Reliability of partially encased steel-concrete composite columns under eccentric loading

The Brazilian design code for composite buildings (NBR8800) has never been subject to a reliability-based calibration of the partial factors used in design. As a consequence, the level of structural safety achieved by using these factors is, in general, unknown. This paper presents a study of the reliability of partially encased steel-concrete composite columns, subject to compression and bending. Literature statistics are used to quantify uncertainty in strength of structural materials and in loads. Reliability indexes are evaluated, via FORM, for two ratios between dead and live loads, and for some values of load eccentricity. It was found that larger load eccentricity leads to a reduction in reliability indexes. These values are larger than minimum values recommended in international design codes; hence one concludes that design of such columns using NBR8800 leads to acceptable safety levels.