Structural load

Structural loads are forces applied to a component of a structure or to the structure as a unit.^[1]

In structural design, assumed loads are specified in national and local design codes for types of structures, geographic locations, and usage. In addition to the load magnitude, its frequency of occurrence, distribution, and nature (static or dynamic) are important factors in design. Loads cause stresses, deformations and displacements in structures. Assessment of their effects is carried out by the methods of structural analysis. Excess load or overloading may cause structural failure, and hence such possibility should be either considered in the design or strictly controlled.

In the Eurocodes, the term actions has a similar meaning to loads, but encompasses applied deformations as well as forces.

The following lists the common loading types primarily for civil infrastructure and land machinery. Structures for aerospace (e.g. aircraft, satellites, rockets, space stations, etc...) and marine environments (e.g. boats, submarines, etc.) have their own particular design loads and consideratio includes dead loads but also includes forces set up by irreversible changes in a structure's constraints - for example, loads due to settlement, the secondary effects of prestress or due to shrinkage and creep in concrete.

Dead load

Dead load

Imposed load

Live snow load

The dead load is the weight of the structure acting with gravity on the foundations below. Snow load is the weight of the dead load and the imposed load but also the weight of the snow on top which could cause damage to the roof.

Live loads

Live loads, or imposed loads, are temporary, of short duration, or moving. Examples include snow, wind, earthquake, traffic, movements, water pressures in tanks, and occupancy loads. For certain specialized structures, vibro-acoustic loads may be considered.

Environmental loads

• Temperature changes leading to thermal expansion cause thermal loads
• loads caused by humidity or moisture induced expansion
• Ice movements
• Water waves
• Shrinkage

Static loads

These are loads that build up gradually over time, or with negligible dynamic effects. Since structural analysis for static loads is much simpler than for dynamic loads, design codes usually specify statically-equivalent loads for dynamic loads caused by wind, traffic or earthquake.

Dynamic loads

These are loads that display significant dynamic effects. Examples include impact loads, waves, wind gusts and strong earthquakes. Because of the complexity of analysis, dynamic loads are normally treated using statically equivalent loads for routine design of common structures.

Load combination

A load combination results when more than one load type acts on the structure. Design codes usually specify a variety of load combinations together with weighting factors for each load type in order to ensure the safety of the structure under different probable loading scenarios.

References

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