Roof Diaphragm Dispute

[UnneutralAxis]

I have a job where the shear flow in a wood roof diaphragm is a little over 400 plf. Blocking is required. The framing sub doesn't want to supply the blocking for whatever reasons and they have the truss supplier (also a PE) saying that the blocking is not necessary. I've never been in this situation before, and blocking is clearly necessary. He says that he's never even seen blocking on a roof diaphragm before. I say he needs to get out more...

I'm trying to resolve this as painlessly as possible. I'm self employed and am always afraid of being sued.

I thought about sending their engineer my calcs and saying he can review, refute, and sign and stamp a letter saying it is not required and then I would consider eliminating the blocking. At the same time, it's required and I'm the engineer on the job so I'm still not comfortable with that.

Can't imagine getting drug into court over some blocking, but stranger things have happened.

 

[Lion06]

unneutralaxis-
Where in the construction process is this project?

If the contract has already been awarded, then the contractor bought the blocking. He owns it, plain and simple. He should NOT be getting extra money for something that was on the drawings the way he bid them. If he can't read the drawings to bid properly, then that's on him.

It pisses me off and it's not even my project.

There are often times where the guys that build the stuff have good ideas. They know how things get put together.

This is not one of those times, though.

 

[msquared48]

It's not healthy to piss off a Lion.

I'll have to agree with him.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[UnneutralAxis]

Lion - all foundation work was completed today. Framing should begin next week.

I can't tell you how much it bothered me today. I think the truss engineer is just that. A truss engineer. Not saying that all are one trick ponies, so please no one take offense at that. I don't think he understood what the blocking was even for because they typically don't have to think about a MWFRS. So (best I can tell) he likely thought that the blocking was to brace the top chord of the trusses in compression. Hate to jump to that conclusion, but from our little discussion today that was the impression I was left with.

I don't care anymore. I decided that I'm not even entertaining suggestions on the blocking. It's going in and that's that. Don't like it... then don't put it in, owner won't get certificate of occupancy, and you won't get paid. Then you can rip the entire roof off and do it again when you decide you do feel like putting in the blocking.

Also, like I said earlier, they say they are giving them money for the blocking. The owner is closely related to the GC... if that explains the $ issue.

 

[BAretired]

Stick to your guns, UA, the diaphragm must be blocked for shears as high as that. Don't get mad, don't get excited, just tell them that this is the way it is. You are right!!!

BA

 

[ron9876]

msquared48 yes I am talking about interior zones of boxes, etc.

 

[a2mfk]

Dear Mr. Engineer:
Why are your foundations so big, your uplift connections have so many nails, your this and your that....?

Dear Mr. Truss Engineer (wait, what? A truss ENGINEER? You talked to an actual truss engineer? Who knew they existed?):
You design the trusses, I will handle the rest.Thanks.That blocking has nothing to do with your trusses, because, I am letting YOU design them. The blocking is for this little thing called a diaphragm. Now, unless you are doing a peer review, I am not going to explain this further to you.
G'bye...



Man I got almost annoyed for you as Lion reading this. That framer has a lot of nerve sticking out his hand for more money when he bid drawings. We as SEs have to bid on napkin sketches sometimes, and scope creep, fahgettaboutit!!!!

 

[Lion06]

I wonder if we could come back to the owner for more money saying, "What? You want a lateral system? I'm going to need more money to do that."

I was extremely annoyed yesterday; now I'm just chuckling.

 

[UnneutralAxis]

Lion, thanks for the solidarity. I appreciate it.

Yes, I was ticked yesterday. First time I've ever had another engineer questioning my work. I'm sure it happens to everyone from time to time, but I'm a younger guy and this was a first for me. We all know that opinions vary greatly, even among engineers. But this seemed as clear to me as whether or not you need a footer at the bottom of a load bearing wall.

I felt much better about the situation after actually talking to the engineer though. It was just something he wasn't all that familiar with.

 

[BAretired]

All's well that ends well. Good for you, UA.

