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calculating loads on concrete forms

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calculating loads on concrete forms

calculating loads on concrete forms

delfina

(Mechanical)

(OP)

9 Dec 03 09:23

Anyone know how to calculate a load due to concrete ( poured )on forms. Is it as simple as if it was water? ( density x height for pressure ? )

THanks

RE: calculating loads on concrete forms

PEinc

(Geotechnical)

9 Dec 03 11:50

Yes, if the concrete has not started to set.  However, concrete pressures are also a function of temperature and pour rate.  I suggest you get a book on formwork design and get some formwork accessory catalogs from suppliers.  These catalogs frequently contain an engineering section with design information.

RE: calculating loads on concrete forms

LPPE

(Structural)

9 Dec 03 12:30

Make sure you use the density of concrete, not water.

RE: calculating loads on concrete forms

delfina

(Mechanical)

(OP)

9 Dec 03 13:32

So the load on the forms is not dependent on the width of the wall correct?

RE: calculating loads on concrete forms

jheidt

(Civil/Environmental)

9 Dec 03 15:28

One of the best investments I made years ago was buying the book Formwork Design by Mary Hurd from the American Concrete Institute (ACI).  You REALLY should do the same.

Your original question says "...load due to concrete (poured) ON forms."  To me that implies a deck or suspended slab.  Your second post implies a wall - there is a BIG difference!

RE: calculating loads on concrete forms

PEinc

(Geotechnical)

9 Dec 03 16:10

As hard as it may be to believe, wall thickness does not affect the pressures.  There is still a column of wet concrete creating a vertical pressure and therefore a horizontal pressure. Whether it's PSF or PSI, it's still the same pressure.  I've never seen a reduction for thinner walls.

RE: calculating loads on concrete forms

delfina

(Mechanical)

With competitive price and timely delivery, Zolo sincerely hope to be your supplier and partner.

(OP)

10 Dec 03 07:25

Thank you for all your help. My ? was a bit confusing. It is a wall and I will get that book.

Boy it is hard to believe that the same lateral load will be experienced by the forms regardless of wall thickness. I know theory dictates it but when you look at it in a practical sense you would think that a 2" thick 5ft high wall would exert a lot less lateral load on the forms than a 10" wall.

Thank you again!

RE: calculating loads on concrete forms

Bbird

(Civil/Environmental)

10 Dec 03 12:57

If the concrete is fluid enough the pressure will get into the 2" wall laterally and so its pressure is no different from a 10" thick wall.

RE: calculating loads on concrete forms

jheidt

(Civil/Environmental)

12 Dec 03 14:33

Just a follow up to give the correct book citation:

Hurd, M.K., "Formwork for Concrete, SP-4", 6th Edition, American Concrete Institute, Farmington Hills, MI, , 500 pp.

Also, the October issue of "Concrete International", the magazine of the Amercian Concrete Institute, on pages 41-46, had an article titled "Using Interactive Spreadsheets for Teaching Concrete Formwork Design".  A good article on formwork and an example of speadsheet design for formwork calculations.

RE: calculating loads on concrete forms

Ginger

(Civil)

12 Dec 03 15:58

For those in the UK, the definitive guide is CIRIA Report Number108.  This gives design tables and design guidance on formwork pressures based on the height of pour, rate of rise up the shutter, concrete temperature, cement content etc etc.  It incorporates factors for walls and columns also.

Regards

RE: calculating loads on concrete forms

AlohaBob

(Structural)

30 Dec 03 19:49

These thoughts seem to presume that concrete is a fluid like water. This in turn would give very conservative predictions for design of formwork for instance, since concrete doesn't behave like this. I just don't think it's so clear cut.

Internal frictions can induce a 2 ft high 8" wall poured over a slab and free to flow out at the bottom. If it were fluid, it wouldn't stand up to this head pressure. It would all flow out the bottom.

I'm sure there's many factors involved. Including mix design and choice of agregates and admixtures. Age of mix, temperature, consolidation, vibration.

I wouldn't so quickly discount the form thickness either. I'm sure a 2" thick wall would stand much higher than an 8 inch wall. It may have something to do with surface friction. In which case, the wall pressure of an 8" wall would be higher than a 2" wall.

The form designers have rules, but they aren't as simple as suggested.

RE: calculating loads on concrete forms

SlideRuleEra

(Structural)

30 Dec 03 20:06

Another factor is the size & spacing of rebar in a wall. Sometimes it takes a lot of mechanical vibration to get the concrete thought the rebar mat where it can exert any pressure directly on the forms (if there is surface honeycomb there must not have been much pressure on the wall forms).
As stated above, treating concrete as a fluid (in a wall) is very conservative; the "slump" of water is 12 inches, compared with 3 to 6 inches for "typical" fresh concrete.

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News

Concrete is one of the most commonly used building materials worldwide. The material has a high compressive strength, which makes it ideal for use in structural construction. One of the most common applications of concrete is in the construction of formwork. Formwork is a temporary structure that is used to support different concrete formwork types until it sets and gains sufficient strength to support itself. However, it is important to calculate the concrete pressure on formwork to ensure that the structure can withstand the weight of the concrete. 

What is formwork?

Before we delve into calculating concrete pressure on formwork, it's essential to understand what formwork is. Put simply, formwork is the temporary structure, usually made from timber, steel, or aluminum, which holds wet concrete in place until it sets and reaches a sufficient strength to support its weight. Formwork can take various shapes and designs, depending on the type and shape of the final concrete structure. 

How to calculate concrete pressure?

The pressure of fresh concrete during placement is known as lateral pressure. The lateral pressure increases with the height and rate of pouring of the concrete mix. Calculating the concrete pressure on formwork is imperative to avoid any structural failures. The formula to calculate the concrete pressure on formwork is P= (hC) / A, where P = pressure in kN/m2, h = height of the concrete in meters, C = unit weight of concrete in kN/m3, and A = contact area of formwork in m2. 

It's important to note that the pressure exerted by concrete on formwork tends to be proportional to the height of the formwork. So, if you're pouring a 25-meter high wall, the pressure exerted on the formwork would be much higher than if you were pouring a 5-meter high wall. 

Importance of calculating concrete pressure on formwork

Calculating concrete pressure on formwork is crucial to ensure that the structure can withstand the weight of the wet concrete. An overestimation of the pressure may lead to the increased design of the temporary structure or an increase in the number of support elements, leading to additional costs. In contrast, underestimating the pressure may cause the temporary structure to fail or collapse, leading to significant safety hazards and property damage. 

In conclusion, the accurate calculation of concrete pressure on formwork, provided by a reputable formwork company, is essential to ensure the safety and success of any concrete construction project. Factors like the height of the wall, the contact area of formwork, and unit weight of concrete all play significant roles in the calculation. As such, it&#;s necessary to use reliable and accurate formulas like the one mentioned above to ensure successful concrete construction projects.

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