Understanding External Loads in Engineering Structures

In the field of engineering, particularly structural engineering, it is crucial to understand the different types of forces and conditions that act upon a structure or component. These forces can be broadly categorized as external loads and internal forces.

External loads are forces or actions that originate from outside the structure itself and are applied to it. These loads cause stresses and strains within the material and the structure as a whole.

Let's analyze the given options to determine which one is NOT considered an external load:

• Those arising from environment: Environmental factors such as wind pressure, snow load, seismic forces (earthquakes), temperature changes, and rain can exert forces or cause effects on a structure. These are clearly external influences acting on the structure from its surroundings. Therefore, these are considered external loads.
• Those arising from cohesion of material: Cohesion is an intrinsic property of a material that describes the internal forces holding its molecules or particles together. It represents the material's internal strength and resistance to being pulled apart. These forces exist within the material itself and are not applied from an external source. Thus, cohesion is an internal characteristic, not an external load.
• Those arising from fluid pressure: When a structure is in contact with a fluid (like water or air), the fluid exerts pressure on the structure's surfaces. This pressure is a force applied from outside the structure (by the fluid) and is therefore considered an external load. Examples include water pressure on a dam or pressure on the hull of a ship.
• Those arising from service conditions: Service conditions refer to the normal use of a structure or component. Loads arising from service conditions include things like the weight of occupants (live loads), furniture, vehicles, impact loads, braking forces, etc. These loads are applied to the structure during its operation and originate from sources external to the structure itself (e.g., people, cars, machinery). These are considered external loads.

Conclusion

Based on the analysis, the option that does NOT represent an external load is "Those arising from cohesion of material". Cohesion is an internal property of the material itself.