ABSTRACT
This method is efficient when the existing structure has no purposely designed lateral load resisting system (the structure is designed for gravity loads only) or it is under-designed. It can be applied with or without local strengthening of elements and connections that have deficiencies (group ii and group iii). For example, a strengthening scheme may involve addition of buckling restrained
1 INTRODUCTION
In many seismic regions, there is considerable concern that older reinforced concrete frame structures (RC), built before 1960’s, may be vulnerable to earthquakes. Seismic experience (e.g., Vrancea 1977, Romania; Kocaeli 1999, Turkey, Greece, 1999 or more recent Sichuan, China in 2008 and New Zealand in 2011) shown the insufficient capacity of such structure to resist the seismic demands. For example, Vrancea 1977 earthquake, with a magnitude of 7.2, was responsible for the total collapse of more than 23 reinforced concrete buildings with more than 7 stories in the largest city, Bucharest. All these buildings were designed before the issuing of the first national seismic design code, in 1963. More recently, the 2008 Sichuan earthquake caused the collapse of many RC frame buildings. Main causes of damage were the lack of confinement for the columns and beams at the joints but also soft story at the ground (Miyamoto, 2009).
