SEISMIC RETROFITTING OF A 7-STORY R.C. BUILDING

Add of concentric steel bracings is a simple and adequate method for retrofitting of existing moment frame R.C. buildings. Because any other retrofitting methods ( including add of shear walls or FRP ) seems to be very expensive. But concentric steel bracings have high stiffness, low ductility and sometimes cause architectural problems in buildings. Hence, the arrangement of these bracings must be studied exactly and then the optimum retrofitting method is selected. In this paper, vulnerability studies and retrofitting method of a 7-story R.C. building with medium moment frame system, in Semnan city is investigated. This building, because of low height of its beams and according to 3rd edition of standard No. 2800, is a flat slab system and must be retrofitted. In the other hand, with adding steel bracings at different levels of existing R.C. building and with regard to structural performance levels, the optimum retrofitting method must be selected. Nonlinear static analyses (push-over) are carried out according to FEMA-356 and ATC-40, and criteria of rehabilitation standard studied. Details of retrofitted elements are presented too.