The overall depth if beam d from equation:
d = k(mt)^1/2 k-coefficient,
The value ranges in between 30-45 adopt average value, this is seventh step used in designing I section.

Consider a beam which is lying over ground provided with a tendon and is free from all external loads such that beam remains unaffected by any external bending moments, tension force and compression force act at same level when no external bending moments are acting over beam and tendon line (p line) or line in which compressive force is acting is known as pressure line and it is also known as P line or C line.

Or modes of failure like transverse shear failure and web crippling are caused due to improper design of member in shear and by providing thin webs in section, in case of pretensioned members, failure of bond between steel and surrounding concrete is likely due to inadequate transmission lengths at ends of members, in post tensioned members anchorage failures may take place if end block is not properly designed to resist transverse tensile forces.

Knowledge of stress-strain characteristics of steel that is used as prestressing tendons is necessary for flexural strength computations by strain compatibility method and a typical short- term design stress-strain curve for concrete recommended in British & Indian standard codes.

The sudden failure of a prestressed member without any warning is generally due to fracture of steel in tension zone, this type of failure is imminent when percentage of steel provided in section is low that when concrete in concrete in tension zone cracks, steel is not in a position to bear up additional tensile stress transferred to it by cracked concrete.

In a concrete member, trapezoidal profile is adopted when beam is subjected to two concentrated loads and parabolic profile is used when it is subjected to UDL, curve and sharp angles of cable develop uniformly distributed and concentrated loads respectively and straight portion of cable does not produce any reactions at end.

The area of tendons `At` is given as At = F/Safe tensile stress in steel by considering this area, provide suitable diameter of wires & determine required number of wires, find number of cables required and in each cable provide 8 to 12 wires spacing for cables should be 120mm, after adopting final dimensions check beam for safety.

These failures are mainly caused due to excessive principle stresses developed in members when y are subjected to transverse loading, prestressed concrete members subjected to transverse loads may fail in shear before ir full flexural strength is attained, if y are not adequately designed for shear, web shear cracks may develop if principal stresses are excessive and if thin webs are used, failure may occur due to web crushing.

In pretension & post tensioned members, value of tensile stress f_p and depth of neutral axis x_u is obtained based on effective reinforcement ratio (Apf/bdf_era) and effective bond (or) un bond between concrete & tendon and se values are given in tables of IS: 1343 code.

The stress distribution in compression zone of concrete can be defined by means of coefficients applied to characteristic compressive strength and average compressive stress and position can be assumed.