Transcript Document 7365610

CORNELL UNIVERSITY
School of Civil and Environmental Engineering
Cold-Formed Steel Frame
and Beam-Column Design
Andrew Sarawit
Professor Teoman Peköz
Sponsored by:
Rack Manufacturers Institute
American Iron and Steel Institute
Objective

To verify or modify the RMI and the AISI provisions
for frame design
Project Outline
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Column Bases
Beam to Column Connections
Members
Cold-Formed Steel Frames
FREE Computer Programs
Cold-Formed Steel Frames
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Two approaches are begin considered
1. Effective length approach (Kx > 1 )
- Concentrically Loaded Compression Members
- Combined Compressive Axial Load and Bending
2. Notional load approach (Kx = 1 )
Effective Length Approach (Kx>1)

Concentrically Loaded Compression Members
Pu  c Pn
Approach 1a  elastic critical buckling load is determined
by using the AISI torsional-flexural buckling provisions
Approach 1b  elastic critical buckling load is determined
by performing an elastic buckling analysis
Effective Length Approach (Kx>1)

Combined Compressive Axial Load and Bending
Pu
Mu

1
c Pn b M n
Approach 1c  elastic critical buckling load is determined
by using the AISI torsional-flexural buckling provisions
Approach 1d  elastic critical buckling load is determined
by performing an elastic buckling analysis
Notional Load Approach (Kx=1)
Pu
Mu

1
c Pn ( L ) b M n
Approach 2a    1 240
  K x  1 168, 1  K x  1.7
Approach 2b    
K x  1.7
 1 240,
Approach 2c    1 240 and a 10% reduced flexural
stiffness analysis model is used
This can done by using a reduced flexural stiffness EI *
for all members and connections in the analysis model
EI *  0.9EI
Isolated Rotationally
Study 1:
Restrained Sway Column
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The finite element method was used as the basis for
evaluating the accuracy of the design approaches
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540 models were studied
- 3 material yield stresses (33, 55, 70 ksi)
  L 240
- 20 different rotational end-restraints
P
GA ranging from 0 to 60
GB ranging from 0 to 
 
L  60 in.
L
- 9 column sections
1000
C1
C2
C4
C3
C5
P
C7
C8
C9
C6
Effective Length Approach
Buckling load
from AISI TFB Eq.
Approach 1a
Pu  c Pn
Buckling load
from FEM
Approach 1b
Effective Length Approach
Buckling load
from AISI TFB Eq.
Approach 1c
Pu
Mu

1
c Pn b M n
Buckling load
from FEM
Approach 1d
Notional Load Approach
  1 240
  K x  1 168, 1  K x  1.7
 
K x  1.7
 1 240,
Approach 2a
Approach 2b
Notional Load Approach
  1 240
  1 240 and EI *  0.9EI
Approach 2a
Approach 2c
Study 2: Cold-Formed Steel Frames
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972 pallet rack configurations were studied
- 3 frame dimensions (bays x stories: 2x3, 6x3, 6x6)
- 2 upright frame configurations
- 9 column sections
- 3 Material yield stresses (33, 55, 70 ksi)
- 6 beam to column connection stiffnesses

2 load cases were considered
Gravity load case
Seismic loads case
Gravity Load Case: Effective Length Approach
Pu  c Pn
Pu
Mu

1
c Pn b M n
Approach 1a
Approach 1c
Gravity Load Case: Notional Load Approach
  1 240
  K x  1 168, 1  K x  1.7
 
K x  1.7
 1 240,
Approach 2a
Approach 2b
Gravity Load Case: Notional Load Approach
  1 240
  1 240 and EI *  0.9EI
Approach 2a
Approach 2c
Seismic Load Case: Effective Length Approach
Pu
Mu

1
c Pn b M n
Approach 1c
Seismic Load Case: Notional Load Approach
  1 240
Approach 2a
  K x  1 168, 1  K x  1.7
 
K x  1.7
 1 240,
Approach 2b
Seismic Load Case: Notional Load Approach
  1 240
  1 240 and EI *  0.9EI
Approach 2a
Approach 2c
Conclusion
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Notional load approach agrees better with the finite
element results than the effective length approach does
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Notional Load Approach 2c is recommended
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Use the effective length factors Kx = 1, Ky = 1, and Kt = 0.8

Use the notional load parameter  = 1/240

A 10% reduced flexural stiffness analysis model is used
- This can done by using a reduced flexural stiffness
EI *
for all members and connections in the analysis model
EI *  0.9EI