Wood is often described as “nature’s composite.” It’s composed of long cellulose fibers that are aligned along the direction of stress—and those fibers are all bound together by a lignin (organic polymer) matrix.
If you substituted the word “cellulose” with “carbon fiber,” and then exchanged the word “lignin” with “epoxy,” you would be describing a basic carbon fiber reinforced plastic (CFRP) composite!
With that in mind, how is it even possible to improve upon wood? Nature is the best designer, after all. Well, wood is great, but it’s pretty difficult to make curved geometries that maintain the natural strength of wood. That may be about to change, thanks to a company in Austria that has developed a wood-carbon fiber composite system. And the best part about this system is that it’s modular, so it can be assembled into large spanning structures.
And whereas nature relies on evolution to determine what works and what doesn’t, Austrian architectural design firm Digital Architects relies on composite simulation to give its product evolution a kick-start.
The Digital Architects composite system comprises several layers of wood that are ply bonded to carbon fiber layers (as shown in Figure 1). This concept was first developed for the façade of the new Varna Library, located in Varna, Bulgaria. Since then, the system has evolved and the construction process used to assemble these panels into larger structures is now known as the active grid monocoque (AGM) method. These panels can be assembled to form structures of all sizes, providing thin, high-spanning structures, with three-dimensional curves and high strength-to-weight ratios.
Before we delve into AGM and composite simulation, let’s take a look at the origins of the AGM method that was used in the Varna Library project.
Varna Library
The wood-carbon composite system that was developed for a design proposal for the facade of the Varna Library in Bulgaria is an example of materials used in organic architecture (a phrase coined by legendary architect Frank Lloyd Wright). The proposal was created by Digital Architects and Tokyo-based architectural design firm Archicomplex.
Facades are used extensively in architecture to change the outward appearance of a building’s structure, providing an aesthetically pleasing exterior that can complement the environment in which the building is located. In organic architecture, natural looking curves and flowing geometry are used to achieve the illusion of natural forms.
The wood-carbon composite system allows the creation of these free-form, flowing geometries while still maintaining a high strength-to-weight ratio and a beautiful, natural looking finish.
In the case of the library proposal, the facade was designed to provide an organic, self-supporting structure that would complement the surroundings while allowing natural light into the main building and at the same time providing shade.
"We use new and innovative simulation technology to engineer strong, lightweight wooden composite sections capable of withstanding all the necessary load cases,", explained Atanas Zhelev, architect and founder of Digital Architects. "We used ESAComp software for the preliminary laminate analysis, to evaluate the structural component behavior along with the development of the joint system."
The library facade concept was designed to demonstrate how laminates could be used in architecture, and the case study resulted in the AGM method for assembling the composite panels. This AGM system is now the main focus of the team in Vienna, which is hoping to bring it to market soon.
AGM Method
The team learned a lot from the library exercise, and built upon the lessons it gleaned from this project to design a modular approach to wood-carbon composite construction.
“What we learned from the case study is that using wood-carbon fiber as a beam is good, but it’s not the best way to use it,” said Zhelev. “Because, first of all, we were using it in vertical skyscraper types of buildings, and, in particular, composites are good in tension, so by using them for compression, we [were] not fully realizing the potential of the materials.
“On the Varna Library concept, we had been using the composites as a beam which has a narrow profile,” continued Zhelev. “In a beam, it’s harder to transfer the loads inside the composite in a way that the fibers make sense—the optimum usage seems to be using the composite system as a big shell. So [by] using it as a shell, you can achieve more and better utilize the composite properties properly.
“That was our general understanding, so we decided to use all of the studies that we did to develop a system for large-span shells and roofs.”
ESAComp
So, how did Zhelev and the team use Altair products in designing their façade and AGM system?
The team adopted an incremental approach to researching and testing its composites, simulating on a small scale, then manufacturing a test model of that item. When the team had learned what was needed from the simulation and test results, it could scale up onto larger panels, or swap some components around in the simulation process.
“In regards to ESAComp, we mostly used it to optimize the structure. So, we started with the project in Varna by learning about how composites work in general,” said Zhelev.
“We started by designing models of different woods, and combining them in the software, then testing them. We wanted to learn how the wood laminate behaves at microscale. We wanted to understand the performance of those laminates under different directional forces and out-of-plane shear. Then we moved onto different combinations of carbon and different combinations of resin.”
After the composite system was designed and tested, the team encountered a new challenge: how to mate the panels to traditional architectural structure.
The composite panels still needed to be mated to the concrete, so the team devised a method using epoxy concrete to bond the composite joints to the structural concrete, and also made use of lightweight aluminum honeycomb cores to manufacture the carbon fiber joints for fixing the panels to the structure.
“We created a carbon fiber beam with a good aluminum honeycomb core, and we could simulate how the forces work inside the joints between this carbon/aluminum beam, the wooden facade elements and the polymer concrete. Through ESAComp, we simulated a lot of glues, a lot of different woods, and a lot of different carbon fibers to come up with the best solution for the Varna Library.”
After much simulation, and acting on the advice from their sponsor and technical partner Gurit (a leading global supplier of composite materials and engineering services), the team decided to experiment with a balsa wood core instead of the beech wood used with its previous efforts.
“We thought it was a great idea to use balsa core to make the structures lighter, as balsa is less dense and is still flexible, but we didn’t know how it was going to perform once [we] glued it together. So, we did a test in HyperWorks, and we wanted to achieve the same properties with the balsa as we did with the previous beech core. When we manufactured a material sample in real life, we realized that the balsa behaved much better than we expected, as it soaked up quite a lot of resin and became stronger than what was simulated. Also, the balsa core is much lighter than the beech core, whilst providing similar strength, and reduced the weight of our product quite significantly.”
“We liked ESAComp because it has a great material library, so you don’t have to search through and input data on your own too much—you can use the material property from the library. Normally, properly documented data for various wooden species and thicknesses of wood, with all of the necessary engineering properties, is very hard to find and usually you don't get such data from your local supplier. This is where the ESAComp material library was very valuable to us."
So, the final product will be lightweight, insulated and fireproof, and will potentially make the manufacture of organic forms much easier. And potentially cheaper, too.
According to Zhelev, the AGM system becomes more cost-efficient and competitive with steel/plastic combinations, for highly complex, double curved roof structures over 400 square meters in area.
Coming to a Roof Near You?
So how long before we see wood-carbon composites being used in everyday construction? That might be a while off yet.
“The product at the moment is in the stage where we have successfully constructed a full-scale panel with all the layering inside—with the right carbon, wood and core materials. And we have also done structural testing for the material,” said Zhelev.
“Putting the product on the market requires a few certifications, particularly in the EU, and if we want to pass it in America, we need to follow their certification processes as well. But in terms of the product, we have completed the panel and we have completed the structural tests. There is still more to do, including testing and certification for fireproofing and insulation properties.”
The team is currently working on a couple of smaller demonstration projects with fewer construction regulations, and hopes to scale up to larger projects when it has achieved full certification of its products.
You can read more about ESAComp over at this link.
Altair has sponsored this post. They have had no editorial input to this post. All opinions are mine. —Phillip Keane