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Truss design misconceptions
21

Truss design misconceptions

Truss design misconceptions

3
(OP)
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.


RE: Truss design misconceptions

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?

RE: Truss design misconceptions

2

Quote (ron the redneck)


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?

RE: Truss design misconceptions

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.

RE: Truss design misconceptions

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.

RE: Truss design misconceptions

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.

RE: Truss design misconceptions

(OP)
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.

RE: Truss design misconceptions

Quote (RontheRedneck)

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?

RE: Truss design misconceptions

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

RE: Truss design misconceptions

Quote (RontheRedneck)

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?

RE: Truss design misconceptions

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

RE: Truss design misconceptions

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.

RE: Truss design misconceptions

"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.

RE: Truss design misconceptions

Quote (JStructSteel)

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.

RE: Truss design misconceptions

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

RE: Truss design misconceptions

4

Quote (rontheredneck)

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.


RE: Truss design misconceptions

Quote (XR250)

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.

RE: Truss design misconceptions

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

Thanks for the info.

RE: Truss design misconceptions

Quote (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 +.

RE: Truss design misconceptions

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.)

RE: Truss design misconceptions

I've done delegated design for steel and wood joists. But, not for full truss systems. I'm a little shocked to hear KootK's description. In all the delegated design that I've done, I'm responsible for the determination of all loads applied to the trusses. It's part of the packet what we give them when we delegating that design.

The only times I've see it done the other way is for full metal building systems where the packet we give them is more generalized and they're giving us a complete system. We might give them the LL and DL, and then give them some parameters for them to determine wind and seismic. But, we'd probably specify what the lateral force resisting system is going to be (with the R value) for each direction. Along with a request that no connection exceed 80% of code limits under gravity loads, columns 90% and the rest of the members limited to a maximum of 95% of code limits.

For a truss system, I'm shocked that engineers are not specifying the dead and live loading, as well as identifying which elements are used as drags / collectors for the lateral system. Really?! The key being that I'd want to identify the trusses that we'd be doing our own analysis of when the design back from the truss guys.

RE: Truss design misconceptions

Josh,

I don't think it's entirely a question of the EOR here...it's a question of what the Specialty SE is doing as part of his "delegated design." When I do wood trusses, I define live load for the top and bottom chord, dead load for the top and bottom chord, any environmental loading (or at least the job specific parameters for them to arrive at the correct loading like wind speed, exposure, etc.), and I also identify drag trusses and other unique items along with loading.

The problem is, when I have something that's more than "I want 20/10/0/10 roof trusses at 24" o/c with 120mph wind, exposure B"...there's almost always a correction to be made on the first round of shop drawings. They used 115mph exposure B when it's really 135mph exposure D. They didn't put in the drag truss. They used the wrong duration factor. They used a repetitive member factor for a 2-ply girder. Etc. These are all things that 1) an experience tech probably wouldn't do, and 2) a SSE should pick up on a review of the entire truss system design. But according to RonTheRedNeck and KootK's description of the MPC truss industry MO...they aren't doing that. They're saying "yes, the truss design output is acceptable for the truss program input." No verification of the input, no garbage in/garbage out check. So...nothing of any worth.

RE: Truss design misconceptions

(OP)
I don't have time to deal with all the statements made here. Some of them insulting and false.

When the engineer puts a seal on a drawing, it's only for what's on that drawing. Nothing more, nothing less.

Whomever said that the truss designs coming from the computer are worthless is ignorant. The programs are very sophisticated.

RE: Truss design misconceptions

Quote (RontheRedneck)

Whomever said that the truss designs coming from the computer are worthless is ignorant. The programs are very sophisticated.

Nobody said that the designs coming from the software are worthless. What we're saying is that an engineer's review of a truss drawing is pretty worthless:

1) at the rate of 300/day and;

2) in the absence of any contextual knowledge of the project as a whole.

Yeah, the programs are very sophisticated. We should probably just let AI's "check" the truss designs.

I would urge you to not get overly defensive about the wood truss industry. In the opinion of most engineers, it is an industry that does have some problems from an engineering ethics perspective. As such, it is rather impractical to attempt to manage a "truss design misconceptions" thread without at least acknowledging those concerns.

As I said earlier, we value your input here as an industry insider. That said, you are not the only industry insider here. I've held every job that there is to have at a truss fabrication plant save general manager. In addition, I spent a couple of years at the Wood Truss Council of America back when it was called that. And I'm an SE in Illinois. I am many undesirable things but, I assure you, ignorant about the metal plate connected wood truss industry is not one of them.

RE: Truss design misconceptions

Ron, it would be helpful to understand the Alpine training for techs. Residential truss suppliers are my least favorite gang to deal with. The industry is the most cost conscious group I run into, and trades these days pay little attention. I had always wondered what info the truss eng is provided, and this has been helpful to clear that up. I suspected it was not much given what they are paid per truss design.

RE: Truss design misconceptions

Quote (Ronthe Redneck)

I don't have time to deal with all the statements made here.

Take your time. Threads don't get closed here until months of inactivity have passed. There's really no pressure to be responding in real time.

RE: Truss design misconceptions

Quote (Brad805)

...it would be helpful to understand the Alpine training for techs.

Back in 2000-ish, the training function was sort of delegated to the Wood Truss Council of America (now SBCA) in the form of 4-day, in person courses held mostly at hotels and, sometimes, on site for the larger fabricators. Most of my job at WTCA was in developing, refining, and delivering TTT1, TTT2, and TTT3 from the list below. I've stayed at a ridiculous number of airport hotels in the continental US.

I would absolutely love to share the content of TTT3 with the gang here as that was my baby and there was some great stuff in there. As you can imagine, however, I don't need any additional intellectual property suits this year. Maybe in 2023.



