Thanks for your reply sir as you said tresca theory stands for both force based load & strain based load. In that case whether these loads can be evaluated seperately. I mean to say that since the direction of stresses i.e sustained & expansion both is same & also the conservative equation tells that both are additive (1.25sc +1.25 sh-sl). So as a total i have to apply tresca criterion. Means the above equation can be directly related to tresca if yes then as per tresca the material will fail when max shear stress is half the yield only.