What Is the Maximum Load a Concrete-Filled Cast Iron Pipe Can Support?

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The maximum load a concrete-filled cast iron pipe can support is determined through calculations involving the compressive stress of the concrete, which is limited to 5 kN/m². The outside diameter of the pipe is 200 mm, and the inside diameter is 150 mm. The calculations reveal that the maximum permissible load W is approximately 79 tons, but discrepancies arose due to incorrect area calculations and unit conversions. Proper attention to units and area dimensions is crucial for accurate results in structural calculations.

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  • Understanding of compressive stress and its units (kN/m²)
  • Familiarity with area calculations for circular sections
  • Knowledge of material properties, specifically Young's modulus for concrete and cast iron
  • Proficiency in unit conversions, particularly between mm² and m²
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Civil engineers, structural designers, and students studying material mechanics will benefit from this discussion, particularly those focused on load-bearing calculations and material properties in construction.

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A cast iron pipe is filled with concrete and used as a column to support a load W.If the outside diameter of the pipe is 200mm and the inside diameter is 150mm, what is the maximum permissible value for W if the compressive stress in the concrete is limited to 5 KN/m2.
Take E for concrete as one tenth that of cast iron.

σc=5KN/m2
Area of concrete is 3.14*1502/4=17671*10-3mm2
Area of pipe is 3.14*2002/4=31415-17671=13744*10-3mm2

σp/Ep=σc/Ec

σp=σc*.1N E of concrete one tenth that of cast iron=.1

σp=σc*.1N

σp=5*106N*.1N

σp=.5*106N

F=Fc+Fp

F=σp*Ap+σc*Ac

F=(.5*106N*17771*10-3mm)+(5*106N*13744*10-3MM2)

F=8835.5*103N+68720*103N

F=77555.5N*106

F=77555.5N/9.81=7905kg=7.9tons

The answer in my notes is 79tons, where have I gone wrong with my decimal point
 
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It's really hard to follow your calculations because you don't indicate the units of your results. You must get into the habit of writing the units along with the magnitudes of your results.
 
SteamKing said:
It's really hard to follow your calculations because you don't indicate the units of your results. You must get into the habit of writing the units along with the magnitudes of your results.

The units of my result are in tons which is what is asked for in the question and are indicated Do you see something else I m missing?
 
Yeah, but what about all the calculations it took to get you to the final result? Units are important there, too.
 
SteamKing said:
Yeah, but what about all the calculations it took to get you to the final result? Units are important there, too.

Just so I understand properly would you expect units in this part of the solution

F=(.5*106*17771*10-3)+(5*106*13744*10-3)
 
Yup. And BTW, your area calculations are wrong. 1 m^2 = 10^6 mm^2
 
Any help would be appreciated
 
anthonyk2013 said:
A cast iron pipe is filled with concrete and used as a column to support a load W.If the outside diameter of the pipe is 200mm and the inside diameter is 150mm, what is the maximum permissible value for W if the compressive stress in the concrete is limited to 5 KN/m2.
Take E for concrete as one tenth that of cast iron.

σc=5KN/m2
Area of concrete is 3.14*1502/4=17671*10-3mm2
Area of pipe is 3.14*2002/4=31415-17671=13744*10-3mm2

Incorrect area calculations. If your dimensions are in mm, then area will be in mm2. 1 m2 = 106 mm2

σp/Ep=σc/Ec

σp=σc*.1N E of concrete one tenth that of cast iron=.1

σp=σc*.1N

σp=5*106N*.1N

σp=.5*106N

The units of stress are pascals, not Newtons.

F=Fc+Fp

F=σp*Ap+σc*Ac

F=(.5*106N*17771*10-3mm)+(5*106N*13744*10-3MM2)

Incorrect areas used here.

F=8835.5*103N+68720*103N

F=77555.5N*106

F=77555.5N/9.81=7905kg=7.9tons

The answer in my notes is 79tons, where have I gone wrong with my decimal point
 
σc=5KN/m2
Area of concrete is 3.14*1502/4=17671mm2
Area of pipe is 3.14*2002/4=31415-17671=13744mm2

σp/Ep=σc/Ec

σp=σc*.1pa E of concrete one tenth that of cast iron=.1

σp=σc*.1pa

σp=5*106pa*.1pa

σp=.5*106pa

F=Fc+Fp

F=σp*Ap+σc*Ac

F=(.5*106pa*13744mm2)+(5*106*17671mm2)

F=(6872*106)+(88355*106)

F=95227*1012*9.81=934176.87kg/1000=934tons

Seem to have gone a long way from the correct answer of 79tons
 
  • #10
You've got to remember what the definition of a pascal is. 1 Pa = 1 N / m^2

Check your force calculations. This is why units are important.
 

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