Crazy and Complicated Truss Designs Part 4
A while back I wrote a piece about crazy and complicated trusses that I have done over my career. A few weeks ago I came across another plan that I could add to that list. One of our customers recently gave a plan for a big a church and said here please design us something that works. Well what followed was quite insane if you ask me.
Like most big commercial buildings this plan had very large spans for trusses, by large, I mean 56’ up to 64’. Typically this wouldn’t pose an issue, on this plan they wanted vaulted trusses. By vaulting them, it completely took away the ability to piggy back them. As many of you may know, with trusses that large, deflection starts to play a huge part in design. Multiply that by 3 or 4 and you can see how the issues would arise.
This plan kind of was a rather difficult one to work through in the beginning. Inverted hips with little to no bearing on trusses that were spanning what seemed like an entire football field. The only thing saving this situation was what we were initially told by our customer: “Make it work any way you see fit, do what needs to be done.” However, even that was difficult due to all the wide open rooms and little to no place to grab extra internal bearing where needed. After spending some time deliberating amongst myself and my colleagues, we came up with an idea to make it work. The solution was to design two half trusses and splice them together in the field, due to the overall height.
As you can see, the base truss on one wing of this building is 64’ long and 20’ tall. Now that’s an enormous truss! One-piece, it is impossible to deliver to the job site. The biggest issue (as I had stated earlier) with them is the vertical deflection. This was a MAJOR problem. Trying to get the heels as low as I could go and figuring out how in the world they were going to build them. I couldn’t piggy back them, as I needed as much depth as I could get. It became apparent to us that we were going to have to split them into two pieces, to be assembled in the field. So that’s what we did!
As you can imagine a scissor mono works much easier than the full truss. Because of that and the fact that if we truly wanted to know if they would work, each half had to fully mimic the base. I even had to throw on a “K-Web” at the vertical to prevent shear and allow proper bracing.
So I designed a full-span truss with a quantity of “0” and then designed each “half” to match. But I wasn’t done there! The “half” piece had to match lumber and plating, as if it was the full-span truss. So I had to manually upgrade each chord and plate. I am glad my colleagues pointed this out early on in the design.
As if that was not enough, there is another aspect to this plan that threw another wrench in the design: Attic space.
Because of the attic space the building owner desired, I had use parallel chord trusses for created an inverted hip in the center of the building. If dealing with the larger spans weren’t enough, they want to do what?!?
Here are a couple of cut-through shots to give you an idea of what I mean.
As you can tell, what appeared to be a semi-simple, very large span truss job, turned into a semi-nightmare. This job was quite the challenge and I learned a lot from it.
Here is a view of all the different ceiling condition this plan has. To top it off, the building has an angle in the section where all this transition is going on! Have you ever done that type of design?
Almost nothing is the same. Two sections in this drawing have the trusses broken into 3 pieces because of the parallel chords! Here is a shot of the trusses pieced together, using the “snipping tool.” NOTE: I only did one end, but the parallel vault is on both ends.
As you can see, I had my hands full trying to figure out what do on this one! In the end, I feel that I have come up with a good working solution for this building that suited the building owner’s needs. While these are most certainly the ugliest trusses I have ever designed, they are definitely not the easiest to deal with.
Have you ever seen anything like this? What solution did you come up with to meet what was a seemingly impossible building design?
View Part 1 in this series here.
View Part 2 in this series here.
View Part 3 in this series here.
Stay tuned for Part 5.
Zach Failing – Design Professional
Gould Design, Inc.