Prestressed Concrete Construction: Types and Uses Quiz and Flashcards

10 Questions

______ concrete is a class apart from other types of conventional building materials

Prestressed

After studying this unit, one should be able to understand the concept of ______

prestressing

______ events led to the development of prestressed concrete as an alternate construction material

historical

Civil engineering structures such as buildings, bridges, dams, towers, etc. are generally subjected to various types of ______

loads

Prestressed concrete results in the augmentation of human capacity in the arena of design and construction of various types of articulate, aesthetic, safe, and ______ structures

economical

What is the main objective of prestressing in concrete structures?

To counteract the tensile stresses that may develop under loads.

Differentiate between pre-tensioned and post-tensioned concrete beams.

Pre-tensioned concrete beams have tendons tensioned before casting, while post-tensioned concrete beams have tendons tensioned after casting.

Explain the significance of high strength steel in prestressed concrete beams.

High strength steel allows for higher prestressing forces, leading to more efficient designs.

How does prestressed concrete differ from reinforced concrete in terms of internal forces?

Prestressed concrete has compressive forces induced by tendons, while reinforced concrete relies on steel reinforcement to resist tensile forces.

Discuss the advantages of using prestressed concrete beams over conventional reinforced concrete beams.

Prestressed concrete beams can span longer distances with reduced structural depth, leading to cost savings and greater design flexibility.

Study Notes

Classification of Prestressed Concrete

Prestressed concrete can be classified into two types: Pre-tensioned concrete and Post-tensioned concrete.
The classification is based on when the prestressing tendons are stressed and how the prestressing force is transferred into the concrete.

Pre-tensioned Concrete

In Pre-tensioned concrete, tendons are kept stretched with suitable mechanisms and concrete is cast into the forms through which stretched tendons pass.
The prestressing force is not transferred into the concrete at the start, as tendons are kept in a stretched form using jacks and abutments from both sides.
When concrete gains sufficient strength, stretched tendons are cut from outside, and the stretched length of tendons inside the concrete remains in a stretched state due to its bond with concrete.
The prestressing force of tendons (tensile nature) is passed into concrete in the form of a compressive force, reducing or eliminating tensile stresses produced due to external loads.

Steps in Pre-tensioning

Concrete mould is placed on a prestressing bed.
Tendons are stretched and passed through the concrete mould.
Concrete is filled inside the concrete mould.
Stretched tendons are cut from outside after concrete gains sufficient strength.

Post-tensioned Concrete

In Post-tensioned concrete, tendons are placed inside concrete and stretched after concrete has attained sufficient strength.
Ducts are made inside concrete with the help of tubes or pipes, which are provided in the forms at the time of casting of concrete.
After sufficient hardening of concrete, tendons are placed in these ducts, stretched from both ends from outside with the help of jacks or other suitable devices, and anchored at the ends of the concrete member.

Types of Prestressed Concrete Construction