FRAME BUILDER - VOL7 NO3 / 37 
of the cylinder. 
Fortunately, 
the horizontal 
component of the 
cylinder force F can 
be calculated if the 
vertical location 
of the cylinder to 
frame attachment 
is known. This is 
done by summing 
moments about the 
upper hinge. It can 
also be observed 
that the door weight 
W is equal to the 
sum of W1 and 
W2. It is common 
practice to apply the 
full door weight to 
the jamb columns 
at the upper hinge 
elevation despite the 
fact that a portion 
of the door weight 
is supported by the cylinder and the door frame may 
transfer some load to the foundation if present. This 
practice eliminates the need to calculate W1. The 
need for information about cylinder orientation is 
thus avoided.
The above ignores the contribution of the vertical 
doorframe in distributing the hydraulic ram force. 
The argument for making this assumption here is 
the same as that made in the wind suction case. The 
stiffness of the jamb column is typically several times 
that of the doorframe. Hence the jamb column will 
attract the bulk of the force from the resisting couple 
at a location near the cylinder attachment.
Mono-fold doors can impose significant dynamic 
effects. These have been ignored in the loading 
procedure outlined above. It is believed that the 
redundancy resulting from ignoring the steel door 
frame and the energy absorptive characteristics of 
wood construction allow dynamic effects to be safely 
ignored. Even so, use of soft start/stop technology 
in the hydraulic circuit as a means of minimizing 
dynamic effects is highly recommended.
Building Design
The building, jamb columns, bracing and 
connections must be designed to safely absorb the 
forces produced by mono and bi-fold doors when 
they are included in the structure. Building design 
is beyond the scope of this article. Suffice to say, the 
forces generated by large doors can be significant. A 
competent post-frame design professional should be 
engaged to ensure a successful project.
Conclusion
Mono and bi-fold doors load the buildings into 
which they are installed in unique ways. The large 
sizes of these doors mean the loads can be very 
large, easily controlling the design of door framing 
elements. The above discussion provides a rational 
framework for determining the forces imposed by 
mono and bi-fold doors. Sizing building components 
and connections based on the resulting forces have 
resulted in several buildings that have performed 
well.
Paul Boor Vice President Of Engineering & Product 
Development at Lester Building Systems, LLC
This article was reviewed and approved to be reprinted by 
the NFBA Editorial Committee, which consists of at least 
10 members from engineering and academic organizations 
throughout the United States who are each knowledgeable 
about Post-Frame construction.
YOUR TOOLKIT FOR BUILDING EXCELLENCE
Photo Courtesy of Wick Buildings 

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