Today I’m going to walk us through aligning webs in a series of trusses with differing end conditions on one end. Below is my layout so you can keep track of where I am in the design.
Examining the A series of trusses you’ll notice I did a couple things here. First of all, I made sure the left end of the truss was on the end that remains unchanged throughout the series. This is a nice clean look but it also allows me to use the align webs tool in engineering. If I put the left end on the opposite end then nothing would match up as pictured here:
After examining the layout I chose to engineer A06 first since it has a standard end condition on each end. After playing with the design I settled on Fink webbing. I did this for several reasons.
- It falls within my panel width restrictions.
- It uses less webbing than a Howe arrangement.
- I don’t have to alter my webbing for the FAU space that is centered under the ridge.
Because this is a production job I need to work on optimizing before I use this as a template for the other trusses. Look at how the truss came in by default:
Using the optimization tool I dialed my webbing in to get the most economical webbing pattern I could achieve while not exceeding panel limitations. You’ll notice that all the webbing could come out of (3) 12’ lengths, (1) 16’ length of 2×4. My top chord and bottom chord lengths still aren’t ideal but this client prefers on panel splicing.
For the most part, the rest is a matter of aligning webs and splices for the remaining trusses in the “A” series. Looking at the layout the garage wall juts into the garage before stepping back in. Selecting the align webs tool will match all the webs that it can and aligning webs we see the profile of A06 in the background. All the webs are matched up except for the last panel on the right we add a web down to the bearing. The splices were matched so that everything about A02 is the same as A06 except for the stubbed condition.
We’ll notice that we now have two CLB’s on this shorter truss. As we saw in this GDI post on bracing, we know that we need our webs to be aligned in order to use CLB’s which we have.
A03 is 2’8” shorter than A02. Everything remains the same except the right end condition. Again we can see the shadow of A06 in the background.
The only difference between A03 and A04 is the FAU. Here we need to add the load and the stacked BC for the platform, but notice how all the webbing still matches up.
A05 is the same as A06 except for the FAU. For fun, I’ll show you the difference between the Fink webbed FAU and the Howe.
Here we’ve created a nice uninhabitable room for the FAU and service personal with this Howe truss, but it’s a $142.
Now compare with our fink webbed truss coming in at $105 dollars which serve the purpose of providing space for the FAU and service personal, it has an elevated platform that they will attach plywood to in the field. Not to mention the ease of building in the shop. It’s a win-win.
Since we started with A06 only A07 remains. It is the same as A03 except that it has an overhang on the right end, so I’m going to align webs with A03.
While this was a very simple gable roof to truss, you can see that by thinking proactively and trying out different web arrangements and optimization on a sample truss, that we were able to design this roof with an effective plan, and an efficient design that satisfies the design requirements while also making life easy on the shop personal when assembling these trusses. The left side doesn’t change at all with only slight changes on the right throughout the series.
What tips or tricks do you have for efficient design? We’d love to see your comments below!