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SWH Solar Racking Installation Guide | Version 12.10.v2
23
[2.1.] Using Standard Beam Calculations, Structural Engineering
Methodology
ASCE 7-10
Step 6: Determine the Uplift Point Load, R (lbs), at
each connection based on rail span
You must also consider the Uplift Point Load, R (lbs), to
determine the required lag bolt attachment to the roof
(building) structure.
Total Design Load (uplift):
P
psf
Step 1
Module length perpendicular to rails:
B
x
ft
Rail Span:
L
x
ft
Step 3
/2
Uplift Point Load:
R
lbs
Table 9. Uplift Point Load Calculation
Table 10. Lag pull-out (withdrawal) capacities (lbs) in typical roof lumber (ASD)
Lag screw specifications
Specific
5
⁄
16
˝ shaft,*
gravity
per inch thread depth
Douglas Fir, Larch
0.50
266
Douglas Fir, South
0.46
235
Engelmann Spruce, Lodgepole Pine
(MSR 1650 f & higher)
0.46
235
Hem, Fir, Redwood (close grain)
0.43
212
Hem, Fir (North)
0.46
235
Southern Pine
0.55
307
Spruce, Pine, Fir
0.42
205
Spruce, Pine, Fir
(E of 2 million psi and higher
grades of MSR and MEL)
0.50
266
Sources: American Wood Council, NDS 2005, Table 11.2A, 11.3.2A.
Notes: (1) Thread must be embedded in the side grain of a rafter or other structural member integral
with the building structure.
(2) Lag bolts must be located in the middle third of the structural member.
(3) These values are not valid for wet service.
(4) This table does not include shear capacities. If necessary, contact a local engineer to specifiy lag bolt size
with regard to shear forces.
(5) Install lag bolts with head and washer flush to surface (no gap). Do not over-torque.
(6) Withdrawal design values for lag screw connections shall be multiplied by applicable adjustment factors if
necessary. See Table 10.3.1 in the American Wood Council NDS for Wood Construction.
*Use flat washers with lag screws.
Thread
depth
Use Table 10 to select a lag bolt
size and embedment depth to
satisfy your Uplift Point Load Force,
R (lbs), requirements. Divide the
uplift pointload by the withdrawal
capacity, this results in inches of
5/16 lagbolt embedded thread
depth needed to counteract the
bolt is used (as with a concrete
or steel), consult fastener mfr
documentation.
It is the installer’s responsibility to
verify that the substructure and
attachment method is strong
enough to support the maximum
point loads calculated according
to Step 5 and Step 6.