Building loads

Words by BSBG Media Team, Wednesday 18 November 2015

hall we use timber, masonry, steel or concrete? This question always comes at the beginning of every project, and there are many factors that determine the answer. But the first key question relates to building loads, and is: “what are the loads of the building?”

As shown in the above image, the loads on any structure are either gravity loads, which act vertically in the direction of gravity, or lateral loads, which act horizontally.

Types of building loads

Dead load/certain load

This is the weight of the materials used in the construction of any structure. The weights of these materials are well known and easy to determine, eg. concrete, steel, aluminium, marble etc.

Live load/uncertain load

This load is always an allowance due to uncertainties, and is dependent upon the function of the building. The live load allowance will differ from residential, to commercial, to hospital buildings, and so on.

Wind load

This is one of the most critical lateral loads, especially for tall buildings and structures. The structure will experience wind load on a daily basis, however the wind forces will differ from day to day and from one location to another, based on the current wind speed. When the wind blows on a structure it causes a positive pressure on the windward and negative (suction) pressure on the leeward as shown in the following image. The side walls and roof will also be subjected to negative pressure.

Earthquake load

This is the load caused by ground motion that causes seismic waves. Designing the structure to withstand earthquake load as per governing design code provisions will ensure minor or no damage during minor earthquakes, and also prevents collapse under major earthquakes.

Lateral load due to earth pressure and water pressure

A clear example for this case is an underground water tank or a reservoir. The tank walls will be subjected to lateral pressure from soil on the external face while being subjected to lateral pressure from water on the internal face. Worst case scenarios are considered in the design. While the tank is under testing (tank is full) the tank walls will be subjected to water pressure only, in operation (when the tank is full) the tank walls will be subjected to both soil and water pressure and in maintenance (when the tank is empty) the tank walls will be subjected to soil pressure only.

Blast and impact loads

These loads are caused by explosions or similar situations. Not all buildings are required to be designed for blast and impact loads, however any structure will have an inherent resistance to withstand a magnitude of blast and impact load.

The above is a quick summary of the loads that structural engineers usually consider while designing any structure, and helps those with no structural background understand the meaning of building loads.

Images courtesy of www.canadianarchitect.com and www.dlsweb.rmit.edu.au

BSBG Media Team

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