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Architecture 544Wood Structures
Glue Laminated TimbersGlulam
• Properties• ASD approach • NDS criteria • Wood Beam Analysis• Wood Beam Design
University of Michigan, TCAUP Wood Slide 1 of 25
Glulam Properties
• Grading – AITC or APA-EWS• Orientation – x and y axis• Density values• Resawn glulams for narrower sections
University of Michigan, TCAUP Wood Slide 2 of 25
Glulam Properties
Dimensions
• Limited mostly by transport
• Standard dimension given in NDS
Supplement
• Depth based on lam thickness
and number
• Flatter members use 1 ½ ” or
1 3/8” lams
• Tightly curved members use
thinner lams, ¾”
University of Michigan, TCAUP Wood Slide 3 of 25
Glulam Properties
Effects of Defects
Joining methods
University of Michigan, TCAUP Wood Slide 4 of 25
Glulam Properties
Layup Strategies
• outer vs core• top vs bottom• effects on stress• effects of orientation
University of Michigan, TCAUP Wood Slide 5 of 25
Actual Flexure Stress fb
fb = Mc/I = M/S
S = I/c = bd2/6
University of Michigan, TCAUP Wood Structures Slide 6 of 25
Allowable Flexure Stress Fb’
Fb from tables determined by species and grade
Fb’ = Fb (usage factors)
usage factors for flexure:CD Load Duration FactorCM Moisture FactorCt Temperature FactorCL Beam Stability FactorCV Volume FactorCfu Flat UseCc Curvature FactorCI Stress Interaction Factor
Allowable Stress Design by NDS – Ch. 5Flexure
Actual Shear Stress fv
fv = VQ / I b = 1.5 V/A
Can use V at d from support as maximum
University of Michigan, TCAUP Wood Structures Slide 7 of 25
Allowable Shear Stress Fv’
Fv from tables determined by species and grade
Fv’ = Fv (usage factors)
usage factors for shear:CD Load Duration FactorCM Moisture FactorCt Temperature FactorCvr Shear Reduction Factor
Allowable Stress Design by NDSShear
Actual Compression Stress fb
fc = P/A
University of Michigan, TCAUP Wood Structures Slide 8 of 25
Allowable Compression Stress Fc’
Fc from tables determined by species and grade
•Fc’ = Fc (usage factors)
• usage factors for flexure:
– CD Load Duration Factor
– CM Moisture Factor
– Ct Temperature Factor
– CP Column Stability Factor
Allowable Stress Design by NDSCompression
Adjustment Factors
University of Michigan, TCAUP Wood Slide 9 of 25
Adjustment Factors
Allowable Flexure Stress Fb’
Fb from tables determined by species and grade
Fb’ = Fb (CD CM Ct CL CV Cfu Cc CI )
Usage factors for flexure:CD Load Duration FactorCt Temperature Factor
University of Michigan, TCAUP Wood Slide 10 of 25
2012 NDS
Adjustment Factors
Allowable Flexure Stress Fb’
Fb from NDS tables
Fb’ = Fb (CD CM Ct CL CV Cfu Cc CI )
Usage factors for flexure:CM Moisture FactorCfu Flat Use
University of Michigan, TCAUP Wood Slide 11 of 25
Adjustment Factors
Allowable Flexure Stress Fb’
Fb from NDS tables
Fb’ = Fb (CD CM Ct CL CV Cfu Cc CI )
Usage factors for flexure:CV Volume Factor
University of Michigan, TCAUP Wood Slide 12 of 25
Adjustment Factors
Allowable Flexure Stress Fb’
Fb from NDS tables
Fb’ = Fb (CD CM Ct CL CV Cfu Cc CI )
Usage factors for flexure:Cc Curvature FactorCI Stress Interaction Factor
University of Michigan, TCAUP Wood Slide 13 of 25
Adjustment Factors - CLAllowable Flexure Stress Fb’
Fb from tables determined by species and gradeFb’ = Fb (CD CM Ct CL CV Cfu Cc CI )
University of Michigan, TCAUP Wood Slide 14 of 25
CL Beam Stability Factor
CL is calculated using equation 3.3-6
The maximum allowable slenderness, RB is 50
CL is not used together with CV. Use the lesser.CL is not used together with CI. Use the lesser (see commentary).
