Institute of Structural Engineering Page 1
Method of Finite Elements I
Method of Finite Elements I
Part 2 : Results Interpretation
Practical application of the MFE
Institute of Structural Engineering Page 2
Method of Finite Elements I
FE Modelling of a Slab
Physical
PROBLEM
Analytical
SYSTEM
Finite Element
MODEL
Institute of Structural Engineering Page 3
Method of Finite Elements I
Linear support
Line of symmetry
Point support
y
SIMPLE SLAB
FE mesh + reactions
Mesh dependency of results
Institute of Structural Engineering Page 4
Method of Finite Elements I
3
482412
2 6
Mesh dependency of results: Displacements
Institute of Structural Engineering Page 5
Method of Finite Elements I
Mesh dependency of results: Stresses
'Raw' stress results
within each element
'Optimized' stress results
for the mesh of elements
REMEMBER: Stresses are NOT in equilibrum
….just a little bit of window dressing
Institute of Structural Engineering Page 6
Method of Finite Elements I
3
482412
2 6
Mesh dependency of results: Moments
Institute of Structural Engineering Page 7
Method of Finite Elements I
Quality of a Model
• Good models lead to good results
• Good results are realistic and understandable
• The simpler the model the better you understand
the results
What is a good model ?
Simpler models lead to better results!
Institute of Structural Engineering Page 8
Method of Finite Elements I
Quality of a Model
• Only readily available results are good results
• Fast computers quickly produce results
• The simpler the model the quicker you get results
(valid for computers as well)
What is a good model ?
Additional aspects from engineering practice:
You are more productive with simpler models!
Make it as simple as possible, but not simpler
Principle:
Institute of Structural Engineering Page 9
Method of Finite Elements I
FE Modelling
• Tendency towards overly complex FE models:
„The more detailed I specify my model, the better
results I will get“
• Tendency towards black box application:
„The output must be true“
Beware of ‘blind trust’:
= MISBELIEF !
= RELIGION not KNOWLEDGE !
There is no way to avoid proper modeling !
… fortunately,
because nowadays everyone can input a 3D model
and let the computer produce colorful pictures !