Since the first one generated so much interest I figured I’d try another one.
Like the first one, this is NOT a strength issue. Since the design loads vary so much where all our posters live I don’t think questions about strength would be a good idea.
The following is a picture of what I’d call a “cathedral” truss. Pretty typical of what I see on a day-to-day basis.
What you see here is the web pattern that the design program would typically generate. And it does a LOUSY job of it. I only take the webbing the program comes up with about 20% of the time. The rest of the time I change it for various reasons.
So what would you guess I would change on this truss? View Image
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Replies
Eliminate W3.
blue
Just because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
W3 is probably the most critical piece there. It's in tension, keeping the bottom cord from straightening out under tension.
W1 and W2, on the other hand, aren't contributing a whole lot, other than to prop up the rafter a bit.
Just wanted you guys to know I've been reading the posts. I just figured I'd let it go a while to give more folks a chance to look at it. After thinking about it, I may have been a little misleading in saying that what I would change would NOT be strength related. The way I would design the truss MIGHT not work in some northern regions with REALLY heavy snow loads. But it should work fine anywhere in the midwest. Y'all are on the right track thinking about the webs.
Never give in, never give in, never, never, never, never . . . In nothing, great or small, large or petty. Never give in except to convictions of honour and good sense. [Winston Churchill]
Rotate W2 CW at the top and maybe add a W1B in there?
if the trusses were built i would rotate w4. or send em back. if not would go on breaktime & see if boss hog could help. it looks like the whole thing right of w3 is wrong
move joint at w4, w5, w6, b2 to the right
PS: still dont like the ends, esp using plywood, nails, and glue vs. hydraulic presses and truss plates <G>
As a novice that I am, I am loving this sort of thing. I had no idea of what people were talking about, top chord, bottom chord and all that sort of stuff, but I figured out most of it.
Had I known most of this stuff it would not have cost me a 6 pack of beer to have a GC take a look at what is holding up my roof. He said that I had a "nearly free standing" roof. There for, I only need to put in minimal support when I take out a load bearing wall, 2 2 x 10 with a ply spacer.
I do have a suggestion to make. When you make your heading (what shows up on the subject list) please change the number. "What is wrong with this truss #1", "What is wrong with this truss #2" and so on.
Here is my uneducated answer. Take out W2. I see no value in it, in any form. If anything the weight of the piece is adding to the load. As for W4, if cost is a concern then take it out, if cost is not, then it could be left in.
Thank you so much for this education.
Dane
I will always be a beginner as I am always learning.
I asked the moderators to change this thread to "#2". Looks like they did that around the time you were posting. Web #2 definitely is needed - Can't take it out. Trusses HAVE to be triangulated. (Although there are exceptions)Atached you should find a picture that shows what truss parts are typically called. That should help with some of the terminology.
If you are good, you will be assigned all the work.
If you are really good, you will get out of it.
Quick related question, I have seen strongbacks installed on the lower chord, (just dropped down from your diagram). Is this acceptable?
Bracing isn't typically required on a bottom chord. The ceiling does the bracing. And most bottom chords are in tension anyway. The exceptions would be:1. No ceiling attached. Then they recommend braces 10' O.C. anyway.2. Bottom chord in compression, like where it cantilevers over a porch. 3. Wind uplift conditions where the bottom chord is in compression and there's no ceiling. The required spacing could vary greatly.4. Building codes which may require it for one reason or another. 5. Seismic stuff. I don't have much experience with that.6. Overall building bracing. Some folks like to run braces and then use them to brace gables, etc.7. Other situations I may not have thought of at the moment.Does that answer your question?
There is no idea so good that everyone benefits.
W2 should be like W4
{It's just a guess. If you did move it like that it would look nicer too }-----------------------------------------------------------------------------
"Have you seen my baseball?"
I was talking about the ladder floor truss.
Ras,
I think Boss misunderstood your question. Strongbacks should be a close to the bottom chord of the floor truss as possible.
That was what I thought too.
You're right - I did misunderstnd the question. Strongbacks aren't REQUIRED to be installed at the bottom. But some say that helps prevent torsional vibration. (The trusses moving sideways)I don't know how much difference it reall makes. But it can't hurt.
The grass is always greener when you put manure on it.
Thanks for the picture of the terminology use in your part of the business.
I will be back later on today to see what the real answer is.
It is nice to make these kinds of mistakes here and be able to learn from them, before they cost lots of money out there.
DaneI will always be a beginner as I am always learning.
Extend B1 to W5 so you have a continuous triangle on the left.
I'm sorry, I thought you wanted it done the right way.
My wild guess would be to continue both bottom chords at the center to meet the top chords and remove some of the webs closest to those continuations.
