Can an Ordinary wall considered part of SFR system

[FusionDan]

Good Day,

Currently, an attempt has been made to utilize 'larger diameter Welded Wire' ASTM A1064 (Looks like reba/deformed/diameters range for 8 mm to 15 mm), as reinforcing in subterranean walls of a multi use facility (sub grade levels are parking). The structure is assigned to SDC E design parameters. The problem we are having is the city overseeing the project is stating that the WWR is not allowable as the walls are part of the lateral resistance system and bound by material requirements per ACI 318 Code 21.1.5.2, the reinforcing must be A706 or of equal ductility.

Our argument is that even though the walls are part of the SFR, they are a) squat walls b) bound in earth/retaining walls so they will not experience oscillations into the inelastic range c) N/A d) The Walls were not designated in the permitted plan set as shear walls.<<<To me not being designated is important. Seeing how I see 100's of buildings annually w/in SDC D, E, or F, and none of them designate basement walls as 'SW' unless they are 'SW' above ground, and none of these 100s of projects do the structural's indicate A706 or equivalent, need be used in the walls. The problem is there seems to be nothing in the code that differentiates a structural/retaining wall from a special wall. prominent seismic engineers will tell me "those perimeter walls experience very little shear, ductility is not part of concern". Is there any test studies, or codes that could help our case? What is the standard/why are some walls designated as shear walls and other walls are not (even though they are shear walls??)

 

[rapt]

If it is considered to be part of the lateral resistance system then it cannot be "ordinary". So either remove it from the lateral resistance (you said it does not do much anyway so take it out of the analysis) or reinforce it as special.

Mr Plan Checker has to follow the rules!

 

[KootK]

Yeah, that's tough. It's an area where somebody probably needs to make a prescriptive judgment on what the standard practice ought to be. My thoughts:

1) In general, I agree with you. I feel that basement walls are unlikely to experience significant inelastic demand and, as such, should not be required to meet the high ductility requirements applicable to other elements that are.

2) I know of no "evidence" that I could point you to for definitive guidance.

3) How tall is this thing? At two stories below grade for a moderate height building, unless your slabs are disconnected from your designated shear walls, the shear probably is transferred out to you basement walls. Back-stay effect and all that jazz with your designated SW below grade seeing monster shears and your basement walls seeing baby shears.

4) Taken on its own, I don't find the "squat" argument to hold water. All other things being equal, a 10' basement wall may well have the same vertical shear demand as the horizontal shear demand in a 10' long shear wall delivering load directly to it.

5) I know that the hot-shot seismic guys out west have also been expressing concerns about shear demand in the "panel zones" of shear walls dumping out onto basement walls. It might be worth checking to see if your reviewer has this particular concern in mind. You ought to be good in that regard since I think that your panel zones are designated shear walls in this situation.

6) I'd argue that a basement wall should generally be designed as a foundation would be (piles/pads). That being capacity designed for the maximum load that can be delivered but without providing exceptional capacity for ductility. Explained in that light, perhaps your reviewer would be inclined to come along for the ride. We don't apply these kinds of requirements to the flexural rebar of the footings that support special moment frames. At least I don't think that we do.



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.

 

[FusionDan]

Thank you Rapt and KootK,

Rapt, the WWR is in place and ready to shoot. No one wants to tear it down, and its to late for redesign...as no one foreseen this as a problem, considering I've supplied the same product 100x's in the same zones, with 0 problems.

KootK,

1) sounds good to me, glad we agree. 2 bucks and cup of coffee is in the mail.
2) I hear the "Know of no evidence"...Read all this brief on seismic design of of CIP special walls...

https://www.curee.org/projects/nehrp-jv/publications/nistgcr11-917-11REV1.pdf

and it made 0 mention of basement walls, that aren't noted as shear.<<<<that right there tells me it was left out because the shear is not privy to concern.
3) Height = 2 lvls below, 8 lvls above = approx 115' from TOF to Top of Roof Shear wall. Oh yeah the Shear walls are beefy, every bar contained. Actually trying to promote some Welded Reinforcement Grids on a tall project.
4) Admittedly was reaching on the squat wall subject
5) I know a few of those hot shot out west guys...they all seem to be on vacation atm. The reviewer won't speak to me, I'm not he DOR, just a manufacturer rep that tries to actually have a clue
6) I will use this.

