Is this truss profile manageable?

[E M]

Is this truss profile manageable?

65'-0" span with bearing points far left and right of the profile.

Need the end extensions so can work with some slope concerns with getting the truss elevated at the center. The thinking goes that basically just build in a parallel chord truss and piggy back another truss on top. But in reality just build the truss this way.

It's kind of bugging me in one way but also seems ok to me in another.

If can design this way then will eliminate the need for 2 additional beams and all the additional support structure if they were needed to be placed at the normal heel location.

Figured this was a good place to start with the question.

Thanks.

 

[rb1957]

do you mean no bracing ? well that doesn't sound right ??

or are you concerned about the "end extensions" ? use a solid web in thee places ? extra loading ??

Would the supporting walls be at the extreme ends of the extensions, or at the end of the conventional truss (the sloping part of the roof) ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[BAretired]

Should be okay if you have enough depth at each end.

 

[E M]

RB1957. This is the profile only. Yes, I understand that there will be web members.
Good point on the extra loading which ultimately will become important. There will be overbuilt roofs both left and right side of the truss.
Yes, support will be at the extreme ends.
Thanks for the iterest.

BARetired.
Thanks for the help with the proof of concept.
-Out of curiousity what makes this particular profile jump out at you as needing 10" cmu? Just because of the span?
-Any idea what kind of depth at the extensions might be required? Just a very rough guess would help. I currently have drawn as 2'-6" total depth at the extensions. I have some constraints but do have some flexibility. Would rather get the concept down to worst case scenario on paper first.

 

[BAretired]

You're welcome.
I did not suggest 10" minimum cmu. More information is needed to determine that.

The yellow configuration below should be possible because similar trusses have been used before. The problem could be the depth, particularly at the right hand side. You can see your outline faintly below. You may need to lift the overbuilt part a bit to enable the top chord to pass straight through to the support.

According to my scaling, the maximum height would be 15'-2" which could present transportation issues. You may want to consider a piggy-back truss at a height of about 10'.

 

[phamENG]

You need a truss manufacturer on board now, even if only a an advisor/ consultant. This is at least a two and possibly 3 part truss. Design, transportation, and erection will all be complicated.

 

[E M]

BARetired-
Sorry for the 10" cmu part of my post. Have no idea where I got that from at this point.
The profile you're showing could possibly work this end if that profile is ok with truss fabricator.
IYO if the profile you show will not work then do you think something along the lines of what I was originally showing would work?
Going to sketch this out in my model to see how might affect things architecturally. Might be better actually.... but will need to change the ridge position to get equal slopes....

Understand on the piggy back condition. That in itself is not a problem. That's kind of why I was thinking a parallel chord truss at the bottom could work....

PhamENG. Point well taken. Will be doing that soon but wanted to get at least some of my ducks in a row before I involved them.

 

[lexpatrie]

The heck does IYO mean?

 

[SWComposites]

In your opinion ???

 

[BAretired]

E M[/u]]IYO if the profile you show will not work then do you think something along the lines of what I was originally showing would work?

Your profile could work, but the drop-down piece at the right end is a bit weird.

 

[E M]

Ha! Yeah IYO was meant to be “in your opinion”. Maybe i made that up or something…. Seemed right in the “moment”….
Don’t hate it when people do that “totkottmyliubr”…. (That’s short for “throw out things that make you look it up on the internet before responding” btw (by the way just for the sake of clarity.
Sorry couldn’t resist….

Sounds good BARetired. That is helpful! At least i know I’m not all wet heading into a meeting with fabricator!

 

[lexpatrie]

As a side note, next time you post your title needs to contain a description of the question, not a meaningless hyperlink. ideally a material as well. E.g. wood, steel, etc.

FAQ: How can i ask a high quality question

 

[KootK]

Voting as a fellow who was a truss designer from 1995-2000, and then an engineer at the Wood Truss Council of America for a couple of years after that... I vote no.

