The Construction Load And Structural Atability Of Temporary Support For Extra-thick Foundation Slab

At present,China has become the country with the most Super high-rise building in the world,The extra-thick foundation slab is the key and difficult part in the construction of super high-rise buildings.The support system of extra-thick foundation slab is an important support system in the construction process,it has great influence on construction safety.At present,there is little research on the support of extra-thick foundation slab in the academic world,there is no national or industrial standard to guide its engineering application.Therefore,this paper will conduct research on it based on the construction site survey results,and the main work is as follows:Determine the construction load of extra-thick foundation slab:Obtain the original data through the construction site photo record and statistics,Processing original data with a grid division method.The probability model of construction load of extra-thick foundation slab is obtained by using probability statistics method.From the construction live load probability model,calculate the value of the construction load of the extra-thick foundation slab under different guaranteed rates.The value of construction load survey is less than that specified in the general temporary support design specification.The survey and study of the initial defects of extra-thick foundation support:In this paper,the initial bending values of the circular steel tube and the channel steel are measured by high-precision instruments in two construction sites.After processing and analyzing the original data,the initial bending shape and the probability distribution law of the initial bending amplitude of the temporary support bar is obtained.It is found that the initial bending shape of the bar is mainly c-type,but there are also s-type and doubles-type.Through site survey and statistics,it shows that 16% of the joints of the superthick floor temporary support of chengdu tiantou international wealth center project have welding defects of different degrees.Study on the influence of initial defects on the extra-thick foundation support:Through the refined establishment of the finite element model,the influences of initial bending of different shapes,initial bending of different amplitudes and joint welding defects on the stability of foundation slab support were studied.It was found that the failure modes of bars with initial bending of other shapes were close to C type,the initial bending shapes of type C is the most unfavorable initial bending shapes.The initial bending amplitude of the model vertical bar is 1‰ and 3‰,and the corresponding stable bearing capacity decreases by 9.3% and 21.5% respectively.According to the actual distribution law of the initial bending amplitude,the initial bending of different amplitude values was applied to each pole of the model randomly in proportion.The stable bearing capacity of the supporting system was between 1‰ of the initial bending amplitude and 3‰ of the model bearing capacity.After 10% of the welded joints are randomly selected in the model,the overall stability of the supporting system is reduced by about 15%.Parameter analysis of important factors influencing the stability of extra-thick foundation support:Through the parameter analysis of the key factors controlling the overall stability of the support system,It is found that the relationship between the vertical bar spacing,the horizontal bar spacing,the weak axial inertia moment of the vertical bar and the bearing capacity of the support system can be well described by power function.Comprehensive analysis: for the support with a height of more than 2 meters,it is suggested to improve the overall bearing capacity of the structure by reducing the distance between transverse bars and increasing the arrangement of inclined supports;For the support less than 2 meters,it is suggested to give priority to improving the overall bearing capacity of the structure by reducing the horizontal bar spacing.If the engineering demand cannot be met,then the weak shaft inertia moment of the vertical bar can be increased by reducing the vertical bar spacing.