SYSTEM RELIABILITY ASSESSMENT OF 3D STEEL FRAMES DESIGNED PER AISC LRFD SPECIFICATIONS

This paper presents the system reliability analysis of a three-dimensional steel frame designed per AISC LRFD with respect to the collapse limit state under the dead and live loads. The system reliability is evaluated using the first-order reliability method (FORM)-based adaptive response surface approach. The uncertainties in the material properties, geometric properties of frame members, initial geometric imperfection of the structure, dead load and live load as well as the spatial variability of the live load are accounted for in the reliability analysis. The analysis results suggest that the system reliability of the example frame is similar to that of the planar steel frames designed per AISC LRFD and evaluated in a previous study. It is observed that the spatial variability of the live load leads to a decreased system reliability. Results of the sensitivity analysis indicate that the failure probability of the example frame increases by almost one order of magnitude if the coefficient of variation of the steel yield strength increases from 0.06 to 0.1. Furthermore, the system reliability decreases drastically if the upper bound of the magnitude of initial geometric imperfection is greater than 0.4% of the overall height of the example frame.