Timber Gridshell Research Articles

Structural behaviour of asymptotic geodesic hybrid timber gridshells

Asymptotic geodesic gridshells are a novel structural system that is fabricated from straight and flat planks. The planks are elastically bent and twisted around their slender dimension to achieve the desired geometry, while the tall dimension creates structural stiffness. This system combines the geometric features of asymptotic and geodesic curves to create a hybrid tri-hex network on doubly curved surfaces, and provides a stable grid to resist its self-weight and external loads. To comprehensively explore the structural capabilities of asymptotic geodesic gridshells, a full-scale timber gridshell prototype was designed and built. Loading tests, including local and one shell asymmetrical loading, were carried out to examine the structural behaviour of the gridshell. A nonlinear finite-element model was developed and subsequently validated using experimental data. The evaluation of the timber gridshell revealed its high performance under uniformly distributed loads, and the simulation indicated a viable live load capacity of 7.0 kN/m². In a parametric study, the influence of the polar array layout, the joint rotation stiffness, and the support condition on the structural performance of the hybrid gridshell are analysed. Parameters influencing the achievable span are discussed regarding strength, stiffness and buckling behaviour for future design considerations.

Analysis of factors affecting the stability of large-span cable-braced timber gridshells

Global stability is a significant performance indicator for gridshell structures. This article takes the Dome of Taiyuan Botanical Garden, which is currently one of the largest timber quadrilateral gridshells in the world, as the research background to study the global stability of the large-span cable-braced timber gridshell system. It conducts a comprehensive parametric analysis of the influences of material nonlinearity, boundary conditions, joint stiffness, cable, and imperfections. The results indicate that introducing a cable-bracing system can significantly enhance the stability of the timber gridshell. An approximate logarithmic relationship between joint stiffness and the ultimate bearing capacity suggests that logarithmic curves can be used to design stacking joints in engineering. Furthermore, using the first-order buckling eigenmode as the imperfection shape is inappropriate since the first-order buckling mode may not be the most unfavorable imperfection shape. Instead, the failure modes of geometry nonlinear elastic analysis or geometry and material nonlinear analysis can be utilized as the imperfection shape. Finally, the influence of material nonlinearity on the stability of the cable-braced timber gridshell system may be less significant than that of the traditional gridshell systems.

Construction Material Selection Criteria for Timber Gridshell Application: A Literature Review

Timber gridshells have the potential to be a sustainable and cost-effective solution for long-span applications and free-form architecture. Despite this, their overall use has been limited, and there is a lack of research focusing on their construction materials. This literature review aims to investigate timber gridshells and their construction materials to identify the criteria used in selecting suitable materials for gridshell applications. A review of peerreviewed scientific articles, books, and theses was conducted to gather information on timber gridshells, construction materials used in gridshells, timber used in active bending structures, and building standards. The research findings identified six main factors that are important when selecting a suitable material for timber gridshell application: structural strength and strength grading, bending strength and behaviour, bending strength/bending elasticity ratio, durability, commercial availability, and cost. These findings are also discussed to identify the characteristics that make a material suitable for timber gridshell applications, depending on the gridshell’s context, whether in a tropical or international context. This review serves as a necessary reference for architects and engineers when selecting materials for their timber gridshell projects, providing insight into the selection criteria for construction materials and sharing information on the material properties of suitable timber gridshell materials.

Aluminium nodes for timber gridshells: Parametric detailing of node principles

Gridshell nodes are key elements regarding structural performance, visual appearance and assembly of any gridshell that have been given little attention in recent research. This paper explores aluminium as a material for timber gridshell nodes. First, existing gridshell nodes are categorised regarding bulk materials, gripper types and connection methods and based on this, a set of novel node principles in aluminium are deducted and proposed for a timber gridshell on the geometry of the British Museum Great Court. A finite element analysis is done on the proposals to increase the understanding of the node principles’ structural behaviour and feasibility. Together, the set of node principles, their evaluation and the utilised procedure can provide new options in the future design of gridshells and gridshell nodes.

Design and fabrication of smooth poly-hypar timber gridshells

This paper introduces the timber gridshell designed and fabricated as smooth poly-hypar surface structure, a new type of doubly curved freeform shell which is combined smoothly (G1 degree) from hyperbolic paraboloids (hypars). It is locally ruled, while globally appears to be a doubly curved freeform. Compared to the elastic timber gridshell designed through form-finding method, smooth poly-hypar timber gridshells have more advantages in terms of structural behaviour and construction method. Structurally, smooth poly-hypar gridshells are able to resist different loading cases with mainly membrane actions. In terms of construction, as a locally ruled surface, it can be prefabricated in modules with straight components, which effectively reduces the construction cost. In this paper, an open theatre, Hypar Wave, is presented as a case study to show the structural and constructional advantages of smooth poly-hypar gridshell in timber. Advances made in this research have added to the knowledge of gridshell behaviour and construction, thereby making the design and construction of future timber gridshells a more viable option.

Design Framework for Selection of Grid Topology and Rectangular Cross-Section Size of Elastic Timber Gridshells Using Genetic Optimisation

This work presents a design framework for the selection of the topology and cross-section size of elastic timber gridshells, taking as constraints the shape of the structure and the maximum value of bending stress that can be reached in a given area of the gridshell. For this purpose, a parametric design environment and a genetic optimisation algorithm are used, which provides a set of solutions (optimal and near-optimal) that can be examined by the designer before adopting the final solution. The construction of the parametric mesh model is based on a geometric approach using an original adaptation of the Compass Method by developing two algorithms. The first one plots geodesic curves on a surface given a starting point and a direction. The second algorithm adapts the accuracy of the Compass Method to the local curvature of the surface, substantially minimising the computation time. The results show that the optimisation process succeeds in significantly reducing the initial bending stresses and offers an interesting solution space, consisting of a set of solutions with sufficiently diverse topologies and cross-section sizes, from which the final solution can be chosen by the Decision Maker, even according to additional non-programmed structural or aesthetic requirements. The design framework has been successfully applied and verified in the design of the PEMADE gridshell, an innovative elastic timber gridshell recently realised by the authors. Finally, the most relevant details of its construction process carried out to ensure the exact position of the timber laths are presented.

Structural Analysis of Timber Gridshell Covered by OSB Panels Considering the Effect of Wind

Structural Analysis of Timber Gridshell Covered by OSB Panels Considering the Effect of Wind

A Grasshopper Plugin for Finite Element Analysis with Solid Elements and Its Application on Gridshell Nodes

Linking architectural models to structural analyses can be demanding and time-consuming, especially when the architectural models cannot be accurately analysed using readily available one- or two-dimensional finite elements. This paper presents a tool for finite element analysis using solid elements developed as a plugin for Grasshopper 3D® that enables designers to include analyses of complex objects within the same software as the design exploration. A benchmark using the tool on a cantilever beam is compared