Structural Optimization of Cross-Laminated Timber PanelsPaul Mayencourt, Irina Rasid, and Caitlin Mueller, IASS 2018 Symposium, 2018
Cross-Laminated Timber (CLT) panels are gaining considerable attention in the United States as designers focus on building more ecological and sustainable cities. These panels can speed up construction on site due to their high degree of prefabrication, and consequently, CLT is deployed for slab systems, walls and composite systems in modern buildings. However, the structural use of the material is inefficient in CLT panels. The core of the material does not contribute to the structural behavior and acts merely as a spacer between the outer layers. This project offers an alternative design of an optimized CLT panel with the goal of reducing material consumption and increasing the efficiency of this building component, which can help it become more ubiquitous in building construction.
In this paper, a theoretical model for the behavior of optimized CLT panels is developed, and this model is compared with scaled physical load tests. The results demonstrate that the theoretical model accurately predicts physical behavior. Furthermore, around 20 % of material can be saved without major change in the structural behavior. The reduced material consumption and cost of the proposed optimized CLT panels can help mitigate the ecological impact of the construction industry, while offering a new competitive building product to the market.
The Arc Lamp workshop at AAG 2018: active bending and digital fabrication
Digital Structures' Caitlin Mueller, Paul Mayencourt and Pierre Cuvilliers were in Gothenburg, Sweden this September 2018, teaching a workshop on active bending at the Advances in Architectural Geometry conference hosted at Chalmers University. In this workshop, we explored the design of bending-active structures with variable cross-sections to fit a target design shape. Over the two days, the participants used computational form-finding tools for bending-active structures, and each designed and built an arc lamp. The participants learned state-of-the-art methods for simulating bending-active behavior and for the control and optimization of their equilibrium shapes. These methods could be applied to the design of large-scale bending-active structures such as elastic gridshells.
After a short introductory lecture on active bending structures, the workshop immediately got very practical, with the participants testing the plywood we would use to build the lamps, determining stiffness and resistance. With these values on hand, it was time to start trying out the design workflow on small-scale prototypes. Small teams formed, first design ideas emerged, and we started comparing the designs against their simulated shapes and against each other. The prototypes were laser-cut sheets of plywood, with rudimentary attachments; this made iterating on designs a lot easier.
This prototyping stage gave everyone a better sense of the design space we were exploring, and let us start exploring the limits of the software tools. For the next step, we designed lamps at a much larger scale: 2-to-4-meter strips of plywood, from 4-mm- and 6-mm-thick sheets. After finalizing the designs, it was time to start up the CNC router.
As soon as the cuts were ready, it was assembly time. We fabricated bases for the lamps in the beautiful wood workshop of Chalmers University, then moved to the conference space where the lamps would stay on display for 3 days.
Most lamps found their spot next to another bending-active structure, a wooden pavillion designed by Alexander Sehlström.
The rest was spread around the conference space, and all were very intriguing.
Some construction details:
All the lamps we built:
Overall, a great workshop. We all learned a lot in these two days!
Joinery connections in timber frames: analytical and experimental explorations of structural behaviorDemi Fang and Caitlin Mueller, International Association for Shell and Spatial Structures (IASS), 2018
Innovations in mass timber have ushered in a resurgence of timber construction. Historic timber structures feature joinery connections which geometrically interlock, rarely featuring in modern construction which utilizes steel fasteners for connection details. Research in the geometric potential and mechanical performance of joinery connections remain disparate. This study seeks to develop a performance-driven design framework for the geometry of joinery connections. Experimental and analytical models for three types of joinery connections are presented and compared. The T* type joint, which uses a T-shaped tenon instead of a dovetail, experimentally showed the highest rotational stiffness. The analytically predicted rotational stiffness of the T* type joint comes within 20% of the experimentally determined value. A preliminary parametric study through the analytical model demonstrates how geometric parameters can be varied to achieve desired rotational stiffness.
