Link zur deutschen Version: Die Schönheit experimenteller Forschung mit LUSET
Disclaimer: In this post, I am sharing my thoughts on experimental research in structural engineering, based on my experiences at ETH Zürich. Other experimental research fields—especially those involving animals—are outside the scope of this blog post.
I remember my first meeting with Prof. Walter Kaufmann. We had a video call and discussed the scope of the research project I had applied for. At one point, he asked if I had experience with experimental research. My answer was “jayn”—a mix of ja (yes) and nein (no) in German—because I didn’t really know what awaited me.
What is experimental research?
What is its purpose, and why do structural engineers need it? How is it applied? What equipment is required? If you’re asking any of these questions, let me briefly explain the principles of experimental research and how (and why) we apply it in our field.
Experimental research is a systematic, scientific approach in which researchers control and change one or more variables of an observed object using a special test setup, machine, or method. Ideally, only one variable is changed at a time, and the results are compared.
In other words: imagine you are a chef in a star restaurant, trying to perfect your new dish. You might cook it 100 times, but each time you change just one ingredient in a controlled way and observe the outcome. One time you add 5 grams of salt, the next time 8 grams—until you finally achieve the perfect Spaghetti aglio e olio.
In structural engineering, experimental research often focuses on understanding how structures and materials behave under different loading conditions. This can range from testing small-scale material samples—such as concrete cylinders—to large structural components like beams, columns, or even full-scale bridge segments. The goal is to capture real-world behavior, validate theoretical models, and improve design methods.
For example, experiments might be conducted to study how a concrete shell deforms under combined bending and membrane forces, or how a bridge girder responds to seismic loading. These tests provide essential data for refining numerical simulations, updating design codes, and ensuring the safety and reliability of structures.
In medicine, chemistry, or physics, isolating the effect of a single variable is often more straightforward than in structural engineering. Here, to obtain clear results, you must have the right equipment—and without it, you simply cannot perform the tests.
Every structural engineering department at any university worldwide has laboratories and testing setups, but their size and quality vary, directly affecting the university’s research scope and capacity. This is one of the many reasons why ETH Zürich’s structural engineering program is ranked second in the world [1] — and in my opinion, it has the best experimental research lab for structural engineering anywhere.
The Bauhalle
When I first stepped into ETH Zürich’s experimental research laboratory at IBK —known as the Bauhalle—I felt like a kid entering LEGOLAND. The space itself is impressive: 120 meters long, 30 meters wide, and 12 meters high. But more important than its size are the testing facilities inside.
I won’t go into all the details here—you can read more about the Bauhalle here [2] — but I can say that it has almost everything an experimental research lab in structural engineering could have. On top of that, it includes special testing facilities like LUSET and MAST.
And this post is all about LUSET—the Large Universal Shell Element Tester [3].
LUSET
Since I started working at ETH Zürich, I’ve spent most of my time with LUSET. I’ve introduced it to so many people I’ve lost count. Anyone visiting me in Zürich sees LUSET first—only after that I let them get to visit the city’s other highlights 😊.
The Bauhalle itself also gets many visitors. In fact, visiting the lab is part of most IBK events. I can confidently say that over 50-60% of visitors are laypersons, yet they are still quite impressed when they see LUSET—and they always have questions, like:
What is a Shell Element?
Briefly, structural elements can be categorized according to their geometry and load-carrying behavior:
- One-dimensional: Beam structures
- Two-dimensional: Surface structures
- Three-dimensional: Volume structures
Two-dimensional structures can be further classified based on their load-carrying behavior:
- Plates: Loaded perpendicular (out-of-plane) to their surface (e.g., floor slabs)
- Membranes: Loaded in-plane (e.g., walls)
- Shells: Loaded both in-plane and out-of-plane (e.g., domes / curved roofs)
Each type has a different underlying theory and varying complexity in terms of degrees of freedom.
What Does LUSET Do?
From the description above, it’s clear that shell elements are the most complex type of surface structures. Testing them in both in-plane and out-of-plane directions—especially at a large scale—requires a highly sophisticated and precise facility.
LUSET is exactly that. It has 80 in-plane hydraulic actuators and 20 out-of-plane hydraulic actuators, making a total of 100 actuators distributed in four directions (20 + 5 in each quadrant). With this setup, LUSET can apply up to 30 MN (3000 tons) in compression, 22 MN in tension, 11 MN in pure shear forces, and more [4]. Theoretically, we can test any load combination a shell element might ever face.
My Experiences with LUSET
The first project I was involved in with LUSET was the testing of masonry walls under biaxial loading. It was the first time a masonry wall had ever been tested with LUSET [5]. To assemble, transfer, and install the wall into the testing setup, we had to design a special installation system. This required a completely different approach—especially in terms of mounting the masonry specimen into LUSET and applying the loads. The process demanded extreme care and precision to ensure the specimen was not damaged before testing.
The second project is my ongoing doctoral research, in which we will investigate the bent corner reinforcement of reinforced concrete (RC) frame railway bridges to define their fatigue behavior. For this, we equipped the bent corner reinforcement with distributed fiber optic sensors along the rebars to capture detailed strain data. In total, we will test four specimens—each with a different reinforcement layout and corner geometry—to better understand the influence of these variables on fatigue performance.
One testing facility—from a 15 cm thick masonry wall to large-scale frame bridges… each project brings different approaches and challenges.
The Beauty of Experimental Research with LUSET
Once you understand what experimental research in structural engineering is—and what LUSET can do—it’s easy to appreciate the beauty of working with such a unique and powerful facility. It’s not only about operating an impressive machine; it’s about creating experiments that answer meaningful engineering questions, developing innovative setups, and learning from the results—whether they confirm your expectations or surprise you entirely.
Conclusion
Over the past 16 months at ETH Zürich in the kfmResearch Group, I have spent most of my time in the Bauhalle—learning new skills, exchanging knowledge with researchers from other chairs, and observing countless tests. Each day in the Bauhalle is a new opportunity to learn something different and to find new solutions to engineering challenges.
To be honest, if someone asked me now whether I have experience with experimental research, my answer would still be “jayn”—because you can never get enough of it. That is exactly why I named this post Beauty of Experimental Research with LUSET.
Before closing, I would like to thank everyone who has been part of my journey in and out of the Bauhalle. Special thanks go to the Bauhalle team and all my student assistants during this period.
And last but not least, of course experimental research has its downsides. It is not always easy. But as engineers, we are already familiar with the sinusoidal curve—its ups and downs are part of the process.
Caglar Onbasi
Referenzen
- Mickein, Iris: ETH Zurich ranked 2nd worldwide in Civil & Structural Engineering – https://baug.ethz.ch/en/news-and-events/news/2025/03/eth-zurich-ranked-2nd-worldwide-in-civil-and-structural-engineering.html
- Experimental Research (expRES@IBK) https://ibk.ethz.ch/research/ResearchFT.html
- The Large Universal Shell Element Tester (LUSET) – https://kaufmann.ibk.ethz.ch/de/forschung/ausgewaehlte-forschungsprojekte/LUSET.html
- Kaufmann, Walter; Beck, Alexander; Karagiannis, Demis; Werne, Dominik: The Large Universal Shell Element Tester – https://doi.org/10.3929/ethz-b-000379657
- Weber, Marius: «Establishment of an inter-university research and teaching group in the field of structural masonry» – https://concrete.ethz.ch/blog/establishment-of-an-inter-university-research-and-teaching-group-in-the-field-of-structural-masonry/