First of all, Why do you need to know about types of loads on structures?
In order to construct buildings or structures to withstand any possible situation and loading conditions, you need to know the typical loadings that are going to act on the structure.
Load depends on various factors such as
- Source – earthquake, wind, snow, construction load
- The direction of action – horizontal or vertical
- Time variation – static, dynamic
Generally, there are 5 most common types of loads.
- Dead Load
- Live Load
- Snow Load
- Earthquake Load
- Wind Load
Let’s see each one briefly…
Dead Loads are the weight of structural elements, non-structural partitions, and other fixtures.
It remains permanent and constant during the lifetime of the structure, such as columns, beams, walls, wooden doors, windows, glass partitions.
Dead Loads can be calculated by multiplying the unit weight of materials used and their volume.
The dead load of the different material listed below
|Plain Cement Concrete||24|
|Reinforced Cement Concrete||25|
Dead Load of 3 m3 Plain Cement Concrete = Unit weight of PCC X Volume
= 24 kN / m3 X 3 m3 = 8 kN / m3
As the name suggests Live loads consists of imposed loads on the floor which is temporary, changeable and dynamic
Live loads are dependent upon the structure.
- People and Furniture Items are live loads for residential buildings.
- Vehicles & pedestrians are live loads for bridges
- Desks & students are live loads for educational buildings
You can refer IS 875 (part 2) -1987 for minimum live load values.
|DESCRIPTION||LIVE LOAD kN/m²|
|Floors in Residential Buildings||2|
|Floors in Office Buildings||2.5 – 4|
|Floors of Banking Hall||3|
|Residential Staircase & Balconies||3|
|Floors of Educational Buildings||4|
|Factory Garages (Light)||4-5|
|Factory Garages (Heavy)||7.5|
Wind load occurs when the wind blows against the structure or building.
Why take wind load for consideration? Because while the wind blows, it creates three types of loads, which may cause the building to fail.
- Uplift Load – It creates a strong uplifting force, much like a kite flying high in the air. Pressures the structure to move upwards.
- Shear Load – Pressures the building over the edge to tilt, which causes walls to crack.
- Lateral Load – Horizontal force which makes the building go against the foundation and slides off.
It may not be required to calculate wind loads for a small or low-level rising building.
However, it should be considered in the following situations.
- High rise building
- Using lightweight material
- Using critical design shapes (especially in elevations)
- The occurrence of the hurricane in the particular region
If the structure is not enough to withstand the wind load, additional substructures or loads need to be imposed. The historical data of the locality usually determine wind load.
For more details on calculating the wind load, please refer IS-875 (Part 3) -1987
Snow Loads are vertical loads that are imposed on the roof by snow during the snowfall.
These loads are considered only in snowfall areas mostly, in northern or mountain regions all over the world.
Snow Loads are not the result of a single action. It occurs overtime on the roof during the wintertime. Snow deposits on the roof can quickly move by wind forces causing unbalanced roof loads and drifting.
That imbalance loads on the roof cause critical loading force on the structures.
Earthquake or Seismic Load
As the name suggests, the load acts on the structure due to an earthquake.
Due to the ground (movement) acceleration, the building moves back and forth, which causes the structure to fail.
Earthquake loads are specific to the seismic region zone. The Bureau of Indian standards has published the seismic hazard maps for India. Every country has its own set of the seismic zone map.
According to BIS, Seismic zone has been classified as below according to their severity
|Zone II||Very High-Risk Zone|
|Zone III||High-Risk Zone|
|Zone IV||Moderate Risk Zone|
|Zone V||Low-Risk Zone|
Structures in high seismic activity zones need to be carefully analyzed and designed to withstand the Earthquake loads.
Apart from the above five most common loads, there are some other special loads.
- Settlement Loads – These types of loads occur when one part of the structure settles more than the other parts. It is essential to design & study the soil conditions to avoid such settlement.
- Thermal Loads – Every material used in the structure may expand or contract with temperature, which causes significant forces on the structure. That is why we provide expansion joints on most of the structural elements such as walls, floors, etc. So, the elements can expand or contract without disturbing other structures.
- Flood Loads – Floods around the foundation cause these loads. It causes erosion of soil and loss of load-bearing capacity of the building.
- Soil and Fluid Pressure – These loads occur due to high water flow on the soil. It eventually affects the density of soil, which creates lateral uplift force.
- Erection Effects – These loads include transportation and installation of structural members by the equipment. For Example, Metro column construction where the heavy vehicle used to erect the members in the place.
Happy Learning 🙂