gusset equivalence
gusset equivalence
(OP)
Here is the scenario, assume there is a pipe (any diameter) that is welded to a flat plate so that pipe protrudes on either side of the plate. Now if one end of that pipe is loaded with a load and a moment, I have been able to determine the stresses at the pipe/plate interface through a nozzle loading analysis.
I am having difficulties when we change the above scenario and install 4 gussets between the pipe and the plate (continuous weld) and apply the same loading conditions. Obviously, there is an increase in strength with the addition of the gussets. The question is how much and is there any sort of assumptions that I could make to take and "equivalent pipe diameter" which could be analized using the same process as with the non-gusseted pipe?
The overall goal of this analysis is to determine if the stresses at the nozzle/plate interface exceed the allowable stresses in the materials.
Any help would be greatly appreciated.
I am having difficulties when we change the above scenario and install 4 gussets between the pipe and the plate (continuous weld) and apply the same loading conditions. Obviously, there is an increase in strength with the addition of the gussets. The question is how much and is there any sort of assumptions that I could make to take and "equivalent pipe diameter" which could be analized using the same process as with the non-gusseted pipe?
The overall goal of this analysis is to determine if the stresses at the nozzle/plate interface exceed the allowable stresses in the materials.
Any help would be greatly appreciated.





RE: gusset equivalence
My first attempt choice would simply be the circle enclosing the gussets, but, of course, with only 4 gussets and a possibly low thickness plate this is not necessarily very representative.
A comparison criterion for you problem could be to take a pipe flange with the same pipe diameter as your nozzle, a comparable pressure rating, and take the number of gussets equal to the number of bolts and the gusset enclosing diameter equal to the flange outer diameter. However, for the comparison to be complete, flange thickness should be the same as your plate, and I'm afraid this is not the case.
Note also that if you wanted to do a detailed FEM analysis of your system, you would find very high stresses at gusset tips: these wouldn't be relevant to static resistance, but would impair the fatigue resistance of the item. In fact your statement that there is an increase in strength is not necessarily true when fatigue is concerned.
prex
http://www.xcalcs.com
Online tools for structural design
RE: gusset equivalence
Using WRC 107 the shell plate stresses were then analyzed for the gusset loads.
This method is not exact, and technically incorrect no doubt, but it was accepted nonetheless in the absence of anything better. Having said that, I am now involved with FEA design, and that's probably the best way to analyze your situation as noted by PREX.
RE: gusset equivalence
Bear in mind that this section property is only valid at the plate, since the gussets taper down to the pipe diameter away from the plate. You could derive an expression for the moment of inertia as a function of distance away from the plate. But there are several assumptions that you could make to speed things up, one being to use half of the gusset height in your section moment of inertia calculation and apply this moment of inertia to the length of gussetted pipe.
You could try using REGION and MASSPROP in AutoCAD, but be careful that you understand why you get the results that you do.Make sure that you calculate the properties for the pipe and not a solid circular section. You will need to subtract the inside diameter moment of inertia from your section results. Do a sample calculation using a hollow shape with known moment of inertia to make sure you do it right.
RE: gusset equivalence
DVD: I used your sort of thinking with respect to determining a larger size of pipe based on the moment of inertia. To me that seemed logical, but I would prefer if there was some reference that I could look up in order to confirm our thinking. Any suggestions?
RE: gusset equivalence
RE: gusset equivalence
prex
http://www.xcalcs.com
Online tools for structural design