DSM Design Guide

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DSM Design Guide
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AISI DSM Design Guide

• Completed in 2006, the AISI - DSM Design Guide
  covers the following areas
• elastic buckling,
• overcoming difficulties with elastic buckling
  determination in the finite strip method,
• beam design,
• column design,
• beam-column design,
• product development, and
• design examples (nearly 100 pages of them).

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Using the Guide
Originally written around 2004 Spec. supplement
the full version of DSM is now in AISI-S100-07
(Spec. and commentary)
(pg. 1)
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DSM Advantages

• Practical advantages of DSM
• no effective width calculations,
• no iterations required, and
• uses gross cross-sectional properties.
• Theoretical advantages of the DSM approach
• explicit design method for distortional buckling,
• includes interaction of elements (i.e.,
  equilibrium and compatibility between the flange
  and web is maintained in the elastic buckling
  prediction), and
• explores and includes all stability limit states.
• Philosophical advantages to the DSM approach
• encourages cross-section optimization,
• provides a solid basis for rational analysis
  extensions,
• potential for much wider applicability and scope,
  and
• engineering focus is on correct determination of
  elastic buckling behavior, instead of on correct
  determination of empirical effective widths.

(pg. 2)
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DSM Limitations

• Limitations of DSM (as implemented in AISI 2004)
• No shear provisions (under research)
• No web crippling provisions
• No provisions for members with holes (proposals
  made)
• Limited number/geometry of pre-qualified members
  (expanding)
• No provisions for strength increase due to
  cold-work of forming
• Practical Limitations of DSM approach
• Overly conservative if very slender elements are
  used
• Shift in the neutral axis is ignored
• Limitations of finite strip method
• Cross-section cannot vary along the length
• Loads cannot vary along the length (i.e., no
  moment gradient)
• Global boundary conditions at the member ends are
  pinned (i.e., simply-supported) (full boundary
  conditions handled soon)
• Assignment of modes sometimes difficult,
  particularly for distortional buckling
  (constrained finite strip method automates this
  difficult step)

yellow comments are May 2009 updates to the 2006
Design Guide
(pg. 6)
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DSM Design Guide

• Introduction
• Elastic Buckling
• Member elastic buckling
• examples
• overcoming difficulties
• Beam, Column, and Beam-Column Design
• Product Development
• Design Examples

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(pg. 10)
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(pg. 12)
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Elastic buckling upperbounds

• Beams
• if Mcrl gt 1.66My then no reduction will occur due
  to local buckling
• if Mcrd gt 2.21My then no reduction will occur due
  to distortional buckling
• if Mcre gt 2.78My then no reduction will occur due
  to global buckling
• Columns
• if Pcrl gt 1.66Py then no reduction will occur due
  to local buckling
• if Pcrd gt 3.18Py then no reduction will occur due
  to distortional buckling
• if Pcre gt 3.97Py a 10 or less reduction will
  occur due to global buckling
• if Pcre gt 8.16Py a 5 or less reduction will
  occur due to global buckling
• if Pcre gt 41.64Py a 1 or less reduction will
  occur due to global buckling

(pg. 9)
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DSM Design Guide

• Introduction
• Elastic Buckling
• Member elastic buckling
• examples
• overcoming difficulties
• Beam, Column, and Beam-Column Design
• Product Development
• Design Examples

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Elastic buckling examples

• C, Z, angle, hat, wall panel, rack post, sigma..

(pg. 16)
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Z-section with lips
(pg. 26)
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Z-section with lips modified
(pg. 28)
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Comparison
(pg. 26 and 28)
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Comparison
(pg. 26 and 28)
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DSM Design Guide

• Introduction
• Elastic Buckling
• Member elastic buckling
• examples
• overcoming difficulties
• Beam, Column, and Beam-Column Design
• Product Development
• Design Examples

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Overcoming FSM difficulties

• The discussions in the following section are
  intended to provide the design professional with
  a means to apply engineering judgment to an
  elastic buckling analyses. When in doubt of how
  to identify a mode, or what to do with modes that
  seem to be interacting, or other problems
  remember, it is easy to be conservative. Select
  the lowest bucking value (i.e., Pcr, Mcr) of all
  mode shapes which includes some characteristics
  of the mode of interest. This ensures a
  lowerbound elastic buckling response. However,
  this may be too conservative in some cases, and
  the challenge, often, is to do better than this
  and use judgment to determine a more appropriate
  (and typically higher) approximation.

(pg. 42)
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including some system behavior
Example of impact of adding rotational restraint
to the flange
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Multiple modes
(pg. 46)
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Global modes at short L
(pg. 47)
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DSM Design Guide

• Introduction
• Elastic Buckling
• Member elastic buckling
• examples
• overcoming difficulties
• Beam, Column, and Beam-Column Design
• Product Development
• Design Examples

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Beam Chart
(pg. 58)
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AISI (2002) Design Manual
(pg. 61)
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Column Chart
(pg. 64)
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DSM Design Guide

• Introduction
• Elastic Buckling
• Member elastic buckling
• examples
• overcoming difficulties
• Beam, Column, and Beam-Column Design
• Product Development (later today)
• Design Examples

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Design Examples

• C-section with and w/o web stiffeners added,
  including strong axis flexural strength and
  compressive strength with different bracing
  conditions,
• SSMA track section, including strong and
  weak-axis flexural strength, compressive
  strength, and beam-column strength,
• track section with flange stiffeners added,
  including flexural strength and compressive
  strength,
• Z-section purlin, including flexural and
  compressive strength for different bracing
  conditions,
• Z-section purlin with stiffeners added and lip
  length modified, including flexural and
  compressive strength,
• equal leg angle with lips, including flexural
  strength, compressive strength, and compressive
  strength explicitly including eccentricity,
• equal leg angle, including flexural and
  compressive strength,
• hat section, including flexural strength,
  compressive strength for different bracing
  conditions, and beam-column allowable strength,
• wall panel section, including flexural strength
  for intermediate and end panels with the top
  flange in compression and flexural strength for
  bottom flange in compression,
• rack post section, including flexural and
  compressive strength, and
• sigma section, including flexural and compressive
  strength.

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Conclusions

• DSM
• approved and available for design
• no effective width, no iteration
• includes web/flange interaction and other
  mechanics
• intended to encourage optimization
• DSM Design Guide
• available, Google DSM Design Guide
• provides detailed coverage of elastic buckling
• includes numerous design examples to aid engineers