Concrete formwork - best approach to counter uplift forces ...

$\begingroup$

View Details

I'm casting a 4m long triangular-profile reinforced gravity retaining wall against soil movement due to a 1 metre jump in ground level.

Zolo are exported all over the world and different industries with quality first. Our belief is to provide our customers with more and better high value-added products. Let's create a better future together.

My concern is countering the vertical uplift forces from the hydrostatic pressure of the fluid concrete when it's poured, which will be about 4 - 5 tons equivalent (40 - 50kN), ie the weight of the "missing" concrete above the slanted face of the form. Basically, I want it not to be lifted off the ground by the fluid concrete. I've thought of several possible approaches to offset this force, but the reality is that I'm just not sure which is best or most foolproof, or if there are standard solutions used in civil engineering that I'm unaware of.

Possible solutions + sketches I've come up with -

1. Reduce the footprint and hence uplift, by making the wall slimmer. Perhaps with strong lateral restraint, rebar, and concrete under an adjacent path, the usual 50% rule of thumb is excessive and I can reduce the width of the wall to ~ 40cm (and therefore the upward force by ~ 30-50%)?
2. Allow the concrete to fill the full vertical space of the wall's footprint, removing the excess pour when set. Precisely zero hydrostatic pressure guaranteed as all concrete is at the same top level; the extra volume can be cast with plywood dividers so it comes away easily in sensible sized slices.
3. Cast in 2 parts, using a smaller 1st cast steel-linked to the form, as a deadweight for a larger 2nd cast. Cast the bottom 1/4 only, but with steel rod embedded to link it to the form, and vertical rebar for the join. Then cast the top 3/4 about 48 hrs later. The bottom 1/4, attached to the form itself, acts as a deadweight to hold down the form against upward pressure when casting the narrower but taller top 3/4. Extra weight still needed but only 1/4 as much; hopefully the vertical rebar linking the pours will ensure long term integrity.
4. Add a 'false floor' in and fixed to the sides of the formwork so the weight rests on the formwork not the ground; remove and underfill this space beneath the wall once the 1st pour is set. 5 tons of concrete along a 4m length can easily be supported on 80 side-by-side 2x4 (50x100mm) timber (weight per 50mm 'slice' about 62kg which is small for a 0.8m clear span). Because the 'floor' is itself supported by the formwork, there is no net uplift force - it's replaced by vertical tension in the formwork which is much easier to handle. After the form has set, remove alternate 50cm sections of these 2x4 timbers, and pour concrete into the void below, to properly support the wall. When that's set, remove the other half of the timbers and pour under the rest of the wall. Needs 3 pours but again, guaranteed to work since there is zero net uplift force and the weight spread across many 50mm slices is small for each slice. Also simple to set up.
5. Brute force. The simple solution. Add about 5 tons of weight. For stability it's added to the heavy members at the base of the form, not on top. problem is that 5 tons is a heck of a lot to move.

How can I easiest ensure the formwork doesn't rise at the base and the pour escape, when it's poured?

Hi all
Haven’t been to break time for many years.
I’m back!

I am developing a new concrete and have a local engineer doing the research on it so I can get my processes and material approved by my states building code. I am going to be building houses with 18″ solid reinforced walls and I am looking at various types of form systems from shop built forms to manufactured forms. I want a system that can easily be taught to carpenters and and as easy on the back as possible. One system I have found is the Gates horizontal rod system. Has anyone had experience with this system. If so what do you think of it, I am trying to get the cost of the forms to be as low as possible, I have a millwork shop in which I could set up to rout all the form boards to accept the snap ties ( saving me having to buy a form system by doing it my self ). I have found a source for 2′ x 12′ x 3/4″ 7 ply form board and am waiting for a price quote. I need a system that is 12′ because my designs have my ceilings between 10′ and 11′ 6″ . The gates system looks good to me because there is no 2 x 4 frame adding to the weight or metal ribs adding to the expense. Gates says that they can produce forms that don’t need framing, ribs or wailers because of the rod system and the extra snap ties that they use.
If you have had experience with this system or a better and cheaper way, please share your expertise.
10-Q

For more concrete wall formworkinformation, please contact us. We will provide professional answers.