पूर्व-प्रबलन (pre-stressing) प्रक्रिया पूरी होने के बाद, प्रतिबल में कमी (loss in stress) निम्नलिखित में से किसके कारण होती है?

A change in the external moments in the elastic range of a prestressed concrete beam results in:

A prestressed beam carrying an external load W has a bent tendon with inclination angle θ and prestress force P. What is the net downward load acting at the center of the beam?