RE: Truss design misconceptions

As an outsider - it seemed to me that the biggest problem facing anyone dealing with trusses is that the surety of the joints can only be determined by testing as there aren't great models of how steel teeth gripping into an inconsistent fibrous material functions, particularly if that fibrous material can vary so much with water content. In particular some plates seem to never have problems while others that at a glance seem similar enough do. On top of that they seem sensitive to handling - they can leave the factory fine and be mishandled and not have a visible disconnection when they are installed.

RE: Truss design misconceptions

Quote (RonTheRedNeck)

When the engineer puts a seal on a drawing, it's only for what's on that drawing. Nothing more, nothing less.

Yes...and no. Context is important. It would be one thing if we were talking about a garage door - it's been analyzed/tested for up to 120mph wind loads, and the drawings say as much, and now it's a mass produced product that can be installed in any house with a design wind speed of 120mph. But these roof truss systems are one offs. They aren't the 'pick-the-truss-from-the-table' jobs of the 60s and 70s. They are sophisticated, unique designs tailored to a specific building in a specific place. So it's important that not only do the results match the input (which is how I understood your earlier statement about engineering reviews)...but also that the input is valid and consistent with the specific requirements of the job. Is it the SSE's job to determine that from local codes? No - the DOR should lay it out on a silver platter for him. But if the SSE doesn't have the structural plans (and hopefully the architectural plans) while reviewing the truss calcs, I don't think they're quite doing their job in full. They need to make sure the system works and meets the requirements from the EOR - and the EOR needs to make sure the system and the building will play nice together.

Quote (RonTheRedNeck)

Whomever said that the truss designs coming from the computer are worthless is ignorant. The programs are very sophisticated.

I'm pretty sure you picked that up from my comment, though I assure you it's not the meaning I was trying to convey. As KootK clarified, I'm not saying the truss software is worthless. Far from it. I'd love to get my hands on some. TPI-1 checks are really tedious to do by hand when I'm checking an existing truss for somebody. But when an SSE is rubber stamping the output without any thought to how the truss fits in the system, they are worthless (at best).


If you read our responses more closely, you'll see that our issues with the industry aren't directed at you. In fact, you seem to be an incredibly knowledgeable truss technician that can probably design circles around most engineers when it comes to trusses. Look for posts about PEMBs. That's another industry niche we love to hate. But really, it's all about economics. Who can produce a code compliant structure the fastest with the least cost? That's PEMBs and pre-fab trusses. Hands down. Unfortunately, they are the least 'changeable' once they're in place. So when you really dig down, most of us just have issues with the construction industry in general and how many of us are constantly under pressure to do more faster and cheaper...like PEMB and Truss shops are able to do through automation...while still providing unique and complex structural designs in a variety of forms and materials.

RE: Truss design misconceptions

Quote (RontheRedneck)

I don't have time to deal with all the statements made here. Some of them insulting and false.

Ron, you began this thread, on a site primarily populated by engineers, by basically saying 'we don't have no stinkin' engineers, and we don't need no stinkin' engineers', and you didn't expect some pushback on that?

We appreciate your straightforward explanation of how the industry functions, but you should be open to some criticism of the apparent lack of 'responsible charge' in some situations. That is a big issue for us engineers, because if there's a failure, our profession as a whole gets blamed.

You may find it offensive, but regardless of how experienced you may be in 'designing' trusses, if you're not a PE, you're not qualified to engineer them, nor would you bear the legal responsibility for a failure. I've tried to follow the posts in this thread, but it's still somewhat murky to me who would bear the responsibility in some situations (such as residential) if a truss system were to fail and someone got killed. We (I think I can speak for pretty much all of us engineers here, at least) take our responsibility for the lives of people who rely on our work very seriously. After 16 years as a PE, I still get a lump in my throat every time I get ready to put my seal on a design, realizing people's lives are depending on me doing my job right. So, yes we get a little defensive about people who aren't engineers doing engineering, and engineers who 'rubber stamp' things without really knowing if they're going to perform like they need to.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Truss design misconceptions

4
Speaking only for myself, I wish that I could go back in time and refrain from participating in this particular thread. The whole "if you don't have anything nice to say..." thing. I very much want for there to be MPCWT representation in this forum and that's just not going to happen if we're constantly beating these guys up over the responsible charge thing, valid as those concerns may be. Nobody wants to hang out in a venue where they're constantly made to feel like an unethical jerk. And it's all but impossible to not take this stuff a bit personally when it's your own industry.

@RontheRedneck, here's what I propose:

1) Stick around and help us out with our technical MPCWT issues. We'll shower you with adulation, interesting conversation, and little purple stars in return.

2) Let's do our best to simply not discuss the "responsible charge" issues. Those issues are:

a) Not of your making and;

b) Not your responsibility to solve.

RE: Truss design misconceptions

I have had pretty good experience with Truss designers, In my area the truss design is submitted with original construction documents, consequently we don't think of it like a deferred design.

We take shop drawing of trusses very seriously because we accept that the truss package is going to be included with our construction documents and ultimately we bear responsibility that it is designed correctly.

But to others' points in the thread, I really don't know what is going on in the truss 'calcs' other than verifying the load criteria and basic geometry matches what we have been asked. I look for the loading and drag truss loading, confirm the shape of the truss (span, heel, slope etc) and if it all looks good its approved.

If there were for example a setting within the truss company's software that changed some assumption drastically it is very unlikely that I would catch it because I have no knowledge in that software. I think this is the role of the truss mfg. engineer who does know the software and should understand what is going on from the loading through to the output.

The way we practice is that EOR is responsible for providing loads roof loading for dead, roof live, and snow loads, and location and axial load of drag struts additionally we provide the ultimate wind speed. We also from time to time supply the truss mfg with details showing special applications of trusses including drag connections, offsets, or large bearings.

I quite often catch the truss designers missing criteria we have specified, but they are always quick to pick it up and never once has anyone tried to argue with me. However I do get the sense that sometimes technicians just march forward with their own assumptions without much regard for what the EOR calls for. This is why the shop drawing review is so important.

RE: Truss design misconceptions

Since no question was asked by the OP, this thread is soliciting opinions or trolling for a debate. Both good and fine. However, one cannot heave a touchy subject over the fence and not expect disagreements.

