WOODEN TRUSS BRIDGE STATICS FINAL CHALLENGE: Which One is The Strongest yet The Most Cost-Efficient?

On one Tuesday morning on the 2nd of May 2023, students of the “Statics” class arrived on campus bringing their most prized creations: wooden truss bridges. These structures were the epitome of knowledge gained from the Statics course after four and a half months… or so we thought.

Under the guidance of Dr. Titin Trisnadewi, the lecturer of the Statics course, we were tasked to build bridges using wooden sticks as the final project. The bridges are constructed by the following requirements: they must not have an overall length of more than 70 cm and their width must be in between 5 and 10 cm. The bridges must also not be taller than 15 cm and have to be able to withstand a minimum weight of 3 kg. Another challenge specifically added for this class – which is comprised of mostly Industrial Engineering students – is that the bridge should be constructed using as little economic cost as possible. This project was expected to be the practical embodiment of the theories of Equilibrium of a Rigid Body and Truss Structural Analysis, while also not forgetting to apply force and moment equations into the analysis of the bridge’s joints and sections. Each group was required to orally present their analysis of their bridges in terms of design, forces held by each section, and also economic cost, before putting the bridge to a physical test.

The first group to present their bridge was Tedy, Dheza, Gisel and Nara, who hit the ground running by presenting a simple, light, yet colorful bridge, igniting the insecurities of other groups whose bridges were only plain-colored. Unexpectedly, Tedy applied his knowledge gained from a different course, Engineering Economy, into his group’s bridge’s cost analysis by determining that the bridge will still be profitable at the end of its 10-year service life. Afterwards, the bridge was put to the test; a total weight of 3 kg was slowly put on top of it as their heartbeats raced all across the room. A breath of relief was sighed as the bridge survived the weight, but not wanting to end there, more weights were put, making it hold a total of 5 kg and fully passing the test.

Next, Farhan, Valencia, Karel and Hanum presented their gigantic bridge, which almost fails its specification requirements; it was exactly 10-cm wide and 14.8-cm tall. All four group members were confident in their bridge’s strength, but even so, palms were sweaty as the weights were being put on top of their bridge. As expected, the bridge survived 5 kg, and so with nothing else to lose, Valencia sat on top of the bridge to the horror of everyone in the classroom, and the bridge still survived!

Afterwards, it was Daniel, Stefan, Stefannie and Deny’s turn to showcase their bridge. Uniquely, it was the “skinniest” bridge out of all, having a width of just 5 cm. Daniel gave his argumentation that having a small width allows the bridge to withstand a greater downward force compared to a similar bridge with bigger width. To prove his point, after the group’s oral analysis, their bridge survived 3 kg, 4 kg, 4.5 kg, and finally 5 kg! The session ended with an applause from everyone.

The tests were continued two days after, on the 4th of May, beginning with Raymond, Tria, Ariel and Zidan’s group. Their bridge was the shortest in length, which was 46 cm, and had the simplest truss structure compared to the others, but this group proved that the size and simple structure of the bridge did not affect its performance to withstand the load. After putting the weight gradually on top of the bridge with a 30-cm edge distance, the bridge still stood stably with 5-kg weight on it, making it pass the test.

The next group to present their bridge was group 5 consisting of Henock, Fajar, Fakhria, Miguel, and Ansel. They had the similar truss design with Tedy’s group but this one was wider in size. This bridge had the cheapest cost among all groups which slightly affected the display of the bridge, but it did not really matter. Even with the least cost, the bridge passed the test in holding the 5-kg weight with the bridge length of 65 cm and 50-cm gap.

Finally, the last bridge to be presented was from Ruben, Richelle, Vero, Nael, and Andi. Their bridge had 3 layers of truss structure to make sure it was really strong to hold the greater weight. Sure enough, the 5-kg weight got nothing to do with this 69cm-long bridge. Their bridge with its neat and pleasant display still survived the load after tested on a 30 and 50-cm gap.

Despite the various bridge constructions from the six groups, all of us successfully passed the challenge to hold 5-kg weight and even more with our wooden truss bridges! With the cost analysis presented by each group, the most cost-efficient truss bridge could not be determined instantly by choosing the cheapest cost because a different cost will result in a different quality of the bridge too. However, most groups spent less than IDR 50.000 to make those strong and aesthetic wooden truss bridges and we thought that was a great deal. Jokingly, Ms. Titin said it was not entertaining because none of the bridges broke down, but we were happy because it proved the strength of our bridges. This kind of challenge gave us a lot of fun in making it while also giving a deeper understanding about the Statics course through a real implementation. Cheers to more exciting projects in the future!