Theoretical Interpretation of Impulse Response Tests of Embedded Concrete Structures

For a concrete beam resting on a bed of sand, an analytical solution technique is derived by which the mobility can be identified. To achieve realistic predictions, significant damping in the bed needs to be introduced. The modest damping of the concrete has little effect on the mobility for small frequencies whereas it has a significant effect for higher frequencies. An imperfection in the bed in terms of a void increases the mobility dramatically for low frequencies whereas the mobility for higher frequencies is almost unchanged. An imperfection in the beam in terms of honeycombing of the concrete, on the other hand, manifests itself by increasing the mobility for high frequencies while leaving the mobility for small frequencies less influenced. These latter conclusions are in good agreement with field experience for concrete slabs resting on soil.