Composite Solid Prestressed Soffit Slab (CSPSS)

Description

CSPSS are a prestressed prefab slab, consisting of high strength concrete, usually C45/55, and strands that are 70% prestressed. On top there is a layer cast in situ concrete, sometimes it is reinforced to increase the stiffness and strength and sometimes it is only a slim unreinforced layer to give the slab a nice finish. It is a slab made for shorter spans and is mostly used between 3 m and 9 m span. As in most prefab slabs, there are options to make CSPSS somewhat continuous over the beams, but the effectiveness is limited, due to a much lower stiffness of the connection over the beam.

The fire resistance of CSPSS is around 60 min, depending on the thickness. This is lower than most of the concrete slabs, due to the combination of high strength concrete and prestressing.

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, CSPSS are very easy to install as only a crane is needed, sometimes they also require propping up, if the cast in situ layer is relevant enough for self-weight and strength. This allows for a fast construction process only slowed down by the curing time of the cast in situ layer.

As in most concrete floors, vibration is not a concern due to the large weight.
The slenderness is very high due to the short span it is used for, for which the self-weight is not that relevant, and the high strength materials. For residential buildings with 3kPa characteristic load, a slenderness of l/h=42 can be achieved, for office buildings with a characteristic load of 4kPa, the slenderness is a bit lower with l/h=40.

Database

Floor type			Composite Solid Prestressed Soffit Slabs
Materials			concrete C45/55 precast_concrete C30/37 in situ_70% prestressed strands 1770N/mm^2
Description			precast slab with cast in place concrete above without rebars
Way of carrying	Does the main span carry in one or two directions?		one way slab
Span width low [m]	Economically possible		3
Span width high [m]	Economically possible		12
Additional measures when installing			propping up
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]		60
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	4
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	42
Slenderness l/h 4kPa	Applied load (without selfweight)	Office building	40
Weight [kN/m3]	per m2 and total height of slab		24
Embodied energy [MJ/m3]	per m2 and total height of slab		6634

References

General information:

Goodchild, C., Webster, R., & Elliott, K. (2009). Economic Concrete Fram Elements to Eurocode 2. Camberley UK: The Concrete Centre.
https://www.precastfloors.info/Precast/media/BPMediaLibrary/Publications/Solid-Prestressed-Composite-Floors_1.pdf?ext=.pdf

Span width:

3 - 12m (https://www.fdb-fertigteilbau.de/planungshilfen/tragfaehigkeitstabellen-zur-vordimensionierung/)

Fire resistance:

60min (Goodchild, C., Webster, R., & Elliott, K. (2009). Economic Concrete Fram Elements to Eurocode 2. Camberley UK: The Concrete Centre.)
at least 60min (https://www.precastfloors.info/Precast/media/BPMediaLibrary/Publications/Solid-Prestressed-Composite-Floors_1.pdf?ext=.pdf)

Slenderness:

l/h=42 for 3kPa, l/h=40 for 4kPa (Goodchild, C., Webster, R., & Elliott, K. (2009). Economic Concrete Fram Elements to Eurocode 2. Camberley UK: The Concrete Centre.)
l/h=41 for 3kPa, l/h=39 for 4kPa (https://www.precastfloors.info/Precast/media/BPMediaLibrary/Publications/Solid-Prestressed-Composite-Floors_1.pdf?ext=.pdf)

Weight:

Calculations

Embodied energy:

Calculations

Photo Source:

https://www.oreillyconcrete.com/products/hollowcore-floors/wideslab-flooring/