 # 8D.D.2.1 Axial Stress

## Tensile Stress

The allowable tensile stress, as calculated in STAAD.Pro as per IS:802 is described below.

The estimated tensile stresses on the net effective sectional area in various members, multiplied by the appropriate factor of safety shall not exceed minimum guaranteed yield stress of the material.

Thus, the permissible stress in axial tension, σat in MPa on the net effective area of the sections shall not exceed

σat = Fy

where
 Fy = minimum yield stress of steel in Mpa

## Compressive Stress

The estimated compressive stresses in various members multiplied by the appropriate factor of safety shall not exceed the value given by the formulae described below.

1. Condition: when (b/t) ≤ [ (b/t)lim = 210/√Fy]:

1. When KL/r ≤ Cc, the allowable compressive stress is (in N/mm2)

Fa = Fy{1 - 0.5[(KL/r)/Cc]2}

2. When KL/r > Cc, the allowable compressive stress is (in N/mm2)

Fa = π2E/(KL/r)2

2. Condition: when (b/t)lim < (b/t) ≤ 378/√Fy:

The equations in condition 1 shall be used, substituting for Fy the value Fcr given by:

Fcr = Fy[1.677 - 0.677·(b/t)/(b/t)lim]

3. Condition: when (b/t) > 378/√Fy

The equations in condition 1 shall be used, substituting for Fy the value Fcr given by:

Fcr = 65,550/(b/t)

where
 Fa = allowable unit stress in compression, Mpa Fy = minimum guaranteed yield stress of the material, Mpa K = restraint factor L = unbraced length of the compression member, cm R = appropriate radius of gyration, cm E = modulus of elasticity, N/mm2 KL/r = largest effective slenderness ratio of any unbraced segment of the member b = distance from edge of the fillet to the extreme fiber, mm t = thickness of flange, mm
Note: The maximum permissible value of b/t for any type of steel shall not exceed 25.