IntermediateTopic 56 of 112Civil & Structural
Prestressed concrete
Pre-compression counters tensile stresses and allows longer spans.
In depth
Steel tendons are tensioned to impose compression in concrete, offsetting tensile stresses. Pre-tensioning (precast beds) and post-tensioning (ducts and anchorages). Advantages: longer spans, smaller depth, crack control; losses from elastic shortening, creep, shrinkage, relaxation and friction.
Key points
- Prestress force and eccentricity
- Stress limits
- Bridge girders and slabs
ExamplePrecast prestressed hollow-core slabs span 10 m or more.
What is Prestressed concrete?
Pre-compression counters tensile stresses and allows longer spans.
Why is it important to understand prestressed concrete?
Prestressing puts concrete in compression before load arrives, which lets it span further with less depth and resist cracking.
What is pre-compression?
A compressive stress applied in the concrete by tendons, which offsets the tension that the loads will produce.
What is the difference between pre-tensioned and post-tensioned concrete?
Pre-tensioned tendons are stressed before the concrete is cast, while post-tensioned tendons are stressed after the concrete gains strength.
How is Prestressed concrete used in practice?
Typical applications include building a long-span bridge deck with post-tensioned tendons, designing a precast floor unit that spans a large distance and reducing deflection of a slab in a car park with prestress.
What should I learn before Prestressed concrete?
Study "Development length and detailing" first (topic 55 of 112 in Civil & Structural). It covers the groundwork this topic builds on.
What are the key points of Prestressed concrete?
Prestress force and eccentricity. Stress limits. Bridge girders and slabs.
Can you give an example of Prestressed concrete?
Precast prestressed hollow-core slabs span 10 m or more.
What comes after Prestressed concrete?
The next topic is "Steel beam and column design", which builds directly on this one.
How difficult is Prestressed concrete?
It is classed as Intermediate in Civil & Structural (topic 56 of 112). It is an intermediate topic. Work through the beginner topics in Civil & Structural first.