Hollow Core
Description
Hollow Core slabs are a prestressed prefab slab, consisting of high strength concrete, usually C45/55, and strands that are 70% prestressed. There are longitudinal holes at mid height to save weight, so it carries like several I-beams next to each other, thus being a one-way slab. Due to the low weight and the high strength of the materials used, hollow core slabs are economical for spans up to 16 m. The high structural efficiency and simplicity allows it to also be economical for lower spans down to 4 m. Hollow core slabs can be made somewhat continuous by using an cast in situ connection system over the beams but this connection is usually not as stiff as the rest of the slab and thus less effective at reducing deformations. For that reason, it is not considered a continuous slab in the database.
The fire resistance of a hollow core slab is at least 60 min but can be increased to 90 min if the slab is at least 200 mm thick. This is lower than most of the concrete slabs, due to the combination of high strength concrete, prestressing and relatively low height.
The flexibility is very low because it is prefabricated and therefore not flexible for changes on site. In addition, the geometric flexibility is also minimal. Building systems cannot be included in the slab, because of the production process. The complexity of the fabrication is medium, because it is on one hand easy to mass produce, on the other hand it involves prestressing. On site, hollow core slabs are very easy to install as only a crane is needed. This makes the construction very fast.
As in most concrete floors, vibration is not a concern due to the large weight.
The slenderness is very high due to the efficient cross-section and high strength materials. For residential buildings with 3kPa characteristic load, a slenderness of l/h=45 can be achieved, for office buildings with a characteristic load of 4kPa, the slenderness is a bit lower with l/h=42.
Database
Floor type |
Hollow Core |
||
|---|---|---|---|
Materials |
concrete C45/55 precast_70% prestressed strands 1770N/mm^2 |
||
Description |
precast slab with longitudinal holes to save weight carries like several I-beams |
||
Way of carrying |
Does the main span carry in one or two directions? |
one way slab |
|
Span width low [m] |
Economically possible |
5 |
|
Span width high [m] |
Economically possible |
18 |
|
Additional measures when installing |
cranage |
||
Prefab? |
Is prefab possible? |
yes |
|
Continous slab? |
Can you build the slab with supports in middle of the slab? |
no |
|
Building systems integratable? |
Can buildings systems be included into the slab itself? |
no |
|
Fire |
Fireresistance without costly measures [min] |
90 |
|
Substructure |
Certain prerequisites necessary? |
yes |
|
Prone to vibration |
no |
||
Environment |
General classification including formwork |
1 to 5 terrible to very good |
3 |
Construction time |
Time on site |
1 to 5 very slow to very fast |
5 |
Flexibility |
Average of the next two |
1 to 5 |
1 |
Flexibility on site |
How flexible is the system to spontaneous changes on site? |
1 to 5 terrible to very good |
1 |
Flexibility geometry |
How good can you adapt the slab to complex geometries? |
1 to 5 not at all to very easy |
1 |
Complexity |
Average of the next two |
1 to 5 |
4 |
Complexity fabrication |
Complexity of floor itself. |
1 to 5 very complicated to very simple |
3 |
Complexity installation |
Complexity installation on site |
1 to 5 very complicated to very simple |
5 |
Slenderness l/h 3kPa |
Applied load (without selfweight) |
Residential building |
45 |
Slenderness l/h 4kPa |
Applied load (without selfweight) |
Office building |
43 |
Weight [kN/m3] |
per m2 and total height of slab |
14.5 |
|
Embodied energy [MJ/m3] |
per m2 and total height of slab |
3164 |
References
- General information:
Goodchild, C., Webster, R., & Elliott, K. (2009). Economic Concrete Fram Elements to Eurocode 2. Camberley UK: The Concrete Centre.
https://www.bison.co.uk/products/hollowcore-floors/
https://www.oberndorfer.at/download/produktinformationen/
https://www.hollowcore.com.au/pdf_files/DetailingManual.pdf- Span width:
7- 12m (Goodchild, C., Webster, R., & Elliott, K. (2009). Economic Concrete Fram Elements to Eurocode 2. Camberley UK: The Concrete Centre.)
5 - 18m (Cement and Concrete Association of Australia. (2003). Guide to Long-Span Concrete Floors. Sydney.)
3 - 18m (https://www.fdb-fertigteilbau.de/planungshilfen/tragfaehigkeitstabellen-zur-vordimensionierung/)
up to 22m (https://ms-element.ch/wp-content/uploads/2018/05/Prospekt_Doppelwand_und_Deckensysteme.pdf)- Fire resistance:
60min (Goodchild, C., Webster, R., & Elliott, K. (2009). Economic Concrete Fram Elements to Eurocode 2. Camberley UK: The Concrete Centre.)
at least 90min https://www.hollowcore.com.au/pdf_files/DetailingManual.pdf)
90min (if tickness more than 200mm) (https://onlinelibrary.wiley.com/doi/abs/10.1002/9783433606803.ch10)- Slenderness:
l/h=45 for 3kPa, l/h=43 for 4kPa (Goodchild, C., Webster, R., & Elliott, K. (2009). Economic Concrete Fram Elements to Eurocode 2. Camberley UK: The Concrete Centre.)
l/h=43 for 3kPa, l/h=42 for 4kPa (https://www.bison.co.uk/products/hollowcore-floors/)
l/h=48 for 3kPa, l/h=45 for 4kPa (https://www.oberndorfer.at/download/produktinformationen/)- Weight:
- Embodied energy:
- Photo Source: