Helping Structural Engineers Incorporate Components into Projects

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Structural building components, including metal plate connected wood trusses, can provide efficient, cost-effective, and quality solutions for residential and light frame commercial projects. But to capitalize on this, it is important that they are specified, coordinated, and installed correctly. The structural engineer of record (EOR) plays a critical role in this process. Specifically, the EOR needs to understand what should be included in the construction documents and what their role and responsibilities are in the process.

The Delegated Design Process

Metal plate connected wood trusses are typically part of a delegated design process where the EOR shifts responsibility for select portions of the design to specialized designers. These specialized designers produce detailed calculations and drawings to meet the performance criteria provided in the construction documents. While this can improve quality and efficiency, it may introduce risk if responsibilities and design criteria are not clearly defined. Ambiguous performance criteria, mismatched interfaces, poor review, and coordination gaps between the delegated portion and the base design can lead to construction or performance issues.

To properly avoid these potential pitfalls, the roles and responsibilities of the registered design professional in responsible charge (EOR or building designer), truss designer, and component manufacturer (truss manufacturer) need to be understood. Both the International Building Code (IBC) and the referenced standard American National Standards Institute's/Truss Plate Institute's National Design Standard for Metal Plate Connected Wood Truss Construction (ANSI/TPI 1) provides guidance for this:

• The building designer is the individual responsible for the design of the building structural system. This individual may also be referred to as the EOR.
• The truss manufacturer is responsible for reviewing the construction documents so that they can provide design parameters to the truss designer. A truss technician often communicates these parameters to the truss designer electronically using proprietary software. The truss technician is typically not a registered design professional.
• The truss designer is the delegated design professional responsible for the design of the individual truss members and preparation of the truss design drawings using the design requirements provided by the truss manufacturer. The truss designer is usually not an employee of the truss manufacturer.

In context of these responsibilities, the delegated design process for metal plate connected wood trusses becomes clearer. Below is a graphical representation of the process.
Within this process, it is critical to understand that the truss designer's responsibility is limited to the design of the individual truss members. Further, the truss designer is not responsible for and does not design floor or roof systems.

Incorporating Trusses in Construction Drawings

To properly incorporate metal plate connected wood trusses into the building design, critical information should be included in the project specifications, general notes, plan sheets, and/or details. The minimum information to be included is provided in ANSI/TPI 1, Section 2.3.2.4, Required Information in the Construction Documents.

Clear communication of complete design load information is important. To accurately determine snow loads, multiple parameters need to be provided. For example, in addition to providing the ground snow load, the EOR should also provide the Risk Category, Thermal Factor, Roof R-Factor, and Winter Wind Parameter so the truss designer can properly determine the roof snow loads.

Specifications

The three-part specification section 06 17 53 is reserved for shop fabricated wood trusses and provides the engineer a means to direct how the trusses are designed, fabricated, and installed. Document submittal expectations, manufacturing quality requirements, as well as any special inspection requirements may also be included. The specification provides a means to direct how trusses are permanently restrained and braced. This is discussed in more depth later in the article.

The Structural Building Components Association (SBCA) provides a specification template for the three-part specification section 06 17 53 in the SBCA Knowledge Center (kcenter.sbcacomponents.com) available for download. The template includes notes to the user to help incorporate them into the construction documents and with other specification sections. The template also includes updated resource references and represents the current state of practice for the industry.

Structural Notes

Similar to the project specifications, structural notes can be used to communicate performance, material, and/or bracing requirements. A series of structural notes specific to metal plate connected wood trusses are also available in the SBCA Knowledge Center for download.

Plan Sheets

The plan sheets can be utilized to define the truss zones subject to the truss delegated design and indicate any special layout requirements, load paths, bearing conditions, and diaphragm requirements. The plan sheets may also provide a means to clearly identify varying serviceability requirements based on material finishes or the structural layout.

Details

The interface and connection between the individual trusses done as part of the delegated design and the building structure is best shown in the details. Details provide an opportunity to clearly define any special design or truss configuration requirements and will help ensure the delegated truss design integrates seamlessly.

Details can be used to show bearing connections, drag struts, blocking, and diaphragm to truss interfaces. Example details are available for download from the SBCA Knowledge Center (kcenter.sbcacomponents.com) and represent the industry's preferred connection methods and configurations. The available library includes typical details for both floor and roof trusses.

Restraint and Bracing

The assignment and development of permanent bracing plans for metal plate connected wood trusses is a critical aspect of incorporating wood trusses into the building design. Wood trusses must be braced in two and potentially three fundamental planes to perform as intended. These three planes include the top chord, the bottom chord, and the truss web plane. Both the IBC and ANSI/TPI 1 establish responsibilities and requirements for the permanent bracing design that vary by the plane to be braced and the configuration of the structure. It is also important to emphasize that when lateral restraint is required, diagonal bracing must also be provided.

Top Chord Plane

Commonly, the top chord plane of trusses is restrained and braced by sheathing, which is part of the roof or floor diaphragm. Because the diaphragm is part of the structural lateral system, it is designed by the building designer. Where there is no diaphragm or rigid sheathing to brace the top chord, the IBC requires a permanent restraint and bracing plan design prepared by a registered design professional.