Extend B2 to meet T1.
Jon Blakemore
"Extend B2 to meet T1."
Actually, stuff like that was common back before truss software became more sophisticated. But it's rarely done now.
A handy telephone tip: Keep a small chalkboard near the phone. That way, when a salesman calls, you can hold the receiver up to it and run your fingernails across it until he hangs up.
This is an interesting exercise, and I'm glad you're posting these brain teasers.
May I suggest adding a quick and dirty theoretical primer on load paths in trusses? Drawings showing tension/compression paths on a generic King post, Fink and scissor truss would help me learn more.
"May I suggest adding a quick and dirty theoretical primer on load paths in trusses?"
Not sure exactly how I'd do that. But I'll give it some thought.
If you want a quick and dirty rule of thumb - Any web that goes up to the top chord peak of a truss is in tension. There are no exceptions that I can think of.
Maybe this one was a bit tougher than I thought. So I'll give y'all a hint.
The first truss pic I posted yeaterday needed some "value engineering", as Blue put it. This one does too.
I want to eliminate human suffering - namely mine.
>>>>"Any web that goes up to the top chord peak of a truss is in tension. There are no exceptions that I can think of."I thought the king post from Truss #1 was in compression?
Is a king post not a web member?Could w4 be eliminated?
Jon Blakemore
The kingpost of the girder truss in #1 was in tension. The only exception I've thought of is along span truss with center bearing - In that case, the kingpost would be in compression.NONE of the webs could just be taken out. The only way to reduce the number of webs would be to eliminate a joint and connect the webs elsewhere.
My inner child is a juvenile delinquent.
Reverse all the webs as in this picture?Edited because I typed edges instead of webs. Guess I'm tired....
Edited 3/31/2005 4:01 pm ET by ACI
that dont look like the origanal at all.
but i would not hesitate to install the one pictured. i see 2 "W" that pleases my eye.
boss posted the answer in #1 it looks similar.
Edited 3/31/2005 4:29 pm ET by Brian
B2 should have extended all the way to the top chord to make scissors truss connection.
Sumptin like dis??
MrT, SamT, DanT,RonT,Ms.T…
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MrT, SamT, DanT,RonT,Ms.T…
Whatever…
Welcome to Breaktime!!!
Where…
The free advice is worth every Penny!!!
:P
I don't like the look of everything LEFT of W3.
Seems odd that W4 joins the top of W3, while W2 joins the bottom of W3. W2 just looks wrong to me.
I'd guess that W2 should run from the BOTTOM of W1 tot he TOP of W3.
Jon
BH.
The left side seems lightly engineered. W2 is at to shallow of an angle. Correct the angle and add another compression strut to the left side. The entire truss could be better engineered with two (as a W) center tension webs strengthening both sides.
I just viewed ACI's truss. He's got the right idea.
Edited 3/31/2005 6:08 pm ET by MRJALAPENO
OOPS - I posted the "solution" pic in the wrong thread.
As I said in the first post, this is NOT a strength issue. There are just too many webs in it. That makes the truss considerably more expensive for no reason.
The truss in the first picture had 8 webs. This one only has 6. But it does the job just fine. And you'll notice the panels are more evenly spaced on B2 this truss.
View Image
I'm gonna get some supper, then I'll post another one.
Out of my mind. Back in five minutes
I was right! Send me the dog bones!
blueJust because you can, doesn't mean you should!
Warning! Be cautious when taking any framing advice from me. There are some in here who think I'm a hackmeister...they might be right! Of course, they might be wrong too!
OK, I also asked this in the wrong thread: Would it be a good idea to combine W2 and B2 into one piece? They're pretty much in a straight line. Would that be stronger? Cheaper or easier to do?
-- J.S.
Running a bottom chord through isn't typically done for a couple of reasons. First would be that web lumber is cheaper than chord lumber. So that would tend to make the truss more expensive.Second would be that it would make it more difficult to get the truss to fit together on the assembly tables. As you well know, lumber is far from perfect. And if things are just a hair off things don't fit right. If you run the BC through you can't slide the pieces around any. With separate webs and bottom chords, you can move them around to some degree to get a tight fit.
Women should be obscene and not heard.
Makes sense... in a bakery style low margin business best is not cheapest right? Someone not entirely cost conscious would not remain in business long when dealing with residential construction.
I got here late... great puzzles Boss, thanks for the view or your world!
L
GardenStructure.com~Build for the Art of it!
as a youngin, i gotta tell you i really enjoyed that post, keepem comming, im learning alot.
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--> measure once / scribble several lines / spend some time figuring out wich scribble / cut the wrong line / get mad