Everyday we use structures or physical objects to carry forces for us. This can be in the form of furniture, consumer products, transportation, buildings, toys, machines etc. As engineers we are expected to build new structures all the time. When designing the structure or object for a specific task we need the material to be strong enough to handle the forces involved with its intended use.
When these external forces are being applied with no movement/acceleration we can use an equilibrium analysis to understand how they will translate to internal forces that the material will have to support. Then we can select a material strong enough to withstand every day use with an added factor of safety.
In your original post, include the following:
Choose a structure or object and explain how to construct a free-body diagram (FBD) of part or all of it.
Show your structure/object and the free body diagram you created for it.
Explain the difference between the external forces on the structure and the internal forces translating through the material itself.
Make sure to choose a real-world example that is different from your peers!
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One structure that can be chosen for this exercise is a bridge. Bridges are essential infrastructure that are designed to support the weight of vehicles, pedestrians, and other loads on top of them.
To construct a free-body diagram (FBD) of a bridge, we need to identify the external forces acting on it. These forces typically include the weight of the bridge itself, the weight of the vehicles and pedestrians on the bridge, and any additional loads such as wind or seismic forces. We can also consider reaction forces at the supports of the bridge.
Imagine a simple beam bridge supported by two columns on either end. The weight of the beam and any vehicles or pedestrians on it will act downwards as a concentrated load at various points. Additionally, we will have bending moments acting along the length of the bridge due to the weight distribution.
The FBD of the bridge will include arrows representing these external forces. The weight of the bridge itself will be depicted as a downward arrow acting at the midpoint of the bridge. The weight of the vehicles and pedestrians can be shown as concentrated loads distributed along the length of the bridge. The bending moments can be illustrated as clockwise or counterclockwise arrows depending on the direction of the moment.
The internal forces in the bridge refer to the stresses and strains that develop within the materials of the bridge to counteract the external forces. These internal forces can include tension, compression, shear, bending, and torsion forces, depending on the type of bridge and the nature of the loads acting on it. It is crucial to design the bridge with materials that can withstand and distribute these internal forces effectively to ensure structural integrity and safety.
Real-world example: For instance, a truss bridge can be a suitable example. A truss bridge consists of a series of triangular structures interconnected at joints. The external forces acting on a truss bridge include the weight of the bridge itself, the weight of the vehicles, and any additional loads. The internal forces within the truss members will mainly be tension and compression forces.
In conclusion, when designing structures or objects, considering the external forces and their translation to internal forces is crucial. Choosing materials with appropriate strength and understanding the equilibrium and distribution of forces becomes essential in ensuring the desired function and safety of the structure.
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