Postprint version. Published in Journal of Structural Engineering, Volume 123, Issue 11, November 1, 1997, pages 1435-1443.
The definitive version is available at http://dx.doi.org/10.1061/(ASCE)0733-9445(1997)123:11(1435).
Earthquake analysis of bridges requires that the period and damping ratio be determined for each significant mode of vibration. Data on these vibration properties, identified from motions of bridges recorded during actual earthquake events, provide the most direct means of verifying and improving the current guidelines. Thus, the aim of this investigation was to measure the vibration properties of a two-span concrete bridge from its motions recorded during actual earthquake events. These data were then used to investigate how abutment participation affected the vibration properties of bridges with integral abutments. It is shown that the vibration period elongated and the damping ratio increased by a factor of over two as the intensity of ground shaking increased. These changes primarily were caused by increased abutment participation with increased intensity of shaking. Finally, the damping data were used to develop empirical formulas for estimating upper and lower bound values of damping in the first transverse vibration mode of bridges with integral abutments.
Civil and Environmental Engineering