Please Help with Load on Beam in Risa

[gb12345]

Hi, This is for learning purposes but i am using a real life situation that I have came across before.

If someone could please show me the steps/explanation of this I WOULD GREATLY APPRECIATE it.

So, there is a vessel sitting on a beam. The vessel weighs 240kip. The vessel is being jacked up with jacking cans. Half of the vessel weight is on one beam and 2 jack cans and other half of the weight is on the other beam and 2 jacking cans. So, we are only looking at 1 beam and 2 jacking cans with half of the weight (120 kip). Beam weight is 1,300 lbs (not too sure if this weight matters). 3'11" of the vessel/saddle is sitting on the beam.

A visual image of what is happening is below:

** What I am looking for: How to run this exact situation (or a similar situation) in RISA 3D with explanation and steps. I realize the beams will most likely break or be very close to it. But i want to know what are the steps in Risa 3d and explanation to get to the solution: Can these beams take this weight when the Jacking cans are pushing the beam and vessel up?

The risa file for the beam is below. Load has not been added to the beam or jacking cans.

THANK YOU VERY MUCH

 

[gb12345]

Risa File:

 

[jayrod12]

I would place it as a single point load in the middle of the span between the jacking cans. If you don't know how to place a point load, then that's what the help file is for.

 

[gb12345]

I do.. but the jacking cans pushing up effect the structural integrity of the beam also?? ... do i put this as a point load pointing Y+ direction (one on each jack) with half the weight on each? But yes i do admit i am not that great with risa and structural analysis. I am trying to learn some of this for what i need. This is not a field I normally work in. I normally work in Heavy haul and rigging/field engineering...

What variables do i need to be checking to ensure that beam is going to be safe? Or will risa basically tell me that it is not safe?

 

[gb12345]

Maybe it is best to "create point loads based on step location of moving loads"?

 

[JAE]

Whether the jacking cans are lifting or static, the beam is supporting the same load...assuming the jacking is done slowly.

As for step-by-step process in RISA - that would be difficult to do here as reference to all of RISA's menus and variables is tough to describe without recourse to lots of menu screen shots, etc.

As for design issues:
1. What size of beam is it? What material?
2. How is the beam laterally braced against lateral torsional buckling?
3. How rigid is the saddle relative to the beam? (affects the distribution of load on the beam but as jayrod suggests, simply using a point load at the center would be conservative).
4. How are the beams supported laterally at the ends near the jacking cans? Is there torsional resistance?
5. Is there a possibility that a jacking can might lag behind others and cause differential distribution of load to the two beams?
6. Can you use a telephone and call an experienced engineer to help you with this?




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[gb12345]

JAE thank you for your response,


1. The beam design is in the risa file which consists of (2) W8x35 w/ 0.75" gussets (not continous) A992 Steel at 201" length.
2. the beam is just sitting on the cans. So i am not exactly sure the answer to this question.
3. point load would be sufficient
4. again i am not sure on this. if you could explain this to me or give me a reading or book that could help please do.
5. this is entirely possible. however, for these purposes we assume the jacking is equal (they dont have to be jacked much, about 6").
6. not really. this is a topic i really am just curious about and thus is not a problem for work. i really want to learn this though. i realize it could take a lot longer than just a post on a website to learn.


Can someone recommend any specific book that deals with this type of problem that could explain the engineering to me? I don't mind buying a good book that can start me off reading on some of this...

 

[gb12345]

When putting the point load on the beam, how do i add the jacking cans or structural supports?

 

[jayrod12]

Treat them as supports. unless you are required to check the jacking can capacity.

In follow-up to your answers to JAE's questions:
2) If the beam is not braced against LTB then you need to make sure you're going through the proper calculations to ensure the capacity is there. I haven't opened your RISA model, nor will I at this point. You need to understand how to calculate this by hand so you then can understand whether the program is running correctly. If you don't know what to expect as an output beam size from the program you could easily undersize or oversize the beam and not know.

4) he's asking if there's a way to stop the beams from rolling over, It certainly doesn't appear as though there will be a direct connection stopping that, however a pair of W8x35s with intermittent plates holding them together likely has enough roll over resistance.

 

[gb12345]

Jayrod12,

Thanks for the info.