Wood Construction: Column Design | Architecture Structures | ARCH 331, Study notes of Architecture

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Wood Columns 1Lecture 16

Foundations Structures

ARCH 331

FOUNDATIONS

S^ TRUCTURES

:

FORM,

B

EHAVIOR, AND

D

ESIGN

ARCH 331DR.

A

NNE

N

ICHOLS

SPRING 2009

lecture

sixteen wood construction:column design

Wood Columns 2Lecture 16

Foundations Structures

ARCH 331

Compression Members (revisited) •^

designed for strength & stresses

-^

designed for serviceability & deflection

-^

need to design for stability^ –^

ability to support aspecified loadwithout sudden orunacceptabledeformations

Wood Columns 4Lecture 16

Foundations Structures

ARCH 331

Critical Stresses (revisited) •^

when a column gets stubby, crushing will limitthe load

-^

real world has loadswith eccentricity

Wood Columns 5Lecture 16

Foundations Structures

ARCH 331

Bracing (revisited) •^

bracing affects shape of bucklein one direction

-^

both should be checked!

Wood Columns 7Lecture 16

Foundations Structures

ARCH 331

Allowable Wood Stress •^

where:

Fc

= compressive strength

parallel to grain CD

= load duration factor CM

= wet service factor (1.0 dry) Ct

= temperature factor CF

= size factor C^ p

= column stability factor

(^

)(^

)(^

)(^

)(^

) p

F t M D c c^

C C C C C F

F^

(Table 10.3)

Wood Columns 8Lecture 16

Foundations Structures

ARCH 331

S2009abn

Strength Factors •^

wood properties and load duration, C

D

-^ short duration -^

higher loads

-^ normal duration -^ > 10 years -^

stability, C

p

-^ combination curve - tables

(^

)^

p D c

p c c^

C

C

F

C

F

F^

′^ =

Wood Columns 10Lecture 16

Foundations Structures

ARCH 331

Column Charts – Appendix A, 12 & 13

Wood Columns 11Lecture 16

Foundations Structures

ARCH 331

Procedure for Analysis1.

calculate L

/de^

min

-^

KL/d each axis, choose largest

obtain F´

c

-^

compute •^

K^ cE

=0.3 sawn

-^

K^ cE

= 0.418 glu-lam

compute F

• c

≈^

F^ c

C^ D

calculate F

cE

/F

*^ c and get C

(Table 14)p^

calculate

(^

(^2) ) d cE L

cE^

e

E K

F^

=

p c c^

C

F

F^

′^ =

Wood Columns 13Lecture 16

Foundations Structures

ARCH 331

Procedure for Design1.

guess a size (pick a section)

calculate L

/de^

min

-^

KL/d each axis, choose largest

obtain F´

c

-^

compute •^

K^ cE

=0.3 sawn

-^

K^ cE

= 0.418 glu-lam

compute F

• c

≈^

F^ c

C^ D

calculate F

cE

/F

*^ c and get C

(Table 14)p^

(^

(^2) ) d cE L

cE^

e

E K

F^

=

Wood Columns 14Lecture 16

Foundations Structures

ARCH 331

S2009abn

Procedure for Design (cont’d)6.

compute

compute P

allowable

= F

′^ ⋅c

A

-^

or find f

actual

= P/A

is P

≤^

P^ allowable

? (or f

actual

≤^

F^ ′

?)c

-^

yes: OK

-^

no: pick a bigger section and

go back to step 2

.

p c c^

C

F

F^

′^ =

Wood Columns 16Lecture 16

Foundations Structures

ARCH 331

Design of Columns with Bending •^

satisfy^ –

strength – stability

-^

pick^ –

section

Wood Columns 17Lecture 16

Foundations Structures

ARCH 331

Design •^

Wood

[] term – magnification factor for P-

Δ

F’ bx^

• allowable bending strength

(^0). 1

1

2

≤ ⎤ ⎥⎦

⎡ ⎢⎣

− ′

⎤ ⎥ ⎦ ⎡ ⎢ ⎣

′

cEx c

bx

bx

c c

F f

F

f

f F

Wood Columns 19Lecture 16

Foundations Structures

ARCH 331

Laminated Timber Arches •^

two & three hingedarches

-^

bent to wide range ofcurves

-^

bending andcompression

-^

residual stress fromlaminating, C

c

Wood Columns 20Lecture 16

Foundations Structures

ARCH 331

Laminated Arch Design •^

radius of curvature, R, limited by lamthickness, t^ –

R = 100t – southern pine & hardwoods – R = 125t – softwood

-^

r = radius to inside faceof laminations

• •^

Fb

’ = F

(Cb

CF^

)c

2

C^

t r

C