounding environment temperature changes within the concrete wall changes of the temperature field,and by ABAQUS finite element analysis of wall internal stress,it is concluded that the concrete wall on both sides of middle temperature higher than the temperature of concrete,and roughly symmetrical on both sides of the concrete temperature changes;The concrete temperature isotherm is in the shape of "eight" at both ends of the concrete,which is basically the same as the position where cracks appear on the concrete wall.The steel bar and concrete bear the tensile stress caused by the action of temperature,the steel bar bears the main tensile stress,and the concrete is in the state of low stress.Finally,the cracks of concrete structure are prevented from three aspects: mix ratio,design and construction.And according to the damage degree of concrete structure cracks put forward a reasonable repair method.