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

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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 !