WWF support
WWF support
(OP)
I have a project that is currently under construction. The contractor is telling me that I need to tell them how to support the WWF reinforcing that we have specified for the SOG and suspended slabs. As in, what types of supports to use and how often to place said supports. In all my years, I have never been asked this question and never really gave it much though. I have told the contractor that this falls under means and methods of construction and that they need to figure out how to place the WWF as shown on the drawings.
Does anyone provide this information on their drawings?
Does anyone provide this information on their drawings?






RE: WWF support
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.
RE: WWF support
RE: WWF support
Seriously though, I agree and when you step into means and methods and you take on more liability.
Now, come to think of it, I think the company I used to work for put a minimum requirement on their drawings for support of chairs (they didn't say how to do it, but they gave a minimum spacing between chair supports). I don't believe in replicating that practice though, because at what point does it end?
RE: WWF support
RE: WWF support
I agree with Koot - Specifying applicable references to means and methods removes your liability.
XR - One contractor i deal with regularly "pulls it up" also. Never heard of an issue. But i wll pass the word on to them what you experienced. I'm surpized it would sink!
njlutzwe - i'd stay away from the minimums.
RE: WWF support
That said, we all know that flimsy WWF is pretty much impossible to position reliably; it's practically chicken wire in most cases. As such, it's far too common for the stuff to just be laid on the ground and then raked up during concreting operations as previously mentioned. At that point, in principle, it's as much on us for specifying something with an unrealistic installation tolerance as it is the contractor for failing to deliver on the construction side of things.
If I'm a contractor, I bring it up during pre-bid that the chairing/bolstering component of the construction cost is going to be significant, and that typical practice is to "rake it up". There's some value in shining a light on the issue in an effort to level the playing field for bids. It's a constructibility issue that deserves attention.
Now, if I'm an engineer and I have a desire to see the reinforcement placed in a manner anywhere close to my detailed "design intent", then I probably get out in front of the matter and avoid specifying the garbage at all. Go with a bit heavier welded wire pattern (say a 6x6 W4/W4 as opposed to W1.4/W1.4 or W2.1/W2.1) and be the GC's friend from day one. Material cost is higher, but labor cost savings make up for it in spades. (The potential flaw in the logic being an assumption that labor is being accurately and honestly priced by the contractor to begin with.)
RE: WWF support
We are balancing this project a bit. The client was very specific about what they wanted as this was the 7th building they have built onsite. The reinforcing has been selected based upon the requirements of what the client has had luck with in the past and in this instance is a 6x6W4.0xW4.0 WWF.
I am beginning to wonder if there is a problem with the bid and now the contractor is trying to get out with this as an excuse. Or maybe trying to change his proposal in a sort of bait and switch tactic. We shall see.
RE: WWF support
"It is imperative Cunth doesn't get his hands on those codes."
RE: WWF support
RE: WWF support
I made the mistake of dismissing a concrete form issue like this saying to myself - "Means and Methods." Everytime I drive by that retaining wall, I think how a little extra knowledge and prudence would have forced the contractor to provide adequate forms so that the final wall wouldn't look like waves on an ocean. As much as the legal requirement is the contractor's, the final product has your name on it too.
RE: WWF support
What I love about engineering (and it used to drive me crazy) was that you ask two different engineers a question and you are likely to get opposite answers. All depends on the perspective. I think as MacGruber pointed out, it's often because "no good deed goes unpunished". In a world of litigation, it's hard to get involved in every detail. But then Teguci makes a great point.
Interestingly, and not to hijack the thread, but it seems like nearly all specifications (book specs not drawing specs) spell out many means and methods requirements. There's a line between means and methods and design, but it's a broad one. Back to point of the OP, I'm guessing you have a good mix of both. And depending on the lawyer, either could get you into trouble. But, if you never want to get sued, you won't ever do any work, and where is the fun in that.
RE: WWF support
Means and methods, of course. Sounds like the contractor is looking for some guidance to do it right.
