Structural members must be designed to support specific loads. Loads are those forces for which a structure should be proportioned. Loads that act on structure can be divided into three categories.
- Dead loads
- Live loads
- Environmental loads
Dead Loads:
Dead loads are those that are constant in magnitude and fixed in location throughout the lifetime of the structure. It includes the weight of the structure and any permanent material placed on the structure, such as roofing, tiles, walls etc. They can be determined with a high degree of accuracy from the dimensions of the elements and the unit weight of the material.
Live loads:
Live loads are those that may vary in magnitude and may also change in location. Live loads consists chiefly occupancy loads in buildings and traffic loads in bridges. Live loads at any given time are uncertain, both in magnitude and distribution.
Environmental loads:
Consists mainly of snow loads, wind pressure and suction, earthquake loads (i.e inertial forces) caused by earthquake motions. Soil pressure on subsurface portion of structures, loads from possible ponding of rainwater on flat surfaces and forces caused by temperature differences. Like live loads, environmental loads at any given time are uncertain both in magnitude and distribution.
