mytion timber onnectors design example · 2020. 1. 21. · myti on timber onnectors design example...
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MyTiCon Timber Connectors | #3-8287 124th St. | Surrey BC | V3W 9G2 | Canada | www.my-ti-con.com
MyTiCon Timber Connectors Design Example
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SWG ASSY® Screws as Tensile Reinforcement in Notched Beams
External loads on cross sections, notched beams, beams with holes, curved or pitched beams can cause
stress perpendicular to the grain. As perpendicular to the grain splitting is among the weakest
properties of wood; forces in this direction are typically a challenge for designers.
Whenever the perpendicular to grain stress exceeds the resistance available by the wood member,
reinforcement is required. In particular, rectangular notched beams experience high stress concentra-
tions which may exceed the specified capacities of the beam. In these areas a combination of stresses
may require beam reinforcement. These issues have been addressed by a publication released by the
Engineered Wood Association in 2006, “Field notching and drilling of glue laminated beams”. This
paper concluded that tensile reinforcement by means of screws is possible, yet it is suggested that re-
sponsibility lies in the designer when choosing the appropriate design methodology to follow.
This document aims to provide practical guidance for designers through a fully worked out example of
the tensile reinforcement of a rectangular notched glue laminated beam, using SWG ASSY® VG screws.
The screws are driven into the member perpendicular to the contact surface at an angle of 90°.
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2 MyTiCon Timber Connectors | #3-8287 124th St. | Surrey BC | V3W 9G2 | Canada | www.my-ti-con.com
Understanding & Specifying Engineered Structural SWG ASSY® Screws
MyTiCon Timber Connectors Design example
DESIGN OF: NOTCHED RECTANGULAR BEAM REINFORCEMENT
Conditions of use: Rectangular glue-laminated timber member with notch at the tension side at
supports (see 3.2.3)
Geometry: b = beam width
d = beam depth
dn = notch depth
= min( 0.1d ; 3”) (NDS 5.4.5)
de = distance from potential crack
to the edge (eff. depth)
Effective thread length: leff,1 = threaded length below potential crack
leff,2 = threaded length above potential crack
Adjusted Longitudinal Shear Design Value:
F’V = FV · CD· CM · Ct · Cvr [psi] (ASD)
where:
CD = Load duration factor
CM = Wet-service condition factor (Table 5A)
Ct = Temperature factor (5.3.4)
CVr = Shear reduction factor (5.3.10)
Adjusted Design Shear: V’r = [ (2/3) · F’V · b · de ] · [de/d]2 [lbf] (Eq. 3.4-3a)
SWG ASSY® VG Screws as
Reinforcement CONDITION: IF V ≥ V’r REINFORCEMENT IS REQUIRED
Tensile design force to be transmitted by the
reinforcing SWG ASSY® VG screws:
Fax,ED = kα · V (EC5, Eq.8.30)
where:
α = (de /d)
kα = 1.3 · [3 · (1—α)2 — 2 · (1—α)3]
Boundary conditions for screw design
withdrawal resistance:
effective screw length: leff = min {leff,1 ; leff,2}
minimum penetration depth: pmin = 6 * d (outside thread diameter) ≤ leff
(smaller penetration cannot be taken into account for beam reinforcement)
Withdrawal Design Value of one SWG ASSY®
VG screw (**as per ICC ESR-3178) W’ = min { **Withdrawal resistance [lbf/in] * leff
SWG ASSY® VG screw Tensile resistance [lbf]
Required number of reinforcing screws: nscrews = 0.9
√ ( Fax,ED / W’ )
de
SWG ASSY® VG
l eff
,1
l eff
,2
Vf
dn
d
Design checks are to be performed following the provisions outlined in NDS-2012; as well as ICC-ESR 3178 Report on fully threaded
ASSY® VG screws by a qualified designer
Minimum design edge distances and spacing between screws in accordance with ICC-ESR 3178
Note: The Reinforcing full thread screw
should be placed 5d away from edge (d=
outside thread diameter)
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3 MyTiCon Timber Connectors | #3-8287 124th St. | Surrey BC | V3W 9G2 | Canada | www.my-ti-con.com
Understanding & Specifying Engineered Structural SWG ASSY® Screws
MyTiCon Timber Connectors Design example
DESIGN EXAMPLE: NOTCHED BEAM REINFORCEMENT
Conditions of use: Rectangular glue-laminated timber member with notch at the tension side at
supports (see 3.2.3): GL 20F-1.5E (20F-V3 ; DF/DF) - 8 ½” x 18”
Bending primarily about the X-X axis
Geometry: b = 8 ½”= beam width
d = 15” = beam depth
dn = 3” = notch depth
= max of 3” (NDS 5.4.5)
de = distance from potential crack
to the edge (eff. depth) = 12”
Relevant Parameters for SWG ASSY®
VG screws:
Assume:
Use of ASSY® VG Cyl. (full thread): 3/8” x 6 1/4”
df = 3/8”
lthread = 145 mm = 5.71”
leff,1 = dn - Cyl. Head = 3” - 0.625” = 2.38”
leff,2 = lthread - leff,1 - ltip = 5.71”- 2.38” - 0.394” = 2.94”
Adjusted Longitudinal Shear Design Value: F’V = FV · CD · CM · Ct · Cvr [psi] & FV = 265 [psi] (Table 5A)
Assume:
CD = 1.0 (Standard Live Occupancy, 10yrs duration)
CM = 1.0 ; Ct = 1.0 ; CVr = 0.72 ;
F’V = 190.8 [psi]
Adjusted Design Shear: V’r = [ (2/3) · F’V · b · de ] · [de/d]2 [lbf] (Eq. 3.4-3a)
= [ (2/3) · 190.8 · 8.5 · 12” ] · [12”/15”]2 = 8,304 [lbf]
SWG ASSY® VG Screws as
Reinforcement CONDITION: IF V ≥ Vr’ REINFORCEMENT IS REQUIRED
Tensile design force to be transmitted by the
reinforcing SWG ASSY® VG screws: V = 9,000 lbf > V’r
Fax,ED = kα · V (EC5, Eq.8.30) ; where:
α = (de /d) = (12” / 15”) = 0.80
kα = 1.3 · [3 · (1—0.8)2 — 2 · (1—0.8)3] = 1.3[0.104) = .1352
Fax,ED = (.1352) · 9,000 = 1217 [lbf]
Boundary conditions for screw design
withdrawal resistance:
effective screw length: leff = min {leff,1 ; leff,2} = 2.38” (leff1)
minimum penetration depth: pmin = 6 * (0.394”) = 2.36” ≤ leff (ok)
Withdrawal Design Value of one SWG ASSY®
VG screw (**as per ICC ESR-3178) W’ = min { W = 194** x 2.38” = 461 [lbf]
SWG ASSY® VG screw Tensile resistance = 2,550 [lbf]
Required number of reinforcing screws : nscrews = 0.9 √ ( Fax,ED / W’ ) =
0.9 √ ( 1,217 / 461 ) = 2.94 = 3 screws
Note: The Reinforcing full thread screw
should be placed 5d away from edge (d=
outside thread diameter)
de
SWG ASSY® VG
l eff
,1
l eff
,2
Vf
dn
d