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Design of Columns and Beam-Columns in Timber. Column failures Material failure (crushing) Elastic buckling (Euler) Inelastic buckling (combination of.

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Presentation on theme: "Design of Columns and Beam-Columns in Timber. Column failures Material failure (crushing) Elastic buckling (Euler) Inelastic buckling (combination of."— Presentation transcript:

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 P Δ L eff

3 Truss compression members Fraser Bridge, Quesnel

4 Column behaviour Displacement Δ (mm) Axial load P (kN) P cr P P Δ Perfectly straight and elastic column Crooked elastic column Crooked column with material failure L eff

5 Pin-ended struts Shadbolt Centre, Burnaby

6 Column design equation P r =  F c A K Zc K C where  = 0.8 and F c = f c (K D K H K Sc K T ) size factor K Zc = 6.3 (dL) -0.13 ≤ 1.3 d L axis of buckling P

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

8 Capacity of a column LeLe PrPr combination of material failure and buckling elastic buckling material failure  FcA FcA π 2 EI/L 2 (Euler equation)

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

10 Column buckling factor K C C C = L e /d KCKC 1.0 50 limit  0.15

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

12 Effective length L eff = length of half sine-wave = k L k (theory)1.00.50.7> 1 k (design)1.00.650.8> 1 non-sway sway* P PP PP P PPPP LeLe LeLe LeLe LeLe * 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 Effective length L ex L ey

17 Round poles in a marine structure

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

19 L/d ratios LeLe L ey L ex d dydy dxdx x x y y y y

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 Effective length (sway cases) L eff = length of half sine-wave = k L k (theory)1.02.0 1.0 { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/13/3613836/slides/slide_25.jpg", "name": "Effective length (sway cases) L eff = length of half sine-wave = k L k (theory)1.02.0 1.0

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

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

32 Combined stresses Bi-axial bending Bending and compression

33 Heavy timber trusses Abbotsford arena

34 Roundhouse Lodge, Whistler Mountain

35 neutral axis f max = f a + f bx + f by < f des ( P f / A ) + ( M fx / S x ) + ( M fy / S y ) < f des (P f / A f des ) + (M fx / S x f des ) + (M fy / S y f des ) < 1.0 (P f / P r ) + (M fx / M r ) + ( M fy / M r ) < 1.0 x x f bx = M fx / S x M fx y y f by = M fy / S y M fy The only fly in the pie is that f des is not the same for the three cases f a = P f / A PfPf

36 Moment amplification ΔoΔo Δ max P P P E = Euler load

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

38 3 storey walk-up (woodframe construction)

39 New Forestry Building, UBC, Vancouver

40 Stud wall construction

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


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