Question about Davit with pipe sections.....

[Jakrayer]

I am trying to analyze a davit constructed with pipe sections. To do this I have been using a couple things, Design Guide 24: Hollow Structural Section Connections, along with AISC 13th Edition Manual. The problem I am having is that in the examples of y connection analysis the forces are given and then using the force in the dominate tension or compression chord the max chord plastification strength is found. I am not given any loads, however, since I am trying to analyze this for the maximum load that the davit can take safely. How would I go about doing this with the equations or is there a better way to go about this?

I have all the dimensions: pipe section, steel properties, weld sizes and strengths.
I am attempting to attach a photo of the davit in CAD...first time posting.

 

[JStephen]

So assume a load and work through the design with that load and see what happens?

You could assume that loading was limited by bending in the vertical leg at the lower Y, or that it was limited by the design of the lugs. In either case, you could calculate a load from that assumption, then start in on the rest of it using that calculated load.

There has to be some limit to the load that can be applied to whatever's supporting the davit, and that might be another assumed load limit. And there should be some practical limit to the load to be lifted as well.

 

[racookpe1978]

Pipe sections are a valid idea, but I strongly recommend NOT using actual "pipes" as structural members.

Use the same size and shape members if you must, but specify an actual "structural strength" material specification. The "pipes" that are certified for liquid (internal pressure) duties are relatively low strength and have poor geometric controls since they are certified and intended for internal pressure applications.

You really want the higher strength and more rigid geometries of "round hollow" structural shapes. That just happen to look like pipes.

 

[Jakrayer]

Well the thing is, it is already in place and since it is so old there isn't documentation on the davit. So to be conservative we assumed since it is a chemical plant and they use a lot of pipe it was made out of pipe. I agree though round hss would be much better.

In response to the first post, if I do assume a weight to plug into the equations how will I know when I reached the max cause when I tried that prior if I increased my assumed load the value for max chord plastification load also went up. Is there a way I can use the I-Beam local buckling and crippling equations and modify them for round shapes?

 

[paddingtongreen]

I don't understand why you are trying to find its strength. I deduce, since you are analyzing the davit, that you have a proposed use for it. Rather than finding out its whole strength, why not check it for the design load you have in mind. You could even simplify it by proof loading it, using an appropriate multiplier.

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

 

[Jakrayer]

Well I am mainly trying to look at the welds between the pipe sections, but have not found a way to do that for a case where a round hss is welded to another round hss.

Is there another equation to look at wall plastification and punching shear besides

plastification:

Pn*Sin(angle)=Fy*t^2*[3.1+15.6*beta^2]*gamma^0.2*Qf

Punching shear:

Pn=0.6*Fy*t*pie*Db*[(1+Sin(angle))/2*Sin^2(angle)]

these are in AISC page 16.1-129 Section K2-2b

 

[Jakrayer]

Ok so following the AISC manual I calculated the following values in the attachment... They seem far to high for this structure can anyone verify the numbers I got and maybe explain the process to me a little. I am very new to doing an analysis on hollow round shapes...