Hi Sash - If the structural element is all concrete then the structural hysteresis is significant as the load and strains are born by that material. One paper I read found by mistake that the filling they used had uncoupled from the steel wall and this produced better damping then the filling that had stayed coupled. ie the friction between the filling and outer was the significant damping factor. This is how leaf springs damp. I think damping a structure is a very complex subject. I do modal analysis on structures and just try to remove pesky low freq wobbles. This means making walls of tubes thick (thin metal pants and oil cans), use triangles where ever possible, use known damp materials (but they have to be in the load path) , use bolted joints vs welded joints, do not cantilever or have free edges. Make asymmetric structures eg if adding braces use an odd spacing because if you use an even spacing you create perfect conditions for vibration.
Re "granite" spent a lot of time in other forums on this sort of thing. Concrete shrinks and will micro crack improving damping by allowing internal movement and creating friction at interfaces (if its in the load path). So also look at plastic or metal fibres as additives. The more materials in the mix the damper it will be. How will you determine dampness via acoustic methods? Sounds interesting... Peter
The way they test mechanical damping is to make a cantilever of the material and vibrate it. They measure the frequency decrement and calculate the "zeta" of the decrement. I'm about to make a rig that uses a large steel ball bearing dropped onto the material and measure its rebound. The restitution ratio should be proportional to the internal damping of the material. Peter