Truss design misconceptions 29

[RontheRedneck]

I mentioned in another thread that I've been designing trusses most of my adult life. I started working in a truss plant in 1984, and it went from there.

Over the years I've run into a lot of misconceptions about how trusses are designed, who designs them, etc. I thought I'd take a crack at explaining the typical process.

The vast majority of truss plants do not have engineers on staff at the plant. Trusses are designed by guys like me. I only have a HS diploma. But I do have a lot of training and experience.

We buy our truss plates from a company called Alpine. They provide the truss design software that we use. They also have engineers on staff. The cost of the software and engineering support is built into the price of the plates.

Since we're in a rural area we don't get an engineers seal on probably 95% of what we do. There's no reason to.

If we do need sealed drawings, it's usually because someone is building in an area where there's a building department that requires them. Or on commercial work we sometimes have to send them to the project architect/engineer for review.

Once we have the trusses designed in our system we can send a job down electronically to Alpine. One of their engineers is assigned to our account, and that person typically reviews our stuff.

The engineer does not alter the truss designs - They're either approved or not approved. If they want something changed we get an email or phone call explaining what they want to see. We revise them and send them back down.

The engineers at Alpine never see the plans. They typically do not know where the job is going or any details about it. They only review what we send down.

So that's the basic process. If you have any questions let me know.

 

[kipfoot]

What's your opinion about engineers calling to ask you to run a truss calculation?

I worked on a project with a truss guy, known to the owner, to lay out a big residential project. Then the owner got another truss place to fabricate the trusses. I really thought the first guy was getting the job, so I felt bad about the time he spent with me on it.

Other times an architect will show something with trusses that feels wrong, but they're in love with the idea and I need to prove that it doesn't work:
1) a bearing wall that's supported on a truss floor system
2) architect wants a mechanical chase in a dumb place, near a bearing point
3) like the other thread, should I use an interior bearing wall for this cathedral ceiling truss?

 

[XR250]

The engineers at Alpine never see the plans. They typically do not know where the job is going or any details about it. They only review what we send down.

So that does not feel good to me. It has to be breaking some regulation.

What exactly is the Engineer signing off on? "Uh, our computer software produces the proper output assuming it had the proper input"

What if there are drag trusses or other situations that you miss that are called out on the plans? Who is responsible?

 

[Settingsun]

XR250, I was wondering about the issue of practising without licence, which is mentioned frequently by US engineers on this forum.

Given the description of the relationship, I'd guess the Alpine engineer checks that the truss plate is being used correctly, subject to the inputs provided by the builder - pretty much what you said.

 

[stanleyshum1997]

Even a piece of furniture has to be sealed by structural engineer by law let alone a trusses. Since the trusses is only a part of an entire structure, you might get away from law with a seal from an vocational institute.

 

[Aesur]

XR250 - I am in agreement with you however understand that the standard process is as RontheRedneck says. Lately I have been rejecting more and more truss shop drawings due to missed added loading, drags, some architectural feature sitting on the truss, mechanical loading, etc.. the most recent one I reviewed was marked as revise and resubmit or rejected 8 times before I finally got a call from the sealing truss engineer asking why they kept being rejected and arranging for him to get a copy of the structural drawings.

The normal shop drawing stamps I have seen puts the ultimate responsibility on the contractor to make sure they conform to the drawings, but then again, they don't understand these special conditions either and just rubber stamp many times as approved.

Another recent project the contractor went ahead and installed, including building finishes before submitting shop drawings, the shop drawings were missing the brace loads and the end wall gable truss was marked as not designed for out of plane loading, because of this it went through multiple rounds of shop drawings, phone calls, being yelled at for not just letting it go without change, etc.. now they are in the process of tearing out finishes to get in there and retrofit. Because of this, I have been spending more and more time reviewing shop drawings, especially the special case trusses for many projects, sometimes this can take a whole day depending on the size of project, and since most architects won't go for hourly CA, the CA budget almost never covers this kind of reviews. I am willing to bet far too many projects get built with this kind of stuff being missed as many junior engineers reviewing shop drawings don't understand this stuff at that point in their career either. I was taught the EOR's review was a quick review of basic loading and special loading, nothing more; this isn't always sufficient.

