عنوان مقاله [English]
Fragility curves are important in the seismic damage assessment of buildings. In this study, with the aim of damage evaluation at various levels of earthquake intensity, fragility curves have been developed for some sets of steel buildings; having Concentrically Braced Frames (CBFs) as their load bearing system. The buildings sets include a set of 2- by 4-bay and another set of 4- by 6-bay plans, having 3, 5, or 7 stories. The buildings have been assumed to be regular in both plan and elevation to avoid torsion effects. For developing the fragility curve, Nonlinear Time History Analyses have been used, by applying 42 different recorded accelerograms to each building, with various Peak Ground Acceleration (PGA) values and, also, different frequency contents. Two different damage indices, the values of story drifts and the amount of axial plastic deformation of bracing elements, have been used. The numerical results show that when PGA$>$0.5g, the variation of fragility curves is less than the variation corresponding to PGA$<$0.5g.The results also show that tthe second index is more reliable for developing the fragility curves of steel buildings with CBFs.