Deep Pit Elastic-plastic Finite Element Numerical Analysis And Support Optimal Design Method

With the increasing of urban constructions, the optimization design of supporting system of deep foundation pits becomes critically important. The key issue is that due considerations should be taken on both economy and safety for such kind of temporal structures. More attentions have been paid in the past to develop the significant optimization method of foundation design. In this thesis, studies on numerical analyses of deep foundation pits and optimization design method of supporting system are performed.Based on evaluation of current analyses and design methods on common practice, an optimization technique which combines the finite element method of beam and column system and Lagrangian multiplier procedure is developed for the design of single bracing. The optimization of design is divided into two steps. First, on the basis of comprehensive consideration of stress, deformation and stability aspects, optimization procedure is performed for defining bracing position and depth of embedment. Secondly, according to the parameters obtained from the former step, reinforcement of row-pile can be optimized by use of multiplier method in order to reduce total fabrication cost. As an example, numerical computations and analyses to foundation pits of the Shenhui Building is made and the computed results are compared with original design scheme. It has been shown that FEM-multiplier method is an efficient optimization method and will be potentially applicable to engineering practice. A so-called MCDP elasto-plasticity model, which based on Mohr-Coulomb yield criterion and Drucker-Prager plastic potential function, is employed to predict the deformation of deep foundation pits. Numerical results of two-dimensional elasto-plastic finite element analyses indicate that the analyses based on optimization can well agree with the theoretical analysis and the feasibility of this numerical model is illustrated.