Concrete Tiltwall - Form Liner 2

[bpstruct]

Working on a big manufacturing facility that will utilize tiltwalls as the gravity/lateral load system. We will be using a formliner. The architect is wanting to use a vertical pattern - 2 inches deep spaced at 4" oc +/-. The structural thickness will be 7 1/4" - total 9 1/4". My concern is regarding the architectural face. I was planning to only use one mat of steel (centered) except where warranted around openings. With just a single mat of steel in the center of the panel, it seems like the architectural surface may be prone to cracking. ACI 318 technically requires only one mat of steel for a wall less than 10" in thickness. But tiltwalls are not required to meet the slenderness limits in ACI 318 (these panels certainly won't), and this total thickness (9 1/4") is close to the limit.

ACI 11.7.2.4 (318-14) states that "flexural tension reinforcement shall be well distributed and placed as close as practicable to the tension face." Since either face could be in tension, the flexural reinforcement is not close at all (5.625"). The project is in Texas (south/central), so it gets hot. Also wondering if I should be concerned about temp/shrinkage.

I have ACI 551.2R-15 and ACI 551.1R-14, but I can't find much help. Maybe I'm looking in the wrong spot.

I wouldn't be concerned if we were using a 3/4" depth, but this 2" depth is a concern to me. Any feedback would be appreciated.

 

[GC_Hopi]

Your concern does not seem to be structural ie about the amount of reinforcement or the location of the bars (center the bars in the wall) but more about the risk of finish on the surface of the panel and getting a unacceptable finish. The issue of finish is really in the contractor's hands since they have control over curing, placement, handling, etc. However there are a few levels that A/E's can use to ensure the finish is acceptable. Here is a list of a few: 1)Requirement on contractor qualifications. 2) Concrete mix requirements 3) Panel mockups 4) Inspection of the initial panels 5) Requirement on curing

 

[JoshPlumSE]

I'm not enough of a tilt-up guy to know the answer. But, I've often thought similar things about singly reinforced tilt up walls. In particular, my concerns would be:
a) Cracking that occurs during the lift / tilt-up portion of the construction. To some extent, this may be the contractors responsibility/ liability. So, the contractor may have some insight about what they will and won't do as far as singly reinforce walls. As an engineer, I'm pretty sure there are requirements about maximum stress during the lift (rupture modulus?). I've just never worked on that side.
b) Cracking that occurs over the life of the concrete. Less of a concer for me. As most of what we're talking about (Temp/shrinkange) happens during the construction phase. If it's related to shear wall cracking or gravity loads then it's no different than a regular wall.
c) Issues associated with slenderness. These are legit. If you're close to the slenderness limit, I think it might make sense to check moment amplification for wind and seismic transverse loading with the slenderness procedures anyway.

 

[cvg]

I am dealing with 2 inch thick formliners also. any suggestions on contractor quals or mix design?

 

[bpstruct]

GC - you are right. I am not really concerned about the structure. It is really a concern about the potential for the exterior to crack. As you know, it is pretty difficult to explain to the owner that concrete cracks are not a structural issue. Good thoughts on quality control.

Josh - design for lifting the panels is a contractor issue. At least in my experience. We require shop drawings to show lifting inserts and additional reinforcing as required to handle stresses due to lifting. Those drawings have to be sealed. Regarding the slenderness ratio, h/50 is allowed for tiltwalls. So we are okay, technically. I may be overthinking this. I hate to add a second mat of steel, but it just seems like the steel would be much more effective in controlling crack widths (whether from flexure or temp and shrinkage) if it were closer to the outside face. I wouldn't be thinking so much about this if the facade was some other type, so maybe it is not a problem.