Wood Member Properties

Last updated September 25, 2023
By Ian Story

Typical Beam Materials

Species_and_Grade	Fb	Ft	Fv	Fc⟂	Fc	E	Emin	G	$/BDFT	Frt(1)	Fb⟂/Ft⟂(2)	Gxx/Gyy
SPF Stud	675	350	135	425	725	1.20	0.44	0.42
SPF #1/#2	875	450	135	425	1,150	1.40	0.51	0.42	$2.69	—	40	~1.00
DF #2 (4x)	900	575	180	625	1,350	1.60	0.58	0.50
DF #2 (6x Beams)	875	425	170	625	600	1.30	0.47	0.50
DF #2 (6x Posts)	750	475	170	625	700	1.30	0.47	0.50
DF #1 & Btr (4x)	1,200	800	180	625	1,550	1.80	0.66	0.50	$4.29	—		~1.00
DF #1 (6x Beams)	1,350	675	170	625	925	1.60	0.58	0.50	$4.13	—	32	~1.00
DF #1 (6x Posts)	1,200	825	170	625	1000	1.60	0.58	0.50	$4.13
GLB 24F-1.8E(3)	2,400	775	265	650	1,600	1.80	0.95	0.50	$5.63	88	26	1.12
GLB 24F-1.8E(3) (pl)	1,450	775	230	560	1,600	1.60	0.85	0.50	$5.63	76	26	1.12
LSL 1.5E	2,250	1,815	505	860	2,105	1.50	0.76	0.50	$13.20	—	20	2.46
LSL 1.5E (plank)	2,525	1,815	150	750	2,105	1.50	0.76	0.50	$13.20	—	20	2.46
LVL 2.0E	2,600	1,895	285	750	2,510	2.00	1.01	0.50	$16.27	—	20	1.46
LVL 2.0E (plank)	2,690	1,895	190	680	2,510	2.00	1.01	0.50	$16.27	—	20	1.46
PSL 1.8E	2,500	1,995	230	600	2,500	1.80	0.91	0.50	$17.61	—	20	1.28
PSL 1.8E (plank)	2,400	1,995	190	595	2,500	1.80	0.91	0.50	$17.61	—	20	1.28

Where

F_b = Allowable stress at extreme bending fiber (psi)

F_t = Allowable tensile stress (psi)

F_v = Allowable shear stress parallel to grain (psi) (don’t need to check shear stress parallel to grain, because it is much higher than shear stress parallel to grain)

F_c⟂ = Allowable compression stress perpendicular to grain (bearing stress on face of member) (psi)

F_c = Allowable compression stress parallel to grain (psi)

E = Modulus of elasticity (10⁶ psi)

E_min = Modulus of elasticity for buckling (10⁶ psi)

F_rt = Allowable radial tensile stress (psi)

F_b⟂/F_t⟂ = Estimated allowable tensile / extreme bending fiber stress perpendicular to grain (psi) ⁽²⁾

G_xx/G_yy = Ratio of shear modulus in beam orientation to plank orientation

$/BDFT = Price per board foot (number from the Dunn Lumber catalog as of 7/23/22)

(1) Use 15 psi for radial tension for any loading other than wind or seismic

(2) Cross-grain tension or bending are best avoided in most cases, because this is a brittle failure mode and is not extensively tested. There are virtually no published engineering standards for this property. The values here are provided as estimates based on in-house calculations, intended as a rough check for incidental load applications. Cross-grain tension exhibits a notable size effect: the larger the beam, the greater likelihood it will contain a weak spot that will cause a failure. So the analysis is probabilistic based on a desired probability of survival. The estimated values presented here are based on ultimate stress calculated at an 95% probability of survival, which are then divided by a safety factor of 2. These values are based on the following member sizes for a 12″ long block (longer blocks will have lower allowed stresses due to the size effect): 2×12 (SPF), 4×12 (DF), 6×12 (DF timber), 6 3/4″ x 21″ (GLB)

(3) Specify 24F-V4 (default option) for simple span glulam beams. Specify 24F-V8 for cantilever glulam beams or other situations where beam has significant negative moment. The V8 specification uses high-strength plies both top and bottom, while V4 uses high strength plies only on the bottom (tension) face.

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