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Design of Columns and Beam-Columns in Timber

Design of Columns and Beam-Columns in Timber. Column failures. Material failure (crushing) Elastic buckling (Euler) Inelastic buckling (combination of buckling and material failure). P. L eff. Δ. P. Truss compression members Fraser Bridge, Quesnel. Column behaviour.

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Design of Columns and Beam-Columns in Timber

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  1. Design of Columns and Beam-Columns in Timber

  2. Column failures • Material failure (crushing) • Elastic buckling (Euler) • Inelastic buckling (combination of buckling and material failure) P Leff Δ P

  3. Truss compression members Fraser Bridge, Quesnel

  4. Column behaviour Perfectly straight and elastic column Pcr P Crooked elastic column Leff Δ Axial load P (kN) Crooked column with material failure P Displacement Δ (mm)

  5. Pin-ended struts Shadbolt Centre, Burnaby

  6. Column design equation P axis of buckling Pr =  Fc A KZc KC where  = 0.8 and Fc = fc (KD KH KSc KT) size factor KZc = 6.3 (dL)-0.13≤ 1.3 d L

  7. Glulam arches and cross-bracing UNBC, Prince George, BC

  8. material failure Capacity of a column FcA Pr combination of material failure and buckling π2EI/L2 (Euler equation) elastic buckling Le

  9. Pin-ended columns in restroom building North Cascades Highway, WA Non-prismatic round columns Actual pin connections

  10. Column buckling factor KC 1.0 KC limit  0.15 CC = Le/d 50

  11. What is an acceptable l/d ratio ?? Clustered columns Forest Sciences Centre, UBC L/d ration of individual columns ~ 30

  12. P P P P P P P P P P Effective lengthLeff = length of half sine-wave = k L Le Le Le Le * Sway cases should be treated with frame stability approach

  13. Glulam and steel trusses Velodrome, Bordeaux, France All end connections are assumed to be pin-ended

  14. Pin connected column base Note: water damage

  15. Column base: fixed or pin connected ??

  16. Ley Lex Effective length

  17. Round poles in a marine structure

  18. Partially braced columns in a post-and-beam structure FERIC Building, Vancouver, BC

  19. Le Ley Lex L/d ratios y y x x y y d dx dy

  20. Stud wall axis of buckling d L ignore sheathing contribution when calculating stud wall resistance

  21. Stud wall construction

  22. Fixed or pinned connection ? Note: bearing block from hard wood

  23. An interesting connection between column and truss (combined steel and glulam truss)

  24. Slightly over-designed truss member (Architectural features)

  25. P P P P P P P P P P Effective length (sway cases)Leff = length of half sine-wave = k L Le Le Le Le Note: Sway cases should only be designed this way when all the columns are equally loaded and all columns contribute equally to the lateral sway resistance of a building

  26. Sway frame for a small covered road bridge

  27. Sway permitted columns ….or aren’t they ??

  28. Haunched columns UNBC, Prince George, BC

  29. Frame stability • Columns carry axial forces from gravity loads • Effective length based on sway-prevented case • Sway effects included in applied moments • When no applied moments, assume frame to be out-of-plumb by 0.5% drift • Applied horizontal forces (wind, earthquake) get amplified • Design as beam-column

  30. Note: This column does not contribute to the stability of the frame Frame stability(P- Δ effects) Htotal = H  = amplification factor H = applied hor. load W H Δ h Δ = 1st order displacement

  31. Minimal bracing, combined with roof diaphragm in lateral direction Haunched frame in longitudinal direction Sway frame for a small covered road bridge

  32. Combined stresses Bi-axial bending Bending and compression

  33. Heavy timber trusses Abbotsford arena

  34. Roundhouse Lodge, Whistler Mountain

  35. Pf fa = Pf / A neutral axis x fbx = Mfx / Sx Mfx x y fby = Mfy / Sy Mfy y fmax = fa + fbx + fby < fdes ( Pf / A ) + ( Mfx /Sx ) + ( Mfy / Sy ) < fdes (Pf / Afdes) + (Mfx /Sxfdes) + (Mfy / Syfdes) < 1.0 (Pf / Pr) + (Mfx /Mr) + ( Mfy / Mr) < 1.0 The only fly in the pie is that fdes is not the same for the three cases

  36. Moment amplification P Δo Δmax PE = Euler load P

  37. Interaction equation Axial load Bending about x-axis Bending about y-axis

  38. 3 storey walk-up (woodframe construction)

  39. New Forestry Building, UBC, Vancouver

  40. Stud wall construction

  41. wall and top plate help to distribute loads into studs joists top plate wall plate d L studs sill plate check compression perp.

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