ABSTRACT
Field investigation a n d observat ion of s t rong ear thquakes , l abora tory tests on structures and theoretical studies of s tructural v ibra t ion are three fundamenta l activities in ea r thquake engineering. Unders tand ing of the actual behavior of s tructures in a s t rong ea r thquake is the ul t imate purpose of these activities; bu t such behavior is so complex tha t the unders tanding is usually only quali tat ive, no t quant i ta t ive, because there are so m a n y uncer ta in factors involved in bo th the g round mot ion and the s t ructure . I t is also limited to wha t informat ion existing structures can provide.
