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Join Date: Apr 2008
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Concrete Block

05/28/2008 6:28 AM

hi everybody

i want to add 100KN additional weight to the tower foundation in the form of concrete block 10KN each. please help me to find the dimensions of the block and the composition of the concrete. No reinforcement is required. the shape of the block does not matter whether cubiod or cube.

thanks in advance

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Guru
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#1

Re: concrete block

05/28/2008 7:05 AM

The dimensions of the block will be determined by the density of the concrete. What is it - 2300kg/m3, 2500kg/m3, 2800kg/m3, more?

An example calulation at 2500kg/m3 -

  • 10kN / 9.81m/s2 = 1.02 x 103kg
  • 1.02 x 103kg / 2500kg/m3 = 0.407m3.
  • 3√ 0.407m3 = 0.74m, i.e. a cube a little over 29in to each face.

Simply substitute the actual concrete density for the 2500kg/m3 suggested figure and re-run the calculation, adjusting the shape of the block to suit site conditions while maintaining its volume.

Does that help?

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#2

Re: Concrete Block

05/29/2008 10:39 AM

Here in the US, concrete density is between 145 and 150 lb/ft3. 100 kN is 22,481 lbs, and a 10 kN chunk of concrete is 2,248 lbs. Using 145 lb/ft3 as the density, you'll need to make the concrete cubes 30" X 30" X 30", or 76 cm X 76 cm X 76 cm.

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#3
In reply to #2

Re: Concrete Block

05/29/2008 1:48 PM

density is lower if using lightweight or air entrained concretes

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#4
In reply to #3

Re: Concrete Block

05/29/2008 1:55 PM

O. K. fine!

Why would anyone be interested in using lightweight or air-entrained concrete for ballast? He could use 100 kN of feathers for that matter.

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#5

Re: Concrete Block

05/31/2008 6:27 AM

Thanks everybody

As I am an electrical engineer I don't have any idea of civil works. Now I want to know the ratio of material i.e. (Sand:Gravel:Cement:water) to be used to get the density of 2500Kg/m3.

With thanks and regards

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#6

Re: Concrete Block

06/02/2008 4:53 AM

If you are adding extra ballast, this is presumably to stop overturning.

If you are adding 10kN over an area of 0.5m2 then this equates to an additional static bearing pressure of 20kN/m2.

If the wind (again an assumption) is the reason for the ballast, then the maximum addtional bearing pressure may be twice this: 40kN/m2.

Is the ground on which you are building able to support this additional bearing pressure without giving way?

Although several assumtions have been made here which may not necessarily be correct, it highlights a secondary problem which you may not be aware of.

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#7

Re: Concrete Block

06/02/2008 6:47 AM

Thankyou omw7

Basically the towers are installed for a passenger ropeway project. In addition to main hauling rope the towers are supporting 24 pair electrical cable with 16mm2 steel rope. We are going to replace this cable with 32 pair electrical cable with 18mm2 steel rope. At some towers the cable is passing below the tower yoke exerting an upward force on said towers. Some of the towers are tilted at some angle. As per the manufacturer recomendations we should add additional weight to the towers mentioned above. The weight for each tower is also recomended by manufacturer.

Now we have already started concreting with Sand:cement:aggregate=1:1:2 to obtain a density of 2500kg/m3.

Thanks again to all.

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#8
In reply to #7

Re: Concrete Block

06/02/2008 8:51 PM

Forget it! You will not reach a density of 2500 kg/m3. You might reach 2300 kg/m3 if you use normal sand and gravel. To reach 2500 kg/m3, you would need extremely heavy aggregate.

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