You probably won´t ignore a warning sign on the highway, as you can easily imagine the consequences of doing so. We can face similar situations when designing trusses and the end result is that whatever we do in the software can end up in the real world somewhere on a jobsite.
Because of the nature of this job, it is common to lose touch with the reality of the rest of the process. A component designer can be jumping from one job to another during the day and be involved in several projects at the same time. They may fail to see, or worse, may ignore some warning signs along the way (either in an office or a remote location). Sometimes the result is that we simply are unaware of some warning messages.
One of these signs is the PLY-TO-PLY-NAILING issue. In some versions of design software, this message is just a warning and some designers in a rush could overlook it. In recent versions of MiTek, ply-to-ply nailing is considered a failed truss and obligates the designer to correct it. This happens most often on roof girders which could require 3 or 4 plies.
You see, trusses work as a single entity of themselves as they apply to a truss system. These factors are totally contingent upon what settings are selected based on the reality of materials to be applied on the job site. However, when multi-ply trusses are combined, each single entity becomes joined together. Multi-Ply trusses are commonly known as “girders”. A girder is a truss that carries another truss (or carries some type of load or framing on the project).
What this error message is telling you is that the connection of the plies as they attach to each other is what is failing. The truss itself my work to carry the loading that attaches to it, but the fasteners of the ply attachment is inadequate. Or it may be that the total number of connectors (nails/screws) is insufficient to be applied based on the selected chord size.
When this failure occurs, we can have issues in the field such as:
- Shear transfer problems
- Unsafe installation
- Future failure and collapse
- Lives placed in danger
Maybe the main problem is the shear stress because forces are acting parallel to a rectangular surface causing displacement and producing failure.
We have all been there…worked on a big job for several days and get down to the last girder or two and it just will not work. It passes, but has a ply nailing issue! We “play” with it a bit to try to get it to pass and nothing. We are stumped. With 613 designs in the job, it will take a bunch of re-work (not to mention lost productivity) to get this job off our desk. What do we do?
There are 5 main ways to resolve this matter
- Change chord size(s): The simplest and most efficient way is to bump the Top Chord or Bottom Chord sizes. Sometimes it is necessary to do both and, depending on the severity, you may even need to bump up web sizes.
- Adjust connector type in engineering: The next alternative is to use the analysis to your advantage and adjust the “Nails and Screws” attaching the plies together. There, you can change your nail conditions or select screws. Selecting stronger connector could solve your issue. Realize though, this method will require input from your manager. Most component manufacturers DO NOT stock the screws or nails needed to solve the problem and will have to be special ordered. This is critical in ensuring proper fastening, especially if your company does the fastening in-house. On a truss like this, even if you do not fasten them in the plant, you should in this case. Leaving this up to the guys in the field may cause an additional problem that could be very costly.
- Verify layout: This problem commonly happens when a girder is carrying an important section of the roof, directly or indirectly (maybe is supporting another girder). So check if there is a different way to configure truss placement. Determine if there is a way to avoid the girder or reduce the load. Also you may check the clear span of the girder a look a way to reduce it.
- Review plans: Verify walls maybe you are not considering as load bearing. If you have to select an interior bearing to be used, always check the support below so reactions are transferred to a member capable of supporting that load. If you are also providing the floor system, remember to add that extra loading and support to the system itself. In case you aren´t, but this the only solution, make sure to provide all the info in your layout so builder is aware and it can be reviewed by the Engineer of Record.
- Notify customer or your supervisors: If the problem is over your head, then you can do something at the edge: Ask for help! Chances are another staff member has encountered this before and can assist you efficiently to keep you moving forward.
Here at Gould Design, Inc. we use a peer mentoring system so the designer can ask for a solution. This could be from that designer’s own mentor that was assigned or it could be an open query so any of the available colleagues can help. Not everyone has seen everything that may come up, so it is important our team of remote designers have access to all team members that work in different locations than they do. GDI uses Skype to accomplish this. By utilizing this type of communication, each and every person on the team has the answers to each and every problem that arises. More on this in a future article.
Looking for help is not a sign of weakness. It is a way to recognize the world around you and improve yourself and your perspective. If you have to use an unconventional solution, then notify the customer so they can discuss the issue with you and the other parties involved.
If you decide to overlook a warning, then it is up to you to take responsibility for consequences that may result. Maybe you are driving or working in a computer. Maybe you are not the only one implicated in a decision. Remember there are a lot of people trusting in your judgment and even lives could be in danger for overlooking a detail. Of course the software could be far from real failure but is designed to work on the safe side so we as designers can implement a similar mindset.
Do you or your company have a solution for problems that arise like these when designing? Have you ever thought about it consulting an unbiased expert to help with that solution? Please share your thoughts in the comment section.