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Re: Uplift Pressure of Wet Concrete?

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The design requirements and pressures for formwork can be found in ACI 347, "Guide to Formwork for Concrete".  The basic formula is just the liquid weight of the concrete as if was like water.  However, there are additional formula that can reduce this pressures based on your specific concrete unit weight, cement type, temperature, height of pour, and rate of pouring.  I do not think there is one magic number but the formula are easy and may give similar results.  There is also a section on pouring concrete underwater but it basically refers you to the above formula minus the water displaced buoyancy

Thomas Hunt, S.E.
Fluor



"Gary L. Hodgson and Assoc." <design(--nospam--at)hodgsoneng.ca>
04/16/2010 04:53 AM
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Re: Uplift Pressure of Wet Concrete?





It came to me after I sent my reply, it was about the max pressure on
vertical formwork. It said that the pressure increased with depth to a
maximum of 800-850 psf after which it did not increase any more at
greater depths.  Thanks for your replies.  I will have to pause before I
send another question.
Gary

On 4/16/2010 7:44 AM, Gary L. Hodgson and Assoc. wrote:
> --------------------------------------------------------------------------
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> Your following message has been delivered to the list
>  seaint(--nospam--at)seaint.org at 04:44:19 on 16 Apr 2010.
> --------------------------------------------------------------------------
>
>
>
> Robert, Thor and Harold,
> 145-150 pcf.  That's what this old beer-addled brain keeps telling me,
> but I seem to remember something about fluid pressures of concrete
> actually being more.  It was an article from an engineering
> publication about formwork design and that is what I can't find.  It
> had to be at least 31 years old because I had found it at a previous
> employer where I left in 1974.  It's Friday!
> Gary
>
> On 4/15/2010 4:55 PM, Harold Sprague wrote:
>> Gary,
>> It is just the weight of the volume of displaced concrete at 145
>> pcf.  It is easier to use multiple lifts so that there is less volume
>> displaced for any given lift thus reducing the tie-down demand.
>>
>> I was going to develop this priciple myself, but Archimedes edged me
>> out by about 2200 years.  In geologic terms it was a dead heat.
>> http://en.wikipedia.org/wiki/Buoyancy
>>
>> Regards, Harold Sprague
>>
>>
>>
>> > Date: Thu, 15 Apr 2010 13:34:39 -0400
>> > From: design(--nospam--at)hodgsoneng.ca
>> > To: seaint(--nospam--at)seaint.org
>> > Subject: Uplift Pressure of Wet Concrete?
>> >
>> > List,
>> >
>> > I'm currently working with some 1980mm (78" dia.) penstocks at an old
>> > hydro plant that are being renovated or replaced.
>> >
>> > I have to design the temporary tie-downs at the thrust blocks or
>> support
>> > points when they pour concrete around them. I did a similar project
>> > about 15 years ago but I can't find my reference material.
>> >
>> > Does anybody know the uplift pressure (buoyancy) of wet concrete?
>> >
>> > Gary
>> >
>> >
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