You do not model "caps" or "flat closures" in CAESAR II. This is ok since the pressure is assumed not to cause any system deflection. The effects of pressure are considered in the stress equations in the form of the longitudinal pressure stress component.

If you find a situation where you feel the "end cap effect" is required, compute the "P*A" value and apply it as a concentrated force at the appropriate node. After doing this, make sure you adjust your load cases to include the "F1" component where necessary.