The loads acting on buildings can be broadly divided into two groups, namely geophysical and human-induced.
Geophysical loads are caused by changes occurring in nature and one can distinguish loads caused by gravity, meteorological and seismic phenomena.
The group of loads caused by gravity includes permanent and variable loads caused by human activity during the use of the building. Meteorological loads change over time and depend on the geographic location of the structure. These burdens include: wind action, temperature, rain, snow and ice. Seismic and parasiteismic loads are caused by the movement of the subsoil.
The loads can act on the building in a static or dynamic manner. Loads can be constant and variable.
Load is a permanent load, whose value, the direction and position remain the same during the life of the structure. Permanent loads include the self-weight of fixed building elements and structures, including load-bearing and cover elements, own weight of the soil and the resulting pressure.
One of the variable loads is the load, whose value, the direction and position may change during the life of the structure. Variable loads are divided into: entirely long-lasting, partly long-term and partly short-term.
Fully long-term loads include the self-weight of these parts of the structure, whose position may change during the use of the structure, and the own weight of devices permanently connected with the use of buildings, etc..
Long-term loads include ceiling loads in storage rooms, industrial, residential, loads from lifting and transport equipment, e.g.. bridge cranes, the burden of people, devices and materials in places where machines are repaired, etc..
Fully short-term loads include snow loads, the wind, the influence of the temperature of the climatic origin and the loads arising during the execution, transport and erection of building structures, etc..
In the design of structural elements and building systems, constant and variable loads are taken into account, which may occur during construction (assembly of the structure) or during the useful life of the structure.
The less favorable value of total loads is taken for the calculations.
Permanent loads on elements, structures and structures are determined on the basis of the designed or existing dimensions of the elements (volume m3) and the standard volumetric weights of the materials used. The loads obtained in this way (Gk) are called characteristic loads.
Internal forces (M — moment, N - axial force, Q - shear force) in structural systems is determined using the methods of building mechanics, the theory of elasticity or plasticity.
In accordance with the applicable regulations and technical standards, structural cross-sections are dimensioned using the limit state method.