Wrong size welded wire in foundation slab is it a problem?
Wrong size welded wire in foundation slab is it a problem?
(OP)
I have a subcontractor that installed 6x6 - W1.4xW1.4 welded wire fabric instead of the 6x6 – W6xW6. This does not meet the temperature and shrikage requirements of ACI 318.
The owner is concerned that his concrete will crack because of this error. the slab measures 6 inch deep on 1 foot of gravel, and is 20' x 20'. with all the piping installed. There is no structural loading concern as it will be used to store misc. lightweight equipment.
I recommended an epoxy coating on top, however the owner feels that this is still not what he paid for so he wants to demo (remove) and reinstall with the correct size wire.
Is this excessive or needed?
The owner is concerned that his concrete will crack because of this error. the slab measures 6 inch deep on 1 foot of gravel, and is 20' x 20'. with all the piping installed. There is no structural loading concern as it will be used to store misc. lightweight equipment.
I recommended an epoxy coating on top, however the owner feels that this is still not what he paid for so he wants to demo (remove) and reinstall with the correct size wire.
Is this excessive or needed?





RE: Wrong size welded wire in foundation slab is it a problem?
If he wants LESS (Not NONE) shrinkage cracks in his storage building, then he should replace the slab. The obvious best option, in my opinion, is for the owner to accept that there will be MORE shrinkage cracks, but since it is a storage building, cosmetics probably won't be an issue, and the contractor should give him a credit for the difference in steel.
Whether it is excessive or needed really depends on the owner. If he really doesn't want more than usual shrinkage cracks because he's worried about cosmetics, then it isn't excessive. If he isn't sure what the difference between the two meshes is, and just wants to do it on principle, then yes, it's probably excessive.
As an aside question: When you recommended the epoxy coating, did you recommend they fill in any cracks that appear with the epoxy? Or did you recommend laying it on the surface of the existing slab immediately? I haven't seen someone layer it on a whole slab, but then I don't usually see incidents like this. Thanks.
RE: Wrong size welded wire in foundation slab is it a problem?
RE: Wrong size welded wire in foundation slab is it a problem?
With that said, I suggest two options to avoid having to remove and replace the slab. Both will have costs in time and money that may not be worth the trouble.
1. Negotiate a financial settlement (reduced cost to the Owner) to accept the slab "as-is".
2. Retain a qualified third party to evaluate, and possibly test the slab to offer an independent opinion on it's acceptablity. Even then, a financial settlement may still be required.
I recommend that you make a brief attempt at Option 1. If unsuccessful, for a slab that size the most cost-effective thing will probably be removal/replacement, then get on with the project.
Note: At various times, I have been on each of the three sides of the situation, Contractor, Engineer, and Owner's Representative.
www.SlideRuleEra.net
RE: Wrong size welded wire in foundation slab is it a problem?
That's a lot of shrinkage/temp. steel in a 6" slab - its .0077 x Ag.
Its similar to #4 @ 6" o.c.
RE: Wrong size welded wire in foundation slab is it a problem?
0.0018
Per ACI 318 code section 7.12.2 ( = 0.18%)
As = 6 inch (slab depth) * 12 (in-to-ft)*0.0018 = 0.12 (sq. in. per one foot of slab) REQUIRED
The 6x6 - W1.4xW1.4 provides 0.029 sq. in. per foot < 0.12 (sq. in. per one foot of slab)
Therefore we are undersized according to ACI 318
The 6x6 – W6xW6 provides 0.12 sq. in. per foot REQUIRED.
Where is the 0.0077 Ag coming from?
thanks
RE: Wrong size welded wire in foundation slab is it a problem?
so for a 6x6 mesh, you have two wires per foot = 2 x .276
= 0.552 sq. inches per foot.
0.552 / (12 x 6) = 0.0077
RE: Wrong size welded wire in foundation slab is it a problem?
RE: Wrong size welded wire in foundation slab is it a problem?
RE: Wrong size welded wire in foundation slab is it a problem?
thread592-4955
thread507-20302
There are a number of methods of determining steel in SOG - I can't get to my reference materials right now - later today I'll try to look some up - PCA has a good book along with ACI 360R.
RE: Wrong size welded wire in foundation slab is it a problem?
RE: Wrong size welded wire in foundation slab is it a problem?
JAE: Isn't the area of the WWR 0.12 sq.in/ft? i.e. 2 x the csa of each wire = 2 x 0.06 = 0.12 sq.in. I think you inadvertently multiplied the diameter of the wire rather than the csa. I always remember the wire gage size as being the csa x 100, which conversely means the csa = wire gage size/100. BTW, your contribution to thread 592-4955 was very informative and worthy of all those stars...plus one more for interjecting it in this thread, because of its elucidative value.
RE: Wrong size welded wire in foundation slab is it a problem?
h
Kind of along the same info I found from JAE's thread link... dealing with the subgrade drag formula.
RE: Wrong size welded wire in foundation slab is it a problem?
RE: Wrong size welded wire in foundation slab is it a problem?
However, the owner sees this as a black and white. Basically its stated on the drawings. That's what they want. (period)
RE: Wrong size welded wire in foundation slab is it a problem?
Sorry for the confusion, adurbin. 6x6-W6xW6 is indeed 0.12 sq. in / foot.
RE: Wrong size welded wire in foundation slab is it a problem?
From a technical point of view, it depends on the loading anticipated. Generally, a plain concrete slab 6" thick if cast using a reasonable low slump will likely perform OK. I've got piles of info on slab on grade construction and a 20'X20' 6" thick is not unreasonable. You might want to research the ACI or PCA data on the effect of slab reinforcing.
RE: Wrong size welded wire in foundation slab is it a problem?
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Wrong size welded wire in foundation slab is it a problem?
RE: Wrong size welded wire in foundation slab is it a problem?