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Types of Loads

Before designing any building or its different elements such as beams,columns or slabs, the designer has to first determine the number of natural and man-made loads acting on them.

These loads may be classified into two groups:
1. Direct Loads: Dead loads, imposed loads, snow, ice, and earth loads, and hydraulic pressure are caused due to mass and gravitational effect.

2. Indirect loads: Indirect loads are caused due to environmental effects such as temperature difference, settlement, and shrinkage.

Any structure should be designed to sustain any set of  following loads:

Dead Load:

The load that is fixed in magnitude and position is called the dead load.
Calculation of the dead load of a structure requires the estimation of the weight of the structure components along with its ally ‘non-structural’ components.

Imposed loads:

Imposed loads (also referred to as live loads) are the loads other than dead loads and include items such as occupancy by people, stored materials such as books or machinery, movable equipment and furniture within the buildings.

Impact loads:

The impact load is an important criterion in bridges and also in industrial structures where machinery is mounted on floors.
Impact loads due to moving machinery, vertical crane and so on is converted empirically into equivalent static loads through an impact factor, which is normally a percentage (20% to 100%) of the machinery load (as specified in IS 875—Part 2).

Snow and ice loads:

Snow and ice loads are to be considered in the hilly (Himalayan) regions in the northern parts of India. The roofs in these areas should be designed for the load due to snow or for the imposed loads as specified in IS 875 (Part 2), whichever is more severe.

Wind loads:

Winds are produced by the differences in atmospheric pressures, which are primarily due to the differences in temperature.
Horizontal wind flow exerts lateral pressure on the building envelope and hence has to be considered in the design.
Code IS 875:1987 (Part 3) provides the provisions to determine wind loads.

Seismic Loads:

Seismic loads are the loads that any structure tend to bear during earthquakes.For the purpose of determining seismic forces, India is classified into four seismic zones (zones II to V) by IS 1893 (Part 1) code. The structure should be designed so strong that even major and infrequent earthquakes should not cause collapse since the structure may become dysfunctional for further use, but should stand so that occupants can be evacuated and property recovered.

Erection Loads:

This is the load structure has to bear during its construction process. It is also important to temporarily brace the structures during erection for safety and stability.

  • Erection loads are very important for precast concrete members. 
  • Formwork should not be removed until the concrete attains the strength sufficient to carry the construction loads.

Flood Loads:

The structure should be designed so that it may sustain against floods as the unbalanced environment has resulted in heavy, unprecedented floods in various parts of the world.

Rain induced erosion and localized scour may lower the ground surface around the foundations of buildings and cause loss of load-bearing capacity and loss of resistance to lateral and uplift loads.