## Prestressing force and Ecentricity

**Prestressing Force & Eccentricity**

Once the actual Z_{t} and Z_{b} have been determined, the next step is to determine what combination of prestress force, P and eccentricity, e, to use at that section. Taking each stress limit in turn:

**Tensile Stress at Transfer**

This is a linear equation in P_{1 } and e. Therefore a plot of these two quantities will give a region that is acceptable and a region that is not acceptable, according to the inequality.

**Compressive Stress at Transfer**

Another linear equation which gives the feasible region

**Compressive Stress in Service**

This equation can again be graphed to show the feasible region. However, this line can have a positive or negative slope. When the slope is negative, P_{1} must be under the line; when the slope is positive, P_{1} must be over the line. A simple way to remember this is that the origin is always not feasible.

**Tensile Stress in Service**