Finite element analysis

[rukmuddin]

I am working on structural analysis of steel fabricated structure, fabricated by using box section.
For bending and stress analysis which will be best meshing beam elements or shell elements

Regards
Rukmuddin

Rukmuddin
rukmuddin@hotmail.com

 

[PVRV]

Solid elements (8-nodes)

 

[jte]

PVRV-

Good one! LOL

jt

 

[PVRV]

About 10 years ago, I worked on FEA program developed by Rasna Cooperation called Mechanica, Version 6.0. Prior to starting FEA, 2-D/2-D AxiSymmetric & 3-D options are outlined.

Shell elements for 2-D analysis are rectangles or triangles. Of course, autogeneration of elements may be utilized.

I work on locomotives trailers, purpose was to remove as much weight as possible while retaining structual integrity or a SF of 2.5

I used solid elements as outlined previously aside from being accurate they were easier to work with.

Cheers

 

[jte]

PVRV-

I can understand using solid elements for analysis of parts or components. I will use them also where they make sense. However, try modelling a structure built of say 8"x8"x½" structural tubing which has four legs and a deck on top - a very simple platform. Let's say that the platform is 15' tall. To keep an aspect ratio no more than 8:1, you would need elements no more than 2" by 2" (You do want a node in the middle of the thickness, right? So two elements thick). That means you're looking at 14,000 elements (100,000+ nodes) before too long. This is for a very simple structure. Using beam elements the entire structure could be modelled with say 16 elements; I'd probably use use more like roughly 40 (120 nodes). The results are the same as far as sizing the beams goes. OOOOps - it's overstressed. Now let's try 5/8" thick beams. A simple change with beam elements, messy with solids. Probably the worst part with solids is modelling the connections. With typical structural analysis you pull the loads at the ends of the beams and design the bolted or welded connection with some help from the AISC "steel book". How does one get the forces and moments at the end of a beam when you use solid elements to model them?

jt

 

[PVRV]

rukmuddin,

Please elborate on the structure dimensions.

 

[bvi]

if you are trying to calculate bending stresses in plate sections (through wall bending) from which this box section is fabricated, you are best off with plate elements. They will give you good membrane and bending results for structures fabricated from plate. Using brick elements, you would need to check that you have a sufficient number through the thickness to accurately calculate the through wall bending stress. If you need peak stresses for a fatigue analysis, you would need to use brick elements, and/or use stress intensification factors you apply to calculated membrane and bending stresses.