how do you calculate the area of angular plate say 50x50x4 x 1m long ?

Am i right in thinking that consider each surface as rectangle and add the areas of each surface using length*breadth ? i know he weight of this section from handbook i want to calculate how much stress this can withstand with breaking ..whats the procedure ? will the wt of section by its area (load/area) give me the stress it can handle or there is another formula ?

In concern to above question, this is further question, i have got yield strength of mild steel to be 250 to 550 Mpa now how do i use this information to fix my problem ? i got weight of each angle n flat and also surface area. how do i calculate cross sectional area with help of surface area is there any formula or relation between the two.?

I recall you mentioning you are a mechanical engineer. You should recall the formula Stress = M * c / I

If this formula is not familiar to you, I suspect your design challenge is beyond your current set of skills. In which case, you should defer to an experienced engineer and have these fundamentals explained thoroughly.

You have the correct approach if you are looking for surface area, however, it sounds like you are probably looking for the cross-sectional area. This would be the area of the ‘L’ shape you see by looking at the end of the angle. The area of that shape would be 50×4 (horizontal rectangle) + 4×46 (vertical rectangle) = 384.

The allowable stress is a property of the material rather than weight or geometry. Stress as you have noted is a unit of force over an area. From a materials handbook, you should be able to find the yield stress for the material. This is the amount of force/area you can apply before the material deflects in a plastic mode. Up until that stress, the material will spring back to its original shape when the load is removed. Beyond that stress, the material will be permanently deformed. The ultimate stress is when the material will fail in a catastrophic mode (ie. break). These are both properties of the material and do not have anything to do with your geometry.

In your particular design, there are various calculations you will need to do to determine the amount of stress you are exerting on the angle. Then you will have to compare this stress to the material’s properties to deterimine if you have exceeded the yield/ultimate stress of the material.

The Euler-Bernoulli beam theory [1] goes into the details of calculating the stresses in a beam. That website I shared earlier [2] provides some calculators to help out.