Measures of Structural Robustness Requirements

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Measures of Structural RobustnessRequirements
Applications

• Uwe Starossek Marco Haberland
• April 2008

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Content

• Introduction
• Basics
• Review
• Conclusions

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Introduction

• Structural robustness a desirable structural
  property
• Progressive disproportionate collapse
• Demand of robust structures
• Measure examine a structure concerning
  robustness
• Scope
• Proposal of basics for the development of
  measures, not proposal of a usable measure

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Definitions

• Disproportionate collapse
• disproportion between cause and effect
• Progressive collapse
• cascading chain reaction of failures
• Collapse resistance
• insensitivity to accidental circumstances
• Structural robustness
• insensitivity to local failure

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Measure of Robustness

• Questions
• What is a measure of structural robustness?
• What is the purpose of a measure?
• Answers
• Quantify the robustness of a structure
• Express influence of local failure
  on design objectives

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Applications

• Evaluation
• Optimization
• Regulation
• System partial safety factors

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Requirements

• Expressiveness
• Objectivity
• Simplicity
• Calculability
• Generality

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Reviewed Approaches

• Lind (1995)
• Baker et al. (2007)
• Maes et al. (2006)
• Frangopol et al. (1987)
• Wisniewski et al. (2006)

• Smith et al. (2006)
• Starossek (2007)
• Harte et al. (2007)
• Biondini et al. (2008)
• Agarwal et al. (2003)

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Bases of Measures

• Structural behaviour
• Deterministic
• System load capacity
• Damage progression
• Energy
• Probabilistic
• Probability of failure
• Risk
• Consequences

• Structural attributes
• System stiffness matrix
• System topology

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Methodology of Measures

• Assumption of an initial damage
• Investigation of resulting structural behaviour
• Comparison of damaged state
  and undamaged state
• Comparison of damaged state
  and reference values
• Identification of a collapse sequence

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DiscussionTheses

• Aims of suggested approaches differ
• Application in terms of checking design
  objectives is not intended for all cases
• Fulfillment of requirements
• Approaches fulfil requirements to different
  degrees none has proven to be clearly superior
• Limitation of requirements
• Requirements are partly in conflict with each
  other they may have to be limited

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DiscussionThesis Fulfillment of requirements

• Measures based on structural behaviour
• Often appear expressive
• Hardly realistically calculable large effort
  for necessary structural analyses
• Measures based on structural attributes
• Usually easier to calculate
• Expressiveness is not yet adequate
• Not illustrative

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DiscussionThesis Fulfillment of requirements

• Probabilistic measures
• Theoretically generally applicable
• Realistic assessment requires an enormous effort
  generally too complex to be useful in
  typical design situations
• Useable as tools to evaluate the performance of
  simplified robustness measures

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DiscussionThesis Limitation of requirements

• Limitation of the generality requirement
• Different types of structure have a tendency
  for particular significant types of collapse
• Development of an all-encompassing measure
  difficult
• Measures specific to types of collapse necessary
  for practical applications

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Conclusions

• Basics
• Structural robustness
  a desirable structural property
• Evaluation, optimization and regulation
  of robustness require a measure
• Requirements to measures expressiveness,
  objectivity, simplicity, calculability,
  (generality)

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Conclusions

• Published approaches to measures
• None has proven to be clearly superior
• Mainly based on structural behaviour
• Mainly assumption of initial failure
• Large calculation effort

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Conclusions

• Outlook
• Measures should be specific to collapse types
• Development of valid measures based on structural
  attributes desirable

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Thanks for your attention