1/23/07 columns07.ppt
Column Design
• Axial Tension–
– net area due to connection
• Axial Compression–
– column stability
• Combined Bending and Tension
• Combined Bending and Compression
'
t t
n
Pf F
A= !
'
c c
Pf F
A= !
1/23/07 columns07.ppt
Net Area
- Nail Hole: discarded
- Bolt Hole: (bolt d + 1/16)*member width ← stress calculation
- Lag Bolt Hole: Appendix L - Split Ring and Shear Plate: Appendix K
1/23/07 columns07.ppt
Connections
Shear Plate Split Ring
1/23/07 columns07.ppt
Tension Example
- No. 1 S-P-F (South)
- D+S
- ¾ in diameter bolt
- MC < 19%
- size 2*6
Analyze this chord
' ( )( )( )( )( ) 598t t D M t F iF F C C C C C= = psi
1/23/07 columns07.ppt
Compression
- Length is Important
: Short vs. Long
1. Away from supports
2. At the connection (short col)
'
P(C is important)c c
g
Pf F
A= !
'
P(w/o C )c c
n
Pf F
A= !
1/23/07 columns07.ppt
Calculate CP
Evaluating le
Slenderness Ratio
Calculating FcE
Calculating CP
* * *21 / 1 / /
( )2 2
cE c cE c cE c
P
F F F F F FC
c c c
+ += ! !
2
'cE
cE
e
K EF
l
d
=
! "# $% &
1/23/07 columns07.ppt
Effective Length, le
e el K l=
1/23/07 columns07.ppt
Sidesway
Lateral flexibility at the top
1/23/07 columns07.ppt
Slenderness Ratio
�
le
r=
effective unbraced length
least radius of gyration of column cross section
General Equation
�
le
ry=
le
IyA
=le
bd312
bd
=le
d 112
!le
d
Rectangular Section
1/23/07 columns07.ppt
CP Example
- No. 1 DF-L
- D+Lr
- MC < 19%
- Normal temperature
- size 4*6
- l = 10 ft
- visually graded
1/23/07 columns07.ppt
Axial plus bending
1/23/07 columns07.ppt
�
ft
Ft'
+fb
Fb*! 1.0
�
ft = TA! actual tensile stress parallel to grain
Ft'
= allowable tensile stress = FtCDCMCFCi [sawn lumber]
= FtCDCMCt [glulam]
fb = MS! actual bending tensile stress; usually fbx
Fb*
= allowable bending tensile stress w/out the adjustement factor for lateral stability
= FbCDCMCtCFCrCi [usually about the x axis; sawn lumber]
= FbCDCMCtCV [glulam]
Case 1: tension plus tension
1/23/07 columns07.ppt
Case 2: Axial compression with bending
• NDS section 3.9.2.
1/23/07 columns07.ppt
Special cases1. Built-up columns from
studs: Use section 15.3of the NDS.
2. Eccentric Loading ofBeam-Columns asshown in figure
