Rebar or wire mesh
Rebar or wire mesh
(OP)
I have a driveway structure on concrete metal deck and steel beams.
6" thick concrete W3 formlok 18ga. metal deck.
For reinforcing (crack/temperature/shrinkage) what is the better:
Wire Mesh or rebar.
concrete Contractors always seem to complain about the wire mesh.
I've never understood why they can't put the mesh in at the end (before pouring) so it's not all trampled on.
6" thick concrete W3 formlok 18ga. metal deck.
For reinforcing (crack/temperature/shrinkage) what is the better:
Wire Mesh or rebar.
concrete Contractors always seem to complain about the wire mesh.
I've never understood why they can't put the mesh in at the end (before pouring) so it's not all trampled on.






RE: Rebar or wire mesh
RE: Rebar or wire mesh
Has anyone ever been sued for doing what the contractor prefers?
RE: Rebar or wire mesh
In certain cases, the tighter spacing of small wires can help reduce crack size, compared to widely-spaced, larger bars. Since you have deck on beams, and most likely have stiffer girders as well, you will need bars extending over the stiffer elements to avoid excessive cracking. Using rebar may be better in your application so you avoid having to place both. Given a particular concrete mix and curing conditions, the sum of widths of all cracks will usually be similar. Closer bar or wire spacing typically results in more, narrow cracks; using widely-spaced bars generally results in fewer, but wider, cracks.
Are you specifying a traffic membrane to keep water intrusion to a minimum? If not, you can expect the deck to begin corroding very soon after the first cracks appear. Without internal reinforcement, moment strength will likely be compromised before the end of a typical design life.
RE: Rebar or wire mesh
WWF is difficult to place such that it works. Contractors like it because it is easy to place, and no one is watching them, so just put it in there...doesn't matter to them whether it is on the bottom or not.
If they use WWF, then make them support it on tied chairs. If they use rebar, make them support it on tied chairs....it all boils down to whether or not you have the gonads to require what is necessary and follow through with it. Be an a$$ if you need to be. There's no harm in forcing the right result.
RE: Rebar or wire mesh
RE: Rebar or wire mesh
RE: Rebar or wire mesh
There is nothing intrinsic to mesh which stops it from being properly chaired.
RE: Rebar or wire mesh
RE: Rebar or wire mesh
Personally I would specify mesh if the sheet is light enough for two men to carry, if not then I would specify bars. The weight is usually the issue that the guys complain about.
As per putting the mesh in last, the problem is that it is the reinforcement that most things like service ducts are tied to.
RE: Rebar or wire mesh
Bottom line, whichever you choose, insist on supports, and go there after they set the reinforcing to be absolutely sure it's sufficiently on the supports.
RE: Rebar or wire mesh
At least I'm not the only cynic (or perhaps realist.)
RE: Rebar or wire mesh
I'm not convinced it's a case of contractors not caring as much as it is a case of them not knowing that their methods are ineffective.
The key point is simple - either works, but must be securely tied in the correct position prior to placing concrete. Depending on which reinforcing is used, the support spacing must be suitable for the material AND the foot traffic it has to endure during concrete placement. Light gage mesh doesn't stay in proper position well under the weight applied by a 250 lb worker's foot, even with a reasonable bar support spacing.
WWF in rolls is a PIA - sheets work best and the placer won't have to deal with the mesh trying to spring back to its rolled shape. Bars require a lot of handling and tying of each piece so if you can achieve the steel area with mesh I think you would be better served.
If you want to better understand the final in-place cost, bid it with mesh and require an alternate for bars.
Ralph
Structures Consulting
Northeast USA
RE: Rebar or wire mesh
RE: Rebar or wire mesh
Kieran
RE: Rebar or wire mesh
Just look at the detail change, for construction convenience, submitted by the contractor, but inadequately reviewed by the engineer, for the Hyatt Regency Walkway collapse back in the 80's. There are many others.
However, I do not think that is an issue here.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Rebar or wire mesh
I stopped the pour to make proper adjustments and was subjected to considerable criticism, harassment and abuse by the foreman and some of his crew. There are times when an inspector's lot is not an 'appy one.
When the concreting crew is a subtrade coming in for the day of the pour and leaving immediately afterward, it is sometimes difficult to obtain their full co-operation, especially in the absence of firm direction from the general contractor.
BA
RE: Rebar or wire mesh
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928
RE: Rebar or wire mesh
Truly, most of the guys on site do not care. As long as they keep their jobs and get home on time they always think of it as someone elses responsibility.
RE: Rebar or wire mesh
csd72 I would beg to differ. All of the craftsmen that I know personally do care - especially when they understand the consequences of doing things incorrectly. The key is getting their supervisory personnel to understand this.
ACtrafficengr & jgailla This is clearly and elevated slab, as hinted at by the OP's statement regarding "W3 formlok 18ga. metal deck". Fibers alone would not be a proper option for main reinforcing.
jgailla Since this is an elevated slab, contraction joints would not be used.
kieran1 You are correct that the 4 layers of mesh could be a problem when the sheets are lined up in both directions. This can be minimized to 3 layers simply by shifting the laps in one direction by half a sheet.
Ralph
Structures Consulting
Northeast USA