WWF support 3

[SteelPE]

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?

 

[hokie66]

I sympathize, MacGruber, but still think it is sad. My opinion is that "construction support" should be mandatory, but acknowledge that it doesn't always happen.

 

[thaidavid40]

KootK,
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

 

[MacGruber22]

Thanks, hokie. I don't think it is sad, because what we are really talking about is whether these services are part of the original contract. US structural engineer consulting is very segmented and specialized. Experienced property owners/developers know that and will tend to turn their head at fees that contain all of those services, beyond typical RFI & shop drawing review/response. Further, if I start including all of this construction support stuff, then my fee will be inflated when compared to the average engineer. It is nearly impossible to know the extent of construction engineering support required on large jobs, because that scope is often developed as construction progresses. I just don't see how that variability fits into the typical lump-sum A/E fee.

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."

 

[RHTPE]

This thread has primarily been about supports for mesh in slabs, which probably does very little good anyway. But the sad thing to me is how many engineers, and you all seem to be in the US, are so afraid of lawsuits that you don't want to get involved in the construction side of your design projects.

AMEN Hokie66!

Ralph
Structures Consulting
Northeast USA

 

[RHTPE]

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

 

[hokie66]

MacGruber22,
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.

 

[Guastavino]

To those that think EOR should be involved in CA. Just know that for many of us out here, our clients don't want us involved in CA. The code doesn't require it, and they often don't want to pay for it. So what would you say to those clients who don't want your CA services? And yet you want to be involved. Do you do it free?

 

[MacGruber22]

Thanks, hokie. Now that I have thought about it, maybe it is sad.

"It is imperative Cunth doesn't get his hands on those codes."

 

[Seppe]

It's the engineer's job to consider criticality of the design with its commensurate level of constructibility. Some things are just difficult to build, and the constraints in play (spatial and/or design-driven) don't leave the GC with an "easier" option. This happens a lot. Not everything is a piece of cake - building stuff is hard. But designing buildable stuff that still satisfies all loading, stability, and serviceability constraints is hard too.

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.

 

[JAE]

A lot of good points made above.

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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[haynewp]

For projects that aren't bid out, what I run into on CM at Risk projects is the contractor tends to run the show. It's the way they want to do it and have done things before (ex. pulling WWR instead of using rebar) or else they tell owner he can't afford the project. Unless it is a Code violation I can point to, it's my installation preference versus the contractor's on things like this and when he says his way is cheaper, the owner will want it the contractor's way every time and not think about the quality until there is a problem later on. In general, U.S. engineers don't appear to have the clout that engineers from other countries that post on here seem to have.

 

[MacGruber22]

You share my thoughts exactly, haynewp.

"It is imperative Cunth doesn't get his hands on those codes."