Seismic retrofiting of an existing steel structure

The primary aim of earthquake resistant design is to prevent building collapse during the seismic event, but severe earthquakes have a low probability of occurrence during the life time of the structure, therefore in contrast to traditional structural design in earthquake design, structures are permitted to work in post-elastic domain under seismic load. It would require a large lateral stiffness of the structure and an expensive resisting system to design the building to have an elastic response. Because of these arguments in case of regular, conventional buildings it is more reasonable to design the structures counting on their ductility capacity, but buildings with a significant importance make an exception and they must be designed to not exceed the elastic domain. Buildings which enter into this category are hospitals, buildings with historical importance, fire stations, structure of larger water tanks, any building which has an importance in emergency situation etc. This paper intends to exam and evaluate the performance of buckling restrained braces implemented as a seismic rehabilitation technique. BRBs are considered to be efficient in increasing the resistance of a structure against horizontal loads and providing an additional energy dissipation capacity. An attempt is made to evaluate and analyze this quantity of added stiffness and energy dissipation by means of comparison of structural response and fragility curves. Because adding braces to a structure modifies the structural system and behavior of the structure 3 different structure were analyzed the original structure, structure with conventional braces and structure with BRBs. In this way a fair evaluation can be accomplished, the retrofitting structure by means of BRBs can be compared to the original structure and to the structure with conventional braces which has the same structural scheme as BRBF structure.