How tall can you go using CFM shear walls 4

[KootK]

I've got a client who wants to build some 14 story buildings in a Canadian low seismic zone using light gauge shear walls as the sole lateral system (walls sheathed/strap braced). I interpret the table below as limiting the height of such a building to six to seven stories maximum. Is there an "out" someplace that would allow a 14 story building to be braced with CFM shear walls in Canada? I swear that I've seen buildings like this constructed taller than seven stories.

In my heart of hearts, I'm hoping that the table below will force the project to use concrete shear walls or conventional steel framing for the lateral system. That said, I need to vet that decision properly before taking it to my client. For comparison, note that US CFM braced non-seismic building heights are only limited by one's imagination and impulse to remain sane.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Trenno]

Have you done a number to see whether they can actually do the job?

 

[KootK]

I'm not sure Trenno. It's quite involved and I'm hoping to avoid the exercise altogether if it's a non-starter code wise. Conceptually, I've been shown a design for a 22 story version. Scary stuff.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Trenno]

Wow... Would be interesting to see what the details were. 10mm thick straps?!?

 

[KootK]

Yeah. The two annuli around the lifts and every partition as shear walls. And each partition comprised of two walls and four strapped panel faces. Drift seems problematic in the same way that it is with multi story wood shear walls.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[XR250]

After doing light gage for over 20 years,I would not touch that. The design and detailing is tricky and they never get built properly (at least in our area). Then you are trying to figure out how to fix their mistake after the fact. I have actually stopped doing load bearing light gage except for one story stuff. Keeps me sane.
I looked at an 8 story hotel being built here out of light gage. The amount and size of strapping they installed led me to believe it could not possibly have been cheaper to do it that way.

 

[KootK]

The design and detailing is tricky and they never get built properly (at least in our area).

Certainly, I agree that it's a sketchy proposition. To some degree, however, we have a leg up on the quality control issue. Our client is a manufacturer of CFM wall panels and they're running some solid CNC-ish automated fabrication machinery. Tight tolerances and pre-drilled starter holes etc.

The quote below is from a CFM industry expert (academic). It is less than encouraging.

"I am not aware of any buildings that height being constructed with CFS shear walls, even if there is no seismic loading. We have never looked into anything this height under wind loading. As such, I cannot offer an opinion as to whether it is possible or not.

Regarding the AISI and other related US codes; this is more likely the case of a design along these lines was never considered in the past and this is why it is not covered in the design standards, rather than explicit permission that buildings of 14 storeys may be constructed with CFS shear walls. Best to check with the people in the US. "

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[wannabeSE]

Jeff Ellis, P.E., S.E., Director of Codes and Standards for Simpson Strong-Tie Company Inc. will conduct a webinar on CFS Lateral Systems in a couple days (

http://www.steel.org/Global/documen...to-host-webinar-on-cfs-lateral-systems.aspx).

If you contact him, he might be able to point you in the right direction.

 

[bookowski]

steelframing .org says "did you know cfs can be used as the structural system for buildings as tall as 9 stories?". I'm guessing that they'd advertise at the upper limits of what's been done.

 

[KootK]

@Book: that's an excellent point, thanks for making it.

@Brad: funny you should mention BIM. That's my second biggest issue on the project. The client would like to have every stud modeled in order to feed it into the CNC machine. As you can imagine, we're having a hard time reconciling that with our fee and work process. Is that something you've done before yourself? Got any war stories to share?

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[KootK]

@Wannabe: thanks for the tip. I'm registered for that presentation.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[Brad805]

I accidentally deleted the post.