When I delegate any portion of a design, I expect sealed calculations (which I would have to provide if I were doing it myself), the design would be performed by a licensed structural engineer, and it would be a sound, economic, and constructible design. Basically, I hold the delegated design engineer to the same expectations and standard of care that I hold myself to since I am ultimately responsible for his/her design as well.

While I do not doubt that there are people out there perfectly capable of punching numbers into a truss design program and generating a truss that works, that is not engineering. A truss is part of a structure that does need to be engineered because if it fails, it could result in fatal consequences. It goes back to the age old "garbage in, garbage out" mantra. As with our junior engineers that love to sit down and start using software, they also need to be able to perform hand calcs to verify or approximate the results. If you cannot use first principles and basic mechanics, you should not be blindly using any software.

RE: Truss design misconceptions

(OP)
You know, I expected a forum of engineers to be more professional that some of you are. I'm particularly annoyed by the pompous ass who said I'm not qualified to design trusses. I know more abut truss design than most engineers do.


Someone mentioned training truss designers. Most places I know of like bringing guys in from the plant. That way they already know what a truss is. They know what works in the plant and what doesn't.

We start them out slowly - Designing trusses for something like a 23x36 garage. Then we teach them how to input plans in a layout. We have a series of "training plans" that progress from simple to more complex.

It takes time. There's a lot to learn and a lot to remember. I usually figure it will take a year before a designer can work on their own independently. Although that varies depending on how smart they are and how quickly they pick things up.


Jumping back to the issue of an engineer only sealing one truss at a time -

Trusses are components of a roof framing system. Just like a 2X4 stud is a component in a wall.

You wouldn't go to a lumberyard and tell them they have to provide engineering for an entire wall just because they're selling the components of a wall. And the same is true of trusses. We're selling components, not an engineered system. So when an engineer seals one truss design, he's only sealing one part of an overall system.


Someone mentioned truss fabricators being "cost conscious". Why do you suppose that is?

One of my favorite saying is "People are willing to pay for quality - As long as it doesn't cost extra".

If we're not competitive on pricing we don't get jobs. We lose jobs over ridiculously small amounts. It's a constant, daily battle.


Liability is another issue one of you brought up.

In my experience, if you have insurance you're liable for anything that goes wrong. Since I started in the truss business in the 1980s no company I know of has been involved in a lawsuit because of something they did wrong. Every lawsuit has been a money grab. i.e. someone gets hurt on a jobsite and sues everyone who has insurance.

I have seen mistakes made that ended up getting to the jobsite. Every company I have worked for has taken care of problems that were their fault. And often help solve problems that are not their fault.

If truss companies were making sub-standard designs and sending them to the field they wouldn't last long. The lawyers would have a field day with them, and it wouldn't be long before no insurance company would cover them. They'd be bankrupt in no time.


Someone mentioned plate testing. Truss plates have to undergo a tremendous amount of testing in various species and grades of lumber before they go to market. It literally takes years to do the testing, analyze the results, and assign values.

Full sized trusses are also tested to failure to verify design methodology.


KootK, I appreciate you asking me to stick around. For the moment I plan to. But there's a limit to what I'm willing to put up with.




RE: Truss design misconceptions

Quote (RontheRedneck)

KootK, I appreciate you asking me to stick around. For the moment I plan to. But there's a limit to what I'm willing to put up with.

I hear it. That said, I recorded your email address from the other thread. So, should I deem it necessary in the future, I'll simply summon you like a very particular superhero.

RE: Truss design misconceptions

Why are we acting like the code does not spell out the requirements for truss design, truss design drawings and sealing of the drawings, IBC 2303.4. Even if the IBC in the area does not have the section, ANSI/TPI-1 covers many of these items including the responsibility of the manufacturer. You as the manufacturer are providing an engineered system not a component like a 2x4. TPI-1 goes over all of the testing and design of metal plate trusses.

Additionally, some may want to look more into delegated design, as it varies by state. Link is a helpful start.

Design Delegation: Legal Definitions and Practical Effects

RE: Truss design misconceptions

Random thought but there really should be like a small technician certificate for being like a certified truss designer, certified pipe support design, etc. Like an accreditation that won’t require complete structural engineer knowledge but just enough. And it should be recognized, governed, and monitored for corrective action like the P.E. license. It should also have strict limitations and outline the process. Heck we can barely hire enough engineers. Why not allow for something like this?

RE: Truss design misconceptions

@sandman21, I don't believe @RontheRedneck is saying his truss isn't a system, he is saying the truss itself (with all it's components) is the component to our building.

@RontheRedneck - thank you for sticking around, your input is very valuable here, and I think I can speak for most here in saying it is evident of your experience and I doubt anyone questions your knowledge in this area. The issue people have is who is responsible for making sure all the add loads, drags, etc are accurately in the truss designs, and being that the EOR is not familiar with the truss design software, nor has a copy of it, the EOR cannot with confidence say it is 100% correct and therefore relies on the truss engineer to make sure it matches the drawings. This is a common issue as many times in my area, these added loads are missed the first round and the EOR spends a good deal of time reviewing truss shop drawings over and over sometimes without just compensation for their time. Many engineers have notes they place on the drawings saying they didn't review everything and it is the contractor and truss designers responsibility to make sure the trusses meet the projects design criteria. Many truss shops are also reviewed by junior engineers which they themselves lack the knowledge to adequately understand the add loading and why it's required.

In an ideal world, the engineer sealing the truss calculations would seal the layout as well and they would have a set of the structural drawings as they are the delegated design professional. Based on my own experience I can say there are some amazing truss designers out there and some horrible ones, this can be said about ever profession. Lately I have rejected truss shop drawings over and over until the manufacturer finally brought in a professional engineer to review it and it got through without issue then. This was all due to proper application of terrain factors for wind, snow drift loading and drag loads. The first 2 reviews I gave them feedback explaining exactly what I saw was missing, after it still wasn't addressed after the first 2 reviews, it was a simple matter of look for those few calcs, and reject with a note to see previous comments, because like yours, my time is valuable as well and our small CA fees only cover so much.

