System Reliability-Based Design of Three-Dimensional Steel Structures by Advanced Analysis

Abstract

The system-based design of steel structure using advanced analysis leads to a more efficient structural design process and achieves a more uniform level of structural system reliability over the conventional member based design method because of the capability in capturing the limit state strength of a real structure and accounting system effects explicitly such as the load redistribution subsequent to first yielding. Current specifications such as AISC360-10 and AS4100 permitted the use of advanced analysis obviating the check of member resistances, thus provide a comparable or higher structural reliability. The main impediment to adopting this method in practical applications is the apparent difficulty in assigning an appropriate resistance factor to structural system especially in three-dimensional frames. This thesis illustrates the novel framework of the Direct Design Method (DDM) for designing structures by analysis without recourse to a structural design standard and proposed a methodology for development of suitable system resistance factors for accounting inherent uncertainties in ultimate strength of three-dimensional steel frames. New approaches for modelling initial geometric imperfections are introduced. The reliability assessment and system resistance factors for a series of three-dimensional low-to-mid-rise steel frames, which represent the current steel building inventory in Australia are obtained taking into account inherent uncertainty in material and geometry by Monte Carlo simulation. Braced and unbraced (sway) frames with regular and irregular configurations as well as various cross-section types and materials are analysed under various load combinations including gravity and gravity plus wind, and the system resistance factors are derived for different reliability levels to incorporate the effect of uncertainties on frame performance. Member cross-sections are selected to provide different system failure modes such as beam flexural-torsional buckling, beam/column yielding and spatial sway instability with torsion involve. Recommendations are made for the appropriate target reliabilities and associated system resistance factors for use in designing three-dimensional steel frames with both cold-formed Hollow Steel Section (HSS) and hot-rolled I-section at system level by advanced analysis.