32 / FRAME BUILDER - VOL7 NO3
tubes are welded together to form 
a rectangular frame. Often lighter 
tubes, cold-formed shapes, or 
even 2x_ wood elements span 
between the primary structural 
tubes and act as secondary 
framing. The same corrugated 
steel cladding used to sheath 
the building is attached to the 
secondary framing. The steel 
cladding is the weathering 
surface. The steel cladding also 
provides shear strength, effectively 
turning the door slab into a 
diaphragm. Diaphragm action 
makes the door slab nearly rigid 
in plane. However, the door slab is 
relatively flexible out of plane.
Bi-fold doors rely on the building 
for support. The upper hinges are 
bolted directly to the building. 
Rollers located at the lower 
corners of the door roll directly 
on an angle attached to the jamb 
columns. The door is latched to 
the jamb column near the center 
hinge when the door is closed.
Mono-fold doors, despite 
occasional claims to the contrary, 
also depend on the building 
for support. Mono-fold doors 
typically include a tube steel 
perimeter frame that attaches 
to the building framing which 
forms the door opening. The 
perimeter frame can support the 
door vertically if it bears directly 
on a concrete foundation. The 
perimeter frame does absorb 
and redistribute eccentric forces 
generated by the hydraulic ram. 
However, the perimeter frame 
is typically not rigid or strong 
enough to resist the force couple 
resulting from the open door 
or the closed door under wind 
suction. The jamb columns and 
building framing are required to 
provide the strength and rigidity 
for global door stability.
Door Loads
Bi-fold Door — Wind Load
Bi-fold doors typically are large 
enough that it is appropriate to 
use MWFRS wind pressures when 
designing the framing required to 
support bi-fold doors. The actual 
door is designed by the door 
manufacturer.
Wind pressure applied to a bi-
fold door is transferred through 
the sheathing to horizontal and 
vertical frames. The door acts 
as a two-way slab spanning 
both vertically and horizontally. 
Typically bi-fold doors have 
trusses that span across the door 
at the bottom of the lower leaf 
RESEARCH & TECHNOLOGY
continued from page: 31
THE OFFICIAL NFBA MAGAZINE
Bi-Fold Door

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