Two troughs are observed around the first and the

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1.0 in all frequencies. This indicates that the horizontal F.I.M ∆ is always less than the response Us of the ground surface. Two troughs are observed around the first and the second natural frequencies of the surface stratum. Because the foundation footing or the basement possesses normally much higher rigidity than that of the surrounding soil and the growth of the response of the surface stratum is restrained, ∆ forms the troughs at around the natural frequencies. The differences in the horizontal F.I.M are small between both foundation types. The rotational F.I.M becomes larger with increase of frequency. Because the real part of the rotational D.I.F for the pile foundation is much larger than that for the raft foundation, the rotation motion of the pile foundation is more restrained and Θ of the pile foundation becomes smaller than the raft foundation. 3.6 Response Characteristic Resonance curves UT at the roof floors are shown with increase of number of floor . Magnification factor (M.F) denotes UT/2Eo , where Eo is the amplitude of the incident SH wave. M.F for the n=5 building on the raft foundation have two resonance peaks. The lower resonance frequency is 1.25 Hz 1.25Hz which corresponds to the 2.25Hz first natural frequency of the surface stratum. While the higher is 2.25Hz corresponding the natural frequency of the coupling system of a building, a foundation and ground. With increase of the number of floors n, the natural frequency of the coupling system becomes lower and approaches to the first natural frequency of the surface stratum 1.25 Hz. The natural frequency of the coupling system approaches to that of the surface stratum, two peaks converge...
View Full Document

Ask a homework question - tutors are online