calculating rebar diameter for concrete landing

huangyhg

calculating rebar diameter for concrete landing
first of all, let me say, wow! i can't believe the wealth of knowledge that can be found on this site. first time posting and hope to be able to contribute.
i'm supposed to be a design engineer, but manufacturing engineering is my background, so i'm very new to working with structural design.
here's the problem. we are going to be putting in a new concrete landing on our site. approximate size is 190' x 100' by 8" thick.
i'm wondering if there's a good beginning reference for calculating what size rebar we will need for reinforcement. typical items being placed on this pad weigh about 400 tons. the contact patch they have with the concrete is small (about 36 sq. in. each footing, 4 footings).
i think were going to become more and more involved with foundation/concrete design, so what a good beginner's reference?
thanks
check out our whitepaper library.
you need more information.
check reference ringo, anderson -
                 designing floor slab on grade.
that's quite a leap in scope of responsibility.
another highly recommended article for you is: concrete
floors slabs on grade subjected to heavy loads. the army manual# tm 5-809-12 chapter 15. you might be able to search this with google and then print it. make sure you have a thick solid soil/gravel sub-base. are you sure an 8 inch slab is enough?? good luck.
a couple of excellent refernce books:
i'm wondering if there's a good beginning reference for calculating what size rebar we will need for reinforcement. typical items being placed on this pad weigh about 400 tons. the contact patch they have with the concrete is small (about 36 sq. in. each footing, 4 footings).
hmmm,
36 in2 is 0.25 ft2 - so the contact pressure, p, beneath each footing will be:
p = 400*2,000/4/0.25 = 800,000 psf = 800 ksf ~ 5.6 ksi!
while you need to design the concrete for the (very large) imposed loads, be sure to look at the soil-related issues too!
dido wow,
that's 800 kip point loads. i have no doubt you are beyond slab on grade. you probably need a pile foundation and an engineered structural slab - pile cap.
thanks for the replies so far. those books/links look like good places to start.
truth be told: in my mind management should have paid to have a structural expert be in charge of this project, but because i am an "engineer" it's assumed that i know everything engineering. like i said, since we'll probably be involved in determining these types of things in the future, i feel i'd better do the best i can to learn it now so i can make more accurate decisions when the next project comes along.
many of the specifications were chosen from suggestions from others within the company and concrete companies who we will be contracting this work out to. for example, 8" was chosen because our current pad is 6" thick, and of course, is beginning to crack. other suggestions were to use 3/4" rebar spaced 12" apart, and 10guage wire mesh throughout. also, since it was determined that we might possibly build a structure over this pad, we added footings. again, arbitrary numbers of 36" deep and 18" thick were thrown out.
the company that finally got the contract has come back to us saying we probably don't need the wire mesh, and that we only need 1/2" rebar. we feel that it's possible that they are simply trying to cut costs rather than give us sound advice, which is why i decided to come here and find out where i could go so i could start learning this stuff and find out for myself.
any other suggestions would be appreciated. in the meantime, i have a good chunk of info to research and learn. thanks
where is your site?  (city, state only)
is this a cargo dock?  (i have been thinking about what could carry such large loads...)  the loads are way too high to be hauled by trucks...
if these are being placed behind a bulkhead, watch out.  these loads could easily overload the bulkhead, anchorage, walers, etc.  pavement failure is a trivial problem by comparison.  if the site is along the waterfront, insist your employer hire a qualified firm to perform the design.  do not proceed on your own!
you're dealing with unusually high point loads for pavements; alohabobfff"> may be right - you may need a structural system.  then again, management may be willing to accept some problems in return for a reduced cost.  but management needs to understand the risks inherent in their decisions -
first, the contact pressures are a problem by themselves.  since the contact pressure is greater than the likely compressive strength of the pavement concrete i'll guess some of the damage has to do with surficial failure of the concrete.  this can be reduced by resting the 9 inch square legs on "thick" steel plates to distribute the load and reduce the contact pressure.  if the containers are always placed at specific locations (which seems doubtful), you could embed larger panels of steel plate into the surface of the concrete.  you could also put more reinforcement in these specific areas to support the plates.
you could always go to a double matted slab; but this won't be much cheaper than alohabobfff">'s approach.
and you still haven't addressed the overall stability of the load/pavement/soil system -
those rotten buggas. the serviceability for what you are doing would likely far weigh cost in the process of making good decisions. most likely less costly in every respect. glad to be of help. give me a ring i'll be right over.
ok, here's some more info. focht3...we're in el paso, tx. while we are close to the rio grande, i wouldn't exactly call it waterfront. we're well over 1000 feet from the river. also, the river has been completely bone dry for quite some time. don't know how that affects it though.
i also just learned that flexural strength we requested from the concrete contractors was 3000psi concrete. on page 3-3 of tm 5-809-1 it only goes up to 700psi concrete. so i wasn't able to get a quick comparison for stationary live loads, but regardless, here's another problem.
while the original intention was using the pad for the assembly of parts (we build car shredders), it's very possible that they will want to drive our portable crane over this thing. i'll need to investigate but i'd think the crane is pretty dang heavy.
regarding point loads: the original number i gave was very approximate. depending on what we're assembling at the time, the contact area between the pad and part ranges anywhere from 300sq. feet to a couple square inches. yes, inches.
i will try and post some pictures and weights of what i'm talking about. will have to check with my supervisor first.
ok, here are some pictures that may shed some light.