Once state codes or local jurisdictions adopt the 2009 International Building Code (IBC), owners of a project with metal-plate-connected (MPC) wood trusses will be required to engage a registered professional to design and inspect both temporary and permanent bracing for such trusses when spanning 60 feet (18 meters) and greater. What does this mean for designers of these schools, places of worship, and retail projects?
The owner’s responsibility for engaging a design professional for these purposes is also defined by American National Standards Institute/Truss Plate Institute (ANSI/TPI) 1-2007, National Design Standard for Metal Plate Connected Wood Truss Construction, which is the 2009 IBC-referenced standard for MPC wood trusses.
Before the 2009 IBC, the code did not require a registered design professional (RDP) to be responsible for the temporary bracing or the inspection of the permanent bracing. These items were usually left up to the general contractor (or truss erection subcontractor). Truss industry safety literature recognized the professional expertise needed to safely erect long-span wood trusses by making the recommendation: Consult a professional engineer for trusses longer than 60 feet (from Building Component Safety Information (BCSI) 2008, Guide to Good Practice for Handling, Installing, Restraining, and Bracing of Metal Plate Connected Wood Trusses).
|
The approach of "recommending" professional involvement in temporary bracing for erecting long-span trusses has not provided consistent results over the past 35 years as construction-related injuries or deaths have been reported in the media. (See also Figure 1, above.) With the implementation of the new code requirements for installing 18 meter and longer wood trusses, the number of truss-related accidents should be greatly reduced.
This article explores the new requirements under the 2009 IBC, pointing to areas of professional responsibility per ANSI/TPI 1-2007 frequently overlooked by designers specifying MPC wood trusses. It also provides background information on two parallel-chord-truss long-term deflection issues – design considerations to prevent roof ponding and brittle floor covering failures.
Truss bracing design and special inspection requirements
Figure 2 (page33) gives an example of a complex roof system under construction. From IBC Chapter 23 on Wood, Section 2303.4–Trusses:
|
2303.4.1.3 Trusses spanning 60 feet or greater. The owner 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.
This section requires the owner to "contract with any qualified registered design professional" for the design of the temporary and permanent truss bracing. It highlights the need for owners to allocate funding for the truss bracing designs during the project’s contract stage.
It should be noted "any qualified registered professional" can assume the role of temporary and permanent bracing designer for the project. Realizing wood trusses are typically designed by a truss engineer and approved by the RDP of record (i.e., building designer) after the contract phase of the project, the use of the word "any" allows the owner (or owner’s agent) the flexibility of engaging an RDP with expertise in wood truss bracing design and inspection. Modern long-span roof truss systems can be complicated as illustrated in Figure 2. From 2009 IBC Chapter 17,
Section 1704–Special Inspections:
1704.1 General. Where application is made for construction as described in this section, the owner or the registered design professional in responsible charge acting as the owner’s agent shall employ one or more approved agencies to perform inspections during construction on the types of work listed under Section 1704.
This paragraph requires owners to "employ one or more approved agencies to perform inspections" on certain work listed under Section 1704. An "approved agency" must meet the requirements set forth in Section 1703 regarding independence, equipment, and personnel. Section 1704.6.2 identifies a type of truss work that must be inspected:
1704.6.2 Metal-plate-connected wood trusses spanning 60 feet or greater. Where a truss clear span is 60 feet (18,288 mm) or greater, the special inspector shall verify that the temporary installation restraint/bracing and the permanent individual truss member restraint/bracing are installed in accordance with the approved truss submittal package.
The practical value of these sections clearly require the owner (or his/her agent) to "employ one or more approved agencies to perform inspections during construction" of the temporary truss bracing work and permanent truss bracing work "in accordance with the approved truss submittal package." For the 2009 IBC, Section 2303.4.3 defines the content of the "Truss Submittal Package."
It is not precisely clear how the new requirements for the design and inspection of wood truss bracing will be approached or managed by the local building code departments. Referring to the last sentence in 2009 IBC Section 107.3.4.1:
107.3.4.1 General….. The registered design professional in responsible charge shall be responsible for reviewing and coordinating submittal documents prepared by others, including phased and deferred submittal items, for compatibility with the design of the building.
The temporary and permanent bracing designs per 2009 IBC Section 2303.4.1.3 could logically be submitted as part of the Truss Submittal Package (Section 2303.4.3). Regardless of when the temporary and permanent bracing designs are submitted to the authority having jurisdiction (AHJ), the construction documents should contain a list of the deferred submittals that specifically includes temporary and permanent bracing designs for the project. The responsibility and process for deferred submittals are defined by the second paragraph of 2009 IBC Section 107.3.4.2:
107.3.4.2 Deferral of any submittal items shall have the prior approval of the building official. The registered design professional in responsible charge shall list the deferred submittals on the construction documents for review by the building official.
In summary, the 2009 IBC defines new requirements for the design and inspection of both temporary and permanent MPC wood truss bracing. It should be noted the language in ANSI/TPI 1-2007 on wood truss bracing responsibilities for the application of long-span trusses is consistent with the 2009 IBC requirements.
Frank E. Woeste, PE, PhD, is a professor emeritus and a wood construction and engineering consultant. He can be reached at e-mail at fwoeste@vt.edu. Donald A. Bender, P.E., PhD, is a professor of civil engineering and director of the Composite Materials & Engineering Center at Washington State University. He can be reached at bender@wsu.edu.
This article originally appeared in the May 2011 issue of The Construction Specifier (vol. 64, no. 5), the official publication of the Construction Specifications Institute. Visit www.constructionspecifier.com.