34 / FRAME BUILDER - VOL7 NO3
RESEARCH & TECHNOLOGY
door slabs will distribute the dead 
load toward the jambs, this is not 
typically acknowledged in the 
design process. Rather, the entire 
weight of the door is applied as 
a uniform line load to the head 
assembly. This is conservative and 
accounts for loads that will be 
transmitted to the head assembly 
as the door opens.
Each jamb column must be 
designed to support half the dead 
weight of the door applied at the 
elevation of the upper hinge. 
As the door opens the weight 
of the door begins to move 
away from the building wall. 
This causes eccentricity in the 
rigid body door assembly. This 
eccentricity causes the door 
to want to pull out of the door 
opening. A force couple develops 
to counter this force. The eccentric 
deadload and the resisting force 
couple are at the maximum when 
the door is fully open.
Eccentric couple = W x H/4
Resisting couple = F x X
W = door weight (lbs) = 6 psf x 
width (ft) x height (ft) - (Use 8 psf 
if the door is lined)
H = door height (ft) (Not opening 
height. Distance from floor to 
hinge line.)
X = distance from hinge line to 
rollers (Roller location in the fully 
open position is
typically top of door opening but 
can be lower with some specialty 
door assemblies.)
 F = Force of resisting couple
 Solving: F = WH / 4X
The force couple is shared equally 
by both jamb columns. Each jamb 
also supports half the dead weight 
of the door.
Mono-fold Door — Wind Load
Similar to bifold doors, MWFRS 
pressures will be used when 
designing the framing required to 
support mono-fold doors.
Positive and negative wind load 
applied to a mono-fold door is 
transferred through the sheathing 
to light horizontal tubes that act 
as girts. The light tubes frame into 
heavy vertical tube framing. The 
vertical framing is spaced roughly 
10 feet on-center. The vertical 
frames transfer the load down 
to the wind truss located at the 
bottom of the door and up to the 
header attached to the building 
frame located at the top of the 
door opening. Mono-fold doors 
require special load cases for wind 
pressure and suction forces.
continued from page: 33
THE OFFICIAL NFBA MAGAZINE

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