Dead loads
There are a number of different types of load that can act upon a structure, the nature of which will vary according to design, location, and so on. Design requirements are generally specified in terms of the maximum loads that a structure must be able to withstand.
Loads are generally classified as either dead loads (DL) or live loads (LL).
- Dead loads, also known as permanent or static loads, are those that remain relatively constant over time and comprise, for example, the weight of a building’s structural elements, such as beams, walls, roof and structural flooring components. Dead loads may also include permanent non-structural partitions, immovable fixtures and even built-in cupboards.
- Live loads (applied or imposed loads) may vary over time. Typical live loads might include the weight of the audience in an auditorium, the books in a library, traffic loads and so on.
Dead loads comprise the weight of the structure or other fixed elements before any live loads are taken into consideration. Live loads are added to the dead load to give the total loading exerted on the structure.
Assessing dead loads forms part of an engineer’s structural calculations – a crucial part of ensuring the safe design of building structures and other built assets such as tunnels, bridges and dams.
Dead loads can be calculated by assessing the weights of materials specified and their volume as shown on drawings. This means that in theory, it should be possible to calculate dead loads with a good degree of accuracy. However, structural engineers are sometimes conservative with their estimates, minimising acceptable deflections, allowing a margin of error and allowing for alterations over time, and so design dead loads often far exceed those experienced in practice.
NB The Scottish Building Standards, Part I. Technical Handbook – Domestic, Appendix A Defined Terms, defines dead load as: ‘…the load due to the weight of all walls, permanent partitions, floors, roofs and finishes, including services and other permanent construction and fittings.’
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