Felix Amtsberg's Bamboo Pavillion "Sombra Verde" opened in Singapore2018-05-09, Tags: 3d-printing additive-manufacturing digital-manufacturing fabrication
The bamboo pavilion “Sombra Verde” combines digital fabrication technology (I.E. 3D-printing) with natural grown resources in a spatial grid structure. Visual sensing digitizes the section geometry of each bamboo pole, which is used in two ways.
The bamboo poles are placed according their load-carrying capacity
The specific section geometry informs the digital model to fabricate a bespoke dowel system
Conventional 3D-Printers on PLA base materialize the 36 joints and 234 connectors using eco-friendly PLA and merge natural and "digital" materiality.
The project, which was developed and designed by Felix Amtsberg, Felix Raspall and Carlos Banon of AIRLab, can be visited in Duxton Plain Park until the 15th of June.
Paul Mayencourt presents at 2018 International Mass Timber Conference2018-03-21, Tags: conference digital-manufacturing optimization structural-optimization timber fabrication
Paul Mayencourt is presenting his work on "Digital Fabrication and Structural Optimization of Timber Beams" at the 2018 International Mass Timber Conference in Portland, Oregon on March 21, 2018. Demi Fang will also be attending the conference to represent Digital Structures.
Design, mechanics, and optimization of interlocking wood jointsResearch, 2017 - Present
Despite the longstanding craft of interlocking wood joints in North American and East Asian carpentry, modern timber structures frequently use metal connectors in mid-rise construction. This research explores the structural capabilities of interlocking joints between beams and columns for mid-rise timber frame construction. Research methods include parametric design, structural modelling, digital fabrication, and experimental load testing.
Computational tools and experimental making in timber construction: In conversation with Christopher Robeller
Of the many exciting innovations in digital fabrication permeating architecture research today, the work of Christopher Robeller stands out in the growing field of timber construction. Robeller completed his PhD in 2015 on the integral mechanical attachment of timber panels at Ecole Polytechnique Federale de Lausanne (EPFL)’s laboratory for timber construction, IBOIS. He spent the following two years as a post-doctoral researcher at the Swiss National Centre in Research (NCCR), applying his research to the construction of a fully functioning building: the Vidy Theatre. Recently appointed Junior Professor in Digital Timber Construction at TU Kaiserslautern, Robeller presented his process and experience working on the Vidy at the ACADIA 2017 conference at MIT in early November of this year.
Robeller also stopped by to chat with us about his work and his thoughts on wood, the built environment, and the importance of experimentation in making. The questions and responses below have been edited for clarity.
Digital Structures: How did you get to be interested in and involved with wood?
Christopher Robeller: My family has been working with timber for a couple of generations, but for more pragmatic things like making windows. My fascination from childhood was always that wood was a nice material to work with - it’s not too dirty, and it’s something you can craft. It’s even got a nice smell to it! It’s a material I’m very passionate about.
DS: Can you describe your training in architecture and/or engineering?
CR: I studied architecture at the London Metropolitan University. It was not a mixed course, but I was always very interested in engineering at the same time. I was very impressed by all of the creativity and ideas being generated in architecture school, but there was a point where I realized that in order to make it really work, you have to overcome a lot of engineering challenges, and only if you really manage that can you make really great architecture.
I have combined my interests in architecture and engineering in the last few years. I first worked with Achim Menges, through which I collaborated a bit with Jan Knippers’s laboratory, a team of mostly engineers. When I went to IBOIS at EPFL for my PhD, I found that I was one of the few architects - there were times when I was one of two architects on a ten-person team.
It would be a shame for a building to have a strong and interesting architectural concept but have details that don’t match the quality of the rest of the building. I found an opportunity through the PhD to focus on those more in-depth aspects of geometry, fabrication, and engineering.
DS: What are your thoughts on relationship between architecture and engineering?
CR: In my traditional experience in architecture, there is not much interaction. You expect the engineer to figure it out, and most projects rely on the state-of-the-art. Architects and engineers get to work much more closely together in more experimental projects in academia.
