Live loads
Contents |
[edit] Introduction
Loads are forces that may cause stresses, deformations, displacement and accelerations on a building. Different types of load can act upon a structure or building element, the nature of which will vary according to design, location, and so on. Assessing 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. 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 live loads (LL) or dead loads (DL).
For more information see: Types of load.
[edit] Live loads
Live loads (also known as applied or imposed loads, or variable actions) may vary over time and often result from the occupancy of a structure. Typical live loads may include; people, the action of wind on an elevation, furniture, vehicles, the weight of the books in a library and so on.
A live load can be expressed either as a uniformly distributed load (UDL) or as one acting on a concentrated area (point load). It may eventually be factored into the calculation of gravity loads. In the UK and much of Europe, live loads are expressed as kilo Newtons per square metre (kN/m2) while in the US the unit is pounds per square foot (PSF).
NB Loads such as wind loading are sometimes considered separately from live loads as environmntal loads. For more information see: Types of load.
[edit] Dead loads
In contrast, dead loads (also known as permanent or static loads, or permanent actions) remain relatively constant over time and comprise, for example, the weight of a building’s structural elements, such as beams, walls, roof and flooring components. Dead loads result from the weight of the structure or other fixed elements before any live loads are taken into consideration. They may include permanent non-structural elements such as partitions, immovable fixtures and even built-in cupboards.
Live loads are added to dead loads to give the total loading exerted on a structure.
For more information see: Dead loads.
[edit] Standards
Eurocode BS EN 1991-1-1:2002 Eurocode 1 Actions on structures (General actions. Densities, self-weight, imposed loads for buildings (formerly BS 6399-1:1996)) is the European code of practice for dead and imposed loads and gives guidance on the structural design of buildings.
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