One question I have that has bothered me for years is how truss manufacturers (at least in my area) don't use the specified species of lumber and many times use "weaker" lumber which affects the h clips, a clips, straps etc.. capacities. I have started just using the smaller capacities (which contractors are noticing since straps are longer and require more nails), but this is the only way to have a properly designed system. As an example, we use Douglas-Fir as the basis for design in my area and specify as such on the plans, however most trusses seem to go with Hem-fir or other weaker species. Many EOR's ignore or don't even realize this, the few I have asked in the past simply said they didn't care. What are your thoughts on this?

RE: Truss design misconceptions

Quote (Aesur)

our small CA fees only cover so much.

That's why all of my proposals now have hourly CA, non-negotiable.

RontheRedneck - thanks for sticking around. I hope you'll give most of us the benefit of the doubt - we're not trying to attack you and we mean no disrespect or offense to you. As others have said, we really appreciate the technical perspective and industry insider viewpoint you can provide. While I think it's true that many of us don't completely understand what goes on 'behind the curtain' in the MPC truss industry, it's also true that some of what you see as our misconceptions are actually a drive for us to push for changes in the way the industry operates. Or, at the very least, how it interfaces with the broader engineering community.

One thing that I hope you'll understand - for the average engineer working in a consulting office, the idea of giving somebody without an engineering degree access to structural analysis software is tantamount to blasphemy. It just isn't done. But it is done in the truss industry. All the time. That's something that many of us just need to make our peace with. But the flip side to that is that it's perfectly reasonable to expect a more detailed review from the engineer who is signing off on the truss system.

sandman21 - nice paper. I especially love this line regarding shop drawing review stamps:

Quote (sandman21's link)

Significant legal battles have been waged over the import of the fine print in these routinely employed stamps, which, truth be told, are often read by no one other than those who first created them and the lawyers that argue about them when something has gone wrong.

RE: Truss design misconceptions

It is clearly stated in the book, "Structural Analysis," by Hibbebler that a truss is statically determinate when b+r=2j and statically indeterminate when b+r>2j. And the truss is unstable when b+r<2j. Where b is number of member, r is number is number of external reaction and j is the number of joints. A truss member is usually moment jointed but the reactions at the end of member are considered as pinned. Similar to the concrete member sitting on concrete girder.

Yes, the regulator is right. Indeterminate truss is stable when b+r>2j and they can be solved by computer.

I have mistaken the truss to be something called external instability when the truss reactions are parrallel when there are interior joints on the bottom of the truss. There is no lockdown in the x direction. The truss can be overlooked if the ends of the truss are not sitting on rigid walls.




RE: Truss design misconceptions

Quote:

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.

Quote:

but then again, they don't understand these special conditions either and just rubber stamp many times as approved.

Quote:

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

Quote:

if the SSE doesn't have the structural plans (and hopefully the architectural plans) while reviewing the truss calcs, I don't think they're quite doing their job in full.

Wow
So, in other words "If I take my blinders off, I might not get paid".
I see...
I don't work in the civil/structural sector, so I'm an outsider and this looks like a load of dirty laundry to me.
Thanks for bringing up the subject Redneck. You have nothing to defend.

RE: Truss design misconceptions

Quote:

I'm particularly annoyed by the pompous ass who said I'm not qualified to design trusses. I know more abut truss design than most engineers do.

Apparently, you're referring to me. However, you need to read my post more carefully. I did not say you weren't qualified to "design" trusses; I said you weren't qualified to "engineer" trusses, and there is a difference. I don't doubt that you know more about truss "design" than many engineers, including myself. All I was saying is that simply by virtue of not having a PE license, you are not legally allowed to practice engineering.

If you can apply the loads to a truss and calculate the force on each and every member of the truss, with just your brain and a calculator, then you may have the skills to do engineering, but unfortunately, that would still not make you legally qualified to engineer anything.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Truss design misconceptions

(OP)
Aesur - You mentioned lumber grades and hold-downs.

We often get plans calling for DF lumber. But it's not readily available in our area.
No one has ever told me that lumber grades are a problem regarding hold-downs.

RE: Truss design misconceptions

My question about training was aimed more about the software, not your specific practice. Most are reading this thread as a discussion to clarify the truss design/production practice writ large. We looked into using the Mitek 3D modelling software years ago to simplify the process of tracking all the loads to the foundation. At that time there was a lot of training required before you were able to use their software. I think this is germane to understand what goes into creating a truss designer. I still encounter many that have difficulty reading drawings, and I can see many lumber companies with hiring practices that do not attract ideal candidates. Again, that is not directed at you.

I mentioned cost conscious. We all understand why. I rarely do residential work, but use wood trusses in commercial work. The wood truss guys take it to the next level and it always causes problems. Now much of that is on the GC that does not look at the quote, nor asks questions. My steel suppliers quote us exactly what is drawn.

"...We're selling components, not an engineered system.."
This one comment highlights the fundamental problem in the wood truss world. The wood truss packages we see are very complicated and the guidance for truss design about their weak axis is limited. In all my 30years in the business I have never been provided a sealed layout plan for wood trusses. Every open web steel joist drawing package comes with sealed calcs, plans, load specs, decking plans.... Why the wood truss guys see their role as less is confusing.



RE: Truss design misconceptions

Ron, I think our issue is a non engineer is taking the engineered drawings, entering the design into the software (Which you may do correctly) and then an engineer stamping it based on what you entered and not looking at the engineered drawings. I think that is what this all boils down to.

In the odd case that you do make a mistake, and the engineer has stamped it, I dont see how he or she is not liable.

