For the purpose of damage assessment of structures during strong ground excitation, it is desirable to identify severity of damage based on the input-output measurement. It is believed that structural identification application from input/output data can lead to an understanding of the deterioration mechanism. A main disadvantage of structural identification has been the lack of experimental information on an actual structure. Both ambient vibration test and forced vibration test can provide information for structural system identification only from low level of excitation. Besides that strong motion instrumentation on structure to collect earthquake response can also provide valuable information for the safety assessment of the structure.