CIV102: Matboard Beam Bridge

I worked on this project with teammates Jeffrey Zhu and Riley Ellison.

Project Description

In this project, our team designed and built a matboard beam bridge to span 1200 mm and withstand the loading of a rolling toy train. Our final bridge design had a Π-shaped cross-section with a multi-layered top flange and varied diaphragm spacings. The bridge was able to withstand a load of 580 N during testing. The design process involved using structural engineering knowledge from the course to write a Python program to calculate factors of safety of our design, and predict how well our bridge would perform during testing.

Opportunity: Design a beam bridge to span 1200 mm and support a rolling toy train

We were tasked with designing a beam bridge using one 32” × 40” × 0.05” sheet of matboard and ~60 mL of contact cement. Some key requirements for the bridge project were as follows:

• The beam had to span the 1200 mm gap illustrated below.

• The deck height was required to be < 200 mm.

• The width of the bridge had to be ≥ 100 mm.

The bridge was to be tested under progressively increasing load cases, ranging from 400 N, and gradually increasing the load until failure.

Final Bridge Design

Below are the drawings for our final bridge design.

Some key features of the design are:

• The Π-shaped cross-section

• The 80-80-90-90-90-158 mm spacing of the diaphragms

• The triple-layer top flange, consisting of three sheets of matboard glued on top of each other

• Small L-shaped reinforcements to stabilize each diapgragm

A photo and a video of our bridge being tested are shown below.

Key Design Decisions

• We chose to use a Π-shaped cross-section instead of an I-shaped cross-section. When analyzing the I-beam, we realized that the factor of safety against compression at the top was much lower than the factor of safety against tension at the bottom. This meant that the top of the cross section was stronger than it needed to be. The Π-shape allowed more material to be distributed to the top of the beam. This moved the centroidal axis closer to the top of the cross-section, thereby reducing the compressive stress near the top of the cross section, and increasing the tensile stresses near the bottom.

• We redistributed material from the webs to create a multi-layer top flange. This also served to increase the cross-sectional area near the top of the bridge and thereby decrease the compressive stresses in that area.

• We also chose to modify the diaphragm dimensions and placements along the span of the bridge. We chose the 80-80-90-90-90-158 mm spacing of the diaphragms because this allowed us to concentrate reinforcements near the extremities of the bridge, where the side flanges were the most susceptible to plate buckling. We also chose to slightly reduce the height of the diapgragms, in order to reallocate material to reinforce other components.

This Project in Context

This project provided a somewhat different experience compared to the other project I was working on at the time (Praxis I project). The bridge project had a narrower scope and the broad design concept was already determined for us (we were asked to build a beam bridge). Moreover, this project involved lots of technical and theoretical knowledge related to the CIV102 concepts themselves, in order to write code to perform calculations throughout the design process. 

This project contributed to forming my value of curiosity & learning in engineering design. One thing I really enjoyed about this project was how it allowed me to consolidate my understanding of the concepts from the course, and this was a genuinely exciting and joyful experience. The skills and understanding I gained through this project made me more confident to potentially apply these concepts in future projects.

In this project, I also consolidated my value of teamwork and further enacted my curiosity & learning. Before starting the project, I had very little programming experience, apart from a few months of coursework. I also had no experience using GitHub, whereas one of my teammates did. Instead of simply letting that teammate do wih all the coding portions of the project, I made a point of learning how to use GitHub to collaborate with him on the code. At the same time, that teammate was able to give me tips and help me familiarize myself with GitHub. By doing this, I was able to acquire new knowledge and skills at a faster rate than I would be able to do otherwise.