Optimization Research On Superstructure Of Tall Buildings And Piled Raft Foundation

Many tall buildings'construction makes the issue of structure optimization one of the most popular problems in the field of structural research. Although the structure optimization theory has a long history and a lot of optimization practice, it is mostly used to small structures. Relatively speaking, for large structure optimization algorithms and programs are still relatively scarce. It was mostly limited by the previous computer calculation capacity, large amount of structural constraints, complex loading combinations, and rich section forms of the components. It is also necessary to establish a comprehensive and practical algorithm involves a very wide scope. Meanwhile, the piled raft foundation is used more and more for its great adaptability advantage However, the traditional"full uniform","equal supporting capacity"pile arrangement make pile length growing, foundation raft thickness increasing and costs spiraling. Based on the background mentioned above, this paper is worked on optimization on tall building superstructure and piled raft foundation.First this paper adopts substructure method to condense the stiffness and load of the whole structure on the foundation and couples with soil and piles for establishing the basic equation of interaction according to the static equilibrium conditions, vertical displacement coordination principles and nodal corresponding relations. The theory of interaction is taken as the theoretic base of the optimization on superstructure and piled raft foundation.According to the rich section form and complex constraints, static determinant and constraint monotonic assumptions are used to divide structural constraints into local and integral constraints and a two-level optimization algorithm is presented, that is to do the second-level optimization based on the optimal result of first-level.This paper established a tall building structure optimization model. In order to minimizing optimization variables but also cooperating to the constraints, this paper make optimization variables all boil down to H and B. According respectively reinforced concrete components and the characteristics of steel structure components, the objective function, local and integral conditions of a large number of projects were handled practically. Because reinforced concrete beams and columns and steel component have different constraints characteristics, their local constraints are dealed with different optimization algorithm. A two-dimensional search technique based on the golden section method is used to concrete components; to the steel structures, an imitative full-stress method with genetic algorithms is used and also proposed for discrete variables and converged means. To integral constraints, it is used Lagrange rule method combined with virtual work criteria. This paper established the virtual work equation with wall element model, and expanded the rule to the wind and seismic loads; finally, this paper realized them in the program and used three different structural forms examples to test the optimization model and optimization algorithm.The objective function for the piled raft foundation optimization is defined as a multi-object with minimizing cost and differential settlements, which could adjust the emphasis of the design with weight coefficient. The variables are the number and coordinates of the piles. Since the norm of the gradient vector of the deflected surface of the raft becomes smaller as the differential settlement of a raft becomes smaller in a global sense, the squared L2 function norm of the gradient vector of the deflected surface of the raft is selected as the objective function which represent the degree of differential settlement of a raft indirectly. Since the objective function is a nonlinear function with respect to the coordinates of piles, the recursive quadratic programming, revised Newton method and a line search technique based on the golden section method are employed to solve the optimization problem.Four examples with different weight coefficients and loading conditions are adopted to test the optimization program. Based on the result of optimization, this paper discussed the two different pile arrangement form of"outwardly weak and inwardly powerful"and"outwardly powerful and inwardly weak".Based on the optimization theory and models of superstructure and piled raft foundation, the paper establishes an integral optimization program, which could consider the interaction between superstructure and foundation during doing optimization. Then a twelve stories concrete frame is used to test the program and the differences of internal force of superstructure are investigated using conventional method and interaction analysis method.