Stiffness-based Approach for Preliminary Design of Framed Tube Structures

A parametric formulation for preliminary design of tubedsystem tall buildings is presented in which some optimality criteria and practical constraints are considered. Here, a minimum compliance optimization formulation, developed by other researchers, is applied to a framedtube structure. The tube behavior is modeled as a cantilevered box beam. Independent variable in this problem is thickness of the box, and a formulation for its optimal value is proposed. The challenge in this research was treatment of the lower bound constraint on thickness in an analytical manner. To deal with this constraint, a critical height parameter is introduced, and the design domain is divided into two zones of constant thickness and constant curvature. This definition allows for computation of optimal thickness distribution along the structure through an analytic dimensionless equation. Most of the previously published papers in the field of tall structures are suitable for abstract analyses but not for design. In addition, most of them are computerbased. Considering these limitations, the current research presents a handcalculation method for preliminary design, suitable for sensitivity analyses and parametric studies. As the presented formulations are dimensionless, they are applicable in any dimensional system. Different static loading patterns are considered; including the concentrated, uniform, triangular and quadratic forms. A numerical example is presented to demonstrate the ease of the proposed method in application, and the analysis results are presented by charts to validate the efficiency of it.