In case of composite sections percentage of tensioned reinforcement is less than that in most simple beams so that section is invariably under reinforced and compression zone generally consists entirely of insitu concrete of lower compressive strength, and value of cube strength of concrete to be used in flexural strength equations will obviously be that of insitu cast concrete.

The known sectional properties of precast prestressed beam is calculated in order to support required design service load, calculated overall depth of composite slab by assuming trial depth and add trial depth to depth of standard prestressed beam.

Section modulus Z = 667×10³, moment due to slab weight is 1200nm
Stresses due to slab weight in precast sections = (1200000/667×10³) = 1.8n/mm².

In general, appropriate technology must necessarily involve prevailing local infrastructure like raw materials, man power, plant and machinery, power and financial resources and an excellent example of appropriate technology can be found in low cost suspension bridges built by Girish bharadwaj in south India.

The required top and bottom fibers of precast prestressed beams are calculated in 7 step y are expressed as:
P_t > or less than (P_tw/? + M/?Z_b + Ml/?Z_b?)
P_b > or less than (P_tw ? M_min/Z_t) where P_t = characteristic tensile strength of concrete (n/mm²), P_b = stress at bottom fiber (n/mm²).

The permissible values of horizontal shear stress for different types of contact surfaces is specified as: 0.6n/mm² when ties are not provided and contact surface of precast element is free of laitance and intentionally roughened to an amplitude of 5mm and 25n/mm² when minimum vertical ties are provided and contact surface is roughened to an amplitude of 5mm.

The dead load stress developed in precast prestressed units can be minimized by Propping m while casting concrete in situ this method of construction is termed as propped construction and if precast units are not propped while placing insitu concrete, stresses are developed in unit due to self weight of member and dead weight of insitu concrete and this method of construction is referred as unpropped construction.

The phenomenon of differential shrinkage between concrete cast insitu and prestressed units also contributes to monolithic action of composite members and composite construction was first tried for a way bridge in 1940 and detailed calculations were prestressed by morch in 1943.

In case of conventional method, re will be a steel beam and slab construction in which components carries ir entire load transmitted by slab and re will be no composite action between members when compared than conventional method of construction precast unit?s method facilitates a greater structural efficiency.

When modulus of elasticity of precast and insitu cast concrete are different flexural rigidity is worked out by computing equivalent second moment of area of composite sections using modular ratio and deflections computed under service loads should not exceed limiting values prescribed in codes.