Recent development in research and practice for curved cross-laminated timber (CLT) opens up novel and interesting possibilities for applications of slender surface-active shell structures in architecture. Such typologies provide advantageous structural behaviour allowing for efficient and lightweight structures while simultaneously determine the envelope and space of a building. The high degree of prefabrication combined with a sustainable and renewable building material makes CLT an ecological and economic solution for future construction. This paper presents the design development and construction of the Urbach Tower for the Remstal Gartenschau 2019: a structure made from high curvature CLT components on a building scale. This research contribution illustrates a sophisticated integrative design to construction process emphasizing computational and structural design, fabrication and detailing for curved timber components in complex spatial structures. The authors further explore the structural potential of self-shaped curved CLT investigating the influence of curvature radius on the load-bearing behaviour of the tower structure. The Urbach Tower translates these technical developments into practice arising at the intersection of digital innovation and scientific research.
This paper presents an integrated design tool for structures composed of engineered timber panels that are connected by traditional wood joints. Recent advances in computational architecture have permitted to automate the fabrication and assembly of such structures using Computer Numerical Control (CNC) machines and industrial robotic arms. While several large-scale demonstrators have been realized, most developed algorithms are closed-source or project-oriented. The lack of a general framework makes it difficult for architects, engineers and designers to effectively manipulate this innovative construction system. Therefore, this research aims at developing a holistic design tool targeting a wide range of architectural applications. Main achievements include: (1) a new data structure to deal with modular assemblies, (2) an analytical parametrization of the geometry of five timber joints, (3) a method to generate CNC toolpath while integrating fabrication constraints, and (4) a method to automatically compute robot trajectories for a given stack of timber plates.
Traditional wood-wood connections, widely used in the past, have been progressively replaced by steel fasteners and bonding processes in modern timber constructions. However, the emergence of digital fabrication and innovative engineered timber products have offered new design possibilities for wood-wood connections. The design-to-production workflow has evolved considerably over the last few decades, such that a large number of connections with various geometries can now be easily produced. These connections have become a cost-competitive alternative for the edgewise connection of thin timber panels. Several challenges remain in order to broaden the use of this specific joining technique into common timber construction practice: (1) prove the applicability at the building scale, (2) propose a standardized construction system, (3) develop a convenient calculation model for practice, and (4) investigate the mechanical behavior of wood-wood connections. The first building implementation of digitally produced through-tenon connections for a folded-plate structure is presented in this work. Specific computational tools for the design and manufacture of more than 300 different plates were efficiently applied in a multi-stakeholder project environment. Cross-laminated timber panels were investigated for the first time, and the potential of such connections was demonstrated for different engineered timber products. Moreover, this work demonstrated the feasibility of this construction system at the building scale. For a more resilient and locally distributed construction process, a standardized system using through-tenon connections and commonly available small panels was developed to reconstitute basic housing components. Based on a case-study with industry partners, the fabrication and assembly processes were validated with prototypes made of oriented strand board. Their structural performance was investigated by means of a numerical model and a comparison with glued and nailed assemblies. The results showed that through-tenon connections are a viable alternative to commonly used mechanical fasteners. So far, the structural analysis of such construction systems has been mainly achieved with complex finite element models, not in line with the simplicity of basic housing elements. A convenient calculation model for practice, which can capture the semi-rigid behavior of the connections and predict the effective bending stiffness, was thus introduced and subjected to large-scale bending tests. The proposed model was in good agreement with the experimental results, highlighting the importance of the connection behavior. The in-plane behavior of through-tenon connections for several timber panel materials was characterized through an experimental campaign to determine the load-carrying capacity and slip modulus required for calculation models. Based on the test results, existing guidelines were evaluated to safely apply these connections in structural elements while a finite element model was developed to approximate their performance. This work constitutes a firm basis for the optimization of design guidelines and the creation of an extensive database on digitally produced wood-wood connections. Finally, this thesis provides a convenient design framework for the newly developed standardized timber construction system and a solid foundation for research into digitally produced wood-wood connections.
The rise of digital fabrication has increased the use of wood-wood connections inspired by traditional carpentry in modern timber constructions. With recent developments on standard construction systems, the mechanical behavior of such joints for in-plane loading configurations is an essential parameter for the structural design. However, only few design guidelines exist on this topic in building codes such as Eurocode 5 and research has been mainly focused on the rotational behavior, which is important for free-form structures. Therefore, this work presents an experimental campaign on the load-carrying capacity of digitally produced through tenon connections for commonly available engineered timber products such as oriented strand board, laminated veneer lumber, and multiply solid wood panels. Shear and compression failure modes were studied and two test setups were developed. The scope of the study was limited to five different materials, a grain orientation parallel to the joint, and three different tenon lengths. The test results showed significant differences between the product specifications given by manufacturers and real performances observed for oriented strand board and cross laminated timber, while laminated veneer lumber had more accurate specifications. Nonetheless, a spreading of the compression strength was highlighted only for the OSB material and was also observed for the shear strength of laminated veneer lumber specimens. The existing Eurocode 5 guidelines generally underestimated the load-carrying capacity of the connections by 25% and only the capacity of oriented strand board connections was overestimated. Finally, the study demonstrates that different design approaches can be defined according to the material employed in through tenon connections. Design diagrams based on tests are preferred for materials with a high variability between product specifications and real performances while design criteria from building codes can be applied for the others.
Proceedings of the International Symposium on Automation and Robotics in Construction
Robotics, mass timber, and parametric design are all key technologies that are underutilized in construction. To fully take advantage of these new technologies requires a rethinking of the entire process from design to construction. The Greenbuild Pavilion represents a new construction workflow, in which a digital parametric model is communicated directly to a robot fabricator. The robot, equipped with various tools, can manipulate dimensional lumber into complex geometries with industrial precision. This workflow has the potential to drastically improve the sustainability, quality, cost, and time of construction.
Project contact is André Potvin at Université Laval
The biomimetic approach in architecture explores the genius of organic natural forms resulting from a long process of environmental adaptation. These forms often have a high compactness and an optimal material / volume ratio in line with the importance of reducing the material in the building to limit its environmental impact in terms of energy and resources. What are the natural forms and processes of growth of the form most appropriate to the physical properties of wood? What design process promotes the integration of a biomimetic approach from the earliest stages of design? Based on a review of the main achievements claiming this approach, this project will develop a taxonomy of the different biomimetic typologies and identify the most promising in the context of a wood realization. A digital manufacturing process will be developed to reflect the complexity of natural shapes and flows in an organic architecture that optimizes environmental performance and aesthetics.