Structural design methodology in Integrally-Attached Timber Plate structures

The immediate application of research discoveries requires a global and exact understanding of the structure under consideration. To gain insight into the complex behavior of structures, numerical simulations are carried out in parallel to physical experiments and digital fabrication, computer-aided geometry explorations, and assembly planning. The role of the digital model in the process of designing timber structures is to open the field of possibilities to new structural forms, new construction methods, and consequently, new assembly technologies. The design framework introduced in this chapter aims to include the geometry generation, the definition of the assembly sequence, the fabrication process of the wood-wood connections and their mechanical behavior, kinematic of timber plates, equilibrium equations that govern the structural behavior, and associated numerical simulations of Integrally-Attached Timber Plate (IATP) structures. This chapter is then supported by Chapter 3, where a wide range of case studies from medium- to large-scale structures is presented.

Experimental and numerical study on structural behavior of a single timber textile module

Markus Hudert, Laurent Humbert, Meisam Sistaninia, Yves Weinand

The present work investigates an innovative class of timber structure with potential applications in roofing, facade and bridge construction, called Timberfabric. The development of Timberfabric structures originates from the approach of harnessing the structural, modular and qualities of textiles in timber construction (Weinand and Hudert, 2010) [9]. Timberfabric structures are comprised of repetitive arrangements of one or more structural unit cells called Textile Modules. When properly designed, one obtains a modular and lightweight structure with interesting and unusual geometrical and structural qualities.This paper focuses on the single timber Textile Module. Based on the finite element (FE) method, a reliable procedure is proposed for modeling the overall assembly process of the Textile Module. For comparison, Textile Module prototypes are constructed at two different scales (large and intermediate scales) with different assembly conditions. The proposed geometrically nonlinear FE model allows evaluation of the stresses that are induced during the construction process and which may affect the structural integrity of the module. In particular, the risk of failure during assembly is identified using the anisotropic Tsai-Hill criterion. The structural behavior of the timber Textile Module is then investigated through bending tests using the constructed prototypes. During the loading procedure, the vertical deflections are measured at different locations on the prototype surface by means of external displacement transducers. Using the FE model, the corresponding deformed shapes are simulated by applying the bending loads on the prestressed Textile Module. Experimental displacements and FE predictions are thus compared and found to be in good agreement.

Elsevier2013

Integrally attached timber folded surface structures

Andrea Stitic

In structural engineering, folded surface structures present one of the concepts for construction of self supporting column free systems. They utilize structural benefits of folding to achieve material saving and improve structural efficiency. The folding principle can be simply described as stiffening a thin surface by placing its material further away from the axis of flexure. The application of folded surface structures in timber engineering is motivated by multiple advantages of relatively recently developed, high-performance engineered wood panel products. When used in folded systems, such panels can provide for a sustainable and lightweight solution with high load-bearing potential and high prefabrication possibilities. However, same as all timber products, these panels have limitations concerning the dimensions of the prefabricated units. These limitations are dictated by demands of transportation, assembly and, more stringently, by available manufacturing techniques. These factors influence the selection of timber structuresâ potential folded form, by constraining the dimensions of their discrete elements. Accordingly, structural forms with multiple elements along the span are needed for facilitating large spanning timber folded surface systems. Consisting of a large number of discrete plane elements, their realization requires proper edgewise connection details for ensuring an efficient load bearing system. For structures made of thin timber panels, this presents a great challenge when using the conventional joining techniques. For this reason, the use of timber folded structures for civil engineering applications has been very limited. However, recently, the re-discovery of integral mechanical attachments resulted in a new technical solution for edgewise joining of thin timber panels, which utilize digital prefabrication to integrate connectors through plate geometry. This thesis aims to facilitate the realization of large span timber folded surface structures which use one-degree-of-freedom multiple tab-and-slot joint integral mechanical attachment technique. Regarding the material, the presented work concentrates on certified Kerto-Q laminated veneer lumber panels. Taking into consideration the constraints of material, fabrication and chosen connection detail, various folded form topologies were examined for the considered application. Moreover, a relation was established between the structural form and the mentioned constraints, allowing for their implementation into the folded form design from the very start. The structural behaviour of folded systems was studied by performing extensive experimental tests. The innovative test setup developed for this purpose is presented. The results of this in-depth experimental analysis provide new insights regarding the substantial influence of the semi-rigid connection details on the global behaviour of timber folded surface structures. In addition, for analysing their feasibility, the tested structures are reviewed in terms of fabrication time, assembly and on-site construction. Furthermore, based on the experimental test results, a pertinent numerical model for predicting the load bearing behaviour of the regarded structures is provided. Using finite element method the semi-rigid structural behaviour of multiple tab-and-slot joints, as well as the entire timber folded system, was modelled with sufficient accuracy. Using the developed numerical models, a correlation is established...

EPFL2017

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.