Study On The Control On Crack In The Structure Of Concrete In Construction Projects Of Changchun

Cracking-control in concrete structures is one of the important research topics that impair structures'serviceability. On the basis Of theoretical study of cracking-control in structure caused by drying shrinkage and temperature difference of atmosphere,the author presented a new fonnula calculating temperature stress under the boundary conditions with level stress and apply the cracking-control theory to analyze project examples , e.g.,zhongyuanBuilding in changchun.Using the new formulas,it can get the result that crack analysis of concrete slab around core cylinder.This paper consists of three parts:The first part:This paper derives the formulas of temperature stress,the interval of crack and width of crack,under the boundary conditions with level Stress . It is the improvement of the current theory of concrete crackoing-controlThe second part:The author analyses the 2.2 m thick mass concrete of the raft shape foundation with the theory of cracking-control.In order to control the creation of cracks and the temperature difference between inside and outside of mass concret, Temperature and wetting protect method of"wafer-stored the surface of the concrte"is introduced.In order to control shrinkage crack inside mass concrete,the author has calculated the temperature stress satisfied with concrete cracking-control.The author has also calculated the maximum length pouring the mass concret one,to find out whetherit is necessary to place construction seam. Other constuction technical methods are used to protect the construction quality of mass concret.The third part:The reason of cracks generating through the56m long concrete wall is analyzed.Through calculating the average interval of cracks and the width of cracks after 2 days dismantling formwork,it proves that the cracks due to temperature-fall suddenly,the main reason is dismantling formwork too early and level pouring distance too long.Then,the author gives the maximum length pouring cocrete during3-7days under two conditions:the lowest and normal temperature.The author also presented the relation between the interval of back-pounng seam and the time of dismantling formwork.This provides the guidance suggestion for construction of similar concrete long wall.