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STRUCTURAL DETAILS
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| Manufacturing method |
Prestressed / Slipformed |
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Standard depths available:
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120mm, 150mm, 200mm and 250mm
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Standard widths:
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1 200mm
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Non-standard widths:
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In 100mm increments
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Min. recommended characteristic strength of concrete at transfer
* Clause 5.1.5.1 of SABS 0110-1 Ed 2.2 shall apply |
35mPa for 120mm, 150mm, and 200mm deep slabs,
40mPa for 250mm deep slabs
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Minimum recommended characteristic strength of concrete at 28 days
* Clause 5.1.5.1 of SABS 0110-1 Ed 2.2 shall apply
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50mPa for all slab depths
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Recommended limits on span/depth ratios for hollow-core slabs
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For roof slabs a span to depth ratio limit of 50 is suggested. For floor slabs a span to depth ratio limit of 45 is suggested.
Note: when 1.) fire endurance, 2.) openings, or 3.) sustained live loads do not control the design.
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Prestressing wire type:
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5mm dia. triple indented low relaxation wire
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Prestressing strand type:
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9,53mm dia. stabilized strand
12,5mm dia. stabilized strand
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Suggested bearings:
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On brickwork – 100mm
On steel – 75mm
On concrete – 75mm
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Fire resistance level (FRL) of a floor is specified in the building codes as the period in minutes during which the floor must retain it's:
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Structural adequacy: 180 minutes
Integrity: 90 minutes
Insulation: 90 minutes
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| Cantilevers |
Suggested cantilevers are limited to 8 times the depth of the slab
120mm - 960mm
150mm - 1200mm
200mm - 1600mm
250mm - 1800mm
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| Weight saving |
30% lighter than a solid slab of the same depth |
Higher strength materials
(both for concrete and steel) |
The higher strength steel is tensioned and anchored against the concrete which produces a number of desirable effects:
- The prestressing tends to neutralise tensile stresses and strains induced by the load
- The full concrete section becomes active in resisting the load
- Higher strength concrete may be used to obtain a more economical hollow core section than with reinforced concrete
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Hollow-core slab deflections
Total deflection is defined as the upward camber of the slab due to the eccentricity of the pre-tensioning less the downward deflection due to applied loads, including the long term effects of prestress loss, creep and shrinkage |
Final long term deflection: Span/250
Variable long term live movement: Span/500
Overall long term movement: Span/500s
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Service holes
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Up to 90mm may be made in the panel on site |
| Service holes larger than 90mm |
Should be referred to the Design Engineer and should be formed by Echo in the factory. these holes require more specific strengthening. |
| Skylight and stair openings |
Are formed by specifically fabricated steel hangers which are supplied and erected by Echo |
| Open cores |
The tops of the hollow cores can be opened to receive tie steel when slabs are used in composite action with steel or concrete beams. (See more detail in the composite section) |
| Angled cuts |
Angled /skew ends can be cut in the factory with a diamond tipped saw blade specifically manufactured to accurately cut an angle. |
| Installation |
This service is provided by Topfloor and is included in the price - refer to Services Offered |
| Grouting |
This service is provided by Topfloor. Materials supplied by the contractor / client - refer to Services Offered |
| Levelling screed / Structural Structural topping not included in the Topfloor price |
Suggested 40 - 50mm deep note that in some areas additional screed may be necessary to level the positive camber in the units resulting in a thicker screed at the ends of the slab. See screeding specifications. |
| Soffit / ceiling finishes |
Specification available from Topfloor |