MONTE CARLO SIMULATION FOR UNCERTAINTY IN STEEL MOMENT FRAME DESIGN

Seismic design of steel moment-resisting frame (MRF) involves a large amount of uncertainties of parameters with initial imperfection, such as plate thickness, beam-column connection configuration, material strength, sizes of members, etc. Monte Carlo simulation is implemented to evaluate the influence of design parameters variation. To investigate the scenarios in seismic loading, nonlinear time-history analysis is performed by using finite element method to build up three-dimensional models of steel MRF connection, for the sake of load-deformation relationship. The obtained correlations are then employed to modify the stiffness of steel MRF members designed traditionally. The steel MRF is one of a few structural systems that building codes permit to be adopted in buildings exceeding 160ft in height. Also, the steel MRF may provide at least 25 percent of lateral strength to the building in seismic area that can replace other structural members designed for lateral resistance, such as diagonal braces or shear walls which sometimes confuses architects when the building goes through a retrofit. Large seismic events occur at average intervals of hundreds of years. It would be expensive and impractical to design a structure to remain elastic as they resist such rare events only. Thus, the steel MRF is generally expected to experience inelastic behavior when it is subjected to seismic events, which allows some structural damage to occur. With a high level of uncertainty regarding earthquake demands on a building and design parameters, a probability analysis is needed for engineering designers to provide a ductile design for life safety. In this study, the inelastic deformation is investigated in several beam-column joint options available. The concern is to check if the structural behavior satisfies the requirement by design philosophy that the sum of column flexural strengths must exceed the sum of the beam flexural strengths at each joint. In that case, a more uniform lateral drift can be expected if the column remains elastic outside the inelastic panel zone. Effect on structural stiffness induced by the layout geometry is considered which optimizes the design of structural members in turn. Final results are expressed in terms of the probability of failure with respect to bearing capacity and lateral drifts, which conclude that the steel MRF is an economical framing system for tall buildings in high-seismic area rather than some alternative systems.