Spacing for wire mesh chairs 4

[RememberTheAlamo]

Hi

Pouring 5000 sq ft 6" slab in basement. Using W4xW4-4x4 WWF mesh (plus fiber). Need to purchase plastic chairs for the mesh . . . have a hunch I need 1 per 4 sq ft . . . 1250 chairs . . . the concrete will be pumped . . . believe the crew will operate from plywood over the mesh . . . just moving back the plywood back as they progress.

So what is the correct spacing for the chairs and mesh?

Thank you,

Larry

 

[Ron]

Put as many chairs as necessary to hold the anticipated load and keep the WWF straight. No set number or spacing.

 

[cvg]

spacing should be 2 - 3 feet, see attached design guide

 

[Ron]

cvg...agree with the guide, but that's assuming nothing but concrete falls on the steel. When plywood floats are being used, I would suggest pulling the spacing in a bit, maybe 18-24".

 

[dik]

My personal preference is not to use WWM, but if used, it should be supplied in flat sheets. I've had too many problems with it winding up on the bottom of the slab... right next to the granular fill...

Dik

 

[cvg]

I would agree with dik, #4 at 24" OCEW would be better

 

[RememberTheAlamo]

Hi All,

Great advice!

My takeaway . . . should have about 1,250+ chairs to handle the 5,000 sq ft of mesh . . . that would be 24" spacing ~~ 4 sq ft per chair.

Now I just need to talk the contractor into using the plywood walkboards to avoid crushing all the wire and chairs . . . smiling.

And agreed . . . originally only intended to use 6" of fiber concrete . . . contractor preferred 4" . . . I made mistakes on the drains and we were back to 6" . . . then he realized the machine room would be handling some heavy tanks of water, an elevator and geothermal pumps. . . . and suggested we wire reinforce . . .

Thank you all!

Larry

 

[hokie66]

I hope you are not counting on plastic fibres to help structurally. Steel fibres maybe?

 

[RememberTheAlamo]

Hi Hokie66,

Appreciate the tip.

No, the plastic chairs are just to hold the mesh in place while we pour . . . no structural strength sought from the chairs.

Using fiber concrete to reduce the surface cracking and address where we don't have wire reinforcement.

Wire reinforcement is just to add to the slab integrity . . . we have 15 5x5 deep footers which the slab will be sitting upon, where the distance between footers is never more than 16'.

Make sense?

Larry

 

[Ron]

Larry...all except the use of fibers where you don't have wire mesh. Fiber is not a substitute, as hokie66 noted. Fiber is just a mix enhancer, not a reinforcement, even though it is marketed as "fiber reinforced concrete".

 

[hokie66]

Thanks, Ron. Yes, I wasn't talking about the plastic chairs, as I understand their purpose. But as Ron said, plastic fibres do not reinforce, no matter what a salesman may tell you.

 

[RememberTheAlamo]

Hi Hokie66 and Ron,

Got it!

We have six drains, on a french drain system under the foundation/slab. The mesh stops as we approach the drains (no reason to try to get the mesh right up next to the drains). So, a foot or so next to each drain doesn't have reinforcing . . . with the fiber used to reduce the surface cracking in those areas.

Worked real nice on the slab for the steel building (50x80) . . .Two years and only cracks are where they are intended . . . in the cuts. We did use W6xW6 6X6 . . . and as expected, the mesh was pushed low in the pour (6-9" slab).

We are using the same W6xW6 6x6 in the garage area (vehicles) and the W4 x W4 4x4 in the machine room.

Just have been looking for a way to suspend the mesh so it is easier on the contractor and keeps it up off the bottom. Suspect 1,200+ 3" plastic chairs could be the answer.

Appreciate the support and guidance!

Larry

 

[DTGT2002]

Not to be captain obvious, but you do need to consider the capacity of the chair in all of this. I expect much of the support data comes from wire chairs rather than plastic ones.

There is a lot of variation in chair capacity and capacities assume nicely supported upright chairs, rather than ones dropped on sloping subgrades.

My 275lb self has busted more than one in my walks on rebar, so the walkboards will help spread the load, but make sure your selected chair can carry 4 sq feet of constrution load or at least most of one portly engineer/craftsman.

 

[RememberTheAlamo]

Hi DIGT2002,

Thank you!

Was wondering if somebody would mention the obvious support these chairs would carry!

On the way to purchasing 2000 plastic chairs we discovered every last plastic chair within 250 miles has been purchased. So I am now looking at composite chairs, which are designed to be combined with some rebar to help stiffen the mesh.

As a result, am now looking at a lighter mesh backed with some rebar to keep these sheets lateral.

Along with that I was looking at the size of the walkboards to spread the weight of the walker. Most the workers are around 150 lbs . . .except the foreman who tips in with a healthy 260 lbs+.

Still doing my analysis, but assuming the lilly pads are 4x4 plywood . . . and one has 1 1/2 workers on it . . . that would be 225 lbs spread over 16 sq ft or 55 lbs per chair . . . which is doable in a static scenario (for the composite chairs) . . . 200 lbs of direct pressure would push the chair into the gravel/grade.

Was going to experiment on several 8x20 sheets tomorrow to check the spacing and walk board effort.

Any tips on using the walk-boards?

Larry

 

[rscassar]

I specify that chairs are placed at no more than 32" c/c.

 

[dik]

Some chairs come with bases to help distribute the load. The typical chair in these environs is the 'standee' type of chair and has a horiz leg at the bottom. I've not experienced chairs sinking into granular base, our granular base compacts 'hard' and will actually pond water.

I spec that chairs be supported on 1/8" min masonite when used over void form to prevent the legs from punching through. Many contractors use 1/4" masonite.

Does anyone have information about the capacity of chairs.

Dik