huangyhg

checker board slab on grade
does anyone know the specifications for checker board slab on grade placement. it's a 6 inche slab thick over an area of 300 ft x 700 ft. how do i show this on a drawing? what are the min or max area patterns and where can i find this information.
thank you always
rain
i typically show control joints on the foundation plan. for a 6" slab, spacing of joints should not exceed 18'. in your specifications, or structural general notes, mention that you want the slab poured in a checkerboard fashion.
daveatkins
don't bother with a checkerboard placement scheme. there's no advantage. the shrinkage compensation is so small for the time delay in placement it isn't worth. make sure your joints are properly spaced and cut at the right times and you'll do far more to mitigate cracking than the checkerboard pattern.
joints should be spaced no greater than about 30 times the thickness of the slab, so if you have a 6" thick slab, your joints should not exceed 180" or 15 feet, in either direction. the joints should be saw-cut the same day as placement, as soon as the saw can cut into the concrete without ravelling the coarse aggregate, and should be cut to a depth of 20 to 25 percent of the thickness or 1.2 to 1.5 inches deep in this case.
ron said it well. however, there may be visual reasons for this kind of placement, rather than using sawn joints. if so, carefully attend to ron's recommendations. i hope your results are acceptable.
for 300' x 700', i would also be thinking really carefully about location of expansion joints in the slab, especially if it is exposed to strong sunlight and/or subject to seasonal temperature changes.
i like to echo ron's sentiments regarding checkered slab placement. they do not work that well at all. i have much better luck with well placed construction and contraction joints. the rule of thumb that i use is 2.5 times the slab thickness in feet. i read this rule some where and it served me well.
there are lots of rules, what to do and what not to do for sog joints. also watch for catch basins, they can present a tricky area for joint.
regards,
lutfi
mudadi - in your previous post on this subject you did not give the slab thickness. it is always amazing how each of us has our own (arbitrary) mental picture of the problem. when i said that a checker board pattern was a good way to go i had made an (incorrect) assumption that your 300' x 700' slab was probably 8 or 10 feet thick (not uncommon for an industrial slab that size).
for a 6" thick slab, i totally agree with the advice from ron, and others. here are some links with other backup information:
two additional suggestions:
1. specify a "softcut" saw for cutting the joints. it allows the contractor to cut the joints much sooner than the conventional paving saw.
2. for design recommendations see the book by boyd ringo with a title something like "design of industrial floor slabs" (sorry, i'm not near my bookshelf!)
thank you every one for your info. it was very, very helpful. keep up the spirit, ron slideruleera, emmgjld, sacreblue, lufti, jheidt2543
thank you thank you thank you!
here is the correct citation:
"designing floor slabs on grade, step-by-step proceedures, sample solutions and commentary", 2nd edition, by boyd c. ringo and rober b. anderson, published by the aberdeen group, 426 south westgate, addison, il 60101, isbn 0-924659-75-0
one of the best!
jheidt2543,
isn't the proprietary name you mentioned above spelled "soffcut"? i think it is a concrete saw with a very wide wheel (so it doen't sink into the concrete) and a handle which the operator holds.
daveatkins

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]