## Prestressed Concrete Design Examples

Beams

**Example 1 - Calculating stresses for a simply supported beam subjected to dead loading, live loading, and compression due to pretension**

For the simply supported beam shown below, find the maximum stresses at midspan due to the beam self weight and the following loading and prestressing scenarios:

Uniform live load = 800 lbs/ft

Uniform live load = 800 lbs/ft , Longitudinal compressive force due to prestressing = 259.2 kips Eccentricity of compressive force from centroid of cross-section = 0 inches

Uniform live load = 2000 lbs/ft, Longitudinal compressive force due to prestressing = 259.2 kips Eccentricity of compressive force from centroid of cross-section = 4 inches

Uniform live load = 2700 lbs/ft Longitudinal compressive force due to prestressing = 259.2 kips Eccentricity of compressive force from centroid of cross-section = 6 inches

Normal weight concrete

Compressive strength of concrete = 4500 psi

Allowable compressive strength of concrete = 2050 psi

**Example 2 - Calculating the design flexural strength of a prestressed concrete beam**

Calculate the design flexural strength of the prestressed bonded beam shown below given the following parameters:

Specified Yield Strength of Prestressing Steel, fpy = 240 ksi

Specified Tensile Strength of Prestressing Steel, fpu = 275 ksi

Compressive Design Strength of Concrete, f'c = 5 ksi

**Example 3 - Calculating the deflection of a pretensioned concrete beam**

For the pretensioned rectangular beam shown below, calculate the deflection at midspan immediately after the cables are cut given the following parameters:

Straight cables with initial stresses of 175 ksi and final stresses after losses of 140 ksi

Modulus of elasticity of concrete, Ec = 4000 ksi

Assume that the concrete has not cracked