I would recommend that if they can't put mesh where it is supposed to be (they never can), then use rebar instead.
When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.
-R. Buckminster Fuller
RE: WWF support
If you do not specify a method of support or provide some sort of guidance or reference publication, you don't have a leg to stand on when the contractor supports the WWF using a method you find unacceptable.
RE: WWF support
This is a conundrum for sure. If you have ever watched a crew placing concrete over WWR installed on chairs at a reasonable spacing you begin to realize how futile it seems be to get WWR in the correct location. The placing crew generally knows nothing about how WWR functions and the design requirements driving its proper location. They only see it as an impediment to placing concrete. Similar attitude towards rebar as well.
Means & Methods only? We can have that debate forever. ACI SP-66 covers the detailing of reinforcing and does have a section on reinforcing supports. I have nor reviewed this manual lately and don't know how well WWR is addressed. The Wire Reinforcement Institute has a very good Technical Publication on WWR support (see attached).
I happen to be an engineer heavily involved in the "Means & Methods" side of construction. I consult with contractors to help them to figure out the "how-tos" of construction (and sometime destruction). I do get involved in proper reinforcing support and will 'stick my neck out' to make recommendations. Problems resulting from improperly positioned reinforcing that adversely affected a concrete structure will almost always come back to the engineer of record first. Only after extensive involvement on the EoR's part can the problem be then thrown back at the contractor's failure to do his/her job.
It is my not so humble opinion that the engineer should clearly make his/her expectations know prior to bid time. If it means making a recommendation for WWR supports, so be it. But the issues resulting from poor placement techniques must also be a part of the discussion.
Ralph
Structures Consulting
Northeast USA
RE: WWF support
RE: WWF support
RE: WWF support
Dave
Thaidavid
RE: WWF support
It isn't always about lawsuits - it can be the loss of time arguing over the answer and the creep of scope into being the construction support engineer. They will ask for a foot after you give them an inch. Further, you will run into many contractors in the US who will complain about what you specify for mesh support until you give in to something less with some amount of given restrictions, which ends up being very muddy waters The "real" support required to keep mesh in the upper 1/3 of slabs and nearly rigid during the pour is significant, and if you beef up the mesh gage to reduce the supports you get yelled at for providing an amount of steel that the contractor has "never seen in his 30-years".
That said, a lawsuit (or at minimum a lot of complaining) will come your way with slabs requiring very good crack control, and clients are sensitive to their performance & aesthetic. At a minimum, the lost time fighting contractors is fatiguing and eats away at time better spent doing anything else.
IMHO, 99% of the time that a contractor asks the EOR to specify bar/mesh support, he/she is not looking for the real answer - rather a way to pass responsibility of a tough means and methods task to someone else. It is a lose-lose situation way too often. No thank you.
Besides, if your original contract isn't with the contractor, you need to provide a fee for construction support. You don't "need" to do anything for 1) someone who you don't have a contract with and 2) any task that isn't in the standard practice for EOR's within the building code.
"It is imperative Cunth doesn't get his hands on those codes."
RE: WWF support
My own firm's specs are riddled with these statements that I'd classify as "stupid shit not to do" clauses. I feel that it's the wrong way to go about things because, unlike the list of things to do, the possible list of things not to do is limitless. And referencing some stupid things not to do almost implies that other, unlisted, stupid thing might be acceptable.
4.5.1.2 No hook and lift.
4.5.1.2 Don't allow mesh to sink to a position lower than specified.
4.5.1.3 Don't substitute woven stretched out paper clips for mesh.
4.5.1.4 Don't impregnate your biological sister.
So wait, does that mean that I should impregnate my step sister? I feel that specifications should, for the most part, prescribe rather than proscribe. As with all things, there are surely exceptions.
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.
RE: WWF support
RE: WWF support
Hooking-and-lifting is endemic in these parts. And it NEVER works out well. Some things are better said prohibitively (and proactively) to make sure that there is no room for misunderstanding or "fudging". As was said above, contractors will take a mile if given an inch. The best defense for the owner's quality control is to fight to never give that particular inch to start with. I'm usually a pretty positive person, except when telling grandchildren and contractors, "No!".
