A simply supported rectangular beam is uniformly loaded and is pr
A. Straight, above centroidal axis
B. Straight, below centroidal axis
C. Parabolic, with convexity upward
D. Parabolic, with convexity downward
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Right Answer is: D
SOLUTION
As per the load balancing concept in pre-stresses concrete beam, the profile of tendon must be the same as that of the bending moment diagram (BMD) of beam due to external load only.
For ex, if a simply supported beam is subjected to a concentrated load at mid span, then BMD of that beam will be triangular with maximum BM at mid span and hence, shape of cable will be ‘V’ shape or triangular with maximum eccentricity at mid span (See figure I).
∴ If loading on simply supported pre-stressed concrete beam is uniformly distributed, then BMD of this beam will be parabolic with zero moment at supports and maximum bending moment at mid span, hence; the profile of cable will be parabola with zero eccentricity at ends and maximum eccentricity at mid span (See figure II).
∴ From the load balancing concept, the shape of tendon should correspond to the shape of bending moment diagram is represented as,
