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# RE: Uplift Pressure of Wet Concrete?

• To: <seaint(--nospam--at)seaint.org>
• Subject: RE: Uplift Pressure of Wet Concrete?
• From: "Garner, Robert" <rgarner(--nospam--at)moffattnichol.com>
• Date: Fri, 16 Apr 2010 06:48:22 -0700

```The pressure depends on the rate of the pour but is always based on the
unit weight of the mud.

-----Original Message-----
From: Gary L. Hodgson and Assoc. [mailto:design(--nospam--at)hodgsoneng.ca]
Sent: Friday, April 16, 2010 4:53 AM
To: seaint(--nospam--at)seaint.org
Subject: 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.
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>
>
> 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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