Suspension bridges

12/16/16

“How can we create a bridge using the phenomena of tension and compression?”

 

As the scope of humanity’s ambitions and technology grow, so must it’s fundamental infrastructure such as bridges. So if we would like to create bridges that can cross wide spans without faltering, how can we use our own ingenuity to do so? Well, let’s think about it. We know that we can use tension to keep solid objects up. Furthermore, if we experiment, then we can find out that if we attach a beam-like object with tensile supports on both ends to two heavy vertical beams, it would be kept stable. Now let’s apply this system to build ourselves a bridge. First, let’s take a basic, horizontal beam and put in on two end supports. Then, to balance things out, let’s put in two vertical beams, attach them to the horizontal beam, each not too far away from the supports. Now let’s fashion onto these vertical members a long cable that not only connects each support to each other but also contains supporting cables coming out vertically that will hold up the bridge deck, keeping it level in tension, while transmitting the rest force into the members. This is framework is termed a suspension bridge and is one of the most effective bridge designs ever fabricated. Perhaps the most example of a suspension bridge is the monumental Golden Gate Bridge, a 746-meter long piece of metal whose salient engineering has led it to become the most iconic emblem of the San Francisco Bay Area

Factor of safety

11/19/16

“How do engineers deal with loads near the failure point?”

 

When doing engineering, one has to deal with the maximum load that a system can handle. However, in the real world, it would be quite unwise to have loads even near this limit. The rationale behind this is that such a system could experience an unexpected impingement. To illustrate, let’s suppose that enough people stand in an elevator to have it at maximum capacity, if even a rat were to climb into this elevator, then this capacity would be overloaded and the elevator would experience failure. Luckily, engineers tend to be foresightful people, so when developing structures, instead of designing them just to sustain the expected loads, they are created in respect to a factor of safety. A factor of safety an extra “margin” that a structure can support (in terms of a multiple of the expected load), and can be calculated using the formula FoS =Ultimate stress/actual stress . An example of the factor of safety in use is the famous Eiffel tower, which is designed to sustain 4.5 times as much stress than it typically does. In summation, the factor of safety is an intrinsically necessary tool in modern engineering, and has saved countless of lives all over the world.