A framework to automate the design of digitally-fabricated timber plate structures

The current study uses knowledge from digital architecture, computer science, engineering informatics, and structural engineering to formulate an algorithmic framework for integrated Computer-Aided Design (CAD) and Computer-Aided Engineering (CAE) of Integrally-Attached Timber Plate (IATP) structures. The algorithm is designed to take the CAD 3D geometry of an IATP structure as input and automates the construction and analysis of the corresponding CAE model using a macroscopic element, which is an alternative to continuum Finite Element (FE) models. Each component of the macro model is assigned a unique tag that is linked to the relevant geometric and structural parameters. The CAE model integrity is maintained through the use of the common data model (CDM) concept and object-oriented programming. The relevant algorithms are implemented in Rhinoceros 3D using RhinoCommon, a .NET software development kit. Once the CAE macro model is generated, it is introduced to the OpenSees computational platform for structural analysis. The algorithmic framework is demonstrated using two case structures: a prefabricated timber beam with standard geometry and a free-form timber plate arch. The results are verified with measurements from physical experiments and FE models, where the time needed to convert thousands of CAD assemblies to the corresponding CAE models for response simulation is considerably reduced.

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

Design framework for the structural analysis of free-form timber plate structures using wood-wood connections

Anh Chi Nguyen, Petras Vestartas, Yves Weinand

Geometrically complex timber plate structures using wood-wood connections are increasingly designed thanks to digital fabrication. Whereas their fabrication has been automated using computer-aided design programming, research focused on the development of automated numerical tools for their structural analysis has been very limited. This paper presents a method to automate the generation of a finite element model for the analysis of structures with a large number of joints. The model is developed taking the example of recently developed double-layered timber plate shells. Vertical displacements obtained with the semi-rigid spring model proposed are in good agreement with experimental tests performed on small-scale prototypes, whereas rigid modelling of the connections highly underestimates displacements of the structure. Semi-rigidity of the connections in translation as well as in rotation was shown to highly influence the model. The generation of the numerical model was successfully automated for large-scale structures.

2019

Geometrical description and structural analysis of a modular timber structure

Olivier Baverel, Seyed Sina Nabaei, Yves Weinand

The ambitious goal of the ongoing research at IBOIS, the Laboratory of timber constructions at the Ecole Polytechnique Fédérale de Lausanne (EPFL) is to develop a next generation of timber constructions made out of innovative timber-derived products, through applying textile principles on the building scale. The presented structure is a modular composition of timber folded panels, notably demonstrates an example of applying the geometric techniques used to produce modular patterns and lattices to timber construction context. Effectively, it is shown that complex space structures can be designed using simple connection technology between elements. Moreover, by taking advantage of advanced CAM process, complex planar timber elements are cut in large scale and assembled with high precision as for the prototype of the structure presented in this paper. The folding concept corresponds to a planar reciprocal frame structure. The basic module is consisted of two mutually supporting timber folded panels which are slipped in, consecutively, along their cuts, to build up an arch. The inter-module connection’s stability is provided by contact boundary condition over the slide joints. The fundamental mechanical properties of the structure are examined using Finite Element Method and considering the non-linear contact boundary condition. The static behavior is studied under the self-weight load case as well as the modal dynamic response. According to analysis results, and by aid of a CAD parametric model, structural and geometrical alternatives are proposed to improve the structural performance. A prototype based on this geometric principal has been fabricated and assembled to explore feasibility of the concept in the building scale.

2011

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

Anh Chi Nguyen

EPFL2020