Bottom Chord Plane

The bottom chord plane of trusses is often braced by a rigid sheathing or gypsum board. When a rigid bracing plane is not provided, such as when the floor or roof trusses are exposed, lateral restraint and diagonal bracing must be provided. Minimum lateral restraint spacing will be provided on the truss design drawings. Similar to the top chord, the IBC requires a permanent restraint and bracing plan design be prepared by a registered design professional when no diaphragm or rigid sheathing is present.

Web Plane

To prevent lateral buckling under compression loads, truss web members may require lateral restraint. The truss design drawing will graphically note where lateral restraint is required. The building code does not specify who is responsible for determining the lateral restraint and bracing for the web member plane. Instead, it states that where lateral restraint is required it should be accomplished using one of three methods.

These include:

• Lateral restraint and diagonal bracing installed using standard industry details.
• Individual truss web member reinforcement.
• A project specific restraint and bracing plan prepared by a registered design professional.

Most commonly, either standard industry details or member reinforcement is used when the web member requires lateral restraint. The installer generally determines this, but the lack of specific assignment in the building code can create some confusion. For standard industry details, member reinforcement, or a project specific design, the project engineer (EOR) is the best entity to specify which method should be used or to indicate in either the structural notes or project specifications that the restraint and bracing method should be determined by the installer. This will help reduce jobsite confusion by specifically assigning the task and clarifying responsibilities.

BCSI-2025

SBCA's Building Component Safety Information Guide to Good Practice for Handling, Installing, Restraining and Bracing of Structural Building Components (BCSI -2025) is the structural building component industry's guide for jobsite safety and prescriptive restraint and bracing of metal plate connected wood trusses. It was recently overhauled to be a more comprehensive and user-friendly guide. It includes guidance for both temporary and permanent lateral restraint and diagonal bracing for different truss configurations and spacings, with explicit references to building codes, standards, and OSHA regulations. It also includes content on the component design and approval processes, code requirements, and jobsite planning.

Previously, the three methods of accomplishing lateral restraint for truss web members in the IBC were highlighted. One of these solutions is to provide standard industry details in accordance with ANSI/TPI 1 Section 2.3.3.1.1, Standard Industry Details, or the figures provided in Section 2303.4.1.2, Permanent Individual Truss Member Restraint (PITMR) and Permanent Individual Truss Member Diagonal Bracing (PITMDB) of the IBC. The figures referenced in the IBC are based on the figures and information provided in BCSI-2025. Section 2.3.3.1.1 of ANSI/TPI 1 that specifies the documents BCSI-B3, Summary Sheet – Permanent Restraint/Bracing of Chords & Web Members, and BCSI-B7, Summary Sheet – Guide For Handling, Installing & Bracing of 3x2 & 4x2 Parallel Chord Trusses, should be referenced for the standard industry details. The BCSI-B3 and BCSI-B7 documents are excerpts from BCSI-2025 that are intended to be included in jobsite packages delivered with the trusses to the jobsite for the installer.

Figures 1 and Figure 2 are excerpts from BCSI-2025 showing standard industry details for web member restraint and bracing. These prescriptive solutions provide member sizes, spacing, and connections for the required lateral restraint and diagonal bracing.

The solutions in BCSI's guide may be referenced as standard industry details when there is no diaphragm or rigid sheathing providing lateral restraint for the top or bottom chord, or for web member bracing. However, sometimes replacing lateral restraint and diagonal bracing with web member reinforcement may be a better option. Prescriptive reinforcing solutions are provided in the IBC Figures 2303.4.1.2(2) and 2303.4.1.2(4), which are also derived from the recommendations in BCSI-2025 shown in Figure 3.

Alternatively, when a project-specific restraint and bracing plan is determined to be the best option, the design and layout of these plans may be developed using the prescriptive solutions provided in BCSI-2025, or it may be developed using the design provisions in TPI's document DSB-2022, National Design Standard for Bracing Metal Plate Connected Wood Trusses. When requested, the preparation of a project specific restraint and bracing plan may be done by the truss designer or a specialty engineer. Either way, unless it is specifically specified in the contract documents, it is usually not included as part of a truss submittal package.

The Building Designer's Critical Role

As the party responsible for the building design, the building designer has a full understanding of how the structure is intended to perform. They must understand that the trusses have been designed as single, two-dimensional elements, and need to determine that the trusses will perform as intended as part of a three-dimensional structure. It is vital the EOR thoroughly reviews the truss submittal package to ensure it conforms to their design intent as part of the floor and/or roof system. Additionally, while it is not explicitly assigned to them, it is important for the building designer to understand how any required permanent restraint and bracing is being provided which may be accomplished by assigning responsibility in the contract documents. Following these recommendations will help the building designer successfully incorporate structural components into their design.

About the Author

Greg Greenlee, PE, serves as the Technical Director for SBCA. He has extensive experience in building design, construction engineering, product development, and product design. Additionally, he is an active participant in the model building code development process and serves on multiple standards development committees.