Truss Bracing Responsibilities
Truss Bracing Responsibilities
Component manufacturers (CMs) are frequently asked questions about how to brace trusses. Often, the answers can be found in the Building Component Safety Information (BCSI) book, Guide to Good Practice for Handling, Installing, Restraining & Bracing of Metal Plate Connected Wood Trusses, produced by the Structural Building Components Association (SBCA) and the Truss Plate Institute (TPI).
However, there is a common question about bracing trusses that requires a bit more detail to answer. While it may sound deceptively simple, this question requires delving into building codes and standards, and identifying key players in a construction project.
Who is responsible for truss lateral restraint and diagonal bracing?
For scope of work, the truss industry follows the requirements of the building code and the building code referenced ANSI/TPI 11. Per ANSI/TPI 1 Chapter 2, three items must be addressed:
Temporary lateral restraint and diagonal bracing of trusses during installation
- Permanent building stability bracing of trusses and anchorage to the building
- Individual truss member lateral restraint and diagonal bracing
Temporary bracing is a means and methods issue and is the responsibility of the Contractor in accordance with the construction documents or the truss submittal package. In the absence of a designed temporary bracing plan, BCSI is the industry guideline for the generalized implementation of temporary bracing that framers must follow. BCSI is also referenced in the International Residential Code (IRC)2.
It should also be noted that when a truss clear spans 60 feet or more, ANSI/TPI 1 Section 22.214.171.124 requires that a Registered Design Professional be contracted to design the Temporary Bracing as well as inspect that it was installed correctly. This language is also reinforced by 2009 International Building Code (IBC) Sections 1704.6.2 and 2303.4.1.3 and 2012 IBC Sections 1705.5.2 and 2303.4.1.33.
ANSI/TPI 1 Section 126.96.36.199 Long Span Truss Requirements.
188.8.131.52.1 Restraint/Bracing Design. In all cases where a Truss clear span is 60 ft. or greater, the Owner shall contract with any Registered Design Professional for the design of the Temporary Installation Restraint/Bracing and the Permanent Individual Truss Member Restraint and Diagonal Bracing.
184.108.40.206.2 Special Inspection. In all cases where a Truss clear span is 60 ft. or greater, the Owner shall contract with any Registered Design Professional to provide special inspections to assure that the Temporary Installation Restraint/Bracing and the Permanent Individual Truss Member Restraint and Diagonal Bracing are installed properly.
Permanent building stability bracing, which includes the permanent lateral restraint and diagonal bracing applied by the truss design engineer to the truss web member plane, is the overall responsibility of the Building Designer, who has the knowledge of the building design, connections and the flow of loads through the building. This Building Designer’s responsibility is also explicit in ANSI/TPI 1 Chapter 2 as referenced in the IBC and IRC. In the absence of a designed building stability bracing plan, the referenced BCSI documents may be used.
ANSI/TPI 1 Section 220.127.116.11 Absence of Truss Restraint/Bracing Method or Detail. If a specific Truss member permanent bracing design for the roof or floor Framing Structural System is not provided by the Owner or any Building Designer, the method of Permanent Individual Truss Member Restraint and Diagonal Bracing for the Truss Top Chord, Bottom Chord, and Web members shall be in accordance with BCSI-B3 or BCSI-B7.
Individual Truss Member Lateral Restraint and Diagonal Bracing
The Truss Designer identifies the location of required individual truss member (i.e., web, top chord or bottom chord) restraint/bracing. This bracing serves the purpose of preventing out of plane buckling due to the applied loads shown on the Truss Design Drawing. For an example, see Figure B3-9 from the BCSI book. This figure also provides an answer to another common question: Is it an acceptable practice to apply the continuous lateral restraint (CLR) to either side of the web member? The note in the figure explains that the CLR can be installed on either side.
The individual truss member restraint/bracing is not specifically building stability bracing, though it could be used as part of that system. The overall bracing member size and attachment to the trusses and how it is incorporated into the building stability bracing design is to be thought through and designed by the Building Designer. This can easily include the sizes and connections called out for the truss design restraint/bracing. Again, in the absence of a designed building stability bracing plan, the BCSI book and B-Series Summary Sheets may be used.
Bracing Best Practices – JOBSITE PACKAGES
While CMs aren’t responsible for all of the bracing outlined above, it is in every CM’s best interest to provide accurate information regarding the handling, installing, restraining and bracing of components. The JOBSITE PACKAGE is one way for CMs to supply this information to their customers and fulfill their duty to educate and warn. In the event a project doesn’t go as planned and legal action is brought against a CM related to a construction defect or truss collapse, the JOBSITE PACKAGE can prove invaluable in documenting that the CM provided industry best practices (see April 2011 article, “CM Found Not at Fault in Negligence Case”). To verify that a JOBSITE PACKAGE is included with every job, some CMs list the package as a line item on their invoice, and even charge a nominal amount for these documents. For more information on JOBSITE PACKAGES, visit sbcindustry.com/jobsite.php.
ANSI/TPI 1 Chapter 2 and BCSI Definitions
- Building: Structure used or intended for supporting or sheltering any use or occupancy.
- Building Designer: Owner of the Building or the Person that Contracts with the Owner for the design of the Framing Structural System and/or who is responsible for the preparation of the Construction Documents. When mandated by the Legal Requirements, the Building Designer shall be a Registered Design Professional.
- Construction Documents: Written, graphic and pictorial documents prepared or assembled for describing the design (including the Framing Structural System), location and physical characteristics of the elements of a Building necessary to obtain a Building Permit and construct a Building.
- Contractor: Owner of a Building, or the person who contracts with the Owner, who constructs the Building in accordance with the Construction Documents and the Truss Submittal Package. The term “Contractor” shall include those subcontractors who have a direct Contract with the Contractor to perform all or a portion of the construction.
- Diagonal Bracing: Structural member installed at an angle to a Truss chord or web member and intended to temporarily and/or permanently stabilize Truss Member(s) and/or Truss(es).
- Lateral Restraint: Also known as continuous lateral brace or CLB. A structural member installed at right angles to a chord or Web member of a Truss to reduce the laterally unsupported length of the Truss member.
- Truss Design Drawing: Written, graphic and pictorial depiction of an individual Truss that includes information required in ANSI/TPI 1.
- Truss Design Engineer: Person who is licensed to practice engineering as defined by the Legal Requirements of the Jurisdiction in which the Building is to be constructed and who supervises the preparation of the Truss Design Drawings.
- Truss Designer: Person responsible for the preparation of the Truss Design Drawings.