Geometrical description and structural analysis of a modular timber structure

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.

Geometrical description and Structural analysis of a Modular Timber Structure

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 a 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. This paper is dedicated to bring out the concept, to examine its fundamental mechanical properties and to improve the structural system. The geometrical modularity of the structure is investigated. The basic module is consisted of two mutually supporting timber folded panels which are slipped in, consecutively, along their cuts, to build up an arc. The inter-module connection’s stability is provided by contact boundary condition over the slide joints. Two main modeling approaches and relative geometric developments are described. The structural performance is 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, 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 building scale.

2011

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

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