1) The chords in the extension areas are so close together that there will be a tendency for them to act as two beams as much as a composite truss. As such, lots of moment and shear in the chords.

2) The chords in the extension areas are so close together that it will be tough to build and plate clean webbing and joints in that area. Lots of plate gaps.

3) Curvature in the extensions, and any plate slip there, is going to have a disproportionate -- and difficult to predict -- impact on truss deflection.

Back in my truss technician days, I would have said put through the software and see if it works. With a couple of decades of EOR work, I now wouldn't do this no matter what the software says.

A back of the envelope way to assess this as an EOR is to just pretend that the extensions are nothing but the protrusions of a 2x12 bottom chord. If you run the numbers on those as cantilevers and like how that looks, maybe the idea has legs. If not...

 

[BAretired]

I agree that the extensions appear shallow, but increasing their depth does not change the concept.

 

[E M]

Lexpatrie. Have no idea how the meaningless link ended up in the thread title.
KootK. I hear you. Note that the depth of that area can be pretty much anything it needs to be as long as it doesn't come out of the overbuilt roofs at the left and right sides of the profile.
BARetired. Thanks for continuing to follow this.

 

[RontheRedneck]

The truss profile *might* be workable. I'd need specific dimensions and loading to know for sure.

phamENG, not sure why you said it would be a 2 or 3 part truss. It might need to be piggybacked, depending on the height. But it doesn't look like a big deal to me.

 

[KootK]

KootK. I hear you. Note that the depth of that area can be pretty much anything it needs to be as long as it doesn't come out of the overbuilt roofs at the left and right sides of the profile.

You question cannot be meaningfully answered without specifying the depth of the extensions. At the relative depths that you've shown I feel that the situation is pretty hopeless. Double or triple that depth and it's no problem at all.

It may be prudent to show us what you're doing here in plan view, including the roof lines. Usually stuff like this is much more effectively dealt with by employing girder trusses than monkeying around with bizarre profiles. If your situation is so special that such an option is truly unviable, it would be useful for us to know what creates that condition.

 

[lexpatrie]

Am I mental it's possible to change the post title? This is news to me. Hey look, I learned something today...

I'm going to postulate the flat enda are some sort of replacement for what might normally be overrating.

I'd be less concerned with the profile, the 65' span and the height don't sound particularly practical from a shipping context (beyond 50' is less desiresble) and the height, if it's shipped flat is in the 8' zone. So that suggests piggyback. Which, eh. Can be done.

The end bearing can be problematic (bearing stress) and the wall top plate can be easily ignored in design and wildly overstressed.

Depending on the loads (and usually on these long trusses there's the temptation to use the lowest possible loads) the chords can be challenging, (particularly when you constrain the depth with a flat end both sides).

Special inspection is required beyond 60' span, unless your friendly neighborhood code happens to delete special ibsoections completely (cough Wisconsin cough, and I think Florida as well).

Graphically, those tails look nasty small.

 

[E M]

Sorry. Laughng at this dialog. Not at you lexpatrie. Just interesting to me. It's a profile. A truss profile. Have no idea if I can change the titel of my post. At the time I thought it was pretty self expanatory what I was trying to get at. Again, not pointing any fingers at any one.
So back to your post lexpatrie. good points. I think.
I figured probably piggy back but was not sure. may matter. may not....depending on cost etc.... as I'm sure everyone gathers. Sputh Carolina acutally. Not Florida this case. I'll explain as required.
How deep would you suspect bottom line min would be for the "tails". I'm just trying to get to proof of conccpt here.
Wondering if it kind of revolves around if a parallel chord truss can't span the distance with a piggy back on top then it's just a no can do situation. Is that what I'm looking at?

 

[KootK]

The parallel chord approach sounds excessively conservative to me. Ate you using published span tables etc? If so, you might use the moment capacities implied by those to check against the moment demands at the extension pitch breaks.