Dynamic Response of Block Foundations

This paper presents the results of comparison of the computed and observed response of two block foundations made of concrete. The test blocks measuring 3.0m x 1.5m x 0.7m and 1.5m x 0.75m x 0.70m were cast on level ground. The blocks were excited into vertical vibrations using a speed controlled mechanical oscillator. The amplitudes of vibration at different frequencies of excitation were measured in each case using acceleration transducers mounted on appropriate faces of the block. Dynamic shear modulus at this site was also determined b¥ conducting in-situ tests namely the wave propagation test, the cyclic plate load test, and the standard penetration tests. From this data the dynamic shear modulus versus shear strain plot was obtained. The natural frequencies and the vibration amplitudes of the test blocks were then calculated by (i) the linear spring method, (ii) the elastic half space method. A comparison was then made of the observed and computed natural frequencies and the vibration amplitudes of the blocks. The results of this comparison showed that for the cases of vertical vibrations, the natural frequencies in this case could be reasonably predicted by either of the methods used. The calculated and observed amplitudes, however, showed a wide variation. The details of tests performed and the analysis are discussed in this paper