Dave
Thaidavid
RE: WWF support
The owner restricting my scope (paying me less) and the contractor expecting the additional services (assumed to them as standard of practice) are very conflicting things.
"It is imperative Cunth doesn't get his hands on those codes."
RE: WWF support
AMEN Hokie66!
Ralph
Structures Consulting
Northeast USA
RE: WWF support
Please consider this:
Does the EoR or the contractor determine the length of a cover plate on a steel beam?
Does the Eor or the contractor determine the amount of OW joist bridging required?
Does the EoR or the contractor determine the proper positioning for a P/T strand?
Of course not - that is the EoR's responsibility. Why? Because all are critically related to the design parameters used.
WWR's vertical position in a slab is a similar situation. Its position in a slab has been determined by reasonable parameters for design used by the EoR.
As engineers what we promise to our clients and attempt to convey to the contractor must be constructable. Knowing full well that bad WWR installation can be commonplace and offering no recommendation regarding sensible and reliable installation of WWR is ducking our role in the construction process.
As engineers we should know how to get to the end product that conforms to our design premise.
I know many of you will scoff at my comments. Worried about liability. Worried about scope creep. Etc.
But to me, proper reinforcing installation is an integral part of reinforced concrete design. Insuring that it ends up where it is supposed to be is part of the picture, and we should do whatever it takes to get there. I do not consider it to be scope creep, but rather just a component of good reinforced concrete design.
WWR does spring-back after being deflected - the unquantifiable is the amount of spring-back. Certainly use of a vibratory screed can be helpful to 'liquify' the concrete above the WWR and decrease the resistance to spring-back. Using 2-3 bars under the WWR can assist in spring-back when using very light gauge WWR (or just use a heavier wire). Requiring 'bridges' for placers when appropriate can help. Recommend the use of temporary walk-boards spanning across the bar/WWR supports can minimize foot-traffic directly on the WWR. Requiring the contractor to educate the newly-hired placer and even the somewhat experienced crew about the importance of WWR ending up where it's supposed to be can help. Properly timed 2-layer placement techniques can be successful (very iffy though).
After all, aren't we the ones who are supposed to know how to best to put together a custom structure?
JMNTBHO
Ralph
Structures Consulting
Northeast USA
RE: WWF support
That whole scenario, and you described it nicely, is what I consider sad. That was not my experience when I practiced in the US, mostly in Virginia, but that was almost 30 years ago.
RE: WWF support
RE: WWF support
"It is imperative Cunth doesn't get his hands on those codes."
RE: WWF support
That in mind, I don't believe said argument applies to flimsy mesh with tight vertical placement tolerances that, while not unconstructible in the truest sense of the word, is a very easy target for any contractor trying to abide by the contract documents upon which their bid is expected to be based.
If the contractor doesn't raise a stink during bidding, then he/she is contributing to the problem. It provides precedent upon which the EOR can rely for future, comparable applications.
Both sides need to do their part. Long way to go, though: EOR specification of ultra light mesh is still pervasive.
RE: WWF support
My take on it is that requiring chairs for WWF is NOT means and methods.
Think about this:
In all our specifications (CSI format for example) we have a part 3 which is EXECUTION where we do tell the contractor all sorts of do's and do not's.
This is not means and methods specifically but does try to convey many "best practices" in construction.
On our plans we have a note that suggests that all slab reinforcing be chaired at 4 ft. intervals. How they chair it (manufactured products, concrete bricks) is up to them.
We also have tended to avoid WWF as much as possible and the idea of using a heavier WWF might go a long way to avoid the temptation to pull up the WWF while placing concrete...which is stupid.
I totally agree that pulling up WWF during concrete placement by a guy standing on said WWF is and impossible way to position WWF in its intended location.
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RE: WWF support
RE: WWF support
"It is imperative Cunth doesn't get his hands on those codes."