Seismic Optimum Design of Steel Frames

In the field of civil engineering, structural optimization for static loads is a well-known concept. However, ensuring an optimum design under seismic loadings faces many challenges, such as time-dependent behavior of constraints, changes the design space over time, and the cost of gradients calculations. To prevent such difficulties, response spectrum analysis has been implemented for the seismic analysis of structures instead of using the time history method. In order to guarantee the global optimum design, the obtained results from gradient-based method (SQP) were compared with those of the discrete optimization technique (GA). In the classic approach, the forward finite difference method has been used for gradient calculation and sensitivity analysis. Static analysis is done using finite element method. Consistent mass matrix has been used to avoid simplifying assumptions like shear frame. By considering the geometric stiffness of the structure, secondary effects have been taken into account for linear-elastic static and seismic analysis. After calculation of the elastic response spectrum of the desired earthquake, response spectrum analysis is performed. The capability of these methods is demonstrated by solving numerical examples of low, intermediate and high-rise braced and unbraced steel frames, while satisfying the allowable stress design provisions of the national building code (NBC). The results are compared with each other and the most economical structural system with respect to the height has been determined.

کلیدواژه ها:

Design ، seismic optimization ، steel frames