Reinforcement in pre-stressed concrete serves the purpose of imparting initial compressive stress in the concrete. This is achieved through a process called pre-stressing, which involves applying external forces or loads to the concrete before it undergoes any service loads. The pre-stressing process helps to improve the overall performance and strength of the concrete structure.

Below, I will explain in detail the purpose of reinforcement in pre-stressed concrete:

**1. Providing adequate bond stress:**
- The reinforcement in pre-stressed concrete is typically in the form of high-strength steel strands or bars, known as tendons.
- These tendons are placed in the concrete in a way that they can develop bond stress with the surrounding concrete.
- The bond stress ensures that the tendons are effectively anchored in the concrete and can transfer the pre-stressing forces to the structure.
- By providing adequate bond stress, the reinforcement helps to enhance the overall structural integrity and load-carrying capacity of the pre-stressed concrete.

**2. Resisting tensile stresses:**
- While pre-stressed concrete is primarily subjected to compressive stresses, there can still be tensile stresses present due to external loads or other factors.
- The reinforcement in pre-stressed concrete helps to resist these tensile stresses.
- By resisting tensile stresses, the reinforcement prevents the occurrence of cracks and enhances the durability of the concrete structure.

**3. Imparting initial compressive stress in concrete:**
- The main purpose of reinforcement in pre-stressed concrete is to impart initial compressive stress in the concrete.
- This is achieved by applying external forces or loads to the tendons, which results in the tendons being stretched or pre-stressed.
- As the tendons are anchored in the concrete, the pre-stressing forces are transferred to the concrete, resulting in the development of compressive stress.
- The initial compressive stress helps to counteract the tensile stresses that will be induced by the service loads on the structure.
- By imparting initial compressive stress, the reinforcement helps to increase the load-carrying capacity and overall strength of the pre-stressed concrete.

In conclusion, the purpose of reinforcement in pre-stressed concrete is to provide adequate bond stress, resist tensile stresses, and impart initial compressive stress in the concrete. These functions of reinforcement contribute to the enhanced structural performance and durability of pre-stressed concrete structures.