balsa wood bridge designs for efficiency

All Rights Reserved. 40 Bulls Bridge Road If you are making your bridge for a competition, be ready to see it break. The bridges are usually tested using the following techniques: Most competitions use the hanging weight testing since it is easy and cheap to setup, and also produces spectacular and dramatic bridge destruction events. The thing is, it all depends on how you're loading the weights onto your bridge, how much weight is on it, how much material you have to work with, what you're using to glue your wood together, what joints you're making, etc which is kind of what your teacher is trying to get across and may not be the answer you're looking for. Its a pretty efficient design. I also have laminating glue and very strong wood glue. Good luck! When it comes to civil engineering, less is usually more. Simplicity is your friend. South Kent, CT 06785 Leave enough time for building an another (and hopefully enhanced) bridge. Simpler is better for these competitions. A Pratt Girder truss is a very good truss because all the diagonals will be in tension and the verticals will be in compression. -Look at a 'braced king post truss'. If you can, record your tests using a camera. -You'll be working with fairly short lengths so any complex arch or truss will have an error somewhere and fail through cascade. Only when the bridge breaks can the judges determine how well made it is. Setting the limits on the minimal and maximum width of the bridge, Setting the limits on how long balsa wood bridges have to be dried before they can be deemed eligible for competition, It can have inconsistent density, which may lead to unexpected buckling or snapping when under strong load. Length is 30-40 cm. It is heavier and more expensive, but it is also stronger, resistant to crushing, with same strength throughout entire stick, it can bend more, and it can hold together better at glued joints. Balsa wood bridge building is an educational technology that is often used to promote subjects areas such as engineering, physics, static equilibrium and building trades. Advanced bridges are usually focused on designs based on arched, cantilever and bowstring bridges. If I could go back, it wouldn't have all the truss members connect at the same place. While the bridges can also be created from smaller, lightweight and easily manageable building materials such as toothpicks or popsicle sticks, bridges created using balsa wood are much more durable and versatile. I wanted to reward those who took some risks; in many cases, those risks paid off.. Weights are gradually added to projecting bars connected to the vehicle until bridge failure occurs. Pay attention to your joint construction, you have lots of transfer forces there. Schools often include the balsa bridge building sessions in the curriculum, trying to promote practical application of knowledge that students learned during a section or unit covering a related physics or engineering topic. << /Length 5 0 R /Filter /FlateDecode >> x]6)x(sly;#,YZqdig> "}( 4 0 obj If you have the time and patience, make an arch and then a few supporting members along the arch to create a sort of truss. Don't nail through the basswood obviously, just make the outline for it using nails. Can you confirm or deny? I was wrong on the arch, it is the correct orientation that it could work since you have a tie underneath to balance the thrust. This years winning bridge, with an Efficiency Ratio of 1.20 and supporting an impressive 89 lbs., was engineered by Zhenghao Dong (Qingdao, China). Rong Huangs (Beijing, China) bridge came in third with a 1.67 ER and a 34-pound load, Hayden Giampietro (South Kent, CT) was fourth with a 1.73 ER and 44 pounds, and Jack Robilotti (New York, NY) earned fifth place with a 1.85 ER and 59 pounds. Loading plane is between .3 and .4 cm high. I'd recommend laminating the arch to be 1x2 if not 2x2. Arches rely on thrust resolution at the bottom and your truss is not going to be restrained on the left and right sides to allow arch thrust to develop so it will not be as useful a component as a straight truss part. Your job as an engineer is to fit the design to your purpose, 40cm = simple. Pay good attention to the joints too, if things don't line up well, then you're not going to be transferring loads properly. The max mass is 30 grams and as usual performance based on efficiency. Enjoy! Stagger your splice joints where possible. They can also save the bridge from being destroyed by sensing exactly when the bridge starts to buckle and executing immediate reduction of testing forces. Hanging a weight (usually container that can be filled with various smaller weights) from the specified points on the bridge. Scoring of bridges is done using the following techniques: 2022 - History of Bridges | Privacy Policy | Contact, Requiring builders to achieve at minimum set bridge span, Restricting the maximum mass of the bridge, Restricting the physical size of the bridge, Restricting the size and shape of structural elements of the bridge (the individual pieces of balsa wood), Restricting the amount of glue that can be used during the construction, Limiting the types of glue that can be used for connecting pieces of balsa wood, Requiring the minimum or maximum height of the roadway, Requiring that roadway remains drivable for the selected type of vehicle of the specified size, Restricting the building techniques of the bridge (for example, banning the use of parallel joining pieces), Limiting the use of paints or other forms of sealant, Limiting the use of non-glue materials such as string wires, sticky tapes, gussets, pins. Thanks so much for the advice. The bridge building is also used extensively as a tool that can guide students to understand the desired subject area better, learn more about structural design or the process of building bridge structures. Your truss verticals and diagonals will have the highest