MODAL ANALYSIS OF SOFT-SOIL SITES INCLUDING RADIATION DAMPING

✍ Scribed by ZHAO, J. X.

• Book ID: 101219795
• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 440 KB
• Volume: 26
• Category: Article
• ISSN: 0098-8847
• DOI: 10.1002/(sici)1096-9845(199701)26:1<93::aid-eqe625>3.0.co;2-a

✦ Synopsis

For the one-dimensional analysis of soft-soil layers on an elastic half-space, a general form of analytical solution is developed for converting radiation damping due to energy leaking back to the half-space into equivalent modal damping, allowing the modal analysis technique to be extended to a site where radiation damping has to be accounted for. Closed-form solutions for equivalent modal damping ratios and effective modal participation factors are developed for a single layer with a shear wave velocity distribution varying from constant to linearly increasing with depth. Compact and recursive forms of solutions for equivalent modal damping ratios are developed for a system with an arbitrary number of homogeneous layers on an elastic half-space. Comparisons with numerical solutions show that the modal solutions are accurate. The nominal frequency of a site, i.e. the inverse of four times the total shear wave travel time through the layers, is an important parameter for estimating the high mode frequencies. A parameter study shows that for the same impedance ratio of the bottom layer to the elastic half-space, a system of soil layers with an increasing soil rigidity with depth has, in general, larger peak modal amplifications at the ground surface than does a single homogeneous layer on an elastic half-space, while a system with a decreasing soil rigidity with depth has smaller modal peak amplifications.