Pump plinths

[Camell]

We are currently installing new pumps in an old treatment plant where a completely new set up pumps (new duty and purpose) is required. The pumps are generally recycling and transfer pumps ( Qmax = 600m3/hr, so relativly small installation)The pumps are to be supplied with their own steel frame, but to ensure the correct levels pump plinths are required

As regards the pump plinths, what design principles should I be loking at in terms of the design? I was wondering whether reinforced plinths are required or whether simply a mass concrete base will suffice. Perhaps the mass concrete should be doweled to the existing RC floor.

I know vibrations, thrusts, etc need to be taken into account, but I am looking for guidelines from which to work.

 

[jet1749]

In my experience of relatively small chemical pumps, casting concrete pliths to existing floors has proved effective. As long as you bear in mind what you are actually trying to achieve (stable mounting surface with adequate mass to transmit load and vibration into the ground) Thrust issues should not be a concern as pump installations should be thrust free as far as practicable. My technique has been to survey the existing floor to ensure it has adequate load bearing characteristics. Chip the floor to expose the actual aggregate of the concrete, then seal the surface in order to promote bonding of the new concrete plinth. Drill into the surface and fix as much rebar as you calculate will be sufficient, bond the rebar into the holes using epoxy type cement. When calculating the dimensions of the plinth I ensure that it is sufficiently wide, so that imaginary lines starting at the pump centre line with an included angle of 60* would pass through the plinth bottom and not through its sides (height to width ratio of 1:1.2 pump centre line to plinth width)Ensure that adequate distance between pump baseframe fixings and plinth edge to ensure that the plinth will not crack. Shutter up the proposed plinth, pour your concrete mix in one go and tamp to remove air voids and consolidate your plinth. Do not "float off" the surface, leave the aggregate exposed. Wait about a week until the concrete has sufficiently hardend before mounting your equipment, and then complete your installation as usual as regards levelling and grouting.
regards
John

 

[Camell]

Thanks, John

At this stage my concern is mainly the issue of rebar. From your descrpition, you are definitly in favour of a doweled connection to the RC floor. I am concerned, though, about placing rebar in the plinth itself as this may clash with the anchor bolts for the pump/motor bases. I have seen this type of installation before and special drilling equipment is then required to "cut" through the rebar.

Also, all I can see that rebar in the plinths will do is limit a bit of shrinkage (not an issue because largest plinth is 1.7m x 0.9m) and provide dimensional stability should ancor bolts be drilled into the concrete.

 

[jet1749]

My use of rebar has been to provide a mechanical bond between the floor and the plinth. If you are concerned about fouling the anchor bolts when drilling into the plinth to fix the base frame you could ensure the immediate area around the fixings is free of rebar, perhaps leave grouting pockets for the fixings you have in mind, or alternatively just drill the plinth with a diamond core drill
best of luck
John