| Wind load is one of the controlling horizontal loads in the procedure of structural design for super-tall buildings located near coasts. The concept of wind-resistant structural optimization of super-tall buildings is to adjust the size of frame sections or the thickness shells of a structure to minimize the total cost of the structure and meanwhile to meet the design requirements. That is, the position and length of any frame member would not change in this procedure, and moreover, no damping devices would be added to the structure. Since the material cost of a general structure would cost millions of dollars, it is of great benefit to save a few percents of costs by structural optimization. Therefore, the work presented in this study would be of great theoretical and practical significance and helpful for researchers and engineers involved in structural engineering and wind engineering.At present, studies on structural optimization of super-tall buildings are mainly in the stage of theoretical research, most of the illustrative examples are the imaginary buildings.Generally, they are of simple structural system with not many frame members. Moreover, the cross-sections of theses frame members are usually rectangular. However, the structure of an actual super-tall building is extremely complex. The structural system usually contains a lot of frame members with many kinds of section types and a lot of area members, making the existing formula for structural optimization out of service. The gap between the theoretical studies and actual demands makes this technique difficult to be adopted in practical engineering. In view of the above problems, our work is listed as follows:1. Formula of the concrete-filled steel tube(CFST) member contributed to displacement is deduced. The correctness of these formula are verified through an example, a two-dimensional plane frame structure with 24 floors which is composed of CFST columns and beams with rectangular cross-sections. In addition, three kinds of cross-section types including thin-walled pipe, I-section and box tube in the explicit formulation of displacement constraints are derived in this paper. The derivative of objective functions and constraint functions with respect to design variables are deduced for the above all section types, it is akey step for structural optimization if a deterministic algorithm is adopted to get the solution.These formula can be directly employed for the structural optimization of other similar buildings.2. By a self-defined command flow, we can describe the outlines of cross sections of a super-tall building and the arrangement of testing points along these outlines. We programmed to analyze the command flow file, and together with the wind tunnel test data, the measured wind pressures are transformed into wind forces or moments acting at the center of mass of each floor. Then, the equivalent static wind loads are computed for structural optimization.Though this procedure, the structural optimization under dynamic wind loads is transformed into the structural optimization under static loads.3. A 63-story super-tall building located in the Pearl River New Town Guangzhou is taken as an example to show the whole procedure of the structural optimization and some selected results are illustrated and discussed. The finite element model of the building is of107 section types, 14989 frame members and 5052 area members. After optimization, the total cost of the structure reduced by 47.49% than before, due to the lower limit value of the thickness diameter ratio is set according to the specification, the optimized thickness to diameter ratio has reached the limit, while the steel prices is far higher than the concrete, as a result, the total cost of the structure reduced greatly. In practical engineering, we can appropriately raise the lower limit of thickness diameter ratio of concrete filled steel tube to meet a higher design requirement, the formula showed in this thesis is still applicable. |
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