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RCC Structures Design - Engineering

Q1:

After prestressing process is completed, a loss of stress is due to

A shrinkage of concrete

B elastic shortening of concrete

C creep of concrete

D creep of steel

E all the above.

ANS:E - all the above.

After the prestressing process is completed, various factors contribute to the loss of stress in prestressed concrete members. These factors include:

  1. Shrinkage of Concrete: Concrete undergoes shrinkage as it cures and loses moisture. This shrinkage results in a reduction in the stress applied by the prestressing force. Shrinkage can occur over time and may lead to a gradual loss of stress in the prestressed member.
  2. Elastic Shortening of Concrete: When prestressing tendons are tensioned, the concrete experiences elastic deformation, causing it to shorten slightly. This elastic shortening results in an initial loss of stress in the concrete member. While this loss is typically small and temporary, it contributes to the overall loss of prestress over time.
  3. Creep of Concrete: Creep is the gradual deformation of concrete under sustained loading over time. As concrete creeps, it experiences additional strain, which leads to a corresponding loss of stress in the prestressed member. Creep is a time-dependent phenomenon and can continue to affect the prestressed member for an extended period after construction.
  4. Creep of Steel: Similarly, the steel tendons used for prestressing also experience creep, albeit to a lesser extent than concrete. Creep in the steel tendons results in a relaxation of the prestressing force over time, leading to a loss of stress in the member. While the creep of steel is typically less significant than that of concrete, it still contributes to the overall loss of prestress in the member.
Therefore, the loss of stress in prestressed concrete members is influenced by multiple factors, including shrinkage of concrete, elastic shortening of concrete, creep of concrete, and creep of steel. These factors act over time and can result in a gradual reduction in the prestressing force applied to the member. Proper consideration of these factors is essential during the design and analysis of prestressed concrete structures to ensure their long-term performance and durability.