BA

 

[a2mfk]

Well Lion, we did just have an owner request windows at the ends of our shear walls to the tune of about 80% of our shear wall area, on a building where 75% of the foundations were already placed. Not those foundations thankfully, and they were tilt walls and actually worked out ok with some redesign. The kicker is this- the windows are there for just show!! They are actual windows, but the inside will be covered because it is warehouse space...

If we did not get a sweet ad serve our heads would have exploded.

I think even the architect finally had to tell the owner what a shear wall is, and stop tweaking a building that is being built for pete's sake. He literally had to tell the owner STOP, enough is enough!!

 

[Lion06]

a2mfk-

That's a riot......... coming from an architect!!

 

[msquared48]

Happy Lion... Happy Lion... Nice Lion.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[woodman88]

You might reread what the truss engineer said. Many times to cool off a client they will write something like "The truss designs assumes sheathing to be applied to the top and bottom chords of the truss, except as noted otherwise. This sheathing does not require blocking for the structural stability of the trusses."
This is what was called a make the client “feel good” letter.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[frv]

I'm with Lion and others on this one.

As SE's, we need to stick to our guns more often. A change should be the exception, not the rule.

I'm not suggesting that contractors don't occasionally have good suggestions, but I'm getting tired of contractors wanting to make a change that will take us a few hours to verify simply so they can save 1% on something. Are they paying for our time to redesign something that is just fine to begin with?

 

[a2mfk]

frv- I think what is different in this situation, and I may be misunderstanding it, is that the framer balked at the blocking because the truss engineer said it was unnecessary. Or the framer balked and the truss engineer said it is unnecessary.

Either way, a specialty engineer called out the EOR on his design to the contractor/owner, which in my mind is not how you handle things professionally. I have noticed "areas of concern" in EOR drawings as a specialty engineer before, and I have gotten with that engineer directly and privately to point it out to him, as a another set of eyes, not being confrontational. The response has usually been very cordial, professional, and thankful for my concern and for not making it public so that they can make the change as they see fit.

I think Woodman nailed it, pun intended, and the truss engineer either misspoke about the blocking or it was misunderstood by all but Unneutral.

 

[dhengr]

A2mfk.... you took the words right out of my mouth @ 9JUN11, 10:09, a day ago I wrote the following and then didn’t posted it.

What is a truss engineer, anyway? Are they really a full fledged one trick pony or not (per UA, 8JUN11, 22:19), or have they just been coached (teached) to run a pre-canned computer program that spits out a truss design, with some forces, stresses, deflections, and dimensions, and tells them when special bracing and the like are required to meet the programs design methodologies. And, none of which he could even begin to imagine without the pre-canned program which he more than likely doesn’t understand in the least. If they took away his pre-canned programs he would be like a race horse without legs, not much of a winner. I think the word engineer gets thrown around a bit loosely these days to stroke someone’s ego. You know..., like sanitary engineers drive garbage trucks, space engineers who look off into space, with glazed eyes, when being spoken to... And, UA, you continue to perpetuate this by still calling him a truss engineer in your later posts, whatever he calls himself, he’s just the truss drafter, and is way out of line discussing the plans and details with anyone other than the EOR.

The truss drafter/computer runner might have said, ‘our truss design does not req’r. and special blocking or bracing for stability at the lengths, depths and stresses involved here,’ otherwise, if you have questions talk with the guy who signed the plans. By the way, I have worked with some truss drafters who could do some neat things with their trusses and programs to meet my special needs, once I explained what I needed and about how to do it; they could run the numbers and size the truss members and plates much quicker than I ever could, and to my satisfaction on shop drawing review. So, they ain’t all bad.

 

[UnneutralAxis]

A2mfk,

I agree with most you just posted; however, this guy is an actual living, breathing, licensed P.E. I looked him up on the state board's list to be sure. So, he really is a truss engineer as he meets the same requirements I do to be licensed. I can say though, that the man did not know about designing roof diaphragms.

Well, I think I've about beat this one to death. Thanks everyone for your input. Lot of knowledgable folks on here.