So how about another one of these.
Imagine you’re a framer, and you bought a set of trusses from me. When the trusses are delivered and unloaded you see this girder truss. You know from looking at the layout it’s a 3 ply 24′ girder that carries 36′ trusses tying into it.
After looking it over you get on the cell phone and tell me it’s wrong, and you need to have it replaced.
Why did you make that call?
This morning I woke up to the unmistakable scent of pigs in a blanket. That’s the price you pay for letting the in-laws stay over.
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I am not a structural engineer and would not typically question a truss engineer’s design specifications. So this is just a guess as to why I should make the call.
If these trusses were engineered for the load then I would set them and let the truss company assume liability for their engineering mistake if indeed they made one. The attached documentation is certified by an engineer, is it not?
I may call and question the use of what appears to be lighter than sufficient gang nail gussets at all the splice and web connections because it is not like other trusses of this nature I have experience with. The typical girders we get have much beefier gang plates at those points.
One other questionable issue is the bearing points at the walls are shown inconsistent. (3-1/2” Vs. 5-1/4”). But I do not see a red flag there either.
Another questionable item is the spacing of the truss’s web and cord connection points. They are not evenly divided along the cords.
I have set trusses that have had structural issues in the past because I was told to set them and they would come and fix them on the job or they would send an engineered detail of the needed modifications for us to perform.
The ole “Do something, even if it’s wrong, we'll fix it later”, sad, but true, rule of production construction.
"The attached documentation is certified by an engineer, is it not?"
Nope. Trusses aren't designed by engineers. Guys like me design 'em. Some states/cities/buinding departments require you to get an engineer's seal on drawings. If so, we email them off to get seals.
"One other questionable issue is the bearing points at the walls are shown inconsistent. (3-1/2” Vs. 5-1/4”)."
The W 3"-8 you see refers to a 3 1/2" bearing. The 5"-4 dimension you see is the distance to the center of the scarf. I have no idea why the program puts that dimension on the drawing.
"Another questionable item is the spacing of the truss’s web and cord connection points. They are not evenly divided along the cords."
They virtually never are. Typically they're spaced halfway from the scarf cut to the peak. I don't know that there's a reason for that. "It's just the way it's always been done" (-:
"I may call and question the use of what appears to be lighter than sufficient gang nail gussets at all the splice and web connections because it is not like other trusses of this nature I have experience with"
You're on the right track.
Winning isn't everything. Winning and gloating and rubbing their noses in it ... that's everything!
“Nope. Trusses aren't designed by engineers. Guys like me design 'em. Some states/cities/buinding departments require you to get an engineer's seal on drawings. If so, we email them off to get seals.”
I don’t know for absolutely sure that they are here in Texas but I think they are. At least I know that the liability issue of a Cut roof Vs. Truss roof has been cited to me as why some builders prefer trusses.
All the girders I have installed have also had at least 2/6 Top Cords w/massive connectors at all connections. Some have heavier webs too. I have questioned similar structural issues in the past and have always been told to install them so I have assumed that they are engineered. The truss installation documents are required to be on the job for the framing inspection also.
I have also experienced a failure of over-spanned floor trusses years down the road. What a nightmare that was. It started out with a foundation that was built three feet over the zero property line and snowballed from there. The building was three feet wider than the plans called for. No compensation to the floor system for the added length was made, except for the length. The office building nearly collapsed. The foundation contractor was held liable since he blew it from the get-go. An Absolutely boneheaded nightmare that I was not even told about it until many years later. The builder kept it "under the lid".
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I would want wider members against which to fasten hangers and cleats.
"I would want wider members against which to fasten hangers and cleats."
You certainly could request wider members. But there's no structural reason to.
For truss hangers, we typically send out Simpson HUS26s. Simpson rates them for 3,200# in SYP lumber. That's a 64' truss at 50# loading.
Did you know that with wider lumber, the capacity of the hanger is reduced? Like if you use a 2X6 hanger on a 2X10 supporting member, it's only good for something like 80% of it's rated value.
That doesn't come into play very often. Just thought it was relevant.
Burglars broke into my place and were so appalled, they left a donation!
Why is the bottom chord splice gusst plate off center? That is all that stands out to me
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
"Why is the bottom chord splice gusset plate off center?"
That's more the norm than the exception. The program checks the bending moment wherever you put the splice, and sizes the plate accordingly.
In the first post, the plate was WAY undersized, as I pointed out in my post to DanH. You'll notice the 2nd picture I posted had a much bigger splice plate on it.
Some say that 1/4 of the way betwen joints is where the shear and bending moment are lowest. They claim that bending moments are actually HIGHER at joints.
