Formwork Pressure and EFCO Forms 2

[TS59401]

I am working on a bridge pier cap formwork design. We typically don't get involved with formwork, however the bridge is over the RR and the RR is asking for almost everything to be stamped. The pier cap itself has the basic dimensions 41ft long, 9.5ft deep (center only) and 7.5ft wide. The Contractor is proposing to use 10ft EFCO panel forms (rated at 1200psf) and that seems fine to me since the pour rate wont be more than about 4-5ft per hour.

My question is determining the loads on the EFCO "ties" top and bottom. Through bolts are utilized along the bottom at 4ft centers and yokes (bent steel members bolted to the top of the form) are utilized at the top. Typically we use wire wall ties sized and spaced for our maximum wall pour pressure, however that approach is giving me very high loads in the through bolts and yokes.

How would I draw a wall pressure diagram for my 4-5ft per hour pour rate? Would it be fluid pressure with 5ft height? Once we get the forms full, what would the pressure be at the bottom of the forms. we have the forms continuously supported vertically.

I know the system works since I have seen it used many times, I am just struggling to show why. Thanks for your help.

 

[Wallache]

ASCE 37-14 has formulas for form pressures if you don't have access to ACI 347.

 

[TS59401]

Thank you Wallache. I found ACI 347 and the equations look similar to the Dayton Superior handbook. I notice the pressures for a wall less than 14' and pour rates below 7ft/hr are maximum values. Should I assume a triangular pressure distribution to the top of the wall or to the top of my pour height per hour?

 

[SlideRuleEra]

TS59401 - In addition to the rate of pour, you must account for the following in the calculations:

Concrete mix design (chemistry)
Temperature
Unit weight of the concrete

Here is a Concrete Construction magazine article that gives an example of how the calcs are performed.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Wallache]

Use the total height of the pour for your pressure calculations. The load diagram follows a triangular w*h load until you reach your calculated pressure then stays uniform to the bottom, similar to diagrams shown in link below:

https://books.google.com/books?id=0...ge&q=formwork for concrete structures&f=false

 

[TS59401]

Wallache and SlideRuleEra, Thank you for the advice, I will confirm the intended mix design and get this out the door. Much appreciated.

 

[OHIOMatt]

In a past life, I was a design engineer for EFCO. I would draw the pressure distribution as follows: At the top, the pressure would be 0. It would increase linearly to 1200 psf at 8' from the top of the concrete. The pressure would then be uniform at 1200 psf to the 9 1/2 foot depth. This would give you a tie load of 17.9 kips. By the way, if you assumed full liquid concrete, you would have a tie load of 18.5 kips. In your case, it would be safe to assume that the maximum pressure on the face of the form does not exceed 1200 psf.