It is related to the guaranteed minimum yield point of steel with an appropriate factor of safety. Most of the codes assume a factor of safety of 1.67.
The direct stress in axial tension or the effective net area should not exceed 
given by the equation,
Where, 
= minimum yield stress of steel in 
(MPa).
Indian Standard IS: 226
It stipulates the following permissible stress in axial tension for steel,
| (i) | Plates, angles, tees, I-beams, channels and flats | |
| upto and including 20mm thickness | 150 MPa | |
| above 20mm thickness to 40mm | 144 MPa | |
| Over 40 mm thickness | 138 MPa | |
| (ii) | Bars (round, square and hexagonal) | |
| Upto and including 20mm diameter | 150 MPa | |
| Over 20mm diameter | 144 MPa |
Permissible Combined Stress
When tension members are subjected to both axial loading and bending moment, then the permissible stress is governed by the formula,
Where, 
= axial tensile stress,
= permissible axial stress in tension,
= calculated bending stress in tension in the extreme fibre, and
= permissible bending stress in tension.
