Advantages of post-tensioning floor slabs

  • Larger slab spans requiring fewer columns and providing more freedom in terms of layout
  • Reduced floor thickness which saves overall height and can thus result in an increase in the number of storeys in the structure
  • Better control of shrinkage cracking for improved watertightness and hence greater durability
  • Reduction or elimination of significant deflection in routine service

  • Savings in materials (concrete and steel)
  • Reduced load on foundations
  • Shorter construction programme due to reduced materials to install
  • Elimination of uneven soffits leading to simple installation of electrical, air-conditioning and other services

The use of floors prestressed by post-tensioning results in a significant reduction in greenhouse gas emissions compared with an equivalent traditional reinforced concrete design.  Optimal savings of the order of 20-25% can be realised.

Application fields

Building floors

Freyssinet’s post-tensioning systems can be used in the construction of the floor slabs for a wide range of building types:

  • Residential buildings
  • High-rise office buildings
  • Shopping centres
  • Underground / traditional Multi-Storey Car Parks (MSCP)
  • Public facilities – hospitals / schools / sports halls

Many of the previously described benefits can be achieved for the benefit of architects, owners and contractors alike, particularly for buildings with large plan dimensions or for high rise structures.

Foundation slabs

Foundation slabs are in direct contact with the ground and enable buildings to be erected on soils with poor mechanical properties.
The undulating layout of the prestressing compensates for permanent and variable loads. The permanent compression of the concrete also improves foundation slab sealing against any water ingress.

Transfer slabs

Transfer structures are often very thick slabs, subject to heavy loading, which absorb the loads from columns above that are not aligned with the columns below. They are generally used in high-rise buildings to clear a space without load-bearing elements or to make the transition to the parking levels.

Prestressing allows the height of the transfer slabs to be reduced considerably; in certain cases, C-Range high-strength tendons for civil engineering will be proposed.

Industrial slabs

These slabs bear on the foundation soil. The prestressed tendons are straight, centered and arranged in both directions.
They allow a reduction in the quantity of passive reinforcement, improve the bending strength and ensure control of shrinkage cracking.
Very large areas can be achieved while reducing or eliminating the number of contraction joints. These joints are vulnerable to traffic wear; their elimination is particularly appreciated when surfaces must be flat to accommodate automated conveyor systems.
The permanent compression of the concrete by prestressing improves its watertightness.

Services tailored to your needs

Design & build packages or technical support

Consultancy and design services

In close cooperation with the project designers, Freyssinet carries out the design of the floor slabs and supplies all the calculation data required for sizing the structure.

In-house manufacturing and quality control

In order to ensure high quality products to our clients around the world, Freyssinet manufactures its anchors at its industrial division FPC – Freyssinet Products Company, which is ISO 9001 (quality), ISO 14001 (environment) and ISO 45001 (safety & health) certified.

Installation or technical assistance

Our prestressing specialists are certified through internal training and provide the assurance that the prestressing work is carried out properly and in compliance with all operational requirements. Whilst our preference is to provide the full service, for certain projects we offer technical assistance for installation and provide the site equipment required: jacks, pumps, grouting units, etc.

Range of solutions

Multi-strand PT anchorage system – B Range

The anchorage unit consists of a trumplate, a block and wedges. The cast-iron trumplate is embedded in the concrete and distributes the prestressing load into the structure. The anchorage block rests on the trumplate and the wedges grip the strands.
  • Multi-strand compact prestressing:
    3 to 5 T13 or T15 strands
  • Bonded or unbonded prestressing
  • Separated anchorage block
    for easy installation on-site

Single strand flat PT anchorage system – 1F15 or 1F13

The 1F13/15 single strand system is generally used for unbonded post-tensioning cables. It is made up of (1) Sheathed and greased strand, incorporated directly into the slab before concreting (2) A cast-iron anchorage body with steel wedges, embedded in the concrete which grips the strand and distributes the prestressing force into the structure (3) A plastic connecting tube providing protection to the strand where it is locally unsheathed in the anchorage body (4) A protective cap which is filled with grease and provides permanent protection to the anchoring area.
  • Single strand compact prestressing:
    T13 or T15 strands
  • Unbonded prestressing
  • Adapted to thin floor slabs
    requiring flexible tendon geometry
    using single strand units

Multi-strand PT anchorage system – B Range

The anchorage unit consists of a trumplate, a block and wedges. The cast-iron trumplate is embedded in the concrete and distributes the prestressing load into the structure. The anchorage block rests on the trumplate and the wedges grip the strands.
  • Multi-strand compact prestressing:
    3 to 5 T13 or T15 strands
  • Bonded or unbonded prestressing
  • Separated anchorage block
    for easy installation on-site

Single strand flat PT anchorage system – 1F15 or 1F13

The 1F13/15 single strand system is generally used for unbonded post-tensioning cables. It is made up of (1) Sheathed and greased strand, incorporated directly into the slab before concreting (2) A cast-iron anchorage body with steel wedges, embedded in the concrete which grips the strand and distributes the prestressing force into the structure (3) A plastic connecting tube providing protection to the strand where it is locally unsheathed in the anchorage body (4) A protective cap which is filled with grease and provides permanent protection to the anchoring area.
  • Single strand compact prestressing:
    T13 or T15 strands
  • Unbonded prestressing
  • Adapted to thin floor slabs
    requiring flexible tendon geometry
    using single strand units

B-Range and 1F15/13

Main features
Documentation
Prestressing load
1 to 5 strands with ultimate tensile strength up to 279 kN / strand
Slab minimum thickness
17 cm
Minimum concrete compressive strength
  • B Range for T15 strand: 23.5 MPa (on cylinder) at time of stressing
  • B Range for T13 strand: 20 MPa (on cylinder) at time of stressing
  • 1F15/13: 22 MPa (on cylinder) at time of stressing
    • Certification
    CE Marking no 1683-CPR-0048, according to ETA 06/0226
    Documentation

    Find out more in our case studies

    BUILD
    United Kingdom

    Library of Birmingham, PT slabs rather than steel frame

    Construction of the library of Birmingham was originally conceived as a structural steel frame. During the tender period, and in order to realise the full value engineering benefits, the frame was changed to reinforced concrete with post-tensioned slabs and beams
    Discover more

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