Computational tools offer a chance for architects and engineers to work together. These tools offer control over design, and that control is valuable in both fields. There is only so much you can do with a software that comes off the shelf that was developed for certain purpose; if you want to use the software for a different purpose, you have to modify the software to make it do what you want it to do. Architects and engineers are starting to take advantage of this.
This area is where the two fields reach a bit of a common language. I am seeing computer scientists, civil engineers, and architects work on similar collaborative models. You might find a very interesting solution for your architectural or engineering problem in some algorithm that has just been developed by some computer scientists. Then you can get together and plug in together if you’re working on a common ground such as a common programming language.
DS: What are your thoughts on the relationship between academia and practice?
CR: They can be worlds apart, especially in timber construction. The community of timber construction is highly skilled but can sometimes be rather conservative. On the other hand, there is the creative and artistic community of architects who design amazing things with timber. It’s really interesting how you have to find a balance between these two groups because they can be very far from each other.
Given the complexity of wood, you have to bring the two groups together. You have to talk to the companies in the construction industry that specialize in timber. In design and engineering, we are usually generalists working with many materials, whereas these companies have long ago specialized in one material and have gained a lot of knowledge over the decades. That’s something that should be respected. If you get in touch with them - which you only do through these experimental projects - you learn a lot from them.
There is a lot of discussion right now over the social component of digitalization. There is a danger of neglecting people who are not in the loop. Once again, computational tools allow you to integrate people in industry into the design process. I think we’ve done that with the Vidy Theatre: we went to companies, talked to the experts there, and included them in the process. I specifically developed a program that the fabricator there could use. We didn’t use software that eliminate the engineer and the fabricator from the design and manufacturing process. It’s something we should think about: how these digital workflows can incorporate specialists.
DS: Do you hope to continue bridging these fields - architecture and engineering, and research and practice - through your new professorship?
CR: I am definitely trying to bring the four worlds together. People in practice already know how to do things; they’re absolute professionals in the state-of-the-art. In teaching, the beauty is in not having that expertise yet. This lets you think about things in a completely different way, in a free and open way, and you might come up with interesting and intuitive solutions.
For example, I was making the first prototype for a timber plate shell construction project in the workshop by myself, with my hands. I was assembling the prototype on its side because intuitively it made sense to allow the weight of the elements to help with insertion. But in building design, it was being designed right-side-up as usual, and that was what was causing all the problems when we tried to put together a larger prototype. It wasn’t until we finally thought back to the first prototype that I built sideways that we realized what the problem was. I might not have had that experience if I hadn’t made that prototype myself.
Timber plate shell prototype assembled on its side. Image courtesy of Christopher Robeller.
Great architects and engineers are people who quite often have been working physically themselves making things, making prototypes and models. This very rarely happens in actual architecture-engineering design processes - it’s only in academia that a designer of a building actually goes and makes not only a representational model but a functional model of some joint or assembly - himself.
Robeller (left) chats with DS students Courtney Stephen (middle) and Paul Mayencourt (right).
DS: What is something that excites you the most about future possibilities in wood?
CR: We can do amazing things with timber in fabrication, and I think that’s the biggest development in the last ten, twenty years. If you had shown me our work on the Vidy Theatre ten years ago, I would have thought it was magic. Now having done all of it, it doesn’t really seem like magic anymore.
We have come a far way, and it’s much easier to do these things now. While geometry processing and fabrication have become more manageable, the building implementations allow us to focus on new challenges such as integrated concepts for structural engineering and building physics.
One reason I went to IBOIS is because of their machinery (5-axis CNC machine). If you want to experiment with the making of today, you need the technology to be accessible; you don’t have that everywhere. In educational institutions, it’s very important to not only have the technology but to have it accessible to the greater community.
It’s funny, I talked to companies like Blumer Lehmann - they had their first 5-axis machine in 1985. That’s how long they’ve had it! Mechanically, not much has changed. You probably could have done the Vidy Theatre back then. The computer was surely capable enough. The limitation was accessibility: you didn’t have the CNC machinery in universities, at least in architecture and engineering. CNC technology may have been developed at MIT, but it took a long time for it to come into architecture and building in a way that’s accessible to the architecture research community.