RE: Truss design misconceptions

@RontheRedneck - Take a look at the Simpson DSC capacities for example: Link, you will notice that for SPF/HF the capacity is approx. 15% less than that for DF/SP. This is common on all straps, holdowns, h clips, a clips, etc. This is based on testing, however a comparison of SG of the wood can give a picture of capacities, sim to designs using the NDS. DF has a SG of 0.5, lower SG's topically yield less capacities. Because of the competitiveness in the truss industry, this is something IMO the engineer of record should consider when designing their straps, however most (that I have seen at least) use the largest capacities which is for DF/SP. I'm honestly not sure of a good way to communicate this to the EOR's as it is a commonly overlooked item.

I don't know of the wood availability for trusses in my region, but wonder if it's a sourcing issue as well here. I assumed it was a cost savings issue as 90% of wood stud walls, etc.. are built with DF here, the occasional client wants to use HF to "save a few dollars" on the wood, but at the expense of adding more studs in some walls - I'm not sure this really saves them anything.

RE: Truss design misconceptions

Aesur, I am not sure why in your wood spec the wood species/values are not called out. If a supplier of a component cannot meet the spec, either they have to pass on supplying said component, or let the EOR know, and they evaluate with the client if a redesign is required.

This again does fall thru the cracks, because as Ron said, the low man wins the job.

I always ask for truss calcs so I can review the designs, make sure they are designed to spec and something like this does not happen. Also I like to review reactions, incase there has been some value engineering done to make the truss packet cheaper/easier to build by maybe moving things around.

RE: Truss design misconceptions

In my area, truss suppliers will spec wood to wood hurricane tie connections, so I let them and check behind to make sure I agree. Since trusses are used for economy, I rarely spec a species. I go with a "whatever works" spec. Granted, I've never had to deal with SPF in a truss...all the truss manufacturers seem to prefer SP #3 to SPF. I'm guessing it's because the truss plate capacities drop when they drop to a lower SG lumber as well. (We don't have DF or HF here.)

RE: Truss design misconceptions

JStructsteel - We do specify the wood species/values on our drawings and our specs match every other structural set of plans I have seen in this region for species, etc. The problem is, no local truss manufacturer follows these requirements and other structural engineers just ignore this, hence why we have started just adapting internally to use the lower values for connections knowing that they will most likely use weaker lumber.

Luckily for us, the jurisdictions on the west coast tend to require sealed calculations for all deferred items; therefore we get an opportunity to review the calculations on every project. Many years ago (earlier in my career) I made a comment that we specify DF and the trusses needed meet minimum properties and the response was essentially that they provide the cheapest truss possible without concern for "our connections" and when I talked to my project manager I was told to just ignore it, they know about it, but the standard of care has been set and they can't just start demanding that they use the right lumber or design heavier straps, so they just ignore it. That never set well with me, hence why I design connections for the proper values knowing they will use the weaker lumber.

The truss reactions is one that annoys me, they sometimes use "non-structural" walls as bearing walls creating a short span - long span condition creating large uplifts at the end to get a cheaper truss. (this is similar to PEMB's pushing the cost of the building into the foundation to make their product look cheaper) I have had to reject way too many trusses for this reason. I also try to watch for trusses that are sitting on top of a parallel shear wall as I have seen many designs where the reactions are basically saying uplift, pressure, uplift, pressure on 1' increments with values so large that there doesn't exist a connection to resist these forces. Because of this, I typically design the wall to have a shear transfer with vertical slip to avoid this and rarely do they pickup on that as it requires looking into details (not saying all truss designers do this). Another one that is the contractors fault that annoys me is how they bear trusses on non-structural walls rather than providing the slip connection per the details.

Another local truss annoyance is all local engineers specify the truss to truss connections to be by the truss manufacturer and I would say 90% of the time they refuse to provide these connections until much back and forth. It is also common for if the truss is hanging from a beam or ledger that it is specified that the truss hanger is by the manufacturer, and more often than not, they refuse to design those as well.

RE: Truss design misconceptions

kissymoose, thanks for sending that, I'll give it a try with some contractors and see how it goes.

RE: Truss design misconceptions

(OP)
Brad805 - You said your question about training was more about software than. But all the training has to go hand in hand.

We can have a guy sit and watch one of us work for a day or two, and explain what we're doing. But pretty soon you have to get the guy in front of the computer so he can find the icons for himself.

Along with the software we have to teach them to interpret the crap we get from customers. Many of our jobs have no plans, or maybe have terrible "plans". This is a good example of what we sometimes get:



So they have to learn to read "real" plans as well as crappy sketches. And crappy plans by someone who has a CAD program and thinks they know what they're doing.

They have to learn to ask the right questions when customers call in. Like if that ask for a 24' truss cantilevered 8', does that mean the building is 24' wide and the truss BC is 32' long? Or that the building is 16' wide and the BC is 24?

I always tell them there are a half millions things to learn, and they have to remember them all every time.



Aesur - I understand the nail holding capacity of lumber varies with species. I only said it has never been a problem on a job I was involved in.

You also mentioned truss companies not designing hangers for truss-to-truss connections. They're required to do that. I'll try to document that if you'll give me a day or so to find the info.

If you have a truss manufacturer using non-bearing walls as bearing that's a serious issue. I would never stand for that in anything I was involved in.


Jumping back to the sketches and what passes for "plans" for a minute - Sometimes we're the only design professional on a job. Which means we have to be the bad guy and enforce some of the things that you guys also do.

I'm not going to debate the issue of engineers vs. truss designers any more. My goal was to let you guys know what actually happens and dispel some misconceptions. I think I've done that.

RE: Truss design misconceptions

Hol’ up…someone submitted a plan on a piece of cardboard…without any dimensions…or notes on it. This can’t be real. If this is all you need to do then I’m doing like 1000% too much.

RE: Truss design misconceptions

DayRooster - if you look reallllly close, you'll see somebody did scribble some dims and notes on. Maybe with a pencil? But yeah. That's kinda bananas. I've heard tell of the rather 'loose' rules that exist in the rural mid-west...but I hadn't actually seen proof of it until now. I'm sure there are places not far from me where similar shenanigans go down, but it's no less shocking.

Granted...I did have a shop drawing submittal from a fabricator (railings, I think?) on a piece of notebook paper ripped from a spiral notebook, drawn in a way that would leave my 5 year old plenty to critique, and emailed as a picture taken on the guy's phone. So...it happens.

RE: Truss design misconceptions

(OP)
DayRooster - Yes, it is very real. That's the kind of thing I deal with on a daily basis.

I have a customer who draws "plans" on graph paper. Each square = 2'. I input the walls, then put roof planes on it and send him 3D images. That's what he uses for "elevations".

People used to tear pages out of plan books and build from them. Now they go to house plans websites and email me a PDF to use as a "plan". If he doesn't like how it looks I do a 2nd version. And a 3rd. I think the most I've done is 8.


I had a framer call me once to ask me to look at a truss job and see if any of the trusses could be used. A guy had taken one of those pages from a house plan book to a big box store and asked for a quote on the trusses. They sent it to our main office (not the one I worked at) and they sent a quote back.

Of course the quote was just a half-assed guess, since those plans do not have exterior dimensions on them.

The guy decides to build the house. So he goes to the BB store and tells them to order the trusses. The guy at the BB store calls our main office, gives them the quote#, and tells them it's an order.

So when the framer called me he gave me the dimensions of the actual foundation that was already in the ground. Turns out all he could use was the garage trusses. The other $5,000 or so worth of trusses were junk.


RE: Truss design misconceptions

Glad to see that the truss industry allows everyone to take advantage of them also Shitty drawings given to them, rework, etc). Engineers, etc are our own worst enemy when it comes to scope and rework, etc.

RE: Truss design misconceptions

I am a registered PE and SE, and I agree with most of the frustrations being stated in this thread by other engineers about the sketchy nature of the delegated design process for metal plate connected wood trusses, but I think many of the posters here are barking up the wrong tree with RontheRedneck. Ron and his cohorts are not subverting or otherwise corrupting the delegated design process; he is simply working on projects that have no engineering or other professional design requirements. He states in the OP that 95% of his truss designs do not require an engineer's stamp. I interpret that to mean that 95% of the truss designs are for single-family residential buildings under the International Residential Code or maybe agricultural buildings in rural areas. Guys and gals... news flash... houses in the U.S. are not designed by either architects or engineers, they are simply built by tradesmen who are working for a "contractor" with a pick-up truck and a cell phone.

RE: Truss design misconceptions

gte447f is spot on...which is why I'm always terrified one of those "contractors" with a pick-up truck and a cell phone will bid on the custom houses I work on...

RE: Truss design misconceptions

gte, the intent of the discussion seems to be to dispel misconceptions about the truss industry as a whole. I doubt anyone in the thread is unaware that endless projects are designed/constructed without the assistance of engineers. I have no problem if they design the trusses for those projects using prescriptive code clauses. If we are talking solely about his practice, frankly, I am not overly interested. I do get interested in the process when those same designers submit designs on our projects.

Ron, while the cardboard drawing is unique, a common joke among engineers is napkin sketches. We all deal with that when clients start the project.

I am curious to see what Simpson Strong Tie does to the industry as more and more of their truss plates are used. We all talk to SST reps, and I hope they listen to some of the concerns raised. I asked a SST rep recently and it seemed they may be working on some software to help the EOR with preliminary calcs for trusses. I would gladly spec exactly which plates to use if they will provide more confidence.

Ron, I applaud your effort here. I think it has been an enlightening peak behind the curtains into the truss design process. You clearly care, and take your job seriously. I suspect many of us with concerns are encountering suppliers that care more about pushing product out the door. That happens in all construction industries, but in my experience, the wood world has a terrible residential stink that impacts a lot of decision making.

RE: Truss design misconceptions

Ron,
Thank you for the informative post and continued discussion. Great to have you here.

I'm making a thing: www.thestructuraltoolbox.com
(It's no Kootware and it will probably break but it's alive!)

RE: Truss design misconceptions

Back in the dark ages when I was in college I worked as a draftsman (pencil and ink on vellum) for a structural engineer.
The original formulas for the holding strength of steel nail plates and pressed plates were from his PhD thesis.
Needless to say we did a lot of trusses.
We had 18 - 3" ring binders with truss drawings, each one a different pitch, though the common ones had to vols.
And then specials.
Each page was actually a family of trusses, common pitch and load with different spans/OHs.
And with 40,000 truss layouts on hand we were still designing half a dozen different ones a week.
We tried to avoid working directly with residential builders, usually working with the truss fabs or other engineers/architects.
There were about 6 major mid-west truss fab shops that didn't design their own but only built to our drawings.
We had a very rigorous checklist that you had to sign off before you put any time into a drawing.
Beyond the basic load/moment/shear we did a bunch of other calcs for every case.
All done either with graphical methods or hand calculators.
I always laughed as we would have customers complain that we were too expensive and they didn't need 'that other stuff'.
But we were fast, very precise, and reliable, and they kept coming back.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Truss design misconceptions

(OP)
EdStainless - Who was it that you worked with? I think I know who you mean, but can't recall his name.

I started in the truss business early enough that I used some of the pre-engineered drawings you mentioned. There were books that gave you the length of the webs for each truss design. Like at a 24' span the web might be 4' 11 5/8". For every inch you added to the span the web got 7/32 of an inch longer.


gte447f - I don't appreciate you referring to the truss design process as "sketchy". Nothing could be further from the truth.

What you said about me only designing residential work is not correct. It's a big part of our business. But that's not all that I do. We do a lot of hotels, apartment buildings, retirement homes, etc. So I do deal with architects and engineers.


Jumping back to the wonderful plans we often get - Here's another example:


This customer is building $300,000+ houses from sketches like this.


This afternoon I was thinking about a job we once did. One of the salesmen turned in an order for an addition to a commercial building. He didn't give me the plan, but wrote up what was needed. There was only one truss type.