We tried to get a copy of the software, even offered to pay for it to start offering truss designs as part of our package a while back, however the truss plate companies all refused to sell us their software unless we started building the trusses. We were trying to offer this service as in my area for a while truss engineering was backed up for 6+ months and projects were being delayed.

 

[RontheRedneck]

kipfoot said: "What's your opinion about engineers calling to ask you to run a truss calculation?"

I wish more of them would.

We often get plans with things that don't work. Then we have to deliver the bad news to the owners. If we were asked about things in the planning stages it would save everyone time and money.


XR250 said: "So that does not feel good to me. It has to be breaking some regulation.

What exactly is the Engineer signing off on? "Uh, our computer software produces the proper output assuming it had the proper input"

What if there are drag trusses or other situations that you miss that are called out on the plans? Who is responsible?"


I don't know why it doesn't "feel good"to you. But it's standard practice in the industry.

Roughly as you said, the engineer is signing off on that particular truss given the criteria spelled out on the drawing.

If something is missed on a plan, the responsibilities don't change. Whomever missed it is responsible.

 

[eng-erik]

The cost of the software and engineering support is built into the price of the plates

Interesting. Is this a common business model for plate fabricators?

 

[RontheRedneck]

eng-erik - To the best of my knowledge that's how they all work in the USA. I don't know about other countries.

 

[JStructsteel]

If something is missed on a plan, the responsibilities don't change. Whomever missed it is responsible.

I would 100% say the engineer that stamped it would be responsible. Thats the whole idea behind stamping somthing, they are verifying they have designed it and its correct, or am I missing something?

 

[JStructsteel]

So if someone else designed something, sends to me and I stamp, is that legal??

 

[phamENG]

JStructsteel - that's been debated on the ethics forum ad nauseam. Comes down to jurisdiction and state laws. In several states, simply familiarizing yourself with the work to the level needed to perform the work is sufficient to assume responsibility for the design and seal it. In other states (Virginia being one of them), the letter of the law states that I can't seal any work product that was not generated directly by me or my employee/contractor working for me and under my direction. (Or employee/contractor employed by the same firm where I work if I'm not the boss.) The spirit, of course, is to prevent rubber stamping, but the letter of the law is quite specific in that case.

A lot of this comes down to the relationship between the "Engineer of Record" and specialty structural engineers involved as the result of delegated design. Ultimately, the engineer of record is responsible for everything (structural) in the building. By using licensed SSEs for delegated component design, there is some shared responsibility but the buck stops with the EOR. That's why we still review shop drawings. Even if another engineer designs the connections for a building, I'm going to at least a) make sure they used the right loads, b) make sure their results make sense, and 3) make sure they got all of them. Same with trusses. If I spec drag trusses or special conditions, I'm going to review the shop drawings and make sure they are there. I'll also review the calcs to make sure the right loads are used, the right wind parameters, etc.

 

[JLNJ]

"Responsible charge" is a slippery term. I guess you'd have to look it up State by State to see how your State court has adjudicated it.

 

[JoshPlumSE]

So if someone else designed something, sends to me and I stamp, is that legal??

Perfectly legal.... You're just saying that you are taking "responsible charge" of the design. Now, it could be illegal by the engineering practice codes. Meaning that if you did not sufficiently review the design before stamping, then you could lose your license. But, this is a grey area that isn't all that well defined.

As others have said, this is something that has been discussed before in ethics forums. But, my belief is that the EOR does not have to do any calculations or such in his/her review. If you've got 20 years of experience with trusses and you just know based on that experience that the design is okay, then that should be sufficient.

 

[MJB315]

This is a delegated design issue, is it not?

If it's a commercial project, then the EOR would retain responsibility for the design of everything in the structural system. The code allows the engineer to delegate the design of components away to appropriate third parties...but the EOR is still responsible for the performance of it. If I'm the EOR, I wouldn't want to simply trust the design of a system -- I'd want to see certified calculations first before I allowed it as part of my systems.

