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For architects and building professionals.
4. General composite construction (steel + other materials)
Composite construction uses steel beams, metal decking and concrete in a very efficient way so that the best properties of each material can be used to optimise construction techniques. Beam spans of 6 to 12 m can be created giving maximum flexibility and division of the internal space. Composite slabs use steel decking of 46 to 80 mm depth that can span 3 to 4.5 m without temporary propping. A slab depth of 120 to 170 mm is created. In this way, beams can be arranged along the lines of separating walls so that they do not protrude into the space.
A variety of decking profiles, beam and column sizes are usually available. As well, composite floor systems can be combined with light steel infill walls to form internal walls within dwellings, separating walls between dwellings and backings to façade walls. Composite structures may also be used as a podium to support modular units above and are widely used in mixed commercial and residential buildings.
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Slim construction using composite decking
Slim composite systems constrain the hot rolled floor beam within the depth of the floor slab. Floor slab depths of approximately 300 mm can be achieved with a spanning capability of 5 to 9 m. Some of the longer spanning arrangements may require temporary propping during construction.
One advantage of submerging the steel beam into the depth of the concrete slab is that the beams do not generally require additional fire protection for up to 60-minutes fire resistance. Omission of downstand beams give the system complete freedom in positioning of internal walls. Light fitments and pipes may be included between the ribs of the deep decking.
Slim composite slabs are accepted and have been tested to Robust Standard Details for acceptable acoustic performance when combined with a platform floor covering and plasterboard ceiling.
Slimdek may be used in a wide variety of building types, as well as in renovation projects where minimum floor depth is required. Full height glazing also may be used because of the absence of downstand edge beams.
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Stability cores
Most buildings need a stiff core to provide stability and ensure that, under lateral loads, sway movements are minimised. Either cross bracing in between supporting columns or construction of a very rigid core normally creates stability zones that satisfy most building regulation requirements.
For low rise dwelling,s cross bracing is usually the most cost efficient. The braces can be placed in between fenestration constraints or between columns within walls.
However, for large multi-storey apartment block constructions, a rigid core is more cost efficient. These rigid cores are normally where staircases and lifts are located, and the rigid core is continuous up the height of the building.
Steel concrete sandwich panels can be used to form a rigid core on tall residential buildings.
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A rapidly constructed steel core is constructed of steel/concrete sandwich panels that are welded modules. These are subsequently assembled on site to form the steel core.
The gap in between the two steel plates is then filled with concrete. The plates act as permanent formwork; and when the concrete has set, the sandwich plates act as steel reinforcement.
These modules are relatively light in weight for their size. This makes it possible to erect the structure using standard site equipment.
Building Envelope Systems
A wide range of cladding systems can be attached to steel-framed buildings that produce different textures and colours to provide exciting visual contrasts.
Roofing systems
These can be of the following types:
- Standing seam - Aluminium/steel system with raised seam
- Steel composite panels - Double skin insulated panels
- Built up systems - Individually built up layered system
The roof may be divided in two categories according to the slope:
- High pitched roofs work only under watershedding conditions
- Low pitched roofs work under water-standing conditions
Both types of roofs need different measures and design details to insure weather-tightness, in particular: The requirements for sealing, but also for structural lightweight framing are not only influenced by the slope itself but by other parameters, such as quantity of rainfall, wind force, resistance to people walking on the roof for maintenance, snow build-up and ice damming at the eaves.
Whatever the slope of the roof and the profiles used, special attention has to be paid to the sealing and the fixing of the panels (one to another) and to the perimeter of the building (wind uplift), the penetrating flashings and the roof lights. Critical points are the valley gutters, especially on high-sloped roofs.
The characteristics of the various roof systems are:
Single roof cladding
The profiles of the roofing panels can be categorised as sinusoidal, trapezoidal and ribbed. Steel sheet roofing thickness varies from 0,6 to 0,7mm (according to dead load, insulation load, maintenance load, wind and snow loads).
