Elastic buckling finite strip analysis of the AISC sections database and proposed local plate buckli

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Elastic buckling finite strip analysis of the
AISC sections database and proposed local plate
buckling coefficients

• Seif, M., Schafer, B.W.

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Elastic buckling finite strip analysis of the
AISC sections database and proposed local plate
buckling coefficients

• Seif, M., Schafer, B.W.

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Acknowledgments

• AISC Faculty Fellowship
  Program
• Professor Ben Schafer
• The thin-walled structures research group at JHU

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Overview

• Motivation
• AISC local buckling criteria
• Local buckling finite strip analysis
• Results
• Comparison to AISC Specifications
  limits
• Suggested local buckling coefficients expressions
• Conclusions

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Overview

• Motivation
• AISC local buckling criteria
• Local buckling finite strip analysis
• Results
• Comparison to AISC Specifications
  limits
• Suggested local buckling coefficients expressions
• Conclusions

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Motivation

• Common structural steel design practice is to
  keep sections below w/t limits and avoid local
  buckling. Why consider cross-section stability?

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Motivation

• Common structural steel design practice is to
  keep sections below w/t limits and avoid local
  buckling. Why consider cross-section stability?
• Post-buckling reserve

Pcr
global buckling
d
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Motivation

• Common structural steel design practice is to
  keep sections below w/t limits and avoid local
  buckling. Why consider cross-section stability?
• Post-buckling reserve
• Minimizing material

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Motivation

• Common structural steel design practice is to
  keep sections below w/t limits and avoid local
  buckling. Why consider cross-section stability?
• Post-buckling reserve
• Minimizing material
• Increasing yield stress

Based on flange slenderness at 36 ksi, only 1 of
the 273 standard W-sections is noncompact, but
at 50 ksi 11 W-sections, at 65 ksi 27
W-sections, at 70 ksi 39, W-sections at 100
ksi 94, W-sections at 120 ksi 119,
W-sections...
and much more ...
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Overview

• Motivation
• AISC local buckling criteria
• Local buckling finite strip analysis
• Results
• Comparison to AISC Specifications
  limits
• Suggested local buckling coefficients expressions
• Conclusions

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AISC definition of locally slender
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AISC definition of locally slender
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AISC definition of locally slender
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AISC definition of locally slender
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AISC definition of locally slender
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AISC definition of locally slender
Plugging
into
And solving for
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AISC definition of locally slender
We have from Table B4.1
is 0.7 for compression elements by AISC
implies that fcr2fy
We can calculate k
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Model behind w/t limits
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No restraint between web and flange
web/flange juncture...
k kf 0.43
kw 4
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Full restraint between web and flange
web/flange juncture...
k kf 1.277
kw 6.97
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AISC assumed restraint between web and flange
web/flange juncture...
?????????????????????????????????????????
k kf 0.7
?????????????????????????????????????????
kw 5
?????????????????????????????????????????
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Limitations

• Equilibrium

web/flange juncture...
?????????????????????????????????????????
k kf 0.7
?????????????????????????????????????????
kw 5
?????????????????????????????????????????
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Limitations

• Equilibrium

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Limitations

• Compatibility
• rotation at web/flange juncture
• Bounds are false
• if one element buckles before another it demands
  rotational restraint from the neighbor. simple
  support condition is not a lower bound!
• cross-section local buckling is needed

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Overview

• Motivation
• AISC local buckling criteria
• Local buckling finite strip analysis
• Results
• Comparison to AISC Specifications
  limits
• Suggested local buckling coefficients expressions
• Conclusions

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Approach

• Run Finite Strip analysis for all the
• AISCs data base of shapes under

• Pure axial compression,
• Positive major-axis bending,
• Negative major-axis bending,
• Positive minor-axis bending,
• Negative minor-axis bending.

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Cross-section stability by finite strip method

• mesh cross-section with element strips
• each element follows classical plate bending
  theory
• result of buckling analysis is the local buckling
  mode and stress of the full cross-section

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Lb
Stress
Lb
Half wave length
Axial
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Stress
Lb
Lb
Half wave length
Axial
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Stress
Half wave length
Axial
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Stress
Half wave length
Axial
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Stress
Half wave length
Axial
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Stress
Half wave length
Axial
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Stress
Half wave length
Bending
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Stress
Half wave length
Bending
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Overview

• Motivation
• AISC local buckling criteria
• Local buckling finite strip analysis
• Results
• Comparison to AISC Specifications
  limits
• Suggested local buckling coefficients expressions
• Conclusions

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Results

• Now we have
• We can calculate from

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Results
Axial
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Results
Axial
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Results
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Finite strip results for W-sections
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Simple relations for cross-section stability
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Major axis bending
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Minor axis bending
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Overview

• Motivation
• AISC local buckling criteria
• Local buckling finite strip analysis
• Results
• Comparison to AISC Specifications
  limits
• Suggested local buckling coefficients expressions
• Conclusions

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Simple relations for cross-section stability
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Simple relations for cross-section stability
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Simple relations for cross-section stability
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Simple relations for cross-section stability
Table B4.1
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Conclusions

• Increased consideration of ultimate limit states
  in extreme loading, and the advent of high and
  ultra-high strength steels make consideration of
  local buckling of even greater importance today.
• The AISC Specifications use of
  width-to-thickness limits for each element of a
  cross-section assumes a unique plate buckling
  coefficient exists for each element of a section,
  and that the web-flange interaction is thus at a
  fixed amount.
• Local plate buckling coefficients vary widely for
  a given section and loading. However, the
  variation in k may be expressed as a function of
  the member geometry and loading including
  web-flange interaction.
• The developed expressions provide a potential
  first step towards rationalizing the AISC
  Specification approach to local buckling limit
  states across the different sections.

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Work continues more at
www.ce.jhu.edu/bschafer/aisc