How to calculate the maximum stress in a rib of a complex construction

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SUMMARY

The discussion focuses on calculating maximum stresses in welded ribs of a stiffened construction, specifically under forces and moments of 6 kN and 6 kNm in various directions. The user seeks a hand calculation method without relying on the inertia moment, citing difficulties with integrals and rib positioning. The conversation highlights the importance of visual aids, such as diagrams, to clarify load applications and boundary conditions, and questions the necessity of hand calculations when Finite Element Analysis (FEA) solutions are available.

PREREQUISITES
  • Understanding of structural mechanics and stress analysis
  • Familiarity with welded constructions and rib design
  • Knowledge of Finite Element Analysis (FEA) principles
  • Basic skills in creating and interpreting engineering diagrams
NEXT STEPS
  • Learn how to perform hand calculations for stress analysis in welded structures
  • Study the principles of Finite Element Analysis (FEA) for complex geometries
  • Research methods for calculating inertia moments in irregular shapes
  • Explore best practices for creating engineering diagrams to represent loads and boundary conditions
USEFUL FOR

Structural engineers, mechanical engineers, and students involved in stress analysis and design of welded constructions will benefit from this discussion.

Ham94
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TL;DR
How to calculate a complex construction for the maximum stress or stress in the stiffenerconstruction? there are forces and momentums in the x,y,z, direction. They work in the most worst direction. I don't know how to handle this subject.
A Construction is stiffened by a bottemplate with welded ribs. A flange welded to the inletpipe is bolted at the botomplate. I want to simulate the current situation. Therfore I need a handcalculation of the stresses in the ribs of the constuction. The forces and moments are working in the worst case direction.
fx=6kN
fy=6kN
fz=6kN
Mx=6kNm
My=6kNm
Mz=6kNm
1614166638329.png
underside
Casingdiameter =900 mm
Casingthickness=5 mm
Botemplatethickness=5 mm
squareribs= 400*400
ribthickness=5 mm
height rib= 120 mm
length of ribs form square to circular casing= 4* 162 mm (angle from center 90=°, t=5 mm)
hole bottomplate= 250 mm
flangediamater= 350 mm

I don't know how to handle this situation. I want to calculate the maximum stresses in the ribs OR the stresses in a rib at one point.
Is there a possability to calculate without a inertia moment?
I have tried to calculatie the inertia moment of te ribs, but by second thought it is difficult because of the integrals and the positions of the ribs.
Maybe my thought is even harder than the solution.
 
Last edited:
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Is this homework?

You need a better diagram showing how and where the loads and restraints are applied.
 
What is the purpose of this hand calculation if you have solution from FEA ? Do you want to verify the correctness of numerical analysis ? It might be too difficult to make sense in many cases with complex geometry and/or loading.
Can you attach a picture showing the whole model with applied boundary conditions and loads ?
 

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