PCD Flashcards
A method of prestressing where the tendons (steel cables or rods) are
stretched and anchored before the concrete is poured and cured.
Pre-tensioning
The process of applying an initial compressive force to concrete
members before they are subjected to service loads
Prestressing
A method of prestressing where the tendons are installed in ducts
within the concrete after it has been cast and cured, and then stressed to apply a
compressive force
Post-tensioning
Steel cables, rods, or bars used in prestressing concrete. They are the
components that are stretched and stressed to provide the compressive force
Tendons
The device or system used to secure the ends of the tendons in both pretensioning and post-tensioning systems.
Anchorage
Tubes or channels embedded in the concrete that contain the tendons during the
post-tensioning process. They protect the tendons and allow for the application of
prestress.
Ducts
Release of StressThe process of transferring the prestressing force from the tendons
to the concrete, often done after the concrete has reached sufficient strength
Release of Stress
The initial force applied to the tendons during the prestressing
process, which is transferred to the concrete.
Prestressing Force
The portion of the initial prestressing force that remains in the
concrete member after accounting for losses due to factors such as elastic deformation,
shrinkage, and relaxation.
Effective Prestress
The reduction in the effective prestress force over time due to
factors like creep, shrinkage, relaxation of the tendons, and other effects.
Losses of Prestress
The gradual increase in deformation under a constant load over time,
which affects the amount of prestress that is retained in the concrete.
Concrete Creep
The reduction in the volume of concrete as it dries and cures, affecting the
prestressing force.
Shrinkage
The decrease in the stress within the tendons over time due to
the gradual reduction in the tension they carry.
Relaxation of Tendons
The way in which the internal forces are spread throughout the
concrete member, influenced by the prestressing forces
Stress Distribution
A beam that has been prestressed to improve its loadcarrying capacity and reduce deflection.
Prestressed Concrete Beam
A flat, horizontal structural element that has been
prestressed, commonly used in floors and roofs.
Prestressed Concrete Slab
Devices or systems used to securely attach the ends of the tendons to the
concrete structure.
Anchorages
The adhesion between the tendons and the surrounding concrete, which allows
the transfer of stress.
Bonding
The condition where the strains in the prestressed concrete
member are consistent with the stress-strain relationship of both the concrete and the
tendons.
Strain Compatibility
A system in which the tendons are bonded to the concrete to
ensure that the prestress force is effectively transferred.
Stress-Bonded System
Description: When the tendons are stressed, the concrete immediately experiences a
reduction in prestress due to its elastic deformation.
Impact: This is more significant in post-tensioned members, where the concrete shortens under
the load of the tendons.
Elastic Shortening
➢ Description: Over time, concrete experiences deformation under sustained loads, known as
creep.
➢ Impact: Creep causes a gradual loss of prestress as the tendons elongate and the concrete
continues to deform.
Creep of Concrete
➢ Description: Concrete shrinks as it dries and hardens, leading to a reduction in the prestress
force.
➢ Impact: This loss can be significant in the early days of curing, especially in thin sections
Shrinkage of Concrete
- Description: Steel tendons experience a reduction in stress over time when they are held
at a constant strain. This phenomenon is known as relaxation. - Impact: This can lead to a decrease in the prestressing force, especially in high-strength
steel.
Relaxation of Steel Tendons
- Description: Some losses can occur at the anchorage points where the tendons are
anchored. This may involve friction and slippage. - Impact: These losses can be minimized with proper design and detailing.
Losses Due to Anchorage
Different mixes and curing conditions can affect creep and
shrinkage.
Type of Concrete
Temperature and humidity can influence drying
shrinkage and creep rates.
Environmental Conditions:
Longer durations typically result in greater losses due to creep
and relaxation.
Duration of Load
The type of steel and its properties, including yield strength
and elasticity, impact relaxation losses.
Tendon Properties
Calculated based on the modulus of elasticity of the concrete.
Elastic Shortening
