A ‘Dead load’ is the downward pressure of the structure produced by gravity. When considering a building’s structural footings bearing on the site’s foundations, you need to consider the dead load of the structure and ensure that the support structure is adequate. For example: a suspended concrete slab creates a greater load than timber framed floor.
Dead load values of common building materials (kN/m3):
Mild Steel = 77
Glass = 25.5
Reinforced concrete = 24
Mass concrete = 23.5
Hardwood = 11
Softwood = 8
The scenario below demonstrates the calculation of Dead Load:
Suspended Concrete Beam
Beam length: 6m (single span)
Beam profile: 200mm wide x 400mm deep
Beam volume: 6.0 x 0.2 x 0.4 = 0.48m3
Unit weight of reinforced concrete = 24 kN/m3
Dead load = 0.48m3 x 24 kN/m3 = 11.52 kN
By calculating the volume of each member and multiplying it by the unit weight, an accurate dead load can be determined. It is important to calculate the dead load and the required supporting structure from the top of the building down. The different components can then be added together to determine the dead load of the entire building. Unlike other forces, dead loads do not vary over time. It is also important to remember that dead loads are always exerted in a vertical plane, and will need to be transferred to supporting structures below, even if these are offset.
The Australian Standard that outlines the requirements for dead loads is:
AS1170.1 Part 1 – 1981 Dead and Live Loads
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