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made possible by hydraulics can 
result in significant dynamic 
effects. It is critical we understand 
the structural impact of these 
doors so we can design the 
building to safely resist the 
imposed forces.
This article will discuss 
generalized mono and bi-
fold doors. There are many 
manufacturers of these doors. 
Each door system has unique 
characteristics that could impact 
specific load paths. The designer 
must understand the specifics of 
the door being used and adjust 
the loading and design procedures 
appropriately.
Definitions
Bi-fold door — a door composed 
of two rigid leaves with horizontal 
hinge lines located at the door top 
and the door mid-line. The door 
is opened by pulling the bottom 
of the door toward the top with 
cables or straps that are wound 
around a motorized winding 
device. This shortens the distance 
between the top and bottom of 
the doorframe and causes the 
center of the door to push out 
away from the building. The door 
is supported at the top via hinges 
attached to the building and at the 
bottom with rollers that roll up 
the jamb columns. Typically bi-
fold doors have trusses that span 
across the door at the bottom of 
the lower leaf, and near the center 
hinge point of the lower and 
upper leaves. The trusses can be 
located either inside the building 
(typical) or exterior to the door. 
The trusses carry wind load to the 
jamb columns when the door is 
closed and distribute dead load 
to the door edge when the door is 
open.
Mono-fold door — a door 
composed of a single rigid leaf. 
The door is supported at the top 
via a frame and hinges attached 
to the building. The door includes 
an integral frame to which a large 
hydraulic ram is attached at each 
doorjamb. The bottom of the 
door leaf is forced to pivot away 
from the building by extending 
the hydraulic cylinders, opening 
the door. Mono-fold doors have a 
truss located near the bottom of 
the door. The truss carries wind 
load to the jamb columns when 
the door is closed and distributes 
dead load to the door edge when 
the door is open.
Construction
The door slabs of mono and bi-
fold doors are typically similar 
in construction. Structural steel 
YOUR TOOLKIT FOR BUILDING EXCELLENCE
Photo Courtesy of Wick Buildings 
Mono-Fold Hydraulic Door

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