A Truss Designer’s Opinion on Bracing – Part V
As a junior designer, there is a lot to learn about designing and engineering the (to quote my co-worker) “Cadillac” of trusses. One important criteria of design is in bracing. The intent of this article is to shine some light in this dark area that is often misunderstood.
Trusses must be braced to ensure safety, performance and to complete stability. Ever tried to build a house of cards? What held it together was…you guessed it…bracing! Unfortunately, there is not much proactive training available in the truss industry about bracing. How can this be, if the trusses need bracing to become a total unit?
Let’s explore what the industry associations have to say about bracing:
Permanent bracing is required to ensure that the trusses are integrated into the overall building structure to:
- Prevent buckling of web members loaded in compression
- Share loads between adjacent trusses
- Transfer lateral forces to diaphragms
- Restrain overall lateral displacements
During my first few months of training, while trying to understand what bracing is, I came across the following “rules” from Western Wood Truss Association of Alberta:
- Lateral movement of the lateral bracing shall be restrained by permanently installing cross bracing at the ends of each truss run and at intervals not exceeding twenty feet or as shown on the structural drawings
- If it is not possible to install permanent lateral web bracing as specified on the truss design drawing or if the truss run is less than three trusses of the same kind, a “T” brace shall be installed as per the truss design drawing
T-Brace/I-Brace Detail (ST-T-Brace, MiTek – March 4, 2013)
Here are the official descriptions for “T” & “I” bracing from MiTek. I have also included some pictures for visual representation. This should give you a clear reference point to make clear what the differences are.
With so many bracing options available, do you really know which one your customer would prefer? Have you ever taken the time to ask them?
Another option for builders or truss manufacturers is that trusses can be upgraded if the truss manufacturer chooses to make available metal web bracing that can be installed in the truss factory during the manufacturing process.
I hope this article has given you a better understanding of bracing. How do you determine which bracing type to use?
You can read Part 1 of this series here.
You can read Part 2 of this series here.
You can read Part 3 of this series here.
You can read Part 4 of this series here.
Stay tuned for Part 6 in this series.
Denise Dove – Design Professional (Canada)
Gould Design, Inc.