The principal structural elements of a typical multi-storey building are the floors, beams, columns and foundations. The principal structural elements of a typical multi-storey building comprise floors, beams and columns. A wide variety of alternative forms and arrangements can be used in multi-storey steel framed structures.
The principal structural elements of a typical multi-storey building Floor slabs: Several different types of slab can be used, in either composite or non composite form. A number of different floor slab types can be used in association with a steel frame. The floor slab usually spans one way; it is either simply supported or continuous. Most slab types can be designed to act compositely with the supporting beams if adequate shear connection is provided Composite floors consist of a concrete topping cast onto metal decking. Composite floor slabs use metal decking, which spans between secondary steel beams usually spaced at between 2.5 and 3m centres. Concrete, which may be either lightweight or normal weight, is then poured onto the decking, usually by pumping, to make up the composite system. Metal decking acts both as permanent formwork for the concrete, eliminating the need to provide props, and as tensile reinforcement for the slab. Steel bars are included in the slab to prevent cracking and to provide reinforcement in the event of degradation of the decking in a fire. Alternative arrangements of primary and secondary beams can be adopted for an optimum deck span of 3m. and a typical system is illustrated. There are many types of steel decking available, but perhaps the most commonly used is the re-entrant profile type which provides a flat soffit and facilitates fixings for services and ceilings.
Primary and secondary steel beams
Composite floor slabs have become popular for multi-storey buildings when rapid construction is required. This form of slab construction is particularly popular for multi-storey buildings when rapid construction is required. Some of the advantages of the composite system are: Steel decking acts as a permanent shuttering which can eliminate the need for slab reinforcement and propping of the construction while the concrete develops strength. This leads to simple, rapid construction. Composite action reduces the overall depth of structure. It provides up to 2 hours fire resistance without additional fire protection and 4 hours with added thickness or extra surface protection. It is a light, adaptable system that can be cut to awkward shapes and can easily be drilled or cut out for additional service requirements. The overall weight of this system is low, particularly if lightweight concrete topping is used, reducing frame loadings and foundation costs. The demands on cranage are low as many sheets of steel decking may be lifted at a time, and then laid out by hand; the concrete topping may be placed by pump. Precast concrete units are also often used with a steel frame, offering long spans and quick installation. Precast concrete floors area heavier form of construction than comparable composite metal deck floors, but offer the following advantages: Fewer floor beams since precast floor units typically span 6 to 8m. Shallow floor construction can be obtained by supporting precast floor units on shelf angles. Fast construction because there is no propping and no time is needed for curing and the development of concrete strength .
Precast concrete floor systems
Composite action may be difficult with precast floors, and construction requires a crane. The disadvantages of precast concrete floors are:
Composite action not readily achieved without a structural floor screed. Heavy floor units are difficult to erect, requiring the use of a crane which may have implications on the construction programme. Floor Framing
In floor framing, the subfloor is supported by light beams called floor joists or simply joists which in turn supported by heavier beams...