Discussion. A Study of Dynamic Soil Structure Interaction.

Abstract

Generally, structures are not founded on ground level like that used in the Author's experiments. Although only qualitative results were aimed at, a proper depth of foundation would have been more realistic and might have had an appreciable effect on the dynamic soil-structure interaction.26. In 9 6 the Author states that it is often assumed that the resonant frequency for any one mode is invariant but the results in Fig. 3 show that this is not valid. The variation of the resonant frequency with the angle of excitation is a maximum of about 0.5 Hz. We feel that this may be due to the eccentrically fixed steel platform on the top of the tower and also due to measurement error. 27.Regarding the dependence of resonant frequency on amplitude (8 7), Table 1 for the rigid base tests shows that the changes in resonant frequency with amplitude are not appreciable for either mode. Only for the flexible base (125" mode) is there an appreciable change which may be attributed to the compaction of soil. 28.The assumption that structural damping can be idealized using a viscous model analogy is not far from true. Figure 5 shows that the relation between peak to peak amplitude of motion and cycle number (from 20-140 cycles) is almost linear.29. There appears to be a contradiction in 5 12 as regards the directional properties. It is evident that they do depend on the foundation.30. The difficulty of interpreting the characteristics of soil-structure interaction of the actual structure based on the model performance is indicated in 14. The scaling factor can be reliably determined only by conducting tests on other models to different scales.31. Regarding the soil-structure interaction being beneficial or not, in 16 and 17 the Author only indicates the two possibilities. What are his own conclusions?32. We feel that it would be highly beneficial to obtain a correlation between the power, frequency and damping characteristics of the soil. Perhaps this could be achieved by subjecting the structure to random vibrations (similar to natural conditions) under various foundation conditions and analysing the power spectrum.