Using Fragility Curves for the Evaluation of Seismic Improvement of Steel Moment Frames

There are numerous methods for buildings’ seismic improvement, one of which is to increase the lateral force demand. To do so, adding different types of frames or a shear wall in structures is quite common as a new structural element. The present study selects three steel moment frame structures with four, seven, and twelve stories, all of which have similar floor plans and are designed based on the old seismic design code (UBC 1997 code), which is vulnerable in accordance with FEMA 356 code. For seismic improvement Concentrically Braced Frame (CBF), Buckling Restrained Brace (BRB), and shear wall have been used. The seismic performance level of the primary structure and improved structures were compared by means of seismic fragility curve. Earthquake intensity index is “PGA”. Finally, by selecting an appropriate damage index, fragility curves of the original structure as well as the improved structures were presented and compared with a normal log distribution, the results of which was analyzed.