He asked for a sealed drawing of the truss, and I provided it. The contractor, architect, and EOR all approved the drawing with no exceptions noted.

After the trusses were built the GC called in one day and told me the trusses were wrong. I told him he had approved the drawing, so they were his. He went ballistic.

I asked for and got a set of plans. The salesman who wrote the order screwed up badly. The span, overhang, pitch, and heel height were not correct. I have no clue how he came up with what he did.

The architect and EOR said they had no liability, as they only review for general conformance with the design documents.

The GC went over my head and went to the owner. After much discussion we ended up eating the job and replaced the trusses at our expense.

As a result of that - And of other similar stories - I have little faith in the review process. Doesn't seem to me like anyone really puts much effort into it. (Although there are exceptions)


RE: Truss design misconceptions

I think "sketchy" referred to the lack of a uniform process for this. It's like general contractors can be sketchy. Not all are, but there are enough that abscond with the funds after doing a half-demolition on a kitchen or the wall of a house, leaving it worse off than if they had simply stolen the money up front.

It's good to be out there showing the reasonable and responsible and under-appreciated side of the business. It seems frustrating to be lumped in with "those guys," even if "those guys" are rare. Few come back from a venomous snake bit with the attitude that most snakes are not venomous (Australia aside, where even some shoe laces pack a punch.)

I do feel your pain on dealing with the drawings and such and can only recommend, though not necessarily support by rigorous budget analysis, getting someone to take those drawings and cardboard sheets and creating a CAD model of the building and showing how your trusses will look sitting on it. I find that answering questions like "are those room dimensions the finished interior or are the walls subtracted from them" can help with fitting up to mating parts.

At least they used grid paper.

RE: Truss design misconceptions

I'm sure there are many conducted tests/researches on these types of wooden structure [not lift to speculation]
but No one here, has point it clearly [the governing design manual/ or code of practice/ or manufacturing co guidelines]
I found these resources :
https://drive.google.com/file/d/1sZ0xElhTMCh0ryBCE...
https://drive.google.com/file/d/1uhlprf5f3nFYD91Y0...
https://drive.google.com/file/d/0B-4m6EHIgeA4S2ViQ...
https://drive.google.com/file/d/1N1fXrc_ONccwXqwtM...
https://drive.google.com/file/d/1AMORgb85Yb7aSDeTP...

the ones below is for "KOOTK", i read once he was concern about timber cladding on seafronts environment
https://drive.google.com/file/d/1tJ5RhMLQBBjtwZzKx...
https://drive.google.com/file/d/1Ui8rio-S4o2U8r489...
https://drive.google.com/file/d/1sZ0xElhTMCh0ryBCE...
https://drive.google.com/file/d/1Ybt1mWZy-7Ko7XetE...

NOTE: Respect is free. Disrespect is Wrong.

RE: Truss design misconceptions

RontheRedneck, my comments were not intended to be demeaning toward you, but I stand by my characterization of the delegated design process for wood trusses as sketchy. It sounds like you perform your role within the process quite competently, but you yourself have provided us with several examples of a sketchy process including such practices as plans sketched on cardboard boxes and trusses ordered based on verbal descriptions when plans prepared by an engineer were available.

And again, I was not trying to insult or belittle you by saying that I interpreted your comments to mean that your work is primarily for residential or agricultural buildings that do not require any engineering. You told us in your OP that 95% of your truss designs do not require an engineer's stamp.

Trusses ordered by owners or contractors for projects that have not been designed by an engineer of record are not part of the delegated engineering design process with which many of the posters in this thread are familiar.

RE: Truss design misconceptions

None of this surprises me, but the general public might be surprised when they see how the sausage is made.

As far as the "EOR is always found to be responsible" comments go, I doubt that this is the case. The EOR will be held to the standard of care.

RE: Truss design misconceptions

Quote (Rontheredneck)



This afternoon I was thinking about a job we once did. One of the salesmen turned in an order for an addition to a commercial building. He didn't give me the plan, but wrote up what was needed. There was only one truss type.

He asked for a sealed drawing of the truss, and I provided it. The contractor, architect, and EOR all approved the drawing with no exceptions noted.

After the trusses were built the GC called in one day and told me the trusses were wrong. I told him he had approved the drawing, so they were his. He went ballistic.

I asked for and got a set of plans. The salesman who wrote the order screwed up badly. The span, overhang, pitch, and heel height were not correct. I have no clue how he came up with what he did.

The architect and EOR said they had no liability, as they only review for general conformance with the design documents.

The GC went over my head and went to the owner. After much discussion we ended up eating the job and replaced the trusses at our expense.

As a result of that - And of other similar stories - I have little faith in the review process. Doesn't seem to me like anyone really puts much effort into it. (Although there are exceptions)

Always gotta ask for a plan. Seems this case the sales guy made the mistake. How would the engineer know its wrong if he or she never sees the plans and just stamps the output? Architect approve a truss drawing-LOL! Contractor should have done a better job too, but he or she could be relying on the professionals to get it right.

RE: Truss design misconceptions

Quote (JStructsteel)

Architect approve a truss drawing-LOL!

What's funny about this? It's a team effort - I depend on the architects I work with to do a review of the truss drawings. Unfortunately, due to the constant changeability of drawings and whims of those who build the sort of houses I tend to work on, I usually don't dimension anything above the foundation in residential construction. I don't like it, but it's the only way to 'protect' myself...if I dimension the roof and the client requests a change after permit review, I won't know about it and I'll be stuck holding the bag when the trusses don't fit. It sucks, but it's reality. So my review is for the structural data - did they use the right loads? Is the spacing correct? Right adjustment factors? Does it all make sense? Yes? Good. Big note that says "Approved; reviewed for general conformance to the structural design requirements only. Architect to review and approve dimensions, elevations, pitch, overhangs, and other parameters relating to the architectural design of the building."

RE: Truss design misconceptions

Quote (phamENG)

Unfortunately, due to the constant changeability of drawings and whims of those who build the sort of houses I tend to work on, I usually don't dimension anything above the foundation in residential construction

Same here!

