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June 27, 2022 through July 1, 2022
Structures and Civil Engineering
Our Task This Week
Our Task This Week
We were challenged to create a 4-foot, balsawood bridge that could withstand a shake table while weight is being added to the bridge, increasing the load. Before building the balsawood bridge, we built four other bridges in various programs to learn about the different aspects of structural civil engineering that we needed to master in order to build a successful balsawood bridge.
- Bridge Kit
To start off the week we began our first bridge exploration bright and early Monday morning. We were given an index card and asked to put the metal nuts on until it collapsed. By the end of the activity we had built support beams and traingles to help distribute the force of the nuts pulling down on our index car bridge. This taught us our first lesson: force distribution.
2. Bridge Designer
2. Bridge Designer
This program simulated the cost and functionality of the bridge we designed. In our model, we experimented with a basic Pratt Truss bridge and altered the material that members were built with and the thickness of each of the members. While still maintaining specific compression and tension forces we attempted to make our bridge as low cost as possible. Members that had smaller diameters and were made out of hollow tubes were less expensive and lowered the cost of our bridge. However, those members were less supportive and risked the bridge collapsing. Thus, came lesson number two: managing materials to make a cost efficient design.
Design
Test
Materials
Net Force Calculations
Net Force Calculations
In the application Bridge Designer the tension and compression forces for each member were given. This allowed us to calculate the net force on the bridge and determine how stable our bridge was. In theory, our bridge should have a net force of zero because under zero pressure there should be no movement. For each joint on our bridge, where multiple members came together, we calculated the sum of the forces in the x and y direction using free body diagrams. When we did this we calculated decimals within one whole number of zero. This shows that our bridge was designed in a structural way that the forces were balanced and our bridge would stand.
3. ModelSmart 3D
3. ModelSmart 3D
In this program we built a scale model of the exact bridge that we built out of balsawood. The program showed red arrows where force was being applied through weight. This allowed us to understand how much weight our theoritical bridge could hold and which beams and members would break under the stress. Once we built the bridge we were able to make specific beams thicker and stronger in order to support the weight. This taught us our third lesson: load and how to manage it.
4. Fusion 360
4. Fusion 360
Fusion 360 is a CAD software by Autodesk where we designed our bridge, before building the final wooden model. This program allowed us to dive deep into the building process. We learned that we must insert notches into the sides of our main plank in order to attach our beams and support structure. This was our fourth lesson of the week: building and functionality.
5. Balsawood Bridge
5. Balsawood Bridge
With all the lessons we learned throughout the week, our team designed, executed, and built a successful balsawood bridge that held 20 bricks each weighing 2 to 4 pounds. Our bridge was four feet long and one foot tall. We had limited materials and had to use our wood and glue very wisely.
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