Others claim that joint splices make it more of a pin-joint model, and are better overall.
My opinion is that either one is fine structurally. But I virtually ALWAYS do them off the joints. The plates don't end up being quite so big, so there's less plate that you have to drive hanger nails through.
Or toenails. (-:
We in the industry know that behind every successful screenwriter stands a woman. And behind her stands his wife.
Keep them coming, Boss. I didn't realize until you explained what's up with this one that we had better be reading all the fine print in the problems.
Just gazing at the truss and thinking that it's a visual thing, easily picked up on by looking at web arrangement and relative member sizes, won't do. Now we need to be focusing on all the stuff that truss print is saying.
I am looking forward to numbers 5, 6, 7, 8, and beyond.
I'm learning, I'm learning! Keep it up Boss.
DaneI will always be a beginner as I am always learning.
So what was the fix on this girder truss snafue?
Matt
"So what was the fix on this girder truss snafu?"
It was several years back, so I don't remember every detail.
But the framer had to pull off all but the first ply of the girder. Then they had to slip in a NEW girder truss and bolt it to the old one.
I think they had to knock a hole in an exterior wall and knock down some interior walls to make room to get it done.
I didn't get in a WHLOE lot of trouble over it. I think the owner of the company knew I felt terrible about it. And I don't make all that many mistakes. (Far less than average, I like to think)
Being intelligent is no guarantee against being stupid. [Victor Serebriakoff, founder of American Mensa]
WOW - that's a pretty significant fix.
Matt
It's been a while. I would shy away from a B1+B2 combo, where the joint between the two is a obvious weak spot. For one, the drawing doesn't show a web covering the top and underside of the B1+B2 joint, the area where the highest tension and compression loads will be found. With a joint only covering the sides, its likely that the holding strength of the web there will be exceeded by the shear that the working beams will entail.
So, at the very least, I would expect a top and bottom metal connection between the plates. However, I would be happier with a Truss design that incorporates a lapped joint suitable to sustain a bending moment to make the whole package stronger.
> Why did you make that call?
Because your daughter's piano recital is today, and it was the best excuse you could come up with to knock off work.
Nice try - But not quite there. (-:
MRJALAPENO came the closets in the 2nd post when he questioned the size of the plates.
The truth is, this truss wasn't designed for ANY added load AT ALL. It's only designed to sit 2'O.C. carrying normal roof loads. No allowance was made for the tie-in span I mentioned.
Fortunately, this doesn't happen often. As far as I know I've only done it once in 20 years, where a girder truss was actually designed, built, and delivered with no loading added in the design phase.
That particular truss had been submitted to an engineer for a seal, as well as the project engineer and architect. None of them questioned it. (One of the reasons I think the whole review process is a joke)
The framers were the ones who finally questioned it. I initally blew them off, thinking I just didn't make mistakes like that. But they insisted something was wrong, and I eventually checked it out and found the problem. Unbfortunately the truss was set in place by that time and the roof had plywood on it.
As you might guess, my boss was none too happy. But we came up with a way to repair the girder and paid the framer to do it.
I guess my point is that no one is infalible. Trust your instincts, and question something if it doesn't look right.
Here's what the girder should ACTUALLY look like, if it was designed right. You'll notice the reaction on this girder is 11,312#, where the other one ws only 1,200#.
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A man's only as old as the woman he feels.
Hey! I want my milkbones too!
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!
"I want my milkbones too!"
Sorry - You were the 2nd person to say that, and it wasn't 100% correct.
I find television very educating. Every time somebody turns on the set, I go into the other room and read a book.
Blue,
Between you and me, if BH is so good at eff'in up trusses...
I would rather stick build.
wheres the skill and pride of workmanship in rolling up trusses???
specially if they are always designed wrong!!!
I hate using a catspaw and a sawzall on new construction.
:)
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You're crazy Mr T!
Give me trusses any day...I love those 60 foot spans!
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!
I want my Milkbones!
What else did you change? The only thing I noticed different was some numbers, but we don't care about no stinkin numbers.
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!
"What else did you change? "
The top chord lumber grade was higher, and the web lumber changed.
I thought the 1,200# reaction would tip more people off.
No matter how good she looks, some other guy is sick and tired of putting up with her
I've never read the reaction numbers. I'm just a carpenter doing my job, I figure you'd do your job. I'll review your numbers if you'll come out here and lay the roof ply!
I don't mind making the money for the repair when the stuff fails though!
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!
Those gussets won't fly! They're too girly.
Send be some manly gusseted girders!
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!
the top tie-points are missing