ABSTRACT
The earthquake motion at any point can be resolved into three orthogonal components, two horizontal and one vertical. Penzien and Watabe[1] have shown that two horizontal components, which are approximately radial and tangential with respect to the epicenter, are uncorrelated. Any other orientation of horizontal axes leads to partially correlated horizontal components. This would normally be the case because the buildings or the structures are, in general, unlikely to be placed along the radial and tangential directions. The vertical component of the earthquake motion always has some correlation with the horizontal components. Because of the wave motion, a building is also subjected to three rotational components[2–7]. These rotational components are mutually correlated, and have a strong correlation with the translational components. The structures supported on multiple supports, such as bridges can be considered to be subjected to multiple ‘components.’ These components would have variable degrees of correlation.