Roof panels, whatever the profile, can be flat or curved. There are also roof tile systems, which are sheets that simulate roof tiles. They are produced in a number of different profiles. Some profiles are more difficult to use on a roof with many hips and valleys.
Ready-to-use components, such as hip and corner sheets, sealing strips and chimney pieces are common.
Profiles influence the method and frequency of attachments. The thermal expansion of metal has to be taken into account by using sliding clips or connections and appropriate sealant.
In a double skin roof, the main function of the internal sheet is to support the insulation, although by incorporating suitable perforations it may assist in improving the acoustic properties of the building.
Roof decking
Ribbed sheets (flat or curved) are used for flat roofs to support the insulation and the tightness. The choice of the profile depends on the functionality, the thickness of the insulation and the span.
In such arrangements it is important to ensure that the insulation can safely span the troughs between adjacent upper flanges of the corrugations.
Insulated panels, Composite or Sandwich Panels
Prefabricated systems can consist of panels where the insulating material (polyurethane foam or rock wool) is integrated between two metal skins (galvanised and coated). Composite panels are available with traditional type trapezoidal outer skins and through fasteners.
This composite system gives robust stiff panels, with the further benefit of rapid erection since the whole skin is fastened in one operation.
They are suitable for plane or curved roofs.
The thickness of the sandwich panel depends on the need of thermal insulation and the span. The fasteners distribution depends on the wind loads, snow loads and the thermal gradient.
Wall cladding systems
These can be of the following types:
- Steel composite panels - Double skin insulated panels
- Bricks - Brick slips attached to steel hanger rails
- Clay tilings - Clay/terracotta tiles attached to steel hanger rails
- Cassette Panels - Metallic panels supported on secondary frame
There are four main categories of cladding systems. Their characteristics are:
Wall cladding
Light façade, built of low mass materials as ribbed (sinusoidal or trapezoidal) steel sheets, single or double skin with integrated insulation.
This cladding is mechanically fastened. Giving appropriate attention to joint detailing, wall cladding can be fixed vertically, horizontally, diagonally or in combinations.
Wall cladding is often 0,5mm thick. To allow selection of the required profile and thickness, the majority of manufacturers publish catalogues containing suggested fixing and sealing details together with allowable loads for the range of span conditions for both pressure and suction actions. The cladding suits to new construction and also refurbishment
Liner tray for double skin cladding
This cassettes system realises the inside finishing of the wall. It supports the insulation (mineral wool) and the outside cladding wall (horizontally or vertically fastened).
To improve the acoustic inside the building, the cassettes are perforated on the visible face.
Architectural wall cladding
Cladding with a smooth surface that is mechanically fastened (visible or hidden fastenings) on a light frame.
Those elements generally dont ensure the tightness of the cladding.
Insulated panels: Composite or Sandwich Panels
Prefabricated systems consisting of panels where the insulating material (polyurethane foam or rock wool) is integrated between two metal skins (galvanised and coated) ; the outer skin can be smooth or ribbed.
Pre-fabricated balcony in a renovation project
This composite system gives robust stiff panels, with the further benefit of rapid erection since the whole skin is fastened in one operation.
They are suitable for plane or curved facades.
The thickness of the sandwich panel depends on the need of thermal insulation, the span and the fasteners distribution depend on the wind loads, snow loads and the thermal gradient.
Clay finishes
A range of tiling finishes can be fixed on to the outside face of a steel frame system. The tiles are usually hung on horizontal rails that are fixed back to the structural frame.
Render coatings
Are a common form of finish for residential buildings. They are created by polymer resins and binders which are pigmented. The finish (coloured) coat can be applied in a variety of methods - usually into an insulated substrate which has had a mechanical key added (expanded metal or polyurethane skrim)
The above cladding systems may be used with all of the previously described structural systems. They all share the general applications and benefits.
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Interface details for masonry cladding - External insulation & vertical track for wall ties
Composite panels directly attached to studs
Tile-hanging onto battens fixed to studs
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