University of Michigan, TCAUP Wood Slide 15 of 25
Adjustment Factors for Shear
Allowable Flexure Stress Fv’
Fv from tables determined by species and grade
Fv’ = Fv (usage factors)
Usage factors for flexure:CD Load Duration FactorCM Moisture FactorCt Temperature FactorCvr Shear Reduction Factor
University of Michigan, TCAUP Wood Slide 16 of 25
Glulam - Analysis
Example Problem
University of Michigan, TCAUP Wood Slide 17 of 25
D + Lr1.25
CM = 1.0
Glulam - AnalysisExample Problem
1. calculate shear and moment.
2. determine point of contraflexure
University of Michigan, TCAUP Wood Slide 18 of 25
Glulam - AnalysisExample Problem 20F-V2 SP/SP
University of Michigan, TCAUP Wood Slide 19 of 25
Glulam - AnalysisExample Problem
3. determine factors
use lesser of CL or CV
University of Michigan, TCAUP Wood Slide 20 of 25
Glulam - AnalysisExample Problem
3. Determine factors
use lesser of CL or CV
University of Michigan, TCAUP Wood Slide 21 of 25
Glulam - AnalysisExample Problem
4. Check stress
University of Michigan, TCAUP Wood Slide 22 of 25
Glulam - AnalysisExample Problem
Now check section with negative moment
University of Michigan, TCAUP Wood Slide 23 of 25
Glulam - AnalysisExample Problem
Now check section with negative moment
University of Michigan, TCAUP Wood Slide 24 of 25
Glulam - DesignProcedure
Given: Glulam grade, loading, bracing, conditions (moisture, temperature)
Find: section dimensions
1. Guess section: d” → 0.9 L’ b/d → 1/3 to 1/5
2. Calculate CV
3. Calculate CL
4. Estimate DL
5. Calculate moment
6. Determine actual bending stress fb = M/Sx
7. Determine F’b
8. Check bending stress, revise if required
9. Check shear stress
10. Check bearing
11. Check deflection
University of Michigan, TCAUP Wood Slide 25 of 25
Glulam - DesignExample Problem
1. Guess section: d” → 0.9 L’ b/d → 1/3 to 1/5
University of Michigan, TCAUP Wood Slide 26 of 25
braced at supports and load point
Glulam - DesignExample Problem
2. Calculate CV
University of Michigan, TCAUP Wood Slide 27 of 25
Glulam - DesignExample Problem
3. Calculate CL
use lesser of CV or CL
University of Michigan, TCAUP Wood Slide 28 of 25
vv
Glulam - DesignExample Problem
4. Estimate DL
5. Calculate moment
6. Determine actual bending stressfb = M/Sx
7. Determine F’b
8. Check bending stress, revise if required
University of Michigan, TCAUP Wood Slide 29 of 25
Glulam - DesignExample Problem
9. Check shear stress
10. Check bearing
11. Check deflection
University of Michigan, TCAUP Wood Slide 30 of 25
Glulam – Column CapacityProcedure
Given: Glulam grade, loading, bracing, conditions (moisture, temperature)
Find: section dimensions
1. Estimate section
1. estimate area = P/F*c
2. check l/d
3. estimate CP
4. choose trial size
2. Calculate CP
3. Determine other adjustment factors
4. Determine F’c
5. Capacity P = F’c A
University of Michigan, TCAUP Wood Slide 31 of 25
Glulam – Column AnalysisProcedure
1. Check shear stress
2. Check deflection
University of Michigan, TCAUP Wood Slide 32 of 25