Quality Assurance continues beyond the truss plant, so it’s important to keep that in mind as you’re preparing your products for handling and use by someone else. For example, this article poses the question: should component manufacturers (CMs) mark the ends of trusses? For that marking, CMs typically use paint. In addition to painting ends, other techniques can help to ensure final installation is done properly. Strategies include:
- Tagging each component with identification.
- Providing continuous lateral bracing (CLB) design requirements with each truss, so it’s available to the installer. This can be added to the truss tag using a truss image or URL code that references this information.
- Using “web buddies” via design software to reduce the need for CLB, which is often overlooked by erectors. Web buddies are scab web material plated to webs in plane to reduce effective length and increase stiffness of compressive web applications.
- Marking the top of a truss when supplying floors. This is recommended so they are not installed upside down.
- Making trusses interchangeable when possible. An example is adding interior, alternate bearing locations.
- Building trusses in installation order. Assembling and bundling trusses according to their installation order can help customers during erection, although this is not always feasible for manufacturing and delivery reasons.
- Marking truss ends (MTE), which is shown in the photo and will be discussed in detail next. [For photo, See PDF or View in Full Issue.]
Reasons to Mark Truss Ends
The reasons to mark truss ends (MTE) all involve improving the quality and performance of installation and use.
Despite all of our best efforts, in reality, most trusses cannot practically be built exactly symmetrically. Fortunately, ANSI/TPI 1 allows for reasonable variations. In fact, Table 3.5-1 contains In-Plant Manufacturing Tolerances for Finished Truss Units.
Variations of trusses from design create undesirable situations even when installed accurately. This is often telegraphed as wavy roof planes and undulating ceiling planes once sheathing materials are installed.
Shifting of pressing operations can also result in variations between trusses within a jigging operation. This is often compounded by a lack of heel stops and jigging that would have helped prevent the shifting. This effect is very difficult to address reasonably, and the best approach to take in these situations is to always press each sequential truss initially from the same direction.
When considering truss set-ups, MTE can help your technicians understand the relationships between the trusses included in each set-up. Then, during product installation, this information helps the client understand these same relationships. It helps the erection contractor install trusses correctly, even when trusses appear symmetrical but are not due to manufacturing particularities. This helps the client eliminate repairs and modifications that result when trusses are installed incorrectly due to flipping trusses end to end.
MTE strategy starts with conceptualization of the project design. The designer needs to understand the benefits of marking. Examples include interior bearing situations that do not allow for interchangeable installation. This holds true with both floor and roof trusses.
Variations of truss profiles as the truss is set up are never exactly symmetrical. Classical methods using heel to peak methods inherently have deficiencies that lend to symmetrical variations – this is due in part to variations in lumber widths and inaccuracies in cutting. The symmetry improves using auto-puck systems and lasers, but the characteristic does not disappear. The errors still exist. In the sketch, green represents the truss flipped in comparison to the original black image. [For image, See PDF or View in Full Issue.] If the peak is off-centered, then when flipped the truss-to-truss error doubles. These errors are also exaggerated when the installer lines up trusses by tails or butt cut.
Returning to the photo, it shows the CM using black paint to mark floor truss ends to aid in proper truss installation. By painting the “left end” vs. the “right end” or by painting the “front of the house” vs. the “back of the house,” the prevention of flipping otherwise symmetrical trusses can help eliminate exaggerating differences in trusses. This situation also happens with floor truss depth variations using some older machinery. An intelligently designed and serviced floor machine should eliminate concern, but variations remain a possibility. The CM of the trusses shown not only marked the designated end of the trusses to reference installation positioning of the truss, but also the mark indicates the bottom of the component. Then, this information is referenced in the truss layout used to provide installation details to the installer.
The Bottom Line
Painting the ends of trusses may not be required, but it is a straightforward way to significantly improve the installation of your components. Taking the time and effort to help your client understand proper installation of your products will produce a better outcome for you, your customer, and the end user.
An ANSI/TPI 1 3rd Party Quality Assurance Authorized Agent covering the Southeastern United States, Glenn Traylor is an independent consultant with over four decades of experience in the structural building components industry. Glenn serves as a trainer-evaluator-auditor covering sales, design, PM, QA, customer service, and production elements of the truss industry. He also provides project management specifically pertaining to structural building components, including on-site inspections, expert witness and ANSI/TPI 1 compliance assessments. Glenn provides new plant and retrofit designs, equipment evaluations, ROI, capacity analysis, and CPM analysis.