The failure of prestressed concrete member without additional un tensioned reinforcement, compared to plain concrete, is less severe.

Prestressed concrete is a type of concrete that is subjected to compressive stresses before it is put into service. This is achieved by applying internal or external forces to the concrete, called prestressing, which counteract the tensile stresses that the member will experience during its service life. This technique improves the overall performance and durability of the concrete member.

On the other hand, plain concrete does not have any additional reinforcement to counteract the tensile stresses. It relies solely on the compressive strength of the concrete to resist these stresses. As a result, plain concrete is more prone to cracking and failure when subjected to excessive tensile forces.

Now, let's discuss why the failure of prestressed concrete without additional un tensioned reinforcement is less severe compared to plain concrete:

1. Reduction in tensile stresses: The main purpose of prestressing is to reduce or eliminate tensile stresses in the concrete member. By applying compressive forces, the concrete is effectively "pre-compressed," which helps to counteract the tensile forces that would otherwise cause cracking and failure in plain concrete.

2. Increased load-carrying capacity: Prestressed concrete can carry higher loads compared to plain concrete. The prestressing forces create a state of initial compression in the member, which increases its load-carrying capacity and allows it to withstand larger external loads without failure.

3. Crack control: The prestressing forces in the concrete help to control and limit the width and propagation of cracks. This is particularly important in structures where crack control is essential for serviceability and durability.

4. Improved structural behavior: Prestressed concrete members exhibit improved structural behavior due to the redistribution of stresses. The prestressing forces help to create a more uniform stress distribution, reducing localized stress concentrations and improving the overall performance of the member.

In conclusion, the failure of prestressed concrete without additional un tensioned reinforcement is less severe compared to plain concrete. The application of prestressing forces helps to reduce tensile stresses, increase load-carrying capacity, control cracks, and improve the structural behavior of the member. These factors contribute to the enhanced performance and durability of prestressed concrete.