Design of Columns and Beam-Columns in Timber

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Design of Columns and Beam-Columns in Timber
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Column failures

• Material failure (crushing)
• Elastic buckling (Euler)
• Inelastic buckling (combination of buckling and
  material failure)

P
Leff
?
P
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Truss compression members Fraser Bridge, Quesnel
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Column behaviour
Perfectly straight and elastic column
Pcr
P
Crooked elastic column
Leff
?
Axial load P (kN)
Crooked column with material failure
P
Displacement ? (mm)
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Pin-ended struts Shadbolt Centre, Burnaby
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Column design equation
P
axis of buckling
Pr ? Fc A KZc KC where ? 0.8 and Fc fc
(KD KH KSc KT) size factor KZc 6.3 (dL)-0.13
1.3
d
L
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Glulam arches and cross-bracing UNBC, Prince
George, BC
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Capacity of a column
? FcA
Pr
combination of material failure and buckling
p2EI/L2 (Euler equation)
elastic buckling
Le
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Pin-ended columns in restroom building North
Cascades Highway, WA
Non-prismatic round columns
Actual pin connections
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Column buckling factor KC
1.0
KC
limit
? 0.15
CC Le/d
50
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What is an acceptable l/d ratio ?? Clustered
columns Forest Sciences Centre, UBC
L/d ration of individual columns 30
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Effective lengthLeff length of half sine-wave
k L

k (theory) 1.0 0.5 0.7 gt 1
k (design) 1.0 0.65 0.8 gt 1
non-sway non-sway non-sway sway
Le
Le
Le
Le
Sway cases should be treated with frame
stability approach
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Glulam and steel trusses Velodrome, Bordeaux,
France
All end connections are assumed to be pin-ended
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Pin connected column base Note water damage
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Column base fixed or pin connected ??
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Effective length
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Round poles in a marine structure
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Partially braced columns in a post-and-beam
structure FERIC Building, Vancouver, BC
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L/d ratios
y
y
x
x
y
y
d
dx
dy
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Stud wall
axis of buckling
d
L
ignore sheathing contribution when calculating
stud wall resistance
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Stud wall construction
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Fixed or pinned connection ? Note bearing block
from hard wood
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An interesting connection between column and
truss (combined steel and glulam truss)
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Slightly over-designed truss member (Architectural
features)
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Effective length (sway cases)Leff length of
half sine-wave k L

k (theory) 1.0 2.0 2.0 1.0ltklt2.0
k (design) 1.2 2.0 2.0 1.5
Le
Le
Le
Le
Note Sway cases should only be designed this way
when all the columns are equally loaded and all
columns contribute equally to the lateral sway
resistance of a building
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Sway frame for a small covered road bridge
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Sway permitted columns .or arent they ??
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Haunched columns UNBC, Prince George, BC
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Frame stability

• Columns carry axial forces from gravity loads
• Effective length based on sway-prevented case
• Sway effects included in applied moments
• When no applied moments, assume frame to be
  out-of-plumb by 0.5 drift
• Applied horizontal forces (wind, earthquake) get
  amplified
• Design as beam-column

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Frame stability(P- ? effects)

• Htotal ?H
• ? amplification factor
• H applied hor. load

W
H
?
h
? 1st order displacement
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Sway frame for a small covered road bridge
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Combined stresses
Bi-axial bending
Bending and compression
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Heavy timber trusses Abbotsford arena
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Roundhouse Lodge, Whistler Mountain
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fmax fa fbx fby lt fdes
( Pf / A ) ( Mfx / Sx ) ( Mfy / Sy ) lt fdes
(Pf / Afdes) (Mfx / Sxfdes) (Mfy / Syfdes)
lt 1.0
(Pf / Pr) (Mfx / Mr) ( Mfy / Mr) lt 1.0
The only fly in the pie is that fdes is not the
same for the three cases
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Moment amplification
P
?o
?max
PE Euler load
P
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Interaction equation
Axial load
Bending about y-axis
Bending about x-axis
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3 storey walk-up (woodframe construction)
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New Forestry Building, UBC, Vancouver
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Stud wall construction
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