compression or tension near the ends of the span. Thanks and Merry Christmas! The testing can focus on specific points on the bridge (its usually a middle of the bridge) and different ways of applying the force. So far, I haven't seen any evidence to support this. p`P#]]5.fljn\ q`&0t*`\` a~z.i bui%/? KjGp9 &8f?gvC] pnywqy*uW5q Lap joints are 100x better than butt joints. While project grades were not strictly based on the Efficiency Ratio, he noted, some of the strongest bridges were also the ones which incorporated more complex elements like bent and laminated arches over carefully-constructed substructures. It helps to tie the top chords and the bottom chords together as well as x-brace between the two parallel trusses, (top chord to opposite bottom chord) this will help with stabilization. As for building the balsa wood bridge, there are quite a few tricks I learned in actual construction that made the bridge 10x stronger by reinforcing weak points. Don't do an arch at the top. All the bridges were weighed before the competition and each bridges weight, and total load before failure were used to develop an efficiency ratio. Make sure you add some horizontal bracing to resist buckling. The core forces that govern the stability of loaded and unloaded bridges are Compression (pressing of the bridge component into itself, which eventually leads to buckling) and Tension (the force that wants to rip bridges components apart, which eventually leads to snapping). It's fun and all to have a unique design, but if what you have on paper isn't serving a purpose, then it's just a waste of time, effort, and material Start by satisfying the base conditions like how long and tall you need things to be, then get into beefing up the members that are going to fail under load (typically the center of your span). http://imgur.com/a/1t8av. For making the arch, the important thing is that both arch halves are as identical as possible. Mr. Berghold, the Pre-Engineering teacher, was pleased with boys results. Some devices of this type can also exert predetermined forces or patterns of forces on the bridge. The goal of almost each balsa wood bridge competition is to build a bridge that can withstand the greatest weight before it fails. The best way to prepare for the competition is to build a bridge that you can fully test (and destroy). This annual event challenges each student in the Forms Pre-Engineering class to design and construct a bridge using slender balsa wood strips and glue. Mind including a picture of the materials you get to use? Instead, they would connect along the bottom like a more traditional truss bridge. (860) 927-3539. Number one thing though, have fun! Your diagonals should be at 45 degrees to the chords. Thanks so much. -Before you cut any lengths work out how you're going to arrange your joints. I am designing a bridge(picture linked above) for my high school physics project. Last years winner topped out at 45 pounds. The one I designed was 27g and held about 110 lbs. This is done by making at the same time and also making some sort of frame or restraining system for them. The main test for all balsa wood bridges is seeing how much downward force can it endure. When it comes to the balsa wood, look into laminating the sticks together (doubling them up and lapping the ends). oxS({?S=>aPup]JR/Z)#|O kJ%VD+OCy8x6IE^[M;8 nPMC}E"GlY}Cd^Qrji_^ >tE @8WRytj-s z.w\cAkjAy[xMWh~GxX8#"v:S6u]M=A64^*-"cOzn4/I{z.ATT01. The process of building small bridges involves taking small individual pieces (sticks) of balsa wood, modifying end points to fit the chosen design carefully gluing the pieces one to another until the fully functional bridge framework is created. %PDF-1.3 The best way to analyze what has caused the destruction of your bridge is to record the test using the high-framerate camera (many modern smartphones support this feature). But an engineer can build a wall that just won't fall down. If you're looking to blow the other kids out of the water, I'd suggest taking a look at some simple truss designs on the web (the tried and true designs). However since there is so much variety between each competition, students are often instructed to comply with a vast array of additional challenges, restrictions, and rules. Everyone above has good engineering advice on truss design. Also, i sander down about 5g of glue and wood to get it to 27g. 2nd year civil engineering student here. Zhenghao credited his elaborate substructure for providing his winning bridge with the strength to redirect the considerable forces away from the center of the bridge, adding I also made sure every joint of my bridge was strong, so there would be no obvious point of weakness. Vertical supports from the roadbed to arches also strengthened the road surface under the test vehicle. Using a mechanical or pneumatic testing device that pushes down of the bridge until the bridge breaks. Recently done a balsa wood bridge so have some recent experience. \yn~Ph ,1?)XoS ? z4 Setting limits on the angle at which bridge member pieces can be joined one to another (for example, at least 30 degrees). I have enough of those to build pretty much any 30 gram bridge. Because of this added layer of complexity, bridge building projects that are done before high school are usually not utilizing balsa wood. Some of the most common competition requirements are: While the bridges can be made from various types of woods, balsa remains one of the most popular because of its core properties. If you do 2x1, make it so that the 2 are vertical rather than horizontally stacked. Your top chord will be in compression at mid span and the bottom chord will be in tension at mid span, don't place a splice here. Do this at the middle and at the ends and at quarter points. Patrick Harringtons (Huntington Beach, CA) bridge was a close second with an ER of 1.58 and a supported load of 44 pounds.

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