Different Types of Loads on Structures and Buildings

• 23rd June, 2022

Each and every building or structure has to sustain various forces that could act on it during its lifetime. These forces are considered loads and when the loads are applied to the structure or its components they lead to displacement and stress in the structures.

Generally, the loads on structures can be classified as vertical loads or gravity loads, horizontal loads and longitudinal loads. These loads are used for the analysis and design of the structure. Therefore the knowledge of the different types of loads on structures is crucial.

Different Types of Loads on Structure

Followings are the classification of loads on structures with the different types of loads on structures

• Load Due to Hydrostatic & Soil Pressure
• Load Due to Fatigue or Internally Generating Stress

Dead load is a gravity force exerted by all the stationary or permanent members of the structures like the wall, slab (floors or roofs), column, beam, flooring etc. It’s basically the self-weight of the structure or a building, which remains constant throughout its lifetime. This also includes partition walls, false ceiling, fixtures etc.

The magnitude of dead loads can be calculated if the unit weights of different materials are known. According to the IS 875 (Part 1): 1987 (Reaffirmed 2008), Indian Standard Code of Practice For Design Loads (Other Than Earthquake) For Buildings And Structures- Dead Loads – Unit Weights Of Building Materials And Stored Materials, you can calculate the dead load of the structure.

Gravity forces that are not steady like the dead loads, but keep on changing positions from time to time are called imposed loads or live loads. These include the loads of moving bodies like furniture, humans, books etc. Live loads are variable and can change over time as they depend on usage and capacity.

Usually, live loads are assumed to be uniformly distributed loads or concentrated loads specified by the standard codes of practice. IS: 875 (Part 2) – 1987 (Reaffirmed 1997), Indian Standard Code of Practice for Design Loads (Other Than Earthquake) For Buildings And Structures- Imposed Loads, have specified the live loads for different materials for different types of buildings. For example- the live load of all the rooms and kitchens of a dwelling house of a residential building is 2kN/m2, whereas the live load of the classrooms and lecture rooms of an educational building is 3kN/m2.

You can check here the Live Load: Consideration While Designing a House, which will make your work easy and speedy.

Snow load is the vertical force caused by the accumulation of snow. It is the major concern in the regions likely to heavy and frequent snowfalls where a significant amount of snow can gather and add a generous load to the building.

IS: 875 (Part 4) – 1987 (Reaffirmed 2003)Indian Standard code of Practice, for Design Loads (Other Than Earthquake) for Buildings and Structures – Snow Loads, gives the recommendation for snow load on the roofs of buildings. For the magnitude of the snow load, the shape of the building roof is the most important factor.

Wind load is the horizontal force caused by the wind flow. This pressure is exerted on any building when it obstructs the flow of moving air. Wind load acts horizontally (or perpendicular) on the surface of the structure. The value of wind loads on structures depends upon the velocity of the wind.

IS: 875 (Part 3) – 1987 (Reaffirmed 2003), Indian Standard Code of Practice for Design Loads (Other than Earthquake) for Buildings and Structures- Wind Loads, prescribed different values for different regions based on the geographic location and height of the building.

If you want to know more about wind loads on structures, design wind speed, and terrain for wind speed, then go through our article What is a Wind Load?

Earthquake loads or seismic loads are the internal forces that are developed in the structure because of the ground movement during an earthquake. Earthquake load is both vertical and horizontal pressure. But in the design purpose, horizontal pressure is considered because the vertical pressure doesn’t cause any significant extent to the superstructure. But the horizontal pressure causes movement of the foundation of a structure due to ground motion happening at the time of the earthquake. Indian Standard Criteria for Earthquake Resistant Design of Structures, IS 1893-1984 (Reaffirmed 2003), gives recommendations for earthquake-resistant design of a structure.

We also have written on Seismic Zones of India: All you Need to Know, which will help you to design your structure.

According to the IS 875 (Part-5) – 1987 (Reaffirmed 2008), Indian Standard Code of Practice For Design Loads (Other Than Earthquake) For Buildings And Structures- Special Loads And Load Combinations, Followings are the special loads exerted on the buildings.

The building is designed for a long life of 60 to 100 or even more years. Hence, the building has to be designed for all forces. The building ultimately has to be designed for the worst combination, which it is likely to face during its lifetime, depending upon its location, nature and type of structure. The standard code, therefore, has specified different combinations of loads i.e.

1. DL+IL,
2. DL+WL,
3. DL+IL+EL,

After knowing this, one obvious question will strike in your mind, Which Load Combinations are to be Considered While Structural Designing of a House? So, click on the below link for your answer- know the load combinations for structural designing of the house.

Due to temperature changes, structural materials expand or contract, which occurs the significant loads on the structure.

08. Load Due to Hydrostatic & Soil Pressure

A significant load occur due to the pressure exerted by soil or water, or both. It exerts in the structural parts of below ground level, like foundations, retaining walls, the basement floor walls, etc.

09. Load Due to Fatigue or Internally Generating Stress

A load exert due to internally generating high stress due to creep, shrinkage, differential settlement etc.

Accidental loads occur due to human actions, it includes impacts and collisions, explosions and fire.

• Examples of impacts and collisions are dropped objects from cranes or forklifts, crane failures etc. In brief, impact loads are sudden loads applied to a structure for a short period of time compared to other loads on a structure. Impact loads are caused by the dropping objects/weights vibration of live loads, like moving cranes, moving vehicles, or vibrating machinery. They produce larger stresses in structural members than those produced by gradually applied loads of the same magnitude. Impact loads can be both vertical and horizontal.
• Examples of explosions are boiler failure, external gas cloud explosions, External explosions of high-explosives like TNT, dynamite etc.

In the final notes, there is always a need to pay attention to the types of structural loads that will be exerted on the building because the loads and their impact have a direct connection to the safety aspects of the structure. Anybody not wanting to compromise on the safety factor needs to understand the various loads that the building is faced with during its lifetime.

I hope, after going through this article, you clearly understand the different types of loads on structures or the buildings in their whole life.

Shreya

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