Pump pad that straddles new and existing foundations

[mferg318]

I have a new mat foundation that supports a tank and pump. For various reasons, the pump sits partially on our new foundation and partially on an existing foundation (grey). My concern is differential settlement that might induce some stresses on the pump piping. I've already explored other options (rotate pump 90 degrees, shift everything to right, etc.) and while some are possible, they have sizeable ramifications so I want to see if I can come up with a simple solution. My first idea is to have expansion joint material under the portion of the pump pad that sits on the existing foundation. In my mind, this would compress as the new foundation settles and should limit the differential. Thoughts? Other ideas?

 

[jhnblgr]

Why don’t you have flexible expansion joints in the piping, it’s going to move regardless and have stress otherwise

 

[SWComposites]

seems simple to rotate pump 90 degrees and solve the issue.

 

[TRAK.Structural]

Maybe dowel the new slab to the existing so that they move together? This may depend on how much long term settlement you expect in the new slab from the large tank (green). If its small than maybe this works, if its large than this might cause more damage.

 

[HTURKAK]

My first idea is to have expansion joint material under the portion of the pump pad that sits on the existing foundation

I guess this is a small centrifugal pump in the range of 5- 10 HP. Your approach seems reasonable. Make the pump pad monolithic with the new slab and provide PU/ ESP board expansion material under the portion of the pump pad that sits on the existing foundation.

 

[LittleInch]

Just cut out/ demolish a small section of existing foundation and build a single slab for your pump.

Any thing else is just going to be an issue in years to come or makes the construction of the small slab three time more difficult.

Short term pain for long term gain. IMHO.

 

[mferg318]

Thanks for the input everyone, a lot of good stuff to consider.

To address a couple items: first, like I said in the original post, rotating the pump is not an option because it will require changes to the tank that is already being fabricated. Regarding expansion joints in the piping, I don't have a great answer for that. I do frequently see these but it could be some sort of process related restriction due to the chemical in this piping.

I did also consider doweling into the existing slab, as well as demo'ing out out a notch for the new pad. I think there are severable viable options, I'm just trying to choose that one that has the least cost impact.

I see one person in support of my initial idea of using compressible material under the portion of the pad that sits on the existing foundation...anyone else think this could work? I think that is the most simple and cheapest option.

 

[jhnblgr]

True solution is to have the tank outlet relocated at an angle so the pump suction remains in line and then the whole pump fits. Is there any concern about vibration?

 

[SWComposites]

rotating the pump is not an option because it will require changes to the tank

huh? just change the piping.
and frankly trying to save a bit of $ on the pad seems foolish re potential issues in the future.

 

[mferg318]

huh? just change the piping.
and frankly trying to save a bit of $ on the pad seems foolish re potential issues in the future.

I asked this too. It would require a 90 in the pipe near the suction which is not ideal. I can force whatever outcome I need to if there's no simpler solution that will always work, but I'm trying to be a team player.

 

[mferg318]

True solution is to have the tank outlet relocated at an angle so the pump suction remains in line and then the whole pump fits. Is there any concern about vibration?

Tank is already in fabrication because it's a long lead item...not ideal but that's how it goes sometimes. No real vibration concerns.

 

[mferg318]

huh? just change the piping.
and frankly trying to save a bit of $ on the pad seems foolish re potential issues in the future.

And it's not about saving money on the pad itself, it's about minimizing changes to a tank that is already in fabrication and still having the process piping work as it should. Like I said, I can push for a more difficult solution if need me, I'm just not convinced yet that there's not a simpler solution.

 

[jhnblgr]

Then just rotate the tank as a whole unit or just ask the fabricator about it.

 

[AskTooMuch]

Break the existing pad then and add isolation joint around is not an option?

I work inside a plant and i think you are "overthinking" this differential settlement. That should be fine as is, pipe should have enough flexibility for whatever differential settlement you are worried about.

 

[LittleInch]

Thanks for the input everyone, a lot of good stuff to consider.

To address a couple items: first, like I said in the original post, rotating the pump is not an option because it will require changes to the tank that is already being fabricated. Regarding expansion joints in the piping, I don't have a great answer for that. I do frequently see these but it could be some sort of process related restriction due to the chemical in this piping.

I did also consider doweling into the existing slab, as well as demo'ing out out a notch for the new pad. I think there are severable viable options, I'm just trying to choose that one that has the least cost impact.

I see one person in support of my initial idea of using compressible material under the portion of the pad that sits on the existing foundation...anyone else think this could work? I think that is the most simple and cheapest option.

A pump needs a firm, solid foundation. Introducing flexibility is not a good long term plan.

Demolish or dowel into the existing to create a single solid mass of concrete is my choice.

 

[HTURKAK]

I see one person in support of my initial idea of using compressible material under the portion of the pad that sits on the existing foundation...anyone else think this could work? I think that is the most simple and cheapest option.

I supported your approach with two conditions ; the pump is small centrifugal pump with 5 - 10 HP power and the pump pad is monolithic with the new foundation mat. This option will also minimize the stresses at connection piping.

In case of large pumps ( say more than 50 HP ) the common practice is to provide single mass foundation for each pump .The mass of the concrete foundation should be a minimum of 3-4 times the mass of the pump and have sufficient rigidity.

 

[mferg318]

I supported your approach with two conditions ; the pump is small centrifugal pump with 5 - 10 HP power and the pump pad is monolithic with the new foundation mat. This option will also minimize the stresses at connection piping.

In case of large pumps ( say more than 50 HP ) the common practice is to provide single mass foundation for each pump .The mass of the concrete foundation should be a minimum of 3-4 times the mass of the pump and have sufficient rigidity.

This is a small 20 hp pump.

 

[canwesteng]

That new brown foundation is a monster. Suspect the actual potential for settlement is minimal. If you have clean granular below, the elastic settlement will all occur once you pour the behemoth, so I wouldn't bat an eye over bridging the two with the pump foundation, maybe dowelling the slabs together but no demo. Presumably this is an existing plant as well, so the soil here already saw some load.

 

[HTURKAK]

This is a small 20 hp pump.

And probably the total wt of the pump set is less than 300 Lbs.