Connection Details

 

 General Principles

1. minimize across-the-grain distance between restraining elements

• example

2. accommodate shrinkage and swelling

• example

3. consider connection movement

• rotation
• example

4. principles apply to glulams AND sawn lumber, but importance increases with member size

• example

5. transferring loads by compression ⊥ to grain is generally preferred

• example
• example

 6. cracks render bolts ineffective

  

 

References

1. Textbook

2. American Institute of Timber Construction (AITC) Publications

AITC 104 Typical Construction Details
Timber Construction Manual  $105  (S&T library, 1985)

3. ICC Free Standards

APA The Engineered Wood Association T300 Glulam Connection Details

4. American Wood Council

ASD-LRFD Manual section M10.4 Typical Connection Details

 

 

Example Connections

 

1. typical beam-to-column

a. tee

• example 
• cross-grain tension @ tee
• end rotation @ splice plate
• shape corners for full seat

b. end

 

c. moment splice

• example

 

 

2. beam-to-girder saddle

• compression ⊥ to grain @ three spots 
• different initial heights for shrinkage  (flooring, sheathing)
• bolts near bearing points to minimize cross-grain tension
• avoid boring holes in high-quality outer lams

 

 

3. face hanger

• example
• example 
• bolts in upper half of supporting beam, but not in extreme bending fibers, especially in cantilevers
• shear @ end of supported beam

 

 

4. face clip

• no compression ⊥ to grain  (only for light loads)
• cross-grain tension

 

 

5. cantilever hinge

• section 6.17
• see second photo
• example
• example
• problems
  • compression ⊥ to grain @ bottom of supported beam
  • compression ⊥ to grain @ top of supporting beam
  • 2X vertical movement with shrinkage
  • joint rotation
• fixes
  • balance the eccentric moment
  • note bolt location in slots
  • separate splice plate at mid-depth if needed

 

 

6. uplift

• compression ⊥ to grain
• edge distance
• shear stresses due to uplift
• end distance

 

 

7. beam to continuous column

• problems
  • cross-grain tension
  • horizontal shear
• fix
  • compression ⊥ to grain @ beam seat
  • tension + rotation @ tie clip
  • lateral stability @ clip angle

 

 

8. notch in tension side

• recessed for connection hardware, conduit, etc.
• renovation
  • don't know original intent
  • details covered up
• problems
  • stress concentration
  • Peterson's Stress Concentration Factors
• fix
  • avoid

 

 

9. end notch

• problems
  • reduced shear strength
  • stress concentration
  • exposure of end grain  (non-uniform drying)
• fix
  • lower connection
  • add lateral support
  • APA EWS S560 Field Notching and Drilling of Glued Laminated Timber Beams

 

 

10. inclined beam - lower support

• similar to notch
• problems
  • shear strength
  • exposed end grain on tension side
• fix
  • lower connection
  • bearing on tapered cut
  • exposed end grain on compression side

 

 

11. inclined beam - upper support

• problems
  • shear strength
  • stress concentration
• fix
  • sloping seat, but be careful of eccentricity

 

 

12. suspending multiple loads

• mechanical/electrical equipment OR joists framing into side of beam
• problems
  • cross-grain tension
  • horizontal shear
  • stress concentrations
• fixes
  • above neutral axis 
  • bearing on top

 

 

13. suspending isolated loads

• problems
  • similar to multiple loads
• fix
  • limit to small loads + small fasteners
  • minimum of 6 in.  (AITC 104-2003)

 

 

14. truss heel

• problems
  • eccentricity  (combined stresses)
  • rotation
• fix
  • bearing for top chord
  • concentric forces
  • rotation on single top-chord fastener
  • slotted holes for shrinkage in bottom chord

 

 

15. other truss joints

• example
• example 
• problems
  • eccentricity
  • rigidity  (limited deflection and rotation → prying and splitting)
• fixes
  • separate gusset plates + shims
  • slotted holes

 

 

16. moisture protection

• problems
  • wicking of moisture
  • splashing
  • inability to dry
• fixes
  • treated wood
  • barriers
  • drain holes
  • air gaps