File-Folder Bridge

There is a problem-based experiment called “File-Folder Bridge” ,which provides student with an opportunity to learn Structural Theory and Mechanics of Materials. The Folder can resist tension strongly instead of compression, so in File-Folder Bridge experiment we must design a bridge which uses the property of it: If the member is loaded as compression we must increase the strength of it, conversely if the member is loaded as tension we can use less quantity than compression. In order to analyze or design a bridge, we must obtain the force and stress in each of its member by Method of joint and Method of section. All of these can let students explore Mechanics and be interested in it!

The “Civil Engineering Cup” hold a File-Folder Bridge game every year, and we organized a team to take part in it. Our main design is shown in, Fig. (a), a simple and conventional style:

We use a folder stick to be the column of bridge, which is only subjected to axial compressive force, and two triangle chunks to be the pin support. A folder tape to dangle the load, which can be treated as cable since it is soft enough.

There are many problems you must tackle when design a bridge. For example, stress concentration occurs at section where the cross-sectional area suddenly change, which may increase the stress so that the maximum load decreased. Another problem is the shear force, because the folders do not have enough strength to resist shear force, so we must avoid the shear force occurring at folder tape as much as possible. In our design, the shear force occurs at the pin support, Fig (b), so that the folder tape cracks, Fig (c).












(b)

(c)

There is still a problem called Buckling, when the column is subjected to too much compressive so that the column have lateral deflection, which may decrease the maximum load of column as shown in Fig (d).

(d)

(e)

We produced and tested three bridges in total at NCU Experiment Center of Civil Engineering. Fig (e) is File-Folder bridge experiment instrument at experiment center. First, the bridge can not hold 150kg load (the lowest load of the instrument is 150kg) since folder tape cracked at pin by shear force. Second, the bridge also can not hold the lowest load 150kg, the problem is same. Final, we reduce the wide of tape and make it thicker than before to resist the shear force, and the result of experiment is 160kg load. The standard of rating in Civil Engineering Cup is Efficiency Factor, which is calculated by formula: E=L/w, L : The final load before the bridge fractured; W: The bridge’s weight. The results of the game of our bridge is L=175kg and W=191g E= 916. Unfortunately, we did not win the game.

In my opinion, if we have an another chance to challenge File-Folder Bridge, then there is one thing we can improve: We can try to code a program to analyze the bridge so that we can know the theoretical stress in the member which may help us to design better bridge. Finally, I must appreciate my team members, because the File-Folder Bridge is a hard work, only cooperation can overcome it.

全國大土盃的時候我參與紙橋的比賽
我把這些回憶弄成東工大報名的講稿
弄得不是很好
周老師幫我改了很多
感謝