System reliability-based design of 2D steel frames by advanced analysis

Abstract

The design of steel frames by geometric and material nonlinear analysis also referred to as -inelastic‖ or -advanced‖ analysis, is permitted by most specifications such as AISC360-10 and AS4100. In these specifications, the strength of a structural frame can be determined by system analysis in lieu of checking member resistances to the specific provisions of the Specification, provided a comparable or higher level of structural reliability. In designing by advanced analysis, the system resistance factor is applied to the frame strength determined by analysis. Provided that the design strength exceeds the required strength, the design is deemed adequate, requiring no further check of individual member resistance. The system-based design of steel structures by advanced analysis leads to a more efficient structural design process and achieves a more uniform level of structural reliability. The main impediment to adopting the procedure in practical applications is the apparent difficulty in assigning an appropriate resistance factor to the structural system. This thesis illustrates the novel framework of the system design-by-analysis approach and how to determine suitable system resistance factors accounting for inherent uncertainties in the ultimate strength of a frame. All key parameters influencing the frame strength are modelled as random and Monte-Carlo type simulations are conducted. New approaches for modelling initial geometric imperfections and residual stresses are introduced. The simulation results for a series of 2D low-to-mid-rise steel frames, which represent typical steel building inventory as well as frames from the literature, are presented obtained according to the proposed methodology. Braced and moment resisting frames are analysed under various load combinations and the system resistance factors are derived for different reliability levels.