sizing ms channel

[shirockw]

Hi all,

I am using c-channel as a baseplate structure to hold the pumps. Could anyone advise me how to size the correct MS c-channel example if i have 50 meter MS c-channel size of 100 X 50 mm, what is the maximum weight can i place at the centre before it start to bend.
Currently my supplier base on experience. However i need to be sure with actual calculation.

Please help.
Thanks.

 

[BigInch]

You're talking about one of my great sore spots! Pump manufacturers that make skids and bases that can't remain rigid enough to lift them by using the lift lugs that they themselves provide.

If you are using a C4, I hope this is a very tiny pump!

Do something like this, but change sizes according to pump&motor weights.
|
-----o---- Pump CL
|
| / W6 mounted flush at top with C8
]==== WF6x ====[ Cover both with checkered plate
C8/ \ C8 Leave enough grout holes

Use full fillet welding all around or full penetration welds.

Leave enough space under the WF for grout to flow, if epoxy grout will be used.

Locate anchor bolt holes in lower lip of C section


Back to back channels, with interior WFs
point point
lift load load lift
lug [motor]---[pump] lug
\ | | /
==[o]====V=========V=====[o]==
defl(?)ection
at center.

Now check deflection at center point between lift lugs.
Be sure that deflection will not misalign pump & motor when lifting using the lugs provided!

Find a structural engineer to check deflection and torsional flexibility of the skid with locked rotor and or short circuit loads.


Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[shirockw]

Thanks Big Inch.

Sorry as i might have not indicate clearly

O pump O pump W(panel)
O O W
O O W
O O W
______________________________
_0 (LUG)_________________0 (LUG)

This are vertical multistage pumps weighing around 20 to 50 kg varies depending on model installed for parallel pumping. Hence both pump shal be install on a common baseplate with a common header link bot pump suction and discharge. The baseplate is a construction of 2 nos of C-channel parrallel for the pumps to be installed. hence the weight of each pump is distribute accordingly.
But i do not know how to determine the correct c-channel which will not deflect/bend during lifting or if isolators install at the near four corner.



___D______________________________D______
|_________________________________________|
| | | | | |
| |___________________________| | | |
| |___________________________| | | |
| | | | | |
| | pump2 pump1 | | starter |
| |___________________________| | | |
| |___________________________| | | |
| | | | | |
|_|___________________________|_|_______|_|
|_________________________________________|
D D

D = lifting lugs and mounting hole

Hence i need an example of the calculation to determine the C-channel correct. I have all the C-channel information but too bad i do not now how to use it.
Can you help big inch?? or anybody outthere??

 

[desertfox]

Hi shirockw

I have done bases for pump/motor sets, we calculate how much the channel would bend between lifting lugs on one side of the frame as though it were a simply supported beam,
considering half the total weight of the pump/motor set to be acting on it as a point load.
To determine where the point load acts on the channel we first calculate the centre of gravity of the pump/motor set
on the mass distribution method.
While this method is not the best or by any means the most accurate it seems to work bearing in mind also that we use a huge margin of safety.
If your really struggling then seek some proffesional advice.

regards desertfox

 

[BigInch]

Shiro,

The trouble with channels is that they tend to twist in the "C" direction when loaded. If they are prohibited from twisting, by being connected together with a nice cross beam and securely welded, ]=====[ ,you can neglect torsion for smaller loads.

The easy way (conservative, but not too accurate) to do it would be as follows. If this was a large pump set, it would be too overdesigned, but since they are relatively small pumps, should be OK.

Put, P = 1/2 of all pump, motor and equipment weights, the weight of one channel and 1/2 of any connecting beams and covering plate, at the center of the length of one channel.

P = weights (lbs)

If the skid must be lifted by a crane or hoist, (or otherwise mistreated somehow, sliding off a truck etc) multiply P by 1.5

L = channel length (in)

The maximum Moment, M = P * L/2
Bending Stress, Sb = M/S
S = Section Modulus of Channel in X-X plane (in^2)
Sb should normally be less <= 20,000 psi, or so

Deflection at the center span D in inches = P * L^3 /8/E/I
E = Young's modulus = 29,000,000 psi for steel
I = Channel's Moment of Inertia about the X-X plane (in^3)

Deflection should be less than any misalignment tolerance you have for the onboard equipment and interconnections and should (IMO) be <= span_length/180.

pardon my US units and please try to find some local structural engineer to check your final results.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com