According to Modified Compressiong Field Theory , the shear capacity of RC. upon the cracked angle (theta) . So my question is how can I know the correct cracked angle?
It is usual to accept teta be 45 deg for RC and 30 deg for PC.
You have the sheet of free download ShearEHE.mcd at the Collaboratory for Mathcad 2000 pro where calculation of teta is detailed, and many other sheets delivering the shear strength of RC and PC beams by US codes.
Does it mean Prestressed Concrete Structures text book by Collins & Mitchell ? If yes , there is one PC beam example in chapter 7 it shown that the cracked angle vary along the beam. From text book it doesn't explain so much about how to obtain the angle , it just only refer to table 7.3 that is fix the pairs of angle, v/fc' and strain-x (epsilon-x in the text book) already. Please give me a suggestion on how can I choose the angle if I want to vary angle along the beam. Thank you very much.