Seismic Evaluation and Retrofitting Of a RFC Structure With Flexural Frame and Shear Wall Using Steel Braces by Nonlinear Pushover Analsis

 In recent years, seismic evaluation and vulnerability of the existing buildings, that have been designed based on an earlier seismic design code or designed without seismic design criteria, has been very important. In this paper, the seismic evaluation and vulnerability of concrete buildings, using an old 5- story building with shear walls as an example has been discussed. For this building, Firstly a three- dimensional fully model has been created to simulate the actual nonlinear response of the building due to seismic forces. Then to evaluate the seismic capacity of this building, pushover nonlinear analysis using SAP 2000 as the software has been carried out, based on those given in FEMA- 356. This structure has been evaluated under uniform load and pattern of the first mode in N- S and E- W directions and there has been clarified that there is no capacity of suffering of the predicted performance. Also, based on capacity curves of the structure, it was found that the structural displacement is not enough to carry out the target displacement, and end rotations and shear forces of a lot of beams also the same rotations and axial loads of columns exceed the allowed capacity noted by FEMA- 356. For retrofitting this building, diagonal bracing elements in two directions have been used. Finally the pushover curves after addition of CBF bracing are then compared with pushover curves before addition of bracing form the expected earthquake ground motions and the assessed performances are discussed.