Slimflor and Slimdek construction

A slim floor beam is a special case of a modified section where a flat steel-plate is welded to a standard UC section. This generic system is trademarked as 'Slimflor by Corus. The plate supports the floor slab so that the beam is partially encased within the floor depth, resulting

o in a structural system with no downstand beams, leading to reduced floor to floor heights.

Two variations of Slimflor construction exist:

• precast concrete slabs spanning between the beams13 with or without a concrete topping

• deep decking spanning between the beams with in-situ concrete

to create a monolithic composite floor, see Figure 4.5.

A series of two-dimensional frames is erected with light steel tie-members between the frames. Spans of the order of 6 to 9 m can be achieved using both variants of Slimflor construction.

The decking is designated as SD225, and is 225 mm deep with ribs at 600 mm spacing. This decking is a modern variant of CF210 decking, which is 210 mm deep, and is only used in shorter span applications. The overall floor depth is typically 290 to 350 mm, depending on requirements to control floor vibrations, fire resistance and acoustic insulation.

Slimflor construction was used at New Square, Bedfont Lakes, and the slenderness of its section was expressed elevationally (see Colour Plate 12).

Slimdek offers further advantages in terms of economy and service integration. It consists of a range of rolled Asymmetric Slimflor Beams (ASB) and SD225 deep decking which sits on the wider bottom flange (see Figure 4.6). Three ASB sections were produced initially, 280 ASB 100, 280 ASB 136 and 300 ASB 153, which are designated by their approximate height (in mm) and weight (in kg/m). These sections have been designed efficiently for floor grids of 6 x 6 m, 7.5 x 6 m, and 7.5 x 7.5 m respectively, and do not require additional fire protection for up to 60 minutes' fire resistance. A range of 10 ASB sections is now available, including thinner web-beams, which are designed to be fire protected for over 30 minutes' fire resistance. Details of the use of Slimdek are given in the Corus Slimdek Manual.

Composite action is enhanced by the embossments rolled on to the top flange of the ASB. Openings for services can be created in the ASB between the ribs of the decking. The maximum size of these openings is 160 mm deep x 320 mm wide to facilitate use of flat oval-ducts for services.

What Downstand Beam Construction

4.5 Section through deep decking and Slimflor beam

Slimflor Beams

4.6 ASB section used in Slimdek construction

4.5 Section through deep decking and Slimflor beam

4.6 ASB section used in Slimdek construction

The main benefits offered by Slimdek construction are:

• reduction in floor depth (by up to 300 mm relative to conventional beam and slab construction)

• no downstand beams, offering ease of service installation

• inherent fire resistance (60 minutes can be achieved without fire protection)

• savings in cladding and services costs

• integration of services and fitments.

The deep decking can be placed rapidly to create a working platform. The space between the ribs of the decking may also be used for ducting, lighting and terminal units. Figure 4.7 illustrates the use of active chilled beams and ducting placed between the ribs which form a continuous line along the building. The overall depth of the floor construction, including a raised floor, is only 600 mm.

Doppelboden Aufbau

No offset required for duct to pass through ASB

4.7 Example of service integration in Slimdek: (a) space between ribs used as a duct; and (b) active chilled beam

No offset required for duct to pass through ASB

Torsional Stiffness Rectangular Beam

Perforated ceiling 1 tile 'Air out 'Air 1 out '

Perforated ceiling 1 tile 'Air out 'Air 1 out '


Attachment detail

190 x 70 shear connector

^ Transverse reinforcement

SD225 deck

End diaphragm

: RHS column

4.8 Use of RHS Slimflor beam to support cladding



A rectangular hollow section (RHS) with a welded bottom-plate may be used as a Slimflor edge beam. It provides enhanced torsional stiffness to out of balance loads and also presents a 'pencil-thin' edge to the floor which may be visually desirable in some circumstances, such as fully glazed façades. Cladding attachments may be made more easily to the RHS section than to a concrete slab or encased steel-section (see Figure 4.8).

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