Risk-Based Seismic Design Optimization of Steel Building Systems with Passive Damping Devices

Nonlinear time history analysis software and an optimization algorithm for automating design of steel frame buildings with and without supplemental passive damping systems using the risk- or performance-based seismic design philosophy are developed in this dissertation. The software package developed is suitable for conducting dynamic analysis of 2D steel framed structures modeled as shear buildings with linear/nonlinear viscous and viscoelastic dampers. Both single degree of freedom (SDOF) and multiple degree of freedom (multistory or MDOF) shear-building systems are considered to validate the nonlinear analysis engine developed. The response of both un-damped and damped structures using the 1940 EI Centro (Imperial Valley) ground motion record and sinusoidal ground motion input are used in the validation. Comparison of response simulations is made with the dissertationSEES software system and analytical models based upon established dynamic analysis theory. A risk-based design optimization approach is described and formulation of unconstrained multiple objective design optimization problem statements suitable for this design philosophy are formulated. Solution to these optimization problems using a genetic algorithm are discussed and a prototypical three story, four bay shear-building structure is used to demonstrate applicability of the proposed risk-based design optimization approach for design of moderately sized steel frames with and without supplemental damping components. All programs are developed in MATLAB environment and run on Windows XP operating system. A personal computer cluster with four computational nodes is set up to reduce the computing time and a description of implementation of the automated design algorithm in a cluster computing environment is provided. The prototype building structure is used to demonstrate the impact that the number of design variables has on the resulting designs and to demonstrate the impact that use of supplemental viscous and viscoelastic damping devices have on minimizing initial construction cost and minimizing expected annual loss due to seismic hazard