CHAMPAIGN, Ill. — Bamboo skewers carefully arranged in the form of a truss span the space between two tables in the Temple Buell Architecture Gallery. Students gather around to watch as 5-pound and 10-pound weights are added one at a time, either on top of the truss or hanging from the bottom along its length.
How to place the load? Place the weight evenly. Is this the best place for it along the truss? Will it break or stand another? Gently, gently. Then there is a crash, the clank of the falling weights and the cheers of the students.
Each spring, sophomore students in the School of Architecture at the University of Illinois Urbana-Champaign are tasked with building a truss, using bamboo skewers, that is about 2 feet in length, 6 inches wide and 8 inches tall. In their Structural Fundamentals class, students are introduced to architectural structures through physics, mathematics and physical modelling. Abstract concepts about the distribution of loads are tested in a tactile, hands-on model.
Design in the discipline of architecture is aesthetic and functional. In this case, the object being designed is a structural item that carries the load of the building. Beams, columns, braces and trusses all do this. Load comes from the environment and from the materials themselves. For example, the load on a roof might be rain, wind or snow, and gravity pulls on the roofing materials and the beams that hold them.
The trusses that the students designed for this project are horizontal elements that often support roofs. They have depth but also let light through, making them seem lighter than they are. Trusses are efficient, as the material and form of each truss are positioned to carry a good deal more load than the weight of the truss.
The other key characteristic of trusses is that they are composed of triangular elements. These elements carry the load along their length, and their geometry provides stiffness. Students learn to calculate the forces and their distribution in these members. The project asks students to define the shape of the truss and place triangular members to form a whole truss. The students’ creativity is evident in the trusses’ many configurations.
Over the course of three weeks, students explore designs on paper and then begin to bring their ideas from the page into reality — first, by building small models, and then segments of the full-sized one. They make several single trusses, then connect them. How do they join? How do the individual truss members come together? In a building, trusses are fabricated from steel and wood with carefully crafted details, designed to precisely connect. These connections must both transfer load to each other and be constructable, allowing the human hand to bring the elements together.
In the Structural Fundamentals class, students use stiff bamboo sticks. They shape the cut (diagonal, notched or straight) and choose the connecting material (glue, wire, even dental floss!). The truss is made from multiple pieces. If one connection fails, the whole truss fails too quickly. Though only working in bamboo, students learn the importance of structural connections.
Once their trusses are complete, the students test them to see how much weight they will hold. Each team brings their truss to the testing area, which has blocks or tables to hold them. Students then load the trusses by placing weights on top or hanging the weights with hooks from the truss. Each weight is added slowly and carefully, until the truss breaks and the weights clatter on the floor.
On average, the trusses weigh 0.43 pounds and support 76.5 pounds. Something that weighs less than half a pound carries just over 75 pounds, or 178 times its own weight! Some trusses supported more than 200 pounds. Others carried 300 times their own weight.
The grading of the truss project includes factors such as creativity, design, construction and efficiency — all considerations when designing a structure and a building. In this project, students design and build a truss to investigate material, load paths, truss behavior, structural efficiency and architectural design. Their work was thoughtful and creative. Building, testing and breaking their trusses led to a great event and, hopefully, many lessons learned.
Editor’s note: To contact Marci Uihlein, email muihlein@illinois.edu.
Subscribe to Behind the Scenes for short blog posts, photos and videos from Illinois faculty, researchers, students and staff about their work and lives. Send an email with “SUBSCRIBE BTS” in the subject line.
