Design by Analysis:Present

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Design by AnalysisPresent Future EN 13445-3
Direct Route

• Jim Boyle, University of Strathclyde, Glasgow,
  Scotland

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Design by Analysis

• Pressure vessel design has been historically
  based on Design By Formula (DBF). Standard vessel
  configurations are sized using a series of simple
  formulae and charts
• In addition to the Design by Formula route, many
  national codes and standards for pressure vessel
  and boiler design do provide for a Design By
  Analysis (DBA) route

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Design by Analysis

• All these DBA routes in the major codes and
  standards in the pressure equipment field are
  based on the rules first proposed in the ASME
  Pressure Vessel and Boiler Code, which was
  formulated in the late 1950's before being
  released, originally for nuclear applications, in
  1964

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Design by Analysis

• All these routes lead to the same well-known
  problems, especially the stress categorization
  problem, and all are out-of-step with the
  continuing development of computer hardware and
  software
• Further, all are focused on pressure, and
  possibly, and to a limited extent, temperature,
  treating other actions in an inflexible manner,
  giving them marginal attention only.

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EN 13445-3

• The DBA direct route in CEN's unfired pressure
  vessel standard prEN 13445-3 tries to avoid these
  problems
• by addressing the failure modes directly
• by allowing for non-linear constitutive models
• by applying a multiple safety factor format for
  the incorporation of actions other than pressure
• by specifying mainly the principal technical
  goals of the standard together with some
  application rules as possible methods for the
  fulfillment of these goals.

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Design by AnalysisDirect Route (DBA-DR)

• Design Principles
• Application Rules
• Partial Safety Factors
• Non-linear Design Models
• Design Checks

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DBA-DR New Terminology!

• Action physical influence causing stress
  strain
• Effect response of a component to a specific
  action
• Load Case a combination of coincident actions
• Characteristic Value representative value which
  takes account of the variation of an action

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DBA-DR New Terminology!

• Principle general statement, definition or
  requirement of a given failure mode
• Application Rule procedure to determine whether
  a principle is satisfied
• Design Check assessment of a component by means
  of an application rule

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DBA-DR New Terminology!

• Limit State structural condition beyond which
  the design performance requirements of a
  component are not met
• Resistance the limiting value for a given limit
  state of an action or effect

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DBA-DR Methodology

• Specify Failure Mode Limit State
• Specify the Principle
• Select an appropriate Application Rule
• Carry out the Design Check
• If the Principle is not satisfied, repeat with
  amended loading, geometry or material

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(d) Design Checks

• Define the Load Case and specify Actions
• Determine the Characteristic Value and calculate
  the Design Value of each action
• Calculate the Effect of the actions
• Calculate the Resistance of the component
• Indicate whether or not the Principle is satisfied

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Design Models

• Geometric model
• Structural strains
• Material model
• Linear elastic ideal plastic
• Tresca yield associated flow rule
• Deformation model
• First/second order theory
• Non-linear

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Structural Strain

• Defined as the strain in a stress concentration
  free model
• Idealized Design Model based on real geometry
  with exception of details which cause only local
  stress or strain concentration

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Design Checks

• Gross Plastic Deformation (GPD)
• Progressive Plastic Deformation (GPD)
• Fatigue (F)
• Instability (I)
• Static Equilibrium (SE)

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e.g. Design Check for GPD - 1

• Specified Design Model
• Geometry to provide structural strains
• Linear elastic, ideal plastic
• Tresca yield condition flow rule
• Design strength parameters
• First-order deformation theory
• Second-order for geometric weakening

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e.g. Design Check for GPD - 2

• Principle Design Actions shall be carried by
  Design Models for
• Proportional increase in actions
• Stress free initial state
• Limitation of maximum absolute value of principal
  structural strains

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Design by Analysis The Future?

• The Direct Route is a major step forward in
  Design by Analysis
• Nevertheless Design By Formula remains the
  dominant approach
• In an increasingly technically sophisticated
  society, it may be asked why this should be the
  case?