The concept of load balancing is useful in selecting a tendon profile and y provide suitable force system in concrete member, consider a prestressed concrete beam which is provided with a tendon at an eccentricity and is subjected to a hogging moment such that beam deflects, slope gets modified as beam is subjected to a downward external load, if beam is subjected to a UDL of W per unit run for complete span, n net slope at each end can be calculated as:
? = Wl³/24E_cI ? P_el/2E_cI.

Bent tendons are used in prestressed concrete beams as y tends to provide an upward pressure in beam and hence reduces effect of external loading to a great extent, consider a prestressed concrete beam AB of length l it is subjected to a point load W at centre and a prestressing force of P at ends, tendon is bent at an angle of ? at ends, neglecting frictional losses, tendon will develop an upward force of magnitude 2Psin? at bent at centre of span, upward force reduces effect of externally applied force in beam considering equilibrium in vertical direction, net downward force F = W-2psin?.

The flexural compressive stress in compressive zone closely follows stress strain curve of concrete and properties of concrete stress block can be expressed in terms of characteristic ratios of k₁ & k₂.

If neutral axis of section lies within flange, n moment of resistance of section is given by equation, M_u = f_p a_p (0.42X_u), M_u = ultimate moment of resistance, f_p= tensile stress developed in tendon at failure, a_p = area of prestressing, d= depth, X_u = depth of neutral axis.

The method by which flexural strength of prestressed concrete is estimated based on compatibility of strains and equilibrium of forces acting on section at stage of failure is known as strain compatibility method.

If beam is effected by a moment M, in pressure line n C line moves over P line at a distance x and distance is known as lever arm,
x = M/P = external moment/p, x = shift of C line from P line.

Following are step by step procedure adopted for designing prestressed beam of I section stress f_t, permissible stress of concrete at transferred f_r, f_c, allowable tensile stress f_t, permissible tensile stress in steel, loss of prestress b/w 15 to 20%, moment due to super imposed load M_L, total bending Mt over all depth d, final prestressing force f, area required A, thickness of flange & web in b/w 120mm to 150mm, width of flange b_f, area of tendons At, no of cables required after final dimensions check beam for safety.

In order to prevent this failure a minimum steel reinforcement is provided in cross section of beam IS: 1343 recommended a minimum reinforcement of 0.15% ? 0.2% of cross sectional area in pretensioned units of small sections when a high yield strength deformed reinforcement is used, minimum steel percentage is reduced to 0.15 percent.

The major steps to be followed in strain compatibility method are summarized below compute effective strain, assume a trail value for neutral axis, using stress-strain curve for steel compute total compression L_u & tension T_u, if compressive and tensile forces are equal, evaluate ultimate moment M_u.

In this section large amount of steel is provided which resists stresses developed at failure to reach tensile strength of steel and amount of steel provided in this section should not be greater than steel required for balancing section.