Development of a Spring Model for the Structural Analysis of a Double-Layered Timber Plate Structure with Through-Tenon Joints

Timber plate structures with integral mechanical attachments have been successfully built in the last decades. Previous research has highlighted the influence of these connections in the global behavior of the structures. Double-layered plate shells are one of the latest applications of integral joints. Their fabrication and assembly has been proven efficient. However, their structural behavior remains unknown. Simplified models are required to predict their behavior since an individual detailed modelling of the large amount of joints would be time-consuming and computationally expensive. Current simplifications involve either considering the connections as rigid or hinged and do not allow accurate prediction of their behavior. In this paper, a numerical finite element model in which the semi-rigid behavior of the joints is modeled by means of springs is presented for a double-layered timber plate structure made of 5 by 3 segments. The numerical model is automatically generated in the finite element software AbaqusTM from a simplified geometry. Numerical results are compared to a three-point bending test performed on two specimens. The developed spring model shows promising results for its application to a full double-layered timber plate shell. Only axial and shear stiffnesses were implemented in this model while the other degrees of freedom were considered rigid. This consideration might lead to an overly stiff model.

Anh Chi Nguyen, Yves Weinand

2018

A Structural Design Methodology for Freeform Timber Plate Structures Using Wood-Wood Connections

Anh Chi Nguyen

Over the past decades, timber has gained popularity as a sustainable building material because of the rising environmental awareness. Furthermore, the resurgence of timber has also been encouraged by the advent of the digital age during the 21st century. The development of computer-aided design programming and digital fabrication tools has stimulated significant advances in both architecture and engineering. Within this context, researchers have shown a growing interest in wood-wood connections, inspired by traditional woodworking joints. Geometrically complex timber structures assembled with joints integrated in their plates have been developed using algorithmic geometry processing. However, although their design and fabrication have been automated, research focused on automated numerical tools for their structural analysis has been very limited. This thesis is providing a design methodology for the structural analysis of timber plate structures composed of a large number of discrete planar elements and wood-wood connections. A finite element model, in which the semi-rigid behaviour of the connections is implemented using springs, is proposed. It is applied to a specific case study, namely the Annen Plus SA head office project in Manternach, Luxembourg, which consists of a series of double-layered double-curved timber plate shells. A design framework is introduced to automate the generation of the model and integrate structural analysis into the existing design and fabrication workflow. The numerical model was built for both small- and large-scale structures through custom scripts and subsequently assessed through experimental investigations: first, laboratory tests were performed on small assemblies with simplified geometry; secondly, a displacement study was carried out onsite on a 24 m span structure. Results obtained with the semi-rigid spring model were found to be in good agreement with experimental tests. The proposed model was therefore validated for the serviceability limit state. Furthermore, the semi-rigidity of the connections in translation as well as in rotation was shown to highly influence the model and is therefore crucial for the accuracy of the model. Based on experimental tests observations, an alternative structural system was proposed and compared to the initial one through numerical investigations within the proposed design framework. A significant influence on the structureâs performance was found, demonstrating the possibilities for structural optimisation. Finally, a three-dimensional finite element model for wood-wood connections was investigated. It aimed to predict their semi-rigid behaviour, generally characterised through experimental tests, necessary for their implementation in global models. The material model was evaluated based on shear load tests performed on different engineered wood products. Stiffness and load-carrying capacity of the connections were approximated with numerical simulations. However, experimental tests remain necessary to precisely predict the behaviour of the joints. This thesis highlights the importance of adopting an integrated design strategy encompassing engineering and fabrication aspects for geometrically complex timber structures, as well as establishing a link between local behaviour of the connections and global behaviour of the structure. The gained knowledge can facilitate the design and realisation of large-scale freeform timber structures with wood-wood connections.

EPFL2020

Displacement Study of a Large-Scale Freeform Timber Plate Structure Using a Total Station and a Terrestrial Laser Scanner

Anh Chi Nguyen, Yves Weinand

Recent advances in timber construction have led to the realization of complex timber plate structures assembled with wood-wood connections. Although advanced numerical modelling tools have been developed to perform their structural analysis, limited experimental tests have been carried out on large-scale structures. However, experimental investigations remain necessary to better understand their mechanical behaviour and assess the numerical models developed. In this paper, static loading tests performed on timber plate shells of about 25 m span are reported. Displacements were measured at 16 target positions on the structure using a total station and on its entire bottom surface using a terrestrial laser scanner. Both methods were compared to each other and to a finite element model in which the semi-rigidity of the connections was represented by springs. Total station measurements provided more consistent results than point clouds, which nonetheless allowed the visualization of displacement fields. Results predicted by the model were found to be in good agreement with the measurements compared to a rigid model. The semi-rigid behaviour of the connections was therefore proven to be crucial to precisely predict the behaviour of the structure. Furthermore, large variations were observed between as-built and designed geometries due to the accumulation of fabrication and construction tolerances.

2020

A Structural Design Methodology for Freeform Timber Plate Structures Using Wood-Wood Connections

Anh Chi Nguyen

EPFL2020