Help: Moving 5800 lb Load Across Grating Rated 1000 lb/Sq Mtr?

[racookpe1978]

Need your help (and critism!)

I am deployed overseas (in Europe) in a power plant through the New Year. Our temporary pump and motor unit is on a mounting bed 1.0 mtr x 2.4 mtr (40 inch x 96 inch) weighing 5800 lbs. (A second filter and valve skid is heavier at 9600 lbs, but I can take those pieces apart to lower the net "moving weight" to less than 5000 lbs.)

So the 5800 lb pump is the heaviest load going across the grating. At 4 rollers under each corner of the pump skid, I have a 1450 lb "point" load on a roller of around 4 inch long = way over the grating limit. (The plant (our customer) wants to put 1/8 plate over the grating as a rolling surface, but the point loads seem way too high under each wheel.)

The grating is rated at 1000 lb/sq meter. Fine. But this rgating is mounted on a strutural network of W14 beams 1.5 meter (60 inch) on center. (W30 girders support the W14's below the grating.)

If I put a heavier plate [1/2 inch (12 mm) or 3/4 inch (19 mm)] over the grating so each end of the 1/2 plate is over a W14 beam , then the point load would appear to transfer from the roller through the 1/2 plate through the grating down to the W14.

Will that plate be enough of a cantilever (in the spaces between the the W14's) to avoid collapsing the grating?

 

[cntw1953]

Are the W14's orientated along the direction of traffic? If so, what is the wheel spacing (in direction transverse to the beams)?

You would first to check if the beams can support the wheel loads plus the weight of added plate.
Then, you would need to find method to convert the point wheel load to pressure below plate to check against the grating capacity.

If you can post the plan and elevation view may help to gather thoughts.

 

[racookpe1978]

Yes, the W14's are in direction of travel.

Yes, I am confident the network of W14 beams and W30 girders can support this (relatively small) new rolling load - this because of how the whole turbine building and mezzanine floor is built to hold the pipe and equipment loads. It is the grating that concerns me.

Edge-to-edge, the pump skid is 40 inches (1 mtr) wide. The CL of the rollers are under the skid, a little under 30 inches apart.

End-to-end, the pump skid is 96 inches long (2.4 mtr), the rollers are about 80 inches apart in the "long way" of the skid. The "long way" is also the direction of travel.

 

[cntw1953]

Without the original spec for the grating (it will tell the max concentrate load it supports), I will try the following:

1. Find out the wheel size - 4" x ?
2. Assume 45 degree distribution from bottom of wheel to top of grate.
3. Distribution area = (4"+t)*(?+t)
4. Uniform load = (max wheel load/dist. Area) + weight of plate per unit area.
5. Check moment capacity of the grating = wL/8; w=rated load (1000 lb/M^2), L=beam spacing
6. Check moment under the wheel load - place wheels symmetrically w/r to center of beam.

If results from steps 4 & 6 are both smaller than the capacities, you are in business. Otherwise, increase plate thickness, and repeat the process.

Finally, you should restrict the speed of the vehicle to minimize impact.

 

[cntw1953]

Note:

In steps 5 & 6, I would assume the beam width = 4" (whhel length)+t+grating thickness (again, a 45 deg distribution).

After you have obtained the distributed wheel load, you can use FEM to fasten your analysis. Good luck, and have fun.

 

[MikeHalloran]

I'd remove the grating from the equation entirely, either by physically removing it, or laying sleepers on top of it exactly above the W14s. Then the problem simplifies to moving the skid along the sleepers.

Mike Halloran
Pembroke Pines, FL, USA

 

[racookpe1978]

1 - Correction A) I spent about an hour crawling under grating and pulling dim's.

Smallest two beams underneath is a measured 11" deep WF x 4.5 wide, span of this lightest beam is 18 feet long. I am restricted to a small travel area through this one spot with the two small beams, so I'll focus there.

These two lightest beams are 51 inches apart (1.3 meter) from CL to CL. (The other heavier beams are either also 1.3 meters or 1.5 meters apart.)

All other beams are deeper than these two 11" WF beams, they are an irregular mix of W14, W20, and W30's.

2 - Correction B) Wheels are actually 5.5" in diameter, but only 3" long. My report of 4" long would be the wheel's axle length = obviously irrelevant when you are considering forces at the floor level.

There is 31" between wheel centerlines.

3) Physically removing the grating isn't possible, but putting WF sleepers above it (over the steel plates) so the wheels are rolling inside the sleeper (WF would have the web horizontal) is very attractive. (Gets me up above a small interference at the floor level in one place as well)

4) Speed will be less than walking. Total distance to travel is an "L" approximately 50 ft (short leg) by 150 feet (long leg - the direction of my concern.)

No crane access overhead, or I would not be rolling it.

No accessible beams overhead either, or we could (maybe) use a traveling hook by making successive lifts from a long line of beam clamps overhead.

5) The load can't go on a path perfectly symmetrical over the beams underneath because of interferences to both sides. See rough sketch to folow in a few minutes.

-----

Case 1 (Try to center the load between two WF's underneath.)

Looking in direction of travel, the CL of the left wheel can be no closer than 12" right of the CL of the left beam.

There will be 31" to the next wheel CL.

The CL of the right wheel will then be 8 inches left of the right 11" deep WF.

Not perfectly centered (12" from one WF and 8" from the other), but I can't move any further over to the left.

---

Case 2. Put the right wheel directly over the right 11" WF.

Essentially, this puts all of the right side weight directly down through the plate, through the grating, to the WF.

This puts the left wheel 20" from the left WF.

Not too bad - We only have half the weight of the skid to worry about, and that weight will be separated in direction of movement by the length of the pump skid, or about 70 inch wheel-to-wheel.

 

[paddingtongreen]

Going parallel to the beams means going against the grain on the grating. That means that only one bearing bar at a time will be carrying half the load unless a thick plate is used to distribute to more bearing bars. I would jack the skid up and support it on two timbers, one in front and one at the back, long enough to sit on rollers directly over the beams. Strips of plate would be needed , you have to check the thickness of plate to carry the roller from bearing bar to bearing bar.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[racookpe1978]

Grating isn't the typical "grid" or "ribs and rods" or crossed plated I usually see in the US.

I can see no directional pattern of the grating plates that helps (or hurts) its strength.

 

[MikeHalloran]

Forget the wheels.
Turn it crossways and slide it on the sleepers.


Mike Halloran
Pembroke Pines, FL, USA

 

[cntw1953]

Thick timber is a good idea, it eliminates the inevitable bang due to metal on metal.

 

[racookpe1978]

See Elevation (rough!) Sketch below for an idea using WF sleepers, but leaving the wheels on.

 

[racookpe1978]

Bosses, project management is reviewing costs, availability of people and material, and schedules => It looks like they will take the pump and motor off of the skid and move each part by itself.

---...---...---...

Cook's First Rule of the Critical Path.

If you have plenty of people but little time and no material, throw people and money at the problem.

---...---...---...

Cook's Second Rule of the Critical Path.

If you have few people and lots of material, throw material at the problem until the budget is spent.

---...---...---...

Cook's Third Rule of the Critical Path.

Schedule, Quality, or Budget. Pick any two of the three.

---...---...---...

Cook's Fourth Rule of the Critical

If you have lots of people and plenty of time and lots of material, let me spend your project's budget.

 

[cntw1953]

I always think Cook's 4th rule is exclusively reserved for Nuclear Industry

Good decision. The workers can carry pieces walk over the bridge faster & safer than driving.

 

[BAretired]

Why don't you build a dolly capable of carrying 5800# with wheels running directly over the existing beams?

BA