[TowerTalk] Fluid pressure of concrete

[David Gilbert]

The link you quote does a good job of explaining the situation but it 
only briefly mentions an additional factor other than the weight of the 
concrete itself, which is the dynamic lateral force caused by the 
concrete falling from some height above the pour.  That can be 
considerable, and in my case caused a couple of blowouts while the 
concrete was being poured in the ICF forms of my house.  If you consider 
the volume in the column of concrete in a typical pour falling from a 
height of whatever, and then slamming into the still fluid concrete that 
had already been poured, the net impact can be significant.   I'm sure 
there are ways of calculating that effect, but it's pretty complicated 
since it depends upon the uncertain volume of the column and the 
viscosity of the already poured material.  As you say, the best strategy 
is to overbuild.

I'd also like to point out a lesser potential issue, which is the fact 
that the wood used in most concrete forms can soften when wet. Walls 
that are rigid when dry bow outward if not braced really well, and 
joints can separate as nails or screws pull out of the soft wood ... the 
latter situation being why it is a good idea to try to put fasteners in 
shear (versus tension) whenever possible.

Just some thoughts ...

73,
Dave   AB7E



On 10/13/2018 5:49 AM, Mickey Baker wrote:
> I studied this 30+ years ago... when I was an engineering co-op tasked with
> building a rail loading platform (but EE, so I needed to figure it out.)
> The strategy to build a form is to basically overbuild.
>
> Pressure is dynamic, so you solve for peak for most pours, which occurs
> just before the first bit of a pour sets. Here's a site I found that
> explains the general calculations and the process. I'm interested why you
> ask...
>
> https://theconstructor.org/building/concrete-formwork-loads-pressure-calculations/14521/
>
> Mickey Baker, N4MB
> Palm Beach Gardens
> *“Tell me, and I will listen. Show me, and I will understand. Involve me,
> and I will learn.” *Teton Lakota, American Indian Saying.
>
>
> On Sat, Oct 13, 2018 at 7:30 AM Larry Horlick <llhorlick at gmail.com> wrote:
>
>> Can anyone tell me the fluid pressure at the bottom of a concrete pour,
>> form size 8’ x 8’ x 6’?
>>
>> Larry
>> VO1FOG
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