| An automatic design method based on the optimality criteria and constraint gradients is presented for designing various two-dimensional steel structures subjected to the multicomponent input of static, dynamic, earthquake, and wind forces. The structural systems can be trusses, unbraced and braced frameworks. The seismic input can be one-dimensional and two-dimensional; one-dimension is horizontal, two-dimension is horizontal coupled with vertical. The dynamic forces may be seismic excitations at the base, applied forces at the structural nodes, and wind forces acting on the structural surfaces. The code provisions include Uniform Building Code, Chinese Seismic Design Code, and ATC-3-06.; The structural formulation is derived on the basis of the matrix displacement method and the consistent mass method with consideration of the second-order P-(DELTA) forces. The constituent members of a system are made of either built-up sections or AISC WF sections. The constraints include stresses, displacements, story drifts, natural frequencies, maximum differences between relative stiffnesses, and lower bound of cross sections. The objective function can be either minimum weight or minimum cost. A sophisticated computer program, ODSEWS-2D-II (Optimum Design of 2-Dimensional Steel Structures for Static, Earthquake, and Wind Forces - Version II), was developed for both analysis and design of structural systems.; Seventy-seven numerical examples are provided. The notable observations are: (1) the fundamental period calculated on the basis of mechanics is much higher than the upper bound of the fundamental period, 1.2T(,a), recommended in ATC-3-06, (2) the stability coefficients are much less than the upper bound, 0.1, required in the ATC-3-06 provisions, (3) ATC-3-06 equivalent lateral force method and the modal analysis method produce similar optimal stiffness distributions for a structural system, however, the equivalent lateral force method requires a heavier design, (4) soil-structure interaction within the ATC-3-06 provisions reduces the design base shear, (5) the Uniform Building Code produces the lightest seismic structural design, (6) the K-braced system provides better seismic resistance, (7) the combined vertical and horizontal ground motions associated with the P-(DELTA) forces increases the optimal design weight, (8) the dynamic story drift based on the root-mean-square superposition of modal drifts provides more conservative design than that based on the total dynamic displacements. (Abstract shortened with permission of author.)... |
