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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”
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Glulam Properties
Effects of Defects
Joining methods
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Glulam Properties
Layup Strategies
• outer vs core• top vs bottom• effects on stress• effects of orientation
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Actual Flexure Stress fb
fb = Mc/I = M/S
S = I/c = bd2/6
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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
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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
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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
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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
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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 )
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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).
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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
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Glulam - Analysis
Example Problem
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D + Lr1.25
CM = 1.0
Glulam - AnalysisExample Problem
1. calculate shear and moment.
2. determine point of contraflexure
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Glulam - AnalysisExample Problem 20F-V2 SP/SP
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Glulam - AnalysisExample Problem
3. determine factors
use lesser of CL or CV
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Glulam - AnalysisExample Problem
3. Determine factors
use lesser of CL or CV
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Glulam - AnalysisExample Problem
4. Check stress
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Glulam - AnalysisExample Problem
Now check section with negative moment
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Glulam - AnalysisExample Problem
Now check section with negative moment
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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
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Glulam - DesignExample Problem
1. Guess section: d” → 0.9 L’ b/d → 1/3 to 1/5
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braced at supports and load point
Glulam - DesignExample Problem
2. Calculate CV
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Glulam - DesignExample Problem
3. Calculate CL
use lesser of CV or CL
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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
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Glulam - DesignExample Problem
9. Check shear stress
10. Check bearing
11. Check deflection
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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
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