warehouse slab suggestions

[a2mfk]

Have a client who is unable to provide us any meaningful information about their light industrial and warehouse slab. They just are useless in this department.

Racks similar to "home depot" and could be that tall (b.o. steel around 26ft), storing rather lightweight boxes of vitamins, supplements, etc. Forklifts similar to home depot, we don't know about the traffic (I'd guess light to medium). We know no other details and at this time in regards to weights, rack post spacing, base plates, etc.

Conditioned space in Florida. Sawcut control joints probably around 10' o.c., not sure about WWF, rebar or steel fibers yet.

I was thinking of giving them a design for a couple of different slab sizes and reinforcing schemes, and give them my basis of design, and then they can choose. Maybe in table form on the foundation plan.

I welcome any opinions, especially on conservative rack point loads and base plate sizes, spacing of rack posts, and slab thickness. I have been told by those in the know that the "Cadillac" of warehouse slabs would be #3 @ 14-18" o.c. E.W.

Semi rigid epoxy to fill the CJs, any favorites?

And probably most importantly, I was not planning on providing dowels at CJs , maybe only at construction joints (pour stops for the day...)

I have Part 2 of the ACI Manual of Practice.

Thanks in advance.

 

[OHIOMatt]

Toad. even if you fill he joints just before the owner takes poseesion, you will have additional shrinkage. Typical in Florida, you have high humidity. When the AC turns on, it will act to reduce the ineterior humidity. This will actually draw more water out of the concrete. If you look at the semi-rigid epoxy filler paper work, they address longituidinal filler cracks as well as delamination at the slab face.

In my work in Florida on projects like this, we have used crushed concrete, lime rock, Bahama Rock, and some FDOT road base under the slabs. The projects were sand was used as the base had significantly more cracking and curling. While we could never be 100% sure that sand was the problem, we theorized that the excessive fineness of the sand allowed for rutting and pour clogging issues. Once we went to aggregate bases the issues seemed to be greatly minimized.

One other thing that we found help, was a 7 day wet cure. The afternoon sun would heat and dry the concrete and destroy disapating compounds far too quickly (the buildings were tilt wall, so slab was exposed to the sun).

 

[a2mfk]

OHIO- not saying you didn't use crushed rock, and that it is not the better sub-base, just never seen or heard of that in Florida... I imagine I would get a lot of pissing and moaning.

Completely agree on a 7 day wet cure, I will give that a shot. I know it goes a long way towards crack control. Seems like projects take forever sometimes in design, and financing, and then they have to build it yesterday, so of course there will be resistance but I can explain the benefits of less cracks pretty easily.

RACKS- again, the owner has no idea what they will use, they literally at a meeting said something like home depot in regards to racks and forklifts. Does anyone have a conservative suggestion, website, etc., where I can at least consider some type of reasonable rack loading, ie, 10" sq base plates, 6ft on center, 10kip axial.... Or should I literally go to home depot with my tape measure and assume Xkip per post.

Also in regards to shrinkage, what about placing the slab in staggered strips, and then infilling a couple of days later? This allows a much less restrained movement in the short direction, and then you have CJs in the long direction. Will the complaint be the amount of formwork they have to use at every strip? But the positive is you have easy access to run screeds and finish each strip...

Thanks all for the advice!

 

[OHIOMatt]

For rack loading, check with RMI (rack manufactuer's institute. You may be able to get some typical loading information from them.

 

[Ron]

A2...your idea on infill placement was once an accepted method; however, ACI started recommending against that about 20 years ago.

It is more difficult to implement, increases the placement cost and the benefits are not enough to warrant it.