Question

Please type your answer and make it too short answer just type it.

1- When do I need to check for deflections in a reinforced concrete member?

2- What is the difference between short term and long term deflections?

3- How does ACI estimate the long term deflections in a member?

Answer 1

1) Need of checking

The deflection of a flexure member is calculated to satisfy a limit state of serviceability. The deflection is calculated for the service loads. Since the prestressed concrete member is smaller in depth that an equivalent reinforced concrete member the deflection of of prestressed concrete member tends to be larger. If the deflections are more then the aesthetic view is not good and also occurs 90% failure of the plastering. So need to check the deflection to over come these problems.

2) difference

Short term: these deflection due to prestressing force and self weight and creep and shrinkage are not consider.

Long term: due to prestressing force and gravity loads in which we are consider the creep and shrinkage.

3) Estimation of long-term deflection as per ACI

According to ACI the deflection is estimated based on load balancing method under Analysis for flexure. Estimations of long term deflection is difficult because the prestressing force and creep and shrinkage includes. Calculation of deflection can easily done by increment time step method.