Metal plate connected roof and floor trusses are used widely in residential single family, multi- family, commercial, and agricultural construction. They provide design flexibility, span greater distances than traditional “stick framing,” and allow faster erection of the roof system and installation of electrical, plumbing, and HVAC materials. From time to time, trusses may require modifications or need to be repaired due to damage. This article covers information that will assist MiTek engineers in designing a repair quickly and efficiently for your truss.
If a truss is damaged or modified, it must be repaired. Truss members may become overloaded and cause further damage to the truss. Failure to communicate accurate information, such as the exact location of the damage, accurate dimensions, and description, could jeopardize the effectiveness of the designed repair. This could result in additional costs to redesign the repair or even create an unrepairable condition.
For instance, the crack shown in Repair Example #1 [for all images, See PDF or View in Full Issue], described as being between the splice and the joint, could be interpreted by the design engineer as a clean break located midway between the joints. In this case, the crack is much longer, and the repair material may be specified too short. This could result in additional cost to redesign the repair or an unrepairable condition if the shorter material is already applied to the truss.
Consider another repair description in Repair Example #2 in which the designer circled a web and annotated “BROKEN” on the design. Is this damage a clean break in the middle of the web? Does it follow along the web for a certain distance? Is the entire web damaged and need replacement? The damage description sent with the repair request should clearly depict the answers to these questions.
Photographs
With the improved quality of pictures taken by smartphones and the ability to easily share these pictures, we increasingly see photographs forwarded from the field being sent as the sole repair description information, sometimes with no indication of where on the truss the damage is located. Please note, photographs are helpful as additional information only and cannot be used by the MiTek engineer to try to determine dimensions and locations of the damage. To provide the most efficiently designed repair, a “marked-up” truss design drawing with exact dimensions of the damage or section of the truss that needs to be modified, as well as dimensions to key joints and locations of obstruction(s), must be submitted with the repair request. See example repair descriptions below. Please submit photographs only if they are requested by MiTek engineer.
Order of Operations During Repair Design Process
Depending on the size and location of damage or modification, a repair may consist of a lumber scab on one or both sides, plywood/OSB gussets, or a prefabricated scab truss. Our first option is to start with lumber scabs and/or plywood/OSB gussets attached with gun nails. If connections cannot be made with gun nails, we will try different fasteners, for example, longer nails, MiTek Pro series WS/WSWH wood screws, or a similar solution. If neither work, a prefabricated scab truss design is the final resort. If a scab truss is not an option due to field conditions or distance of the jobsite from the truss plant, please comment when you send the repair through our Transfer Center. A MiTek engineer will reach out to you to discuss specific site conditions and options available prior to validating a prefabricated scab truss design.
Effective communication between the field and the design engineer is vital to providing correctly designed repairs. Repair Request Forms are available on our website at https://www.mitek-us.com/resources/engineering/repair-request-forms-details/. Repair Request Forms can help you to determine what information our engineers are looking for to design the most efficient repair.
In summary, if a repair request form is not submitted, the following information must be included on a marked-up truss design drawing to ensure repairs are made in a timely manner:
- Clear description of what is needed.
- Accurate dimensions to location of damage/modification.
- Available repair material.
- Obstructions that could affect repair.
For additional information, or if you have questions, please contact the MiTek Engineering department.