What is the primary purpose of prestressing in concrete members?

• To increase the weight of the concrete

• To maintain favorable stress conditions under load

• To reduce the cost of materials

• To enhance the aesthetic appearance

What is the maximum stress at the top of a member subjected to axial prestress force?

• P/A - M/z_t

• P/A + M/z_b

• P/A - M/z_b

• P/A + M/z_t

In the context of prestressed concrete, what does 'eccentricity' refer to?

• The angle of inclination of the beam

• The total length of the beam

• The distance from the neutral axis to the point of application of force

• The distance from the centroid to the edge of the beam

What is the notation for compressive stresses in the prestressing steel?

• P/A

• -ve

• M/z

• +ve

What is the minimum prestressed force required to avoid tension in the bottom fibre?

• P_min = M_max + A * z_b

• P_min = M_max * z_b / A

• P_min = M_max / A * z_b

• P_min = M_max * A / z_b

What is the area of a rectangular beam with dimensions 250 mm x 300 mm?

• 75,000 mm²

• 100,000 mm²

• 60,000 mm²

• 90,000 mm²

What is the self-weight of a beam with a cross-section of 0.15 m x 0.3 m and a density of 24 kN/m³?

• 0.36 kN/m

• 1.44 kN/m

• 0.72 kN/m

• 1.08 kN/m

What is the formula for calculating the maximum stress at the bottom of a member under maximum moment?

• P/A + M_min / z_b

• P/A - M_min / z_b

• P/A + M_max / z_b

• P/A - M_max / z_b

In a simply supported prestressed beam, what is the effect of zero eccentricity?

• Increases the bending moment

• Maintains uniform stress distribution

• Increases the tensile strength

• Reduces the maximum stress

What is the section modulus formula for a rectangular beam?

• b²h/6

• bh²/6

• b²h/12

• bh/2