Building components · Concrete & Reinforcement
Post-Tension Anchorage
Explains the anchorage as the location where a tendon's force enters the member, and why that location behaves differently from the rest of the element.
Educational reference entry. What this element has to do, and whether any particular arrangement of it is adequate, depends on the whole assembly, the loading, the exposure, local requirements, the manufacturer's instructions and qualified professional design.
Overview
What a pt anchorage is
In a post-tensioned member, tendons are tensioned after the concrete has hardened and their force is held permanently at the ends. The anchorage is that position: the place at or near the end face where the tendon is gripped and where the force it carries is handed into the concrete around it.
It matters because force that is spread along the length of the member arrives at the anchorage concentrated in a small region. That region behaves unlike the rest of the element — it is locally congested, it is where additional reinforcement is commonly provided, and it is where the tendon passes from being inside the member to being terminated at a face. It is also a position that stays live in the sense that matters: what happens at the anchorage governs whether the force in the tendon remains where the design put it.
Boundaries
How it differs from nearby elements
The distinctions that keep this entry from being a restatement of its neighbours.
- It is not the tendon. The tendon runs through the member and carries the force; the anchorage is the position at its end where that force is transferred into the concrete, and the two are commonly discussed as one thing.
- It is not a reinforcement lap. A lap transfers force between bars gradually through the concrete around them; an anchorage transfers a concentrated force at a point, and the reinforcement provided around it exists to deal with that concentration.
- It is not the arrangement found in a pre-tensioned member. In pre-tensioning the strand is stressed before casting and its force is transferred into the concrete by bond along its length, so there is no terminated anchorage inside the finished element; post-tensioning stresses after casting and leaves the force held at a discrete position, which is why one member type has anchorages to locate before cutting into it and the other does not.
Terminology
Common names and aliases
These names describe the same element. The library keeps one entry per component so that a trade term or a regional name never becomes a second, thinner page.
- tendon anchorage
- stressing anchorage
- live end anchorage
- dead end anchorage
Dependencies
What it depends on
What has to be right elsewhere for this element to do its job.
- The concrete in the region around it, since a concentrated force is being introduced into a small volume of material.
- The additional reinforcement commonly provided in that region, which is there because of the concentration rather than because of the member's general duty.
- The tendon's path as it approaches the end, because where the force enters and in what direction is part of what the anchorage region has to deal with.
- How the anchorage is protected and sealed afterwards, since it is a terminated metal component at or near an external face of the member.
Considerations
Topics that genuinely apply here
Subjects worth discussing about this element. These are discussion topics, never measured values, ratings or performance claims.
The defining feature of the position is concentration: a force distributed along the member arrives here in a small region, and that is why the region is detailed differently from the rest of the element.
An anchorage sits at a face and terminates a component that is under permanent force, so how it is protected from moisture is part of the position rather than a finishing matter.
Anchorage locations are among the few points where a post-tensioned member can be examined, which is why knowing where they are in an existing structure is valuable.
In an existing building, the record of where tendons and anchorages are is the document that governs whether anything may be cut, drilled or altered — and its absence is itself a finding.
Materials
Commonly formed from
Material families this element is commonly realised in. This states common practice only — it is not a statement that any of these materials suits this component in a particular building, which depends on the whole assembly and on qualified review.
Materials
Commonly incorporates
Materials this element commonly contains as a distinct constituent part, rather than being made of.
Assemblies
Building systems this element is met in
The role this component fills inside each assembly. A role describes what the element does there — it is not a statement that this component suits that system in any particular building.
Clarifications
Commonly misunderstood
- That a post-tensioned member can be treated like an ordinary reinforced one once it is complete. Tendons remain under force, and cutting into a member without knowing where they and their anchorages are is a serious matter for a specialist rather than a trade decision.
- That the anchorage is simply a fitting at the end. The position includes the region of concrete and reinforcement around it that exists to receive the concentrated force.
Conversations
Questions for qualified professionals
Questions worth asking someone with the project in front of them. This page cannot answer them.
- Is this member post-tensioned, and what record exists of the tendon and anchorage positions?
- What reinforcement is provided in the anchorage region, and what is it there to do?
- How were the anchorages protected and sealed after stressing, and what is their condition?
- Before any cutting, drilling or opening-up, who has established what lies within this member and authorised the work?
Go deeper
Related Build Design Hub guides
Planning guidance behind the decisions this element involves.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this element comes up.
What this entry does not do
- This entry describes a position. It states no force, no tendon arrangement, no reinforcement detail, no rating and no dimension of any kind, and none can be inferred from it.
- Post-tensioned structures are designed, stressed, inspected and altered by specialists, and any investigation or intervention in one is work for those specialists under the direction of the engineer responsible.
Concrete & Reinforcement Elements
The positions that govern how concrete is placed, joined and reinforced — the joints between pours, the zones around reinforcement, and the faces that form the finished surface.
Browse all concrete & reinforcement entries →