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Engineers have been designing bridges for thousands of years. A lot of thought goes into designing the perfect bridge, to ensure that the structure is safe, reliable and able to withstand the test of time. Of course, engineers today have access to more precise tools than the bridge designers of yesterday, allowing them, among other things, to prototype their work far earlier in the process. Though in historical terms, CAD training is a relatively new discipline for architectural or engineering technicians, bridge design isn’t. If you’re interested in using CAD software to design a bridge, the science of bridge design contains a wealth of experience and information that can be very useful for a Computer Aided Drafter to take into consideration, particularly at the level of specification, standardization, and reliability.

Here are a few elements to take into consideration when designing a bridge in CAD.

Superstructure and Substructure

To understand bridge design, you’ll have to learn the difference between the bridge’s superstructure and its substructure. By the bridge’s superstructure, we mean anything above the bearings, including the hard surface drivers used to travel from one side to the other. By the substructure, we mean the bridge’s foundation, including the columns supporting it. The superstructure and the substructure work together but have different goals. Choosing the shape of the structure of your bridge, for example, will affect the substructure. A bridge can be shaped like an arc, suspended by cables, built primarily using powerful beams and more. These design considerations, of course, are more complex than simply asking “What shape do you prefer?” Even if you’re designing a mock bridge as a project for a course at your CAD school, you should take the time to factor in the environment around the bridge and various economic considerations, such as costs of materials, among others.

Tension and compression

Regardless of the shape of your bridge, its key structural components will be beams, arches, trusses, and suspensions. How you use these elements will determine the quality of your bridge. Two forces you should make sure you understand are tension and compression. To understand the tension, imagine a rope being pulled on from both sides during a game of tug-of-war. This is tension, and it’s a force that will act on your bridge to add stress. To understand compression, just imagine what happens to a spring when you apply pressure on it. That’s right – it collapses into itself, which shortens its length. Compressional stress will also affect your bridge, and it will act in direct opposition to tensional stress. The bridge’s design, therefore, must be able to handle these forces without buckling or snapping.


Resonance is another force that can act on your bridge. Imagine a snowball rolling down a hill and increasing in size and speed. This is resonance. It starts with small vibrations, such as when wind attacks a bridge, and those vibrations can continue increasing over time until they take down the entire structure! There are several ways to deal with resonance, but one of the most popular methods is to incorporate dampeners into the bridge design, which can interrupt the resonant waves and prevent them from growing.