Prestressed Floors

SELF WEIGHT AND FINISHES – Weight – Kg/m2

The above self weights of the various slab depths are 30% lighter than an in-situ slab of a similar depth.
Prestressed slabs achieve longer spans than in-situ concrete of a similar depth. This achievement is attributed to high strength concrete and prestressed wire and strand.

Where Echo Prestress is used as roof slabs or balconies, a minimum Ref. 100 mesh is required in the insulating screed over the panels, as well as a slip joint on the walls. On indoor areas where tiles are specified a minimum Ref. 100 mesh is required in the screed. Expansion joints are required in tiled areas. All unfinished areas also require the same mesh. Refer to the detailed screeding specifications.

SECTIONAL INFORMATION

STRUCTURAL INFORMATION

STANDARD WIRING PATTERNS

LOAD CAPACITY TABLE

Note: Span=Clear span +100mm

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m2.

CROSS SECTIONAL DIMENSIONS

SECTIONAL INFORMATION

STRUCTURAL INFORMATION

STANDARD WIRING PATTERNS

LOAD CAPACITY TABLE

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m 2 .
Span=clear spam +100mm

CROSS SECTIONAL DIMENSIONS

SECTIONAL INFORMATION

STRUCTURAL INFORMATION

STANDARD WIRING PATTERNS

LOAD CAPACITY TABLE

Note: Span=Clear span + 100mm

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m ² .

CROSS SECTIONAL DIMENSIONS

SECTIONAL INFORMATION

STRUCTURAL INFORMATION

LOAD CAPACITY TABLE

Note: Span=Clear span + 100mm

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m².

CROSS SECTIONAL DIMENSIONS

SECTIONAL INFORMATION

STRUCTURAL INFORMATION

STANDARD WIRING PATTERNS

LOAD CAPACITY TABLE

Span = clear span + 100mm

Note: Design loads include self weight, grouting between joints and finishes up to 1,5kNm/m 2 .

CROSS SECTIONAL DIMENSIONS

• Larger cut-outs can be formed in the factory. These holes require more specific strengthening, but can be catered for at the design stage.
• Skylight and stair openings are formed by specifically fabricated steel hangers which are supplied and erected by Echo Prestress. Alternatively a steel, brick or concrete beam can be used as support around the opening.
• The tops of the hollow cores can be opened to take steel when the units are used in composite action with steel or concrete beams.
• Skew ends can be cut in the factory with a diamond tipped saw blade specifically manufactured to accurately cut any angle.

For suspended or other light fittings, simply drill a hole through the slab and into the slab’s hollow core to fit the electrical wiring through.
Any excessive edge chipping is easily repaired with ‘Rhinolite’ or similar material.

Costs of such electrical light points also become more economical as electrical wires and single light transformers can be placed into the horizontal hollow cores of the slabs the day after installation, instead of the traditional light boxes and conduits.

As the panels are designed and manufactured specifically for your project, site dimensions need to be accurate to avoid delays. Site dimensions are checked by Echo prior to manufacture. Sand and cement for grouting between the Echo panels are to be supplied by the customer. The actual grouting is done by Echo.

Window and door openings in load bearing walls up to 2,0 meters wide can be covered by lintols side by side with five courses of brickwork with brick force in every course for slab spans up to 7 meters. Openings wider than 2 meters must be referred to the engineer for detailing of additional structural steel supports.

APPLICATION OF SCREED

All loose material is to be removed from the tops of the slabs. The slabs should be thoroughly wetted and screed applied immediately. The levelling screed should comprise a 1:4 mix by volume of cement and clean river sand. Water should be added to the mixture to an extent that the mixture is relatively dry but remains easy to float finish. The screed should be laid to an approximate thickness of 40mm. Note that in some areas additional screed may be necessary to level out the camber in the units. After laying the screed it should be steel floated and then wetted for 48 hours to prevent shrinkage cracks.

In certain areas, namely balconies, roofs, walkways, tiled areas, car parks and areas where the screed is to be left unfinished, the screed specifications change slightly. On balconies, roofs, walkways etc., i.e. all areas where Echo Prestress slabs are exposed to the elements – a Ref. 100 mesh* must be placed in the leveling screed to counteract the transverse forces created by large temperature differences.

Where tiles are to be used on the slab, a Ref. 100 mesh* must be placed in the levelling screed as for balconies, roofs and walkways. Expansion joints should be allowed in the tiles every 3 metres and particularly where the section alters shape such as doorways. It is recommended that a flexible tile adhesive be used. TAL (Pty) Ltd. have produced a technical specification for tiling on Echo slabs which is available on request from Echo Prestress.

On car parks a Ref. 193 mesh** must be placed in a structural topping of not less than 50mm thickness to help spread the load from one panel to the next. The screed can be left rough to suit the clients requirements.

In areas with exposed screed a Ref. 100* mesh is required to control shrinkage/drying stresses. These areas would also require adequate movement joints.

Where the screed thickness is 50mm or less the mesh should be laid flat on top of the slab and the screed placed on top. Where the screed depth exceeds 50mm the mesh should be placed 20mm from the top surface of the screed.

Providing the above procedures are followed, the screed will adhere extremely well to the prepared surface of the slab. Experience has shown that it is impossible to remove the leveling screed from the top surface of the slab after a few days.

* A ref. 100 mesh is a 4,0mm wire in a square pattern at 200mm centres.
** A ref. 193 mesh is a 5,6mm wire in a square pattern at 200mm centres.

Specifications for the following are available from Echo prestress on request:

• The tiling of Echo Prestressed slabs
• Grouting between joints (generally undertaken by Echo Prestress)
• Structural toppings to enhance the slab capacity
• Methods of finishing Echo Prestress slabs

The Cement and Concrete Institute (Tel. 011 315 0300) have produced a standard specification for sand/cement screeds and concrete toppings for all types of floors. Request a copy from Echo Prestress.