- #1

RohansK

- 37

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The load taken by steel is much greater than what it should have taken as per its area (As) in comparison to the area of concrete (Ac) where total area (A) is : A = As +Ac.

And if load applied is P so Ps/Pc should have been equal to As/Ac if we follow the general rule of load distribution as P/A.

Anyways further on , the equations used are :

σs/σc = Es/Ec , where σs and σc are the stress induced in steel and concrete respectively and the Es and Ec are the Modulus of Elasticity of Steel and concrete respectively.

This means that the stress induced in steel is much larger than the stress in concrete. It means that the load taken by steel is still much greater than that taken by concrete ( in comparison to its percentage area relative to concrete area) as the value of Es is much greater than Ec and also as the area contibuted by steel rods in the section as a whole is much smaller.

And the reason expalined for this is that : Steel having greater Modulus Of Elasticity ( so greater strength) takes a larger ratio of the applied load as compared to concrete.

Bu then if we have a picture of load distribution over a surface as say the section being divided in virtual small square units each of a unit area say 1 cm

^{2}then the load acting on each square would be

**Total Load (P)/Total Area (A)**, and this would be the load per unit area ie the stress σ.

Then as per the theory of reinforced sections as mentioned with the

σs/σc = Es/Ec equation, it suggests that the load is not distributed accrding to the above mentioned criteria ( of uniform distribution per unit area), stating that steel being stronger tkes up greater load as a virtue of its Material Strength.

So, I could never clearly understand

**HOW THIS HAPPENS?**

The Steel does not have a mind of its own neither does the load so as to think and know that steel is stronger, so it( the load) has to enter in larger proortions in steel and less in concrete or neiher the steel has the ability to think and attract larger load portion onto itself bein stronger.

You can compare this with an analogy of the load being like unifromly distributed Iron grits over the cross section of the reinforced beam, and the steel rods being like magnets which will automatically attract larger amount of Iron grits to itself on account of its larger magnetic strength as compared to concrete ( which is not magnetic at all) thereby having a larger concentration of grits on to steel just like larger stress induced in steel ( this analogy is to point out the question - doubt I have)

So

**HOW DOES STEEL TAKE UP GREATER LOAD just almost INTUITIVELY ( such intution is not possible for non living objects!) So, HOW DOES THIS HAPPEN - WHATS THE PHYSICS BEHIND THIS UNPROPORTIONAL LOAD DISTRIBUTION.**

Please explain in detail as it will equally appply to Flitched Beams also.