Effects of Boundary Conditions on Static Health Monitoring Accuracy

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Effects of Boundary Conditions on Static Health
Monitoring Accuracy

• Brian Long

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Presentation Outline

• Introduction
• Leif Johnsons Work
• My Role with Leifs Work
• Results
• Conclusions

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Traditional Methods of Damage Detection

• Visual Inspection (VI)
• Other Methods radiographs, magnetic and
  ultrasonic methods
• Problem with these Methods
• General location of damage must be known.
• Part of Structure must be accessible for testing.

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Structural Health Monitoring

• The detection of damage to a structure by using
  the structures dynamic and static properties.
• Dynamic-based techniques
• Frequency changes, mode shape change, mode
  shape curvature changes, dynamically measured
  flexibility, matrix update, and neural
  network-based
• Static techniques
• Simpler and depend entirely on the stiffness
  properties.

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Leif Johnsons Work

• Uses Static Techniques
• Assumptions
• Structure loaded with same loads in the same
  locations in both the undamaged and damaged
  states.
• Same displacements are measured before and after
  the damage
• Damage is identified as a decrease in the
  stiffness properties.
• The stiffness matrix is a function of the changes
  in moment of inertia.

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Locating Damage involves determining which
elements have a decrease in moment of
Inertia. Quantifying Damage involves determining
the amount of the decreases.
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M Files

• Main
• Model
• ID FEM
• ModelLOAD
• Actual FEM
• Loads applied
• Damage is defined
• Objective

Actual FEM
ID FEM
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Effects of Changing Boundary Conditions

• Changed Boundary Conditions for
• Two-Span Continuous Beam
• One-Bay, One-Story Frame
• Two-Bay, One-Story Frame
• Two-Bay, Two-Story Frame

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Two-Span Continuous Beam
1
3
Left End Fixed
2
6
5
4
1
2
3
4

• 6 Damaged States
• 6 Load Cases

30 ft
20 ft
1
3
Both Ends Fixed
2
5
4
1
2
3
4
30 ft
20 ft
10
Damaged States
Load Cases
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One-Bay, One-Story Frame
1
4
2
5
2
3

• 6 Damaged States
• 7 Load Cases

1
4
10 ft
6
20 ft
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Damaged States
Load Cases
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Little variation in amount of error
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Damage State 4 is most sensitive to changes
in BC
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Two-Bay, One-Story Frame

• 6 Damaged States

• 5 Load Cases

3
5
2
4
7
6
8
2
3
5
6
1
10 ft
1
4
7
9
10
30 ft
20 ft
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Damaged States
Load Cases
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Conclusions

• Boundary Conditions did not have much of an
  effect on the Accuracy
• Changing Boundary Conditions did not show a
  pattern of where errors could be expected to be
  found

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Summary

• Introduce SHM
• Introduce Leif Johnsons Work
• Effects of Changing Boundary Conditions on Static
  Health Monitoring
• Conclusions
• Thanks