Wood Column Design: Form, Behavior, and Design - Lecture 16, Slides of Structural Design and Architecture

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Wood Columns 1Lecture 16

ARCHITECTURAL STRUCTURES: FORM, BEHAVIOR, AND DESIGN

lecture

sixteen

wood construction:

column design

Wood Columns 2Lecture 16

Compression Members (revisited)

• designed for strength & stresses
• designed for serviceability & deflection
• need to design for stability
  • ability to support a specified load without sudden or unacceptable deformations

Wood Columns 4Lecture 16

Critical Stresses (revisited)

• when a column gets stubby, crushing will limit the load
• real world has loads with eccentricity

Wood Columns 5 Lecture 16

Bracing (revisited)

• bracing affects shape of buckle in one direction
• both should be checked!

Wood Columns 7Lecture 16

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 Cp = column stability factor

Fc   Fc  C (^) D  CM  C (^) t  C (^) F  C^ p 

(Table 10.3)

Wood Columns 8Lecture 16

Strength Factors

• wood properties and load duration, CD
  • short duration
    • higher loads
  • normal duration

    • 10 years

• stability, Cp
  • combination curve - tables Fc ^  Fc * Cp   FcCD  C (^) p

http://www.swst.org/teach/set2/struct1.html

• Wood Columns 10Lecture
• Column Charts – Appendix A, 12 &

Wood Columns 11Lecture 16 Architectural Structures

Procedure for Analysis

1. calculate Le/dmin

• KL/d each axis, choose largest

2. obtain F ´ c

• compute
• KcE =0.3 sawn
• KcE = 0.418 glu-lam

3. compute Fc*  FcCD

4. calculate FcE/Fc*^ and get Cp (Table 14)
5. calculate

 

2 d

L

cE cE (^) e

K E

F 

Fc Fc Cp   *

Wood Columns 13 Lecture 16

Procedure for Design

1. guess a size (pick a section)

2. calculate Le/dmin

• KL/d each axis, choose largest

3. obtain F ´ c

• compute
• KcE =0.3 sawn
• KcE = 0.418 glu-lam

4. compute Fc*  FcCD

5. calculate FcE/Fc*^ and get Cp (Table 14)

 

2 d

L

cE cE (^) e

K E

F 

Wood Columns 14Lecture 16

Procedure for Design (cont’d)

6. compute

7. compute Pallowable = F c A

• or find factual = P/A

8. is P  Pallowable? (or factual  F c?)

• yes: OK
• no: pick a bigger section and go back to step 2.

Fc Fc Cp   *

Wood Columns 16Lecture 16

Design of Columns with Bending

• satisfy
  • strength
  • stability
• pick
  • section

Wood Columns 17Lecture 16

Design

• Wood

[] term – magnification factor for P-  F’ bx – allowable bending strength

1. 0 1

2  

    

  

  

  cEx bx c

bx c

c

F F f

f F

f

Wood Columns 19Lecture 16 Architectural Structures

Laminated Timber Arches

• two & three hinged arches
• bent to wide range of curves
• bending and compression
• residual stress from laminating, Cc

Wood Columns 20 Lecture 16

Laminated Arch Design

• radius of curvature, R, limited by lam thickness, t - R = 100t – southern pine & hardwoods - R = 125t – softwood
• r = radius to inside face of laminations
• Fb ’ = F b(CFCc)

2 C r

t C (^12000)  

  

  