NEHRP Clearinghouse
 Title
 Modal Analysis for Structures with Foundation Interaction.
 File

PB294933.pdf
 Author(s)
 Roesset, J. M.; Whitman, R. V.; Dobry, R.
 Source

National Science Foundation, Washington, DC. Applied Science and Research Applications.,
December 1972,
34 p.
 Identifying Number(s)
 ['STRUCTURES PUB329', 'P727']
 Abstract
 Three different analyses were performed on the following cases: rigid structures, a fivestory building, and a fifteenstory building. Analyses included one in the frequency domain using the actual damping matrices CV and CH, providing what is referred to as 'exact' solution. In the second analysis normal modes were assumed, neglecting in effect the offdiagonal terms of matrices QTCVQ and QTCHQ. However, viscous and hysteretic damping terms were kept separate, and the solution was again obtained in the frequency domain. This solution is referred to as modal superposition in the frequency domain. Finally, in the third analysis a modal solution was obtained considering all the modal damping to be viscous. This is referred to as modal superposition in the time domain. The third type of analysis is the one which would be used in practice. Comparison of results for the first and second analyses shows the error introduced by assuming normal modes. Comparison of the second and third analyses shows the additional error introduced by replacing hysteretic modal damping by viscous modal damping. Comparison of the first and third solutions indicates the overall error resulting from use of weighted modal damping.
 Keywords
 Mechanical hysteresis; Mathematical models; Dynamic response; Buildings; Earthquake engineering; Damping capacity; Soil structure interactions; Foundations; Earthquakes; Dynamic structural analysis