Multiple choice

A simply supported prestressed concrete beam is 6 m long and 300 mm wide. Its gross depth is 600 mm. It is prestressed by horizontal cable tendons at a uniform eccentricity of 100 mm. The prestressing tensile force in the cable tendons is 1000 kN. Neglect the self weight of beam.

The maximum normal compressive stress in the beam at transfer is

  1. Zero

  2. 5.55 N/mm2

  3. 11.11 N/mm2

  4. 15.68 N/mm2
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The normal stress at any section is given by (P/A) + (Pe/Z) or (P/A) - (Pe/Z). For a rectangular beam, A = b*d and Z = (b*d^2)/6. Calculating these values with P=1000 kN, e=100 mm, b=300 mm, and d=600 mm yields the maximum compressive stress.

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