Help with Roark for existing plate

[ColinPearson]

Hi all:
Looking for a bit of advice on how to apply some of the Roark tables (or possibly a case from Moody that is not included in Roark, but I do not have access to Moody). I have an additional question regarding LTB that is included in the same design situation. I have uploaded a pdf of the structural steel that makes up the floor under the valve - where I have to roll it across).

I need to find a cart or use some Hilman rollers to remove a valve from a process unit. For discussion, let's call this valve 10kips (rounded up by a couple hundred pounds). This valve needs to be moved across what I would call a continuous sheet of 1/4" diamond plate to where it can be lowered for repair. The diamond plate is sitting on beams at 2'-8" centers and each sheet is welded to the next. I do not see which Roark table directly applies...
- The continuous plate tables do not include very many support conditions
- I don't believe I can reasonably consider all edges fixed.
- Even though the plates are welded together (and welded to each supporting beam), I do not want to guess anything about the quality of the welds, so I believe I could reasonably consider the long edges (along the supporting beams) simply supported, but that leaves me wondering what to do with the short edges (perpendicular to the beams) - surely the continuous plate makes those short edges better than free?
- How would the industry consider the side lengths a and b with a continuous plate like this?

I know that plate itself is no good for the whole weight (despite what our boilermakers say), but I want to find out how much it is good for so I can accurately gauge what additional reinforcement needs to be installed. So, two questions with this plate:
(1) Can someone offer advice on which (if any) Roark case applies to the existing diamond plate?
(2) If I lay plate on top of this existing diamond plate, is it fair to consider all edges of the additional plate as simply supported? (Even though two edges will be over beam and the other two will be supported by the existing plate only).

One final question regarding the existing beams under the diamond plate...
(3) Can anyone offer their advice on what to consider for the unbraced length given that the plate is continuously welded along the top side (middle of flange) along the entire length of the beams?


Thanks all, cheers.
Colin Pearson

 

[JedClampett]

For one, I would not use Roark. With that layout, 1/4 inch plate and that area, I would analyze the plate as simply supported at the 32 inch centers. It will be slightly conservative, but more accurately reflect the actual condition. This is because the plate will tend to deflect at the supports and approach pinned behavior.
The trick is deciding how much plate width is engaged for each concentrated load. Most of the time you use the wheel width plus the depth of plate (Width + 1/2"), but that is going to give you a very low capacity. You probably want to consider some cribbing (timber members)to distribute the load and check that width.
When all is said and done, you're going to pretty much have to design members to carry the whole load. I would try channels with the legs pointed upward, (weak direction) acting as tracks. Using plates will get heavy very fast.
And don't forget to check the W12's below.

 

[dhengr]

Colin:
You need a lot more help than “Help with Roark for existing plate.” I’d enlist the help of a Structural Engineer from the particular plant your are working in or the Consulting Engineers who actually designed the building. You need the building plans so you can get a handle on the member sizes, spacings, member support situation, and material grades used, weld sizes, etc. Maybe the plant millwrights have some of this info. or know who to contact. Sometimes there are designated paths or routes for moving these kinds of loads. You have to know how you are going to move the valve, i.e. cart or Hilman rollers and their spacing so you know how you are loading the .25" thick pl. or the beams. Are the rollers evenly loaded or does one carry 40% of the load by virtue of the way you are supporting the valve and it blocking?

This type of activity should have been anticipated when the building was designed, but moves like this still have to be well planed by someone who understands structures and this particular building and your movement route. Roark doesn’t really cover what’s needed here.

 

[fancypants]

Personally, I would used simple support only for the plate from beam to beam wL^2/8. Then look up what the existing plate can support AISC 360-05 table 3-18a and 3-18b for a start. Pick a reasonable effective width based on how you want to load the plate and go from there. This is tried and true and you don't have to worry to much about mistakes when trying to use Roark's.

You will also need to check the beams in bending and shear. I would say since the plate is welded to the beams on a continuous or near so basis, then you can pretty much consider the beam continuous braced. Also, you will need to check all of the connections for the additional loads you will be applying.

I would just check the beams and connections, and then use a skid track layed across the beams in the direction you want to go. Look for a skid track that can support the load by itself from beam to beam. This is not difficult to find since most skidtrack if very ridged.

Then skid the valve across.

best,
Fancy

 

[ColinPearson]

Thanks Jed, dh and Fancy.
So it seems agreed not to fool with Roark for this issue. I typically have not had much luck getting numbers out of plate that don't leave us laying down 3/4" or 1" plate which in itself is a significant load and a good way to cut off someone's finger.

I do have all existing structural drawings of the area so I can adequately assess the existing beams and their connections. However, nothing (and I mean NOTHING) here has been designed with any kind of future work in mind, though I agree with dh that it would be necessary to look into if that was the situation.

I'll change directions and look to laying down some members that can support the weight and act as tracks for rollers.

Bueno!

 

[BAretired]

If the arrow shows the direction of travel of the valve, I wonder if it would be better to move like a knight in chess, first north, then west (assuming north is at the top of page).

You could use a pair of roller skids (see attached), each directly over a beam for the northerly move, then place two channels normal to the existing beams for the westerly move.

Using this method, you do not stress the existing steel plate at all. I would not place concentrated wheel loads on 1/4" plate.

I agree that the beams may be considered braced by the steel plate.

BA

 

[rb1957]

i found the Moody reference online by googling "Moody Rectangular Plates"