We had him modify it for wood construction. We have done this in wood, but not steel stud. Our clients tend not to worry about the steel stud framer in the field because he is a subtrade. I find that odd considering they end up paying for that time, but that seems to be the norm. I thought that the Tekla add on might have been developed for your client. The guy in Austria that developed it did so for a major metal stud supplier in the US. He goes all over the world creating very detailed tools for customers. There is a company in Montreal (

http://strucsoftsolutions.com/)

that has a BIM add-on for Revit as well. For CNC work I would be careful with the Revit tool. Revit has some unique aspects that we find make it more difficult to maintain accuracy. If you have very experienced modelors, it can work, but they need to know there stuff to set things up for the inevitable arch changes that always happen. I recall talking with the lead modeler at

http://www.thorntontomasetti.com/

years ago and he mentioned it took them 5years or so to get their Archtiect's Revit models to the point they could move them downstream for the detailer's. I have mixed feelings with Revit. There are a lot of ways we can cheat with the software to make pretty drawings, but a shop using a CNC cannot tolerate that.

Did they tell you what their CNC machine needs for coding? If not, I would check what their equipment needs. .dxf files would be very inefficient from your end. With that many stories I would not be surprised if there are more than 100,000 steel stud parts.

For this to work best you will need to get the mech trade on board as soon as you can, not just the mech eng. The mech eng is great at figuring out the design, but they tend to be awful when it comes to deciding where to put things or how much space allowance one should allow around their duct work. Reworking your model for the duct work once the trade is on board could be a huge increase in time. Great if they are paying, but not great if there is a schedule or you have a fixed fee. My comment about the mech eng is not intended to be negative towards mech engs. It is just customary that they draw generic locations and they figure out the specifics in the field. That will not work for your client if they want to realize the maximum savings from their end. The precast company we work with is just finishing a large prison that was done in Revit by the design professionals. The mech model was not great and the trades spent a ridiculous amount of time hand calculating where things would go. Waiting for the trades really slowed down production for the first pod. Luckily the second and third pods were identical.

When it comes to fees I hope you have a clear definition from them as far as their expectations. I imagine they want to fab all of this in their shop, and fly it into place with minimal work on site. The time you spend now can save them a ton in field re-works, but they have to allow you sufficient time. They also need to play their part and help define typical details early on to save both parties time. We engineers tend to focus on minimal materials weights but many times the cost savings is not worth it for them when it comes to coordination or practical aspects such as material procurement. We have quite a few clients that are great at changing their mind after seeing a model, but that adds a lot of time from our end.

 

[MrHershey]

We used StrucSoft as well when we had a job that wanted every single stud framed in Revit. This was just a house though, not a building several stories high. Probably won't do it again. Nothing wrong with StrucSoft, they were great to work with and would recommend for any poor soul who has to do this. Support was tremendous helping us get set up and it helped us out quite a bit. But just not worth the design and modeling hassle for us in the end, especially on a house. Echo Brad's issues getting things exactly where they need to be in Revit and the need to adjust fees accordingly. It may help in the field and may save money overall, but to get to that point there's a lot more effort up front on the engineering/modeling side. Can certainly make things cheaper in construction, but client needs to realize it's not free on the design side. And if the job never happens, they'll lose that money.

 

[KootK]

I kinda lost track of this one. Thanks for all of the excellent advice so far.

I recall talking with the lead modeler at

http://www.thorntontomasetti.com/

years ago and he mentioned it took them 5years or so to get their Archtiect's Revit models to the point they could move them downstream for the detailer's.

I actaully picked up one of TT's BIM wizards this fall (as staff). She's been an enormous help in our efforts.

Did they tell you what their CNC machine needs for coding?

It's called Vertex: Link

For this to work best you will need to get the mech trade on board as soon as you can, not just the mech eng. The mech eng is great at figuring out the design, but they tend to be awful when it comes to deciding where to put things or how much space allowance one should allow around their duct work.

Verified.

When it comes to fees I hope you have a clear definition from them as far as their expectations.

Not at all I'm afraid. Again, I can confirm the importance of this.

Probably won't do it again.

So far, I'd have to say that I agree. It's been very taxing on our people and rewards have not justified the effort thus far. Perhaps the picture will look rosier once we get past the excruciating learner phase.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.