Civil Engineering - RCC Structures Design - Discussion

Since lever arm is the distance between the neutral axis and the effective depth.

Lever arm is the distance between force of compression and force of tension in a beam, represented by z, and z=d-0.42n (as per Limit State Method) , where n is depth of neutral axis and d is effective depth of beam.

The above answer is as per Working stress method. They have not mentioned.

The answer should be (d-0.42n) which they did not mention in options? Please give explanation.

@Argha

Because the answer is in the working stress method that's why d-n/3?

For singly reinforced beam the lever arm length is considered from the bottom steel to the 1/3 of neutral axis depth from the top of the beam.

For example: If we have beam section 50cm * 25cm.
let us consider the neural axis is at 30cm ( count from bottom to top) and Cover is 2cm,

So
From the center of the bottom steel (16mm bars).
0.8 (half of the steel bar because we are taking measurements from centre of the bar+26.4 (from bar to the neural axis)+ 1/3 of depth from neutral axis to top of the beam, ( 20/3 = 6.67cm).

Liver arm distance = 0.8 + 26.4 + 6.67 = 33.87cm.

Lever arm = d - 0.42n.