The Research On The Numerical Simulation Of The Top-Down Construction Method And The Performance Analysis Of Steel Column

With the rapid growth of development of high-rising buildings and underground space, the deep excavation engineering is on the increase. The supporting forms of it are not able to come into full effort due to the limitation of land laws, nearby high-rise buildings and roads. The top-down construction method can save the cost of props and containment so as to heavily reduce the disadvantages to the nearby buildings as well as the structures of props. Not only the inner force and deformation in the process of normal construction method but also the successive walls underground and the differential settlement of nearby steel uprights as well as the differential settlement between uprights, which is peculiar in the the process of the top-down construction method, must be taken into consideration.This thesis takes a project from a city as example. The software of Finite Element method MIDAS/GTS is used to conduct 3D numerical simulation analysis to The top-down construction method so as to understand the regular pattern of the structure itself and the influence on the surface during the process. This is going to be a use for reference for the same project and can be used to theoretically deduce the stability of vertical steel column,Major researches and achievements are as following:(1) The result of the simulation shows that soil movement occurs in the pit with the gradual excavation of the foundation pit; meanwhile settlement occurs on the soil outside the pit as well, but the maximum settlement produced by the top-down construction metdod is only half of that of normal construction method.(2) In the process of the top-down construction,the differential settlement between steel column and wall is steady at about 6mm, which is only one third of the normal construction method, due to the suport action of the floorslab, steel column and erect column piles, the differential settlement between steel columns is gredually reduced as the distance increased between the continuous walls, and the differential settlement of steel column is 0 when reaching the centre of foundation point.(3) Through the deduction of formula of the steel column length coefficient, the bearing capacity of the steel column is increased as the stiffness of the soil around increased. If we take this advantage into consideration, the transverse size can be reduced so that material is saved.(4) The settlement of steel column has influence on the deflection of beam and slab, causing the changes in bending moment, which produces secondary stress to beam and slab. This is not good for the project.This is unfavorable to the project.(5) Forcing a angle of inclination to the steel column is reduced as the angle increased, which is a disadvantage to the project and must be avoided.