If it's a residential project, then it's a tad bit trickier. I am assuming there is still a licensed design professional involved (most likely the architect)...and they would assume the role of the EOR and be responsible for the performance of it. If there is absolutely no licensed design professional involved...then I would assume responsibility would fall to the Building Official to be responsible for the dwelling constructed within their jurisdiction.

If there was a failure (say a truss wasn't braced per the Alpine design and failed)..then I think the blame game would begin...but much of it it wouldn't really land on the technician running the program at the manufacturer, would it?

"We shape our buildings, thereafter they shape us." -WSC

 

[KootK]

I don't know why it doesn't "feel good"to you. But it's standard practice in the industry.

It shouldn't feel good to anybody. That, because the system implies that:

1) The stamping engineer is reviewing the individual trusses designs spit out by the software which we all know is meaningless and;

2) All of the things that one would one would consider to constitute "engineering" in this situation are being done, unsupervised, by technicians. This includes:

a) Determination of environmental loads where required.

b) Load transfer between trusses.

c) General identification of special project concerns that can only be identified by actually reviewing the project.

...

When I was doing trusses in the 90's, I worked with three engineers predominantly, in order:

1) A fellow that invited me out to hang out with him in the big city for a couple of days. I thought that he was going to help me learn to engineer trusses. Instead, he showed up at 9:30 AM both days and took me out for 2HR lunches at interesting places. During a couple of "work" sessions in the morning and afternoon, he probably stamped 300 truss designs.

2) A fellow who clearly did review the project layout to scan for errors. He still didn't stamp the layouts but, at the least, he looked at them. This, I assume, because he understood that was where any, meaningful engineering review actually resided within his scope of work. I learned a lot from this guy. I would hope that this is the situation much of the time.

3) Another engineer who appeared to be rubber stamping and wound up getting sued for various things over the ensuing years that led to him eventually shuttering his practice.

In western Canada, jurisdictions are starting to ask for stamped truss layouts. That is excellent, in my opinion, and I'm hoping that it will open up opportunities for engineers like myself who have significant experience in the MPCWT world and would like to to put that experience to meaningful use within the industry. Of course, this means that the $5/truss design review model needs to come to an end. But, then, it always did. When a guy is trying to bill $150/HR, how much time does $5 buy? And that includes project procurement, mobilization, invoicing, and demobilization.

For what it's worth, all of my MPCWT experience has been in:

1) Western Canada and;

2) The midwest USA.

 

[KootK]

So that does not feel good to me. It has to be breaking some regulation.

1) The plate suppliers recognize the direction that things are clearly headed with respect to board rules: you shouldn't stamp stuff that wasn't produced within your organization.

2) To address #1, the plate suppliers look at the truss designs in isolation with the intent to disavow themselves of having ever stamped the work of the technicians. Rather, what they are claiming is that they have re-engineered the individual trusses themselves using their own, proprietary software.

That plate supplier engineers are consistently and meaningfully reviewing the work of truss technicians is the misconception that most needs recognizing.

 

[XR250]

It's about time you stuck head your head in here!

Thanks for the info.

 

[KootK]

It's about time you stuck head your head in here!

Thanks. I very much like what rontheredneck is doing here and his participation in the forum in general. I think that it's healthier if I'm not the lone voice of the metal plate connected truss industry here. That, particularly given that I've not been immersed in that industry for two decades +.

 

[cliff234]

For what it’s worth,… in the U.S., if an EOR delegates design of structural steel connections to a fabricator, that fabricator then hires a licensed engineer to design the connections. If there is a connection failure, the EOR will be held ultimately responsible for the failure even though another engineer (working for the fabricator) designed the connections. I’m not a lawyer, but I suspect the same would apply if there is a failure with wood trusses. The EOR is ultimately responsible for the safe design of the entire structure – including elements for which design was delegated to another engineer. When the Hyatt Regency skywalk hanger connection failed in 1981, the EOR who signed the drawings, and the project engineer who managed the project both lost their licenses.

I’m surprised at how many engineers think that delegating design absolves them of all responsibility for the delegated design elements. (Of course the engineers who did the delegated design will mostly likely bear some responsibility as well.)