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centrifugal pump foundation criteria
- Thread starter rpclayman
- Start date
Don't know if I've seen an "article" about that. You do mean "building", rather than designing, right?
Here's one you might apply to design of large pump foundations, but it doesn't have your grout and AB details.
Power size and, of course, weight has the most significance. Is it 5 HP or 5000? For less than 250 HP, it doesn't usually amount to much more than meeting some width, depth and mass ratios.
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Here's one you might apply to design of large pump foundations, but it doesn't have your grout and AB details.
Power size and, of course, weight has the most significance. Is it 5 HP or 5000? For less than 250 HP, it doesn't usually amount to much more than meeting some width, depth and mass ratios.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
"Being GREEN isn't easy." Kermit
Through this forum I found a very interesting webseite.
Just search for "pump foundation" on that site (through Google's advanced search) and you find some intersting information. This is one:
Just search for "pump foundation" on that site (through Google's advanced search) and you find some intersting information. This is one:
The forth bullet is BS. You need enough clearance from the anchor bolts to the vertical reinforcing bars, the horizontal ties and still provide the minimum clearence to concrete surface as required by your concrete code. Depending on anchor bolt diameter and load, you may still need more clearance from anchor bolt ato prevent 45 deg concrete cone pullout.
The rest, deal with general arrangement and although reasonably good advice, do not address any foundation design parameters, except for 2, the 5X pump mass and the one about the 30 deg criteria. I could agree with both under some circumstances, but they are not rigorous requirements of any design code I know of.
The mass ratio is mentioned to provide sufficient inertia to limit foundation vibrations to acceptable levels. For a small pump it could easily be reduced to 2X and probably would not often need to be more than 3X, except for the case of very large centrifugals and, of course, for reciprocating type or drop hammer load-type machines. What is actually needed will depend on the operating frequency of the pump when compared to the natural frequency of the machine-soil vibration spectrum, the weight of the spinning components of the engine/motor and pump and the distance of each from the CG of the entire unit, the type of machine and its sensitivity to vibration, and even if the machine vibrates work platforms, or nearby areas often inhabited by humans, which can be more stringent than limits based on mechanical devices only.
The 30 deg plane to foundation bottom edge is an attempt to guarantee sufficient overturning stability, which would normally be handled by providing a minimum weight to overturning moment ratio of 1.5 using the "short circuit" design moment loading condition. The Center of pressure of the foundation also needs to be located under the Center of Gravity of the Machine-foundation system during normal conditions. In some cases where lateral room is limited, too much mass will needlessly increase the foundation height and thus decrease the stability, so more is not better in those situations.
Depth of foundations should always be to firm soil for larger machines, but that would not be necessary for smaller pumps, which are often only placed on "thickened slabs", sometimes isolated from surrounding floor concrete, sometimes not. Also depends on soil, sand layers can be sensitive to vibration, high water tables fatal, whereas others very little. A hard rock layer at the wrong depth can increase vibrations of the machine from reflections. For a very large expensive unit, you would normally want to have at least 1 or 2 soil borings made specifically to determine the exact dynamic characteristics of the soil below, but for a 500 HP unit, that would not be economical.
For smaller pumps, there is usually no need for special grout, a stiff standard masonry grout will suffice, but for larger machines, epoxy grout is usually considered essential, as it intitally flows to contact all bearing areas quite uniformly. Its also nice for the resistance it provides to oil penetration of the concrete underneath, which can prematurely age concrete.
For larger units, J anchor bolts with sleeves, sometimes screwed extensions are preferred and depth to the hook may even control the depth of foundation, but smaller pumps might be placed using simple I bolts with no sleeves, other's I bolts with a bottom pull-out plate.
There really isn't a group of general rules that you can apply to all classes of centrifugal pumps, although you will be able to standardize design of one or the other of the general parameters amongst similar units.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
"Being GREEN isn't easy." Kermit
The rest, deal with general arrangement and although reasonably good advice, do not address any foundation design parameters, except for 2, the 5X pump mass and the one about the 30 deg criteria. I could agree with both under some circumstances, but they are not rigorous requirements of any design code I know of.
The mass ratio is mentioned to provide sufficient inertia to limit foundation vibrations to acceptable levels. For a small pump it could easily be reduced to 2X and probably would not often need to be more than 3X, except for the case of very large centrifugals and, of course, for reciprocating type or drop hammer load-type machines. What is actually needed will depend on the operating frequency of the pump when compared to the natural frequency of the machine-soil vibration spectrum, the weight of the spinning components of the engine/motor and pump and the distance of each from the CG of the entire unit, the type of machine and its sensitivity to vibration, and even if the machine vibrates work platforms, or nearby areas often inhabited by humans, which can be more stringent than limits based on mechanical devices only.
The 30 deg plane to foundation bottom edge is an attempt to guarantee sufficient overturning stability, which would normally be handled by providing a minimum weight to overturning moment ratio of 1.5 using the "short circuit" design moment loading condition. The Center of pressure of the foundation also needs to be located under the Center of Gravity of the Machine-foundation system during normal conditions. In some cases where lateral room is limited, too much mass will needlessly increase the foundation height and thus decrease the stability, so more is not better in those situations.
