Foundation Settlement Tolerance for Rotating Machines

[LobstaEata]

Our firm has been designing block foundations for combustion gas turbine and steam turbines (either pile supported or on-grade) for a settlement tolerance of 1/4". However most soils reports I see arrive at allowable bearing pressure recommendations based on 1/2" of overall settlement. I'm wondering though whether the machine tolerance being used at our firm is overly stringent, as I'm not able to locate the basis to support it in our company materials. Does anyone in this forum have experience in the settlement tolerances required for CTG and STG machines?

Steve

 

[racookpe1978]

???

Commercial powerplant gas turbine bearings are set (tuned) to the 1/10's of a thousandth of an inch and-to-end: Generator bearing, generator bearing, GT inlet, GT middle, GT outlet. Are you sure you're accepting 1/4 movement of the pedestals the GT's are sitting on?

Or are these so small that the whole thing sits on one foundation?

 

[LobstaEata]

Sorry that I wasn't more clear about the scope of projects. We design foundations for small CHP power generation equipment. 10MW to 50MW machines mostly. And yes, the foundations designed are primarily single unit mass substructures supporting an entire machine.