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RE: Uplift Pressure of Wet Concrete?

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Busted.  You really need to go to the ACI 347 for the some sort of answer on this.  There are a lot of factors that go into form work stability, but it won't totally address the particular situation you have.  Concrete is kind of a fluid wannabe.  I have just used the 145 and with a buoyancy safety factor, the actual unit weight has never been an issue. 
 
It is Friday and close to the time of study of true fluids like beer. 

Regards, Harold Sprague


 
> Date: Fri, 16 Apr 2010 07:44:36 -0400
> From: design(--nospam--at)hodgsoneng.ca
> To: seaint(--nospam--at)seaint.org
> CC: spraguehope(--nospam--at)hotmail.com
> Subject: Re: Uplift Pressure of Wet Concrete?
>
> 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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