Depth of foundations should always be to firm soil for larger machines, but that would not be necessary for smaller pumps, which are often only placed on "thickened slabs", sometimes isolated from surrounding floor concrete, sometimes not. Also depends on soil, sand layers can be sensitive to vibration, high water tables fatal, whereas others very little. A hard rock layer at the wrong depth can increase vibrations of the machine from reflections. For a very large expensive unit, you would normally want to have at least 1 or 2 soil borings made specifically to determine the exact dynamic characteristics of the soil below, but for a 500 HP unit, that would not be economical.
For smaller pumps, there is usually no need for special grout, a stiff standard masonry grout will suffice, but for larger machines, epoxy grout is usually considered essential, as it intitally flows to contact all bearing areas quite uniformly. Its also nice for the resistance it provides to oil penetration of the concrete underneath, which can prematurely age concrete.
For larger units, J anchor bolts with sleeves, sometimes screwed extensions are preferred and depth to the hook may even control the depth of foundation, but smaller pumps might be placed using simple I bolts with no sleeves, other's I bolts with a bottom pull-out plate.
There really isn't a group of general rules that you can apply to all classes of centrifugal pumps, although you will be able to standardize design of one or the other of the general parameters amongst similar units.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
"Being GREEN isn't easy." Kermit
electricpete
Electrical
Good discussion. I was under the impression taht the 30 deg thumbrule was used to increase static stiffness of the rocking mode... which is not addressed by the mass ratio but is addressed if the mass is spread far enough horizontally.
=====================================
(2B)+(2B)' ?
=====================================
(2B)+(2B)' ?
You're squeezing it all out of me now,
That helps, but there's a possibility of rocking in both directions, parallel and perpendicular to the machine axis, as well as torsional rocking about the vertical axis through the combined CG from unbalanced rotating forces as they misalign in the horizontal plane too. The 30 deg criteria given only addresses the lateral rocking, so it leaves the others in limbo.
When doing a full dynamic analysis, that rule of thumb would be replaced by actual calcs of the translations and rotations about the CG. The 6 moments of inertias being calculated for the combined mass through the combined CG, Ix, Iy, Iz for translations along each axis and another 3, Irx, Iry, Irz for rotation about each axis too. You then consider the forces 180 deg out of phase to obtain the maximum moments about the CG for rocking. Then forces are considered in phase to find the maximum translations. Both translation and rocking are combined at various phases to arrive at the max absolute amplitudes at the edges of the foundation, at the bearings, important pipe supports, and edges of platforms, etc. to check that all are within their allowable absolute displacement at the operating frequency(ies) and at nearby harmonics.
You'd also check that the natural frequencies of each mode of vibration do not fall near the operating frequency(ies) and that the maximum amplitudes at the natural frequency of the whole system, usually 25 to 50% lower than operating frequency (foundation masses added as required to ensure that is so), are not exceeded during startups or shutdown.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
"Being GREEN isn't easy." Kermit
That helps, but there's a possibility of rocking in both directions, parallel and perpendicular to the machine axis, as well as torsional rocking about the vertical axis through the combined CG from unbalanced rotating forces as they misalign in the horizontal plane too. The 30 deg criteria given only addresses the lateral rocking, so it leaves the others in limbo.
When doing a full dynamic analysis, that rule of thumb would be replaced by actual calcs of the translations and rotations about the CG. The 6 moments of inertias being calculated for the combined mass through the combined CG, Ix, Iy, Iz for translations along each axis and another 3, Irx, Iry, Irz for rotation about each axis too. You then consider the forces 180 deg out of phase to obtain the maximum moments about the CG for rocking. Then forces are considered in phase to find the maximum translations. Both translation and rocking are combined at various phases to arrive at the max absolute amplitudes at the edges of the foundation, at the bearings, important pipe supports, and edges of platforms, etc. to check that all are within their allowable absolute displacement at the operating frequency(ies) and at nearby harmonics.
You'd also check that the natural frequencies of each mode of vibration do not fall near the operating frequency(ies) and that the maximum amplitudes at the natural frequency of the whole system, usually 25 to 50% lower than operating frequency (foundation masses added as required to ensure that is so), are not exceeded during startups or shutdown.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
"Being GREEN isn't easy." Kermit
- Thread starter
- #7
Great. Glad you found all the info useful. I'd go with 3 times the machine mass, but check stability ratios and size anchor bolts using start/stop and/or short circuit torques, if you have them, or if you don't, calculate the torque from the rated horsepower + 50%. Comply with the applicable recommendations you find above and make only a simple static type foundation design with CG over CP for the operating condition. Use a stiff normal grout placed after leveling the machine bases. I do not know of any pipeline or refining company that would require a dynamic analysis for those sizes.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
"Being GREEN isn't easy." Kermit
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
"Being GREEN isn't easy." Kermit
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