The concrete test floor in an impact sound laboratory, usually 140-150mm, is usually resting on a rubber or something else resilient and sealing, sort of a thick "gasket". The plate thus has to behave somewhat similar to a floating floor and with the borders free so the plate is can vibrate free-free.
In addition there must be a couple of "mounting resonances", like e.g. tilting to the two sides, maybe towards the corners as well?
Do anyone know of literature or measurements of resonances and shapes of concrete impact test floors? Does anyone have experience they are willing to share on the behavior of the test floor? Floors in the field usually may be simply supported or clamped, giving a different set of vibration shapes the floating floor on to "see".
Thanks in advance!
Thanks Michael Uebel! These are nice articles for what happens in real buildings. I think the test room is either a "building mock up" or field tests from real buildings. I think I have all of these, but can't find the last one. Eventually they will be found, I hope.
Yes, the literature seems scant on the concrete plate and room modes in the impact lab. The methodology used by these researchers would have revealed what I am looking for in the lab test floor. The problem should be interesting enough for somebody to look into, so maybe it has been at some time, maybe even a long time ago?
I am not aware on any paper on this, and I would assume there are slight differences in the design of different laboratories. It also depends on how the mounting is made concerning making it air tight and coupling to the surrounding floor - in the DTU lab, some of the users (consultants) are mounting the concrete floor using cement mortar, and this will surly influence the BC's.
I would suggest you to do a FEM study or experimental study of your specific situation.
Yes, FEA or scale model the problem if that is possible and do a modal analysis. I do have a modal analysis for a 2mm glass plate on elastic mounting already but it was not intentionally made for a test using a continuous elastic boundary, nor to study this particular problem. The plate is e.g. not thick enough, although the mode shapes are likely to be exactly similar, only with different mode frequencies. A FEA is a little longer to accomplish for me. I have the tools, but are out of shape on it. The problem is pretty simple to model, though. I do have spreadsheet calculations of it on Winkler foundations, and the "zero mode" is simply the floating floor resonance. The next ones are likely to be machine on "vibration insulated foundation" with six degrees of freedon, where the two in plane ones are not excited. We are left with four then, three in addition to the fundamental floating floor mode.
At least two researchers claim that the floor plate acts simply supported. However, it is easy to calculate the mode frequencies and shapes analytically. You typically get 3 below 100 Hz or so, what we see is 7-8 modes up to 90 Hz. Impossible with simply supported plate modes and normal concrete.