Dear Anna:
A recent long span truss collapse during installation reminded me of the new 2009 (and later) IBC bracing requirements for the Owner of a project with metal plate connected (MPC) wood trusses spanning 60 ft. and greater (churches, schools, commercial, retail, and so on). Specifically, the IBC requires the Owner to engage a registered design professional (RDP) to:
- Design the temporary bracing for the MPC wood trusses,
- Inspect the temporary bracing for the MPC wood trusses,
- Design the permanent bracing for the MPC wood trusses, and
- Inspect the permanent bracing for the MPC wood trusses.
The new 2015 IBC made an important change that required the owner or owner’s authorized agent to contract with a qualified RDP:
“2303.4.1.3 Trusses spanning 60 feet or greater. The owner or the owner’s authorized agent shall contract with any qualified registered design professional for the design of the temporary installation restraint/bracing and the permanent individual truss member restraint/bracing for all trusses with clear spans 60 feet (18 288 mm) or greater.” (emphasis added)
The Owner’s responsibility for engaging a design professional for items 1 through 4 is also contained within the ANSI/TPI 1–2007 National Design Standard for Metal Plate Connected Wood Truss Construction which is the IBC referenced standard for MPC wood trusses. Prior to the 2009 IBC, the IBC did not require an RDP to be responsible for items 1, 2, and 4 listed above.
It is unlikely that Contractors who purchase wood trusses would be aware of the IBC and TPI requirements summarized in items 1, 2, and 4 listed above, yet their truss erection work can be dramatically impacted by a lack of a temporary bracing design and inspection by an RDP. Because the greatest risk of long span truss collapse is most likely during the installation process, I believe CM’s and Truss Designers should consider adding a special and prominent note on the Truss Design Drawings (TDDs) that emphasizes the IBC requirements (1 and 2) that can prevent truss installation accidents and related injuries.
Although this 60 ft. rule is present in some industry literature, it is not completely clear that it is an “IBC requirement” versus an “industry recommendation.” The 60 ft. rule is addressed in the 2015 BCSI Book, page x, under the heading of “Building Designer Checklist”:
Required Information in the Construction Documents
Be sure to specify the following in Construction Documents:
- Trusses with clear spans of 60’ or greater require that the Owner contract with a Registered Design Professional for the design of the Temporary Installation Restraint/Bracing and the Permanent Individual Truss Member Restraint/Bracing.
- Trusses with clear spans of 60’ or greater require that the Owner contract with a Registered Design Professional to provide special inspections to assure that the Temporary Installation Restraint/Bracing and the Permanent Individual Truss Member Restraint/Bracing is installed properly.
Most helpful for truss installation safety would be a “standardized note” for TDDs developed by a TPI Committee that could be adopted and used by CMs. This note could alert and direct the Contractor to the Construction Documents for the IBC required “temporary” and “permanent” bracing design work when the Contractor reviews the proposed Truss Design Package. The truss package review stage is a logical time to address the IBC bracing design requirements. The note on the TDDs would also alert the Contractor as to the IBC requirement for Special Inspection of the “Temporary Installation Restraint/Bracing” before moving forward.
As a new graduate student at Purdue University in 1973, one of the first truss issues I learned from the late Dr. Stan Suddarth was the recurring problem of long span truss collapses during installation. He and his peers noted that the most common case involved churches or long-span agricultural trusses. Fast forward four decades, long span truss installation remains a safety issue; however, we now have “code” that specifically addresses the issue which is a positive step forward. The remaining challenge for the industry is discovering methods to reasonably ensure Contractors and Building Designers are aware of the IBC temporary bracing design and inspection requirements for 60 ft. and greater trusses.
The author welcomes comments and discussion. Letters to the Editor should be sent to Anna Stamm.
Frank Woeste, P. E.
Professor Emeritus
Virginia Tech University