Loma Prieta response of an eccentrically braced tall building

Acceleration response records obtained during the October 17, 1989 Loma Prieta earthquake [Ms = 7.1] from the 47-story, eccentrically braced Embarcadero Building (No. 4) [EMB], located in San Francisco, California, are studied. The predominant response modes of the building and the associated dynamic characteristics are determined by spectral analyses and system identification techniques. The first modal frequencies are at approximately 0.19 Hz (NS) and 0.16 Hz (EW). Discontinuity of stiffness and mass at the 40th floor causes excessive drift ratios for the floors above.