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Precast Light Walls for Parking Structures

Precast Light Walls for Parking Structures

Precast Light Walls for Parking Structures

(OP)
I'm laying out a parking facility utilizing precast light walls as shear walls. For the uninitiated (me included), they're just shear walls with a bunch of large openings in them to promote visibility and light transmission. Structurally, they look a lot like concrete Vierendeel trusses. Link

I have no desire to design these things but, before I hand things of to the precaster, I'd like to know that the wall lengths that I've specified are at least in the ball park. Does anyone know of any capacity table that might be available? Or a document outlining the design methods used?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Precast Light Walls for Parking Structures

I've never used that idea, but I believe the analysis would be very straightforward with each vertical element taking wind load in proportion to its stiffness.

If you are the EOR, don't you have to know how to check what the precaster designs?

BA

RE: Precast Light Walls for Parking Structures

So you are going to propose something that you dont know how to design, and make the precaster do it? Why not coordinate with the precaster so they can have some input, and dont have to come back to you and say, this doesnt work?

RE: Precast Light Walls for Parking Structures

I think typically light walls are designed as a series of shear walls with short lengths. The PCI Design Handbook has some good examples of how to design the system in this manner.

RE: Precast Light Walls for Parking Structures

(OP)
Thanks for the tips guys.

The only example that I could find in the PCI handbook (5e) was 3.11.9 Example-3 Level Parking Structure. In that example, they distribute the loads to the individual segments and do a basic net uplift check. This is consistent with BA's suggestion of a simplified analysis.

I expect that the final design is a good deal more complicated, possibly including:

1) Axial loads from the corbels on the wall that will support double tees.
2) Possibly P-Delta effects for more slender configurations.
3) Account of the fact that the walls will not be free at the top. There will be a beam element generating frame action.
4) Vehicular impact loads.
5) Strut & tie design at the joints of the effective Vierendeel truss.
6) Requirements for the size and location of the wall openings.
7) Weird stuff resulting from thermal movement restraint.

You know... stuff.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Precast Light Walls for Parking Structures

(OP)
Based on the comments above, it sounds as though there is concern regarding my use of delegated engineering here. That's an interesting discussion in its own right. Here are my thoughts:

1) This thread only exists because I'm trying to educate myself on the use of the product that I intend to specify. My goals in doing so are intellectual curiosity, professional ethics, and a need to shield myself and my client from poor decisions. So please, put your pitch forks down and return to your respective villages. I'm doing my due diligence in figuring out what I don't know.

2) I do not believe that I am obligated to check the precaster's designs in any rigorous fashion. Nor do I believe that I am obligated to know, to any great level of detail, how the precaster's members are designed. When it comes to delegated specialty engineering, I believe that the following items are EOR responsibility:

a) I should know enough about the products being designed by others that I can specify them confidently and know what looks out of place.
b) When the speciality engineer's submittal comes through, I should insist that it be stamped by a qualified professional engineer.
c) I should check the submittal for compliance with the project specifications and design criteria.
d) I should use my professional judgement and do some numerical spot checking when I see something that appears odd to me.

3) When was the last time that you saw an engineer calculate some pre-stressing losses before specifying pre-cast double tees? When was the last last time that you saw an engineer models some OWSJ in SAP during shop drawing review to check the forces? I've been doing the EOR thing for fourteen years, with six different companies, and in two different countries. I have never witnessed any engineer dong this kind of checking or pre-design. My money says that, if there were no Vulcraft / Spancrete design tables, there would be no double tees or OWSJ.

4) I think that engineers of record should maintain some humility when it comes to speciality engineering. EOR's know a little about a lot of things and have a good eye for the big picture. They usually do not possess the specialized knowledge required to do specialty engineering. As an example, consider specifying metal plate connected wood roof trusses. No EOR would bat an eye at that. However, for trusses that don't have raised heels, I'm willing to bet that 95% of engineers wouldn't know how to check or design the heel connection properly. The reason for this is that the connection eccentricity does some weird things at the heel and TPI recommends that you use an arcane fictitious model to analyse the joint. How do I know? I used to be that specialty engineer.



The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Precast Light Walls for Parking Structures

Wells said, KootK

RE: Precast Light Walls for Parking Structures

I have been a specialty engineer too, for precast products. We had a job where the EOR was a complete idiot. We had to write letters to the owner telling them about huge misses in the drawings. No stability, some columns with no real load path, a 110K joist girder reaction on a 4" fascia panel, etc. It sometimes goes both ways.

RE: Precast Light Walls for Parking Structures

(OP)
Here's an interesting question (I think). What should be the seismic force reduction factors be when using precast light walls? Based on their name, their shear walls. However, looking at the example in the link that I posted initially, they look a lot more like moment frames to me. Is there some way to classify the system as a shear wall or a moment frame based on flexibility?

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

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