2013-4-19 Design of Wood Members Prof.He Minjuan Tongji University,Shanghai China Words and Expressions Design of Wood Members 园 Crushing 压碎 Buckling 1.Tension members Cross-bracing 交叉支推 Bridging 剪刀浮 2.Compression members Notch 缺口，四 (A)Sym 3.Bending members Sendermesraio 长细比 4.Bending combined with tension members 5.Bending combined with compression members Shrinkage crack 1.Tension members 1.Tension members →N -tension -net area(within 150mm) 1
2013-4-19 1 Design of Wood Members Prof. He Minjuan Tongji University, Shanghai China Words and Expressions Crushing 压碎 Buckling 屈曲 Cross-bracing 交叉支撑 Bridging 剪刀撑 Notch 缺口,凹槽 (A)Symmetrically (非)对称地 Slenderness ratio 长细比 Benign 良性的 Brittle 脆性的 Shrinkage crack 收缩裂缝 Design of Wood Members 1.Tension members 2.Compression members 3.Bending members 4.Bending combined with tension members 5.Bending combined with compression members 1. Tension members 1. Tension members Ag An N N t n f A N where —— tension —— net area (within 150mm) —— tension strength N An ft
2013-4-19 2.Compression members 园 2.Compression members 2.Compression members 2.Compression members Pin-ended struts Glulam arches and cross-bracing (交叉支撑) 2.Compression members 园 2.Compression members 园 4444 ●Material failure(crushing.压碎)TT ●Elastic buckling(Euler屈曲) a buckling and material failure) x'El P 2 m 2
2013-4-19 2 2. Compression members 2. Compression members 2. Compression members Pin-ended struts 2. Compression members Glulam arches and cross-bracing （交叉支撑） 2. Compression members Material failure (crushing,压碎) Elastic buckling (Euler屈曲) Inelastic buckling (combination of buckling and material failure) P P Δ Leff 2. Compression members 2 2 eff cr L EI P Displacement Δ (mm) Axial load P (kN) Pcr Perfectly straight and elastic column Crooked elastic column Crooked column with material failure P P Δ Leff
2013-4-19 2.Compression members 2.Compression members (1)Strength N (2) compression 309 —trength -s f g on meml 4 calculation area of stability dered 2.Compression members 2.Compression members ” .9 8上 2.Compression members 2.Compression members 3
2013-4-19 3 2. Compression members (1) Strength where —— compression —— net area —— compression strength (2) Stability where —— coefficient of stability —— calculation area of stability N An fc A0 c n f A N fc A N 0 N L 2. Compression members (1) No notches: A0=A (2) Notches not at the edge: A0=0.9A (3) Notches at the edge symmetrically: A0=An (4) Notches at the edge asymmetrically: Calculation according to eccentrically compression member (5) When calculate stability, bolt holes may not considered as notches. 2. Compression members 2. Compression members 2. Compression members Pin connected Note: water damage 2. Compression members fixed or pin connected?
2013-4-19 3.Bending members 3.Bending members arallel Strand Lumber girder 3.Bending members 3.Bending members Bending failure Lateral torsional buckling Shear failure ●Notch failure ●Bearing failure Excessive deflections 3.Bending members 园 3.Bending members 园 (1)Bending failure in compression (1)Bending failure in tension Most likely failure mode ●Brittle(脆性的) Combnationofshear.atouh 1 tension fracture is the initiating moc 人1 4
2013-4-19 4 3. Bending members 3. Bending members Parallel Strand Lumber girders 3. Bending members 3. Bending members Bending failure Lateral torsional buckling Shear failure Notch failure Bearing failure Excessive deflections 3. Bending members (1) Bending failure in compression Only likely for very high grade material Benign（良性的） failure mode 3. Bending members (1) Bending failure in tension Most likely failure mode Brittle（脆性的） Combination of tension and shear, although tension fracture is the initiating mode
2013-4-19 3.Bending members 3.Bending members (1)Bending failure 6 Cuw here hendine moment net elastic section modulus f. -bending resistance strength 3.Bending members 3.Bending members 触 (2)Lateral torsional buckling (2)Lateral torsional buckling Elastic buckling:Mr=√E,Gg % wher -lateral stability factor of member in flexure.determined based on the ioof the height to width of section. ateral brace and timber strength grade ete. 3.Bending members eral suppo 3.Bending members t spacing Bridging(剪刀)for Prevention of lateral 4 torsional buckling 5 <6.5 9-1.0 <7.5TK- 5
2013-4-19 5 3. Bending members (1) Bending failure —— net elastic section modulus —— bending resistance strength m n f W M where M —— bending moment Wn fm 3. Bending members Lateral torsional buckling of deep I-joists 3. Bending members (2) Lateral torsional buckling x x x y y y y Δx Δy θ Le 3. Bending members (2) Lateral torsional buckling m l f W M where —— bending moment —— section modulus —— bending resistance strength —— lateral stability factor of member in flexure, determined based on the ratio of the height to width of section, lateral brace and timber strength grade etc. M fm W l 3. Bending members Prevention of lateral torsional buckling φl = 1.0 when lateral support is provided as shown h/b Lateral support at spacing: < 4 no support < 5 purlins or tie rods < 6.5 compression edge held by decking or joists < 7.5 top edge plus bridging < 9 both edges h b < 610 mm < 610 mm < 8h 3. Bending members Bridging（剪刀撑） for floor joists