Timber Just Needs To Move: Compliant Joinery and Timber Shrinkage

Transcription

1 Timber Just Needs To Move: Compliant Joinery and Timber Shrinkage Paul Malko Foard Panel

2 Presentation Rules Ask This questions any time. is a conversation, not a lecture.

3 Learning Environment Northeast, mostly New England Long, cold, humid winters with plenty of wind driven precipitation Long coastline Regional architecture New & historic timber Cut & 30+% MC 6% - 9% MC

4 Wood: The Perfect Building Material Plentiful Available Cost Effective Useful Strong Workable Sustainable Wood is so green, it grows on trees. Beautiful

5 Wood: The Perfect Building Material NEARLY Variable, anisotropic properties Prone to fungus decay Grows wet/green - used dry Dimensionally variable with moisture content Wood moves during and after construction.

6 Funny Shapes

7 3-Dimensional

8 Moisture Content (MC) As wood dries, shrinkage: is relatively stable above 30% continues linearly with MC stops when MC stabilizes MC FPL Wood Handbook, Chapter 13

9 How Much Shrinkage? Di (MC f MC i ) Δ D= MC i DD = Dimension Change S T D = Initial Dimension i MCf = Final MC MCi = Initial MC ST = Tangential Shrinkage Value FPL Wood Handbook, Eq. 13-3

10 Green/Inital MC Species White Pine Doug. Fir White Oak Green Sapwood MC 148% 115% 78% FPL Wood Handbook, Table 4-1

11 Final MC - Indoor FPL Wood Handbook, Figure 13-1

12 Air Drying Rate of Green Timber Location Time of year Species Timber size FPL Wood Handbook, Ch. 13

13 Air Drying Rate of Green Timber Low density species (pine, spruce, soft maple, etc) Good climate, good time of year Green to 25%-30% MC days for 1 THICK lumber FPL Wood Handbook, Ch. 13

14 Air Drying Rate of Green Timber High density species (oak, sinker hemlock, etc) Northern locations, wrong time of year Green to 25%-30% MC days for 1 THICK lumber FPL Wood Handbook, Ch. 13

15 How much shrinkage? MCi = Initial MC = 30% MCf = Final MC = 8% ST = Tangential Shrinkage (Wood Handbook, Table 4-3) Species ST % Shrinkage White Pine Doug. Fir White Oak % -5.5% -7.7%

16 KD Lumber? MCi = Initial MC = 19% MCf = Final MC = 8% ST = Tangential Shrinkage (Wood Handbook, Table 4-3) Species ST % Shrinkage Spruce Doug. Fir Yellow Pine % -2.8% -2.8%

17 Stacked Timber 6 heel DF rafter 12 DF deep plate

18 Stacked Timber Rafter (5 )cos(34 deg)(5.5%) = 0.23 Plate (12 )(5.5%) = 0.66 Total: 0.89 = 7/8

19 What To Do...

20 Wait, what about the diaphragm connections? Uplift at rafters? Rolling load on rafter? Out of plane shear load on rafter?

21 Wait, what about the diaphragm connections? Beveled Plate

22 Wait, what about the diaphragm connections? Bevel Blocking on Plate

23 Rafter / Purlin Tails

24 Rafter / Purlin Tails

25 Rakes Same scheme as eaves.

26 Rakes

27 Rakes

28 Rakes

29 Rakes

30 What About Roof Diaphragm Edges? 1 diaphragm or 2? Rolling or splitting load on fork? Maintain alignment to protect air sealing and roofing at ridge

31 What About Roof Diaphragm Edges?

32 What About Roof Diaphragm Edges? Rolling load on rafter? Strap over rafters can interfere with screws

33 What About Roof Diaphragm Edges?

34 What About Roof Diaphragm Edges?

35 Outside Corners

36 Inside Corners

37 KD 2x Shrinkage Matters

38 KD 2x Shrinkage Matters

39 Bridging the Transition

40 2 Types of Compliant Joinery One-time-use Cyclic

41 Cyclic - Moves Forever

42 High Allowable Deflection

43 Pre-Engineered Steel Frames: Very High Allowable Deflections

44 Durability SIPs are tolerant of deflection Air sealed joinery (SIP or otherwise) is not.

45 Risks of Deflection

46 Risks of Deflection

47 Strength vs Stiffness

48 Drywall Cracks

49 Shingle Ridging everywhere

50 Span-wise Joints were OK

51

52 Hinge at Joints Over Rafters

53 Non-compliant joint design forced to comply by L/180 allowable deflection

54 Foard's Internal Design Standards Assume everything is flexible Assume all timber will shrink Ignore air sealing needs only on disposable buildings Start the planning conversations early

55 Foard's Internal Design Standards Embedded Materials Avoid embedded KD Avoid multi-ply elements (Lots of EWP-sized glulam) Wind Bracing Use the frame as much as possible Stiff king studs Don't forget reactions L/240 Live max.

56 Foard's Internal Design Standards Adding timber rafters at rakes is often cost effective Ridge connections are tricky Intersecting roof lines are even trickier

57 Foard's Internal Design Standards Roof Panels: L/360 max. live L/240 max. total Wall Panels: L/240 max. live for mostly solid walls L/360 max. live for badly perforated walls Stiffness usually controls

58 Paul Malko Foard Panel West Chesterfield, NH