AN INVESTIGATION ON THE COLUMN OVER-DESIGN FACTORS FOR STEEL FRAMED STRUCTURES

Abstract

In the earthquake resistance design of frame structures, it is a general requirement to give a suitable target value of the column over-design factor (COF) for which the occurrence probability of unpreferable failure modes can be limited to within a specific tolerance. In the present paper, the likely failure modes of weak-beam-strong-column designed structures under uncertain loads and with uncertain member strengths are investigated and the target value of COF is discussed in probabilistic terms under three failure levels, i.e., Level 1 -- strictly beam-hinging pattern, Level 2 -- beam-hinging pattern and Level 3 -- total collapse pattern. It was found that : (1) For levels 1 and 2,the larger the number of bays and stories, the larger the target value of the COF. For level 3,the target value of the COF is independent of the number of bays. (2) The higher the reliability level is set when the structure is designed, the smaller the target value of the COF is required to limit the probability ratio to within a given tolerance level.