Mass Concrete

[mscme]

I am trying to design a large mass of concrete (6'x8'x50' long) which will carry a trolley on top of it (approx. 6 ksf). Does anyone know of reference material to determine the amount of reinforcement required? It seem unreasonable to use the min of 0.0018bh, however i know that temperature and shrinkage is a big concern on such a large piece of concrete. I have read ACI 207.1 "Guide to mass concrete", however it does not discuss the amount of reinforcement that would be required. If i design it for bending only, roe is very small however i believe that T&S steel should be at least #5@12 on each face and consider the interior portion as filler concrete.

 

[SlideRuleEra]

See thread507-150536

You may want to consider an initial unreinforced mass concrete placement that has a conventionally reinforced structural topping slab (maybe 12 to 18 inches thick). If there will be anchor bolts (or other embeds) for trolley rails, etc. then placing them accurately in a "thin" structural slab should be easier than in a 6' thick mass placement.

http://www.SlideRuleEra.net

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[sebivaq]

Dear mscme,
you should look in ACI 207.2R "Effect of Restraint, Volume Change, and Reinforcement on Cracking Mass Concrete". You should design in accordance to ACI 318, and then check with the Lutz equation (taking into account the volume change tension in steel) the crack width. Please see chapter 5.

As a reference, currently I'm designing a massive concrete retaining wall and we use #9 @ 200mm as a minimum. Best regards,

Sebastian

 

[TXStructural]

You need minimum steel to avoid excessive cracking, but consider the mechanisms at work for mass concrete. Keep the thermal and mix design considerations in check (high volume SCM-replacement of portland, optimize W/C, use admixtures as needed for workability, and ice or nitrogen cooling as needed.)

This time of year in particular, watch maximum temps to avoid DEF, which will doom the placement. Consider hiring services of a mass concrete consultant to provide a thermal control plan and check the mix design.

Don't get too caught up in minimizing the amount of steel, it is not really that expensive in the whole scheme of things, and remediating a very big concrete placement is very expensive. We, as structural engineers, tend to focus excessively on minimizing material weights, which does not always translate to least cost or best value.

 

[csd72]

mscme,

Are you designing it as plain concrete or as reinforced?

Many codes limit the thickness to be considered for shrinkage to 300mm each face (or thereabouts). Not sure about ACI though.