RE: Truss design misconceptions

I'm definitely thankful for Ron giving us this 'peek behind the curtain.

When I build my garage, I'm going to engineer and design the trusses myself, and take my stamped structural drawings to my local truss manufacturer.

A little 'peek behind the curtain of the process for highway bridges at the DOT, just for comparison:

Each component, down to the bearing pads, gets engineered (calculating loads and capacities), checked by another engineer, corrections by the checking engineer are back checked by the design engineer. If the design engineer is a PE, he or she stamps the design. If not, the final design gets reviewed by the PE that stamps it. The stamp on the design is the mark of responsibility that the component is adequate for the design loads.

When the details are complete, our Principal Engineer reviews them, marks any corrections, and stamps the details, certifying that those details are in conformance with the stamped designs.

The details are then reviewed by the Assistant State Bridge Engineer, and the State Bridge Engineer, corrections made, and then they sign each sheet, signifying their approval.

Shop Plans for specified components are submitted, reviewed, and approved for construction (eventually, usually after being returned to the fabricator for corrections once or twice).

After the bridge is built, the DOT construction engineer, who oversaw the construction of the bridge, puts his or her stamp on the "as-built" plans, certifying that the bridge was built in conformance with plans (with any changes made in field marked on the plans).

If there's ever a failure, there's a chain of responsibility that can easily be traced all the way back.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Truss design misconceptions

phamENG - Every Architect I work with forward the truss submittal to be to approve. I usually do the same, look at the loading, check reactions to what I think they should be. Will glance at the spans, usually not that hard to check.

Perhaps they do review for dimensions, and I am not privy to that.

RE: Truss design misconceptions

"...peek behind the curtain of the process for highway bridges at the DOT, just for comparison..."
I think the key difference in bridge work is the fees for engineering are roughly 5%-10% construction cost. Residential work attracts a whole different group of characters with varying ideas of what/when they need help from people like us. Residential fees are crap.

Rod, as for engineering your own trusses, the Mitek or Alpine software designs a perfectly fine truss in 2D. You will not find tables for any of the press plates to check this yourself since that is heavily guarded by those that paid for the testing. All you need to do for your garage is read what you are provided carefully and it will be fine. Not in a million years would I build an old school truss using plywood plates.

RE: Truss design misconceptions

Quote (Brad805)

You will not find tables for any of the press plates to check this yourself since that is heavily guarded by those that paid for the testing.

I disagree here, Brad. TPI-1 (the standard on which those programs are based) is available for free download and is a must read for anyone doing many buildings with MPC wood trusses, and the plates themselves - MiTek and Simpson, anyway - have been tested by the ICC Evaluation Service and have freely available ICC-ES reports with capacity tables for use in the TPI-1 equations.

That said...you'd be nuts to do it by hand unless you're doing it for fun (not sure that changes the 'nuts' thing, though...). The software, even the hands of the most novice tech, can produce a fine truss for a garage...just review it before you buy it.

RE: Truss design misconceptions

pham, I stand corrected. I have asked before, but I guess I am guilty of not searching. Thank you.

RE: Truss design misconceptions

Quote:

Rod, as for engineering your own trusses, the Mitek or Alpine software designs a perfectly fine truss in 2D. You will not find tables for any of the press plates to check this yourself since that is heavily guarded by those that paid for the testing. All you need to do for your garage is read what you are provided carefully and it will be fine. Not in a million years would I build an old school truss using plywood plates.

If I have them fabricated, I'll probably let them use the press plates, and just review that part. If I build them myself, I'll likely use plywood or OSB. I've actually already done the design, including member sizes, OSB plate sizes, and the number of fasteners at each connection.

Quote:

That said...you'd be nuts to do it by hand unless you're doing it for fun (not sure that changes the 'nuts' thing, though...). The software, even the hands of the most novice tech, can produce a fine truss for a garage...just review it before you buy it.

Apparently, I'm nuts. I found designing the trusses by hand to be an interesting exercise, and fairly easy one. Much simpler than designing the 3-bed+drawers combination piece I built for my kids.

Building them wouldn't be difficult, either. I only need 5, since they'll be king trusses.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Truss design misconceptions

Rod, if you enjoy that work I get it. I agree it is not difficult. If you look at the cost of plywood now, and the waste, I am not sure it makes economical sense. The common garage package you find at most hardware stores can be a good deal, but some cheap out with their gable end trusses. I still prefer traditional ladder framing, but I have seen many do not want different truss types for the little packages.

RE: Truss design misconceptions

Brad, my design requires no sheathing, so I'll be saving quite a bit there.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Truss design misconceptions

Rod - if you're doing OSB/plywood plates, that's a whole different animal and I get it. That's not all that difficult and would be pretty fun. (I haven't done a meaningful wood working project since I built a standing cradle for my nephew. He starts middle school next year...) It's the press plates that make the design a headache without the proprietary software.

RE: Truss design misconceptions

(OP)
3DDave - You said "I think "sketchy" referred to the lack of a uniform process for this."

Nothing sketchy about it. I explained the process clearly, and it's pretty universal.

If you don't like the process, feel free to try to change it. But I suspect it would be like trying to turn the Queen Mary with an oar.

JStructsteel - You said "How would the engineer know its wrong if he or she never sees the plans and just stamps the output?"

I'm not talking about the engineer at Alpine - I'm talking about the EOR. If the contractor, architect, and EOR aren't even going to look at shop drawings, what's the point in sending them?

That's why I said I have little faith in the review system.

RE: Truss design misconceptions

Quote:

Nothing sketchy about it. I explained the process clearly, and it's pretty universal.

Yes, you explained it in good detail, and we understand it's fairly universally done that way in your industry. The reservations about the lack of (legally) qualified review of the trusses as a critical component of the overall structural system, remains. That's what makes the process sketchy.

Rod Smith, P.E., The artist formerly known as HotRod10

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