 

[sandman21]

You know of hundreds of buildings which do not comply with the requirements of ACI 318? What prominent seismic engineers will tell you "those perimeter walls experience very little shear, ductility is not part of concern"? ACI 318-14 Table 20.2.2.4a limits ASTM A1064 are not permitted in special seismic systems where the weld is required to resist stresses in response to confinement. lateral support of longitudinal bars, shear or other actions. Even if your prominent engineers say it take minor amounts of shear that does not translate into taking no shear. If you are trying to utilize the provisions for special walls you don't get to ignore it when its not convenient. Do you have anything to show the reviewer that ASTM A1064 has the desired performance and you would like to have the building fall under a performance based approach?

 

[rapt]

FusionDan,

What do you define as 0 problems? Have they performed properly in design level earthquakes? The rules in the code are there for a reason, and your design does not conform.

If the walls were not helping the design, why did you include them in the first place? The code rules provide a Minimum level of design. And they give you a way around higher level of detailing of these walls. You have not provided this minimum level and have not used their get out clause.

 

[FusionDan]

After a week of debate, the involved parties have come to the conclusion that perimeter basement walls were:

a) not designated as SW in the designs b/c they are not calc'd as special walls
b) not bound by the reinforcing material provisions set forth for seismic walls, because they are not calc'd as special walls.

Though they may still be considered part of the Seismic System....

Argument, for now is over, and a win for WWR was used.

When I say, "100's of projects out of code", what is being implied is that: If the DOR does not designate a wall as Special or seismic, than how is the material suppliers/detailers, inspectors, and contractors to know that the wall is part of the Seismic Resisting System and would require A706 or similar propertied reinforcing? Are the material and contractors supposed to understand the behavior of structure in such detail to know that the simple subterranean retaining wall is part of the Seismic Resisting system? Is the DOR not required to label 'seismic sysetem elements' as such (moment frames, shear walls, columns that are part of the SRS). If the typical basement walls are
a) not designated as a SW in the DOR plans
b) not referenced in the seismic elements section of the DOR plans
c) not stated in any other locations of the plans (General Notes/Reinforcing Section)that it is part of the Seismic Resisting system
Then is it not reasonable to believe that most of these projects were built w/o A706 bar?

Thank you all for your time.

 

[rapt]

I doubt that I would call it a win for WWR!

Doesn't the DOR specify the reinforcing type to be used on his drawings?

 

[sandman21]

I would consider this a loss for the owner as they have a building which does not comply with ACI 318 and has shaky engineer associated with it.

 

[MrHershey]

People can designate walls however they like. The building's not going to care about it during the earthquake, though. If the walls are hooked into the diaphragm and sufficiently stiff they'll attract force and be part of your lateral system whether you like it or not. The building decides, not us, and we need to detail accordingly. In this case some of the walls are in the same line as shear walls, even connected directly to shear walls as extensions of those walls. I don't see how one could just claim they don't take any lateral load in this instance. It's not like they're isolated from the rest of the lateral structure.

I wouldn't argue that it doesn't work in real life, it very well may. But in my eyes it's not allowed using the traditional approach in the building codes. I could see maybe if you can find a lenient code reviewer and show them that the basement walls are capable of resisting the in-plane forces/moments times overstrength or similar (while also resisting any lateral earth pressures). But that's really not allowed in the code. Maybe find someone you can convince to let you look at them as 'members not designated as part of the lateral-force-resisting system', but that section of the code is intended for more flexible elements like columns/beams, not walls (the first two words in the 2005 version of the section are 'frame members'). Short of that you're looking at a more performance-based design and showing that you meet the same performance criteria the code forces you into even though you're not following the code. Which, again, you very well may.

Also sounds like you're not necessarily the party in the wrong here, sounds like the engineer made a mistake.