A floor is a composite system consisting of load bearing elements. A floor system can also include:
- The upper surface or finish of the floor
- The lower surface of the ceiling of the compartment below
- Beams transferring the load of the system to the columns or load bearing walls that support the floor
Floors may be simply formed by a series of wide, shallow beams, and therefore behave as such. However, invariably they are composite structures which incorporate a number of components all acting together.
Floors may also be constructed from beams or joists acting as the load bearing members with a skin or boarding over the joists and a ceiling (often plaster or plasterboard) below. The specific materials used and construction (in particular the ceiling materials and beams) will impact on the fire resistance of the floor system.
A floor may be load bearing or a false floor. This is sometimes difficult to identify and could create a cavity, typically these are used for passage of cables. False floors may become spongy underfoot if they are significantly damaged by fire but this does not necessarily mean any impact on the loadbearing capacity of the floor. However, it should be considered that any floor is a loadbearing floor unless it can be determined otherwise.
Floor systems are unlikely to fail as a complete system all at once; there will generally be an initial failure at one point. This may result in redistribution of load throughout the floor system but may also impose additional or lateral loads on supporting walls and columns. Floors constructed as a composite system may also contribute to hidden firespread throughout the building.
Collapse of a structural floor within a building is likely to lead to partial structural collapse elsewhere in the building, particularly where the floor supports other structural elements which then support additional load above.
Ground floor flooring may be floating and constructed in a similar way to the floors above, particularly in domestic dwellings where services and insulation may also be installed.
- There should be clear signs or symptoms that the floor is deflecting and therefore clear signs of potential collapse
- Identification of load bearing floors or false floors can be difficult
- The load bearing structure can be hidden by raised floors therefore making it difficult to see signs and symptoms of collapse
- The gaps between parallel joists produce cavities which provide a means for smoke and fire to travel throughout the structure, particularly in hearth fires
- Connections and the junctions between floors and walls may provide paths for fire and smoke spread from wall cavities into floor cavities and vice versa