Structures must resist lateral force as earthquake without collapse and significant damage to the structural members. On the seismic design, the Korean Building Code requires that the structures should obtain satisfactory design load and seismic reinforcement detail so that adequate ductile response and limiting condition for maximum displacement are assured. Especially, the code specifies that the seismic design should be applied for three or higher story buildings to resist earthquake of magnitude 7.0 on the Richter scale. The types of buildings in Korea are largely classified into 54.3% of residential buildings, 24.9% of commercial buildings, 11.1% of industrial buildings, 5.8% of educational buildings and 3.9% miscellaneous buildings. Among them, only 52.3% of buildings have been constructed since 1990 that seismic philosophy was included in the Korean Building Code. If earthquake occurs, the rest of structures which had been constructed before 1990 will be collapsed with large distortion at the base of building that is strongly affected by the seismic force. Therefore, there are so many researches being carried out to improve seismic performance of existing structures instead of the uneconomic method of demolishing existing structures and building new structures with new seismic performance design.