DSM Design Guide

1
DSM Design Guide
2
DSM Design Guide

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

3
Using the Guide
(pg. 1)
4
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)
5
DSM Limitations

• Limitations of DSM (as implemented in AISI 2004)
• No shear provisions
• No web crippling provisions
• No provisions for members with holes
• Limited number/geometry of pre-qualified members
• 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)
• Assignment of modes sometimes difficult,
  particularly for distortional buckling

(pg. 6)
6
DSM Design Guide

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

7
(pg. 10)
8
(pg. 12)
9
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)
10
DSM Design Guide

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

11
Elastic buckling examples

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

(pg. 16)
12
Z-section with lips
(pg. 26)
13
Z-section with lips modified
(pg. 28)
14
Comparison
(pg. 26 and 28)
15
Comparison
(pg. 26 and 28)
16
DSM Design Guide

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

17
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)
18
Multiple modes
(pg. 46)
19
Global modes at short L
(pg. 47)
20
DSM Design Guide

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

21
Beam Chart
(pg. 58)
22
AISI (2002) Design Manual
(pg. 61)
23
Column Chart
(pg. 64)
24
DSM Design Guide

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

25
Design Examples

• C-section with lips,
• C-section with lips modified,
• C-section without lips (track section),
• C-section without lips (track section) modified,
• Z-section with lips,
• Z-section with lips modified,
• Equal leg angle with lips,
• Equal leg angle,
• Hat section,
• Wall panel section,
• Rack post section, and a
• Sigma section.
• Beam chart construction and Column Chart
  construction