The correct answer is: B. Is increased by $\frac{{{\text{Pe}}}}{{\text{Z}}}$.
The stress at the extreme top edge of a rectangular beam is given by the following equation:
$$\sigma = \frac{{{\text{Pe}}}}{{\text{Z}}}$$
where:
- $\sigma$ is the stress at the extreme top edge
- $P$ is the stressed load in the tendon
- $e$ is the eccentricity of the tendon below the centroidal axis of the longitudinal axis of the beam
- $Z$ is the sectional modulus of the beam
The eccentricity of the tendon causes the stress at the extreme top edge to be increased. This is because the tendon is applying a force that is not acting through the centroid of the beam. This causes the beam to bend, and the extreme top edge is in tension. The greater the eccentricity, the greater the stress at the extreme top edge.
Option A is incorrect because it does not take into account the eccentricity of the tendon. Option C is incorrect because it does not take into account the sectional modulus of the beam. Option D is incorrect because the stress at the extreme top edge is increased, not decreased.