Local, story, and global ductility evaluation for complex 2D steel buildings: Pushover and dynamic analysis

Abstract

A numerical investigation regarding ductility evaluation of steel buildings with moment resisting steel frames is conducted. Bending (μLϕ) and tension (μLδ) local ductilities as well as story (μS) and global ductilities are studied. Global ductility is calculated as the mean values of story ductilities (μGS) and as the ratio of the maximum inelastic to yielding top displacements (μGt). The ductility capacity is associated to drifts of about 5%. Ductility values significantly may vary with the strong motion, ductility definition, structural element, story number, type of analysis, and model. μLϕ is much larger for beams than for columns. Even though the demands of μLδ are considered an important issue they are less relevant than μLϕ. μS is much smaller than μLϕ for beams. μGS for dynamic analysis give reasonable values, but μGt does not. μLϕ, μS and μGS obtained from pushover are larger than those obtained from dynamic analysis and unlike the case of dynamic analysis, μLϕ tend to increase with the story number showing an opposite trend. Considering that: μGt for dynamic analysis results in unreasonable values, pushover analysis does not consider energy dissipation, the strong column-weak beam (SCWB) concept was followed in the model designs, and μLδ is not relevant in framed steel buildings, the ratio (RLG) of global to local ductility capacity is calculated as the ratio of μGS to μLϕ of beams, for dynamic analysis. A value of 1/3 is proposed. Thus, if bending local ductility capacity is stated as the basis for the design, the global ductility capacity can be easily estimated.