Construction of Vidy Theatre. Image courtesy of Christopher Robeller.
Another exciting challenge I see is that not only do we have something very beautiful, but we also have something that can make a positive impact in terms of the ecological construction that we need so much. It’s like having your cake and eating it too! We have something beautiful, something interesting, we can address the challenges of digitalization by making jobs more pleasant and more interesting and less hard manual work, and at the same time we can maybe make it more ecologic. But that’s really a maybe; I’m very self-critical about my work so far, and it has not been something focusing on sustainability - yet. But this is clearly something I see as a realistic possibility and something I want to look more into.
DS: Do you have any advice for young researchers and architects who are interested in exploring and applying timber innovations?
CR: Be passionate and be creative. When you first begin as a student, you’re very free from any state-of-the-art that tells you how things are supposed to work. You have to use the moment. Eventually, of course, you have to learn all of the things, but every stage of the journey is an interesting step.
Computational Structural Optimization and Digital Fabrication of Timber BeamsResearch, 2016 - Present
Structural optimization techniques offer means to design efficient structures and reduce their impact on the environment by saving material quantities. However, until very recently, the resulting geometrical complexity of an optimized structural design was costly and difficult to build. Today, fabrication processes such as 3D printing and Computer Numeric Control (CNC) machining in the construction industry reduces the complexity to produce complex shapes.
This research aims to combine computational structural optimization and digital fabrication tools to create a new timber architecture. A key opportunity for material savings in buildings lies in ubiquitous structural components in bending, especially in beams. This research explores old and new techniques for shaping structural timber beams.
Paul Mayencourt presents at Wood at Work Montreal2017-10-27, Tags: computation fabrication digital-manufacturing embodied-carbon structural-optimization timber
Paul Mayencourt presented research on opportunities for using structural optimization and digital fabrication to shape wood structural beams and building components at the third annual Wood at Work conference in Montreal.
Interdisciplinary Innovation: A Closer Look at Shaping Ultra-Thin Glass with Sophie Pennetier
Structural engineer Sophie Pennetier has worked on a wide range of specialty structures ranging from the National Museum of African American History and Culture to the Mexico City Airport in firms such as RFR, Guy Nordenson and Associates, SHoP Construction, and Arup. Beyond this accomplished track record in structural engineering, all within ten years of graduating from university, Pennetier has already begun to challenge the boundaries of the role of the engineer.
A recipient of the Jerry Raphael fellowship from the Metropolitan Contemporary Glass Group and Urban Glass Brooklyn in 2016, Pennetier was awarded the opportunity to explore the possibilities in cold bent ultra-thin glass and to apply the knowledge as her own “designer, engineer, and maker” of a small glass sculpture. The process was additionally supported by Corning Inc, Coresix Inc, and Arup. Pennetier stopped by MIT in early October to give us a presentation on “Shaping Ultra-Thin Glass.” She shared with us the process of developing of her project, including steps such as testing, design, analysis, and fabrication. She also (bravely) entrusted us with handling a few samples of the glass to feel its flexibility. We sat down with her afterwards to chat about her experiences, her career, and her thoughts.
Pennetier presents her work in ultra-thin glass to master's of architecture students in Prof. Caitlin Mueller's Building Structural Systems II class.
While Pennetier’s sculpture project has greatly benefited from her background as a structural engineer, the work undoubtedly sits on the cusp of art and engineering. She cites Irish structural engineer Peter Rice as an inspiration. “One project I find particularly poetic is the Théâtre de la pleine Lune, the Full Moon Theatre (Saint-Andre-de-Bueges, France, 1992), which is a stage lit by moonlight. Mirrors are oriented such that it captures moonlight and reflects it onto the stage. It’s very inspiring that Rice worked on that project as an engineer. I think it’s essential to be at the border of art and engineering so that we can keep making buildings that inspire us, rather than just containers.”
As elegant as her sculpture is, the project also represents an innovative step. “Ultra-thin glass is particularly lightweight, clear, and scratch-resistant. Corning invented this material decades ago and yet at the time there was no application for it. In parallel, at least two markets are interested in the material: the automotive industry and the electronics industry. The automotive industry is looking to make lighter cars that are still robust enough for security, while the electronics industry is interested in making lighter, clearer, scratch-resistant electronics with the glass.” Pennetier explains that as a company, Corning maintains a hopeful eye on steering the material into the automotive market, which will likely have a quicker and larger return investment than the field of architecture. In contrast, buildings using this material may remain few and far between for now.
Does Pennetier mind that the built environment may not be the primary application for her research? A believer in interdisciplinary innovation, Pennetier points out that Peter Rice’s development of structural glass was informed by aeronautics knowledge. “The demands between cars and buildings may be different, but if anyone pushes the technology, it is beneficial for any industry. No one is really reinventing the wheel.” She adds, “My vision is to design a building envelope with ultra-thin glass, so I’m happy to resolve the material challenges on any path in this direction.”
Pennetier’s ideas on innovation are not purely motivated by the advancement of science. Having practiced in both Europe and the US, Pennetier observes that “innovation comes with breaking the rules.” She noticed that structural innovation was made more possible in the US, where the engineer-of-record was able to take more risks per professional liability, in contrast to the heavy approval process required in Europe to engineer beyond the code. However, she firmly believes that the greater freedoms possible in the US should be tempered by the engineer’s social responsibility. “For example, if I am designing a glass balustrade, I have the responsibility of making a redundant system to protect the lives of people. In the US code today - which will change soon - you can still use non-laminated tempered glass, a very resistant security glass. However, if the glass has no interlayer, it doesn’t prevent you from falling when it’s broken, which can be very dangerous. So I will not design freely just because the code lets me; ethics are an important driver as an engineer and designer.”
Pennetier maintains this social awareness for her future work in ultra-thin glass. “We have glass everywhere, and it is getting thinner in all industries. Ultra-thin glass may take a lot of energy to fabricate, but it is recyclable and lighter than regular glass, coming in spools that make it easier to transport during the manufacturing process. There is potential to use this material to make processes greener. What’s next for me is ensuring there is a viable social context for this material. My sculpture succeeds as a mechanical prototype, but we still need to make sure it has a meaning for our buildings.
What advice would she give to engineering students looking to create art? “Maintain a project-oriented mindset,” she says. She cites her experience as a project manager in practice as crucial to the management of this independent project. These skills include risk management and time management. Her experience as a PM also enabled her to effectively engage with her collaborators; her work was additionally supported by Corning Inc. and Coresix Inc. “At one point my collaborators nearly dropped the project because it was too expensive. I made many phone calls and was eventually able to negotiate a compromise.”
On a more personal level, Pennetier encourages engineering students to “recognize the fun. Find what makes you feel alive; that kind of motivation will take you far. Engineers rarely take the artistic path, so don’t be afraid to let your crazy idea bloom.”
Stress line additive manufacturing (SLAM) for 2.5-D shellsKam-Ming Mark Tam, Caitlin Mueller, James Coleman, and Nicholas Fine, Proceedings of the International Association for Shell and Spatial Structures (IASS) Symposium 2015, 2015
In the field of digital fabrication, additive manufacturing (AM, sometimes called 3D printing) has enabled the fabrication of increasingly complex geometries, though the potential of this technology to convey both geometry and structural performance remains unmet. Typical AM processes produce anisotropic products with strength behavior that varies according to filament orientation, thereby limiting its applications in both structural prototypes and end-use parts and products. The paper presents a new integrated software and hardware process that reconsiders the traditional AM technique of fused deposition modelling (FDM) by adding material explicitly along the threedimensional principal stress trajectories, or stress lines, of 2.5-D structural surfaces. As curves that indicate paths of desired material continuity within a structure, stress lines encode the optimal topology of a structure for a given set of design boundary conditions. The use of a 6-axis industrial robot arm and a heated extruder, designed specifically for this research, provides an alternative to traditional layered manufacturing by allowing for oriented material deposition. The presented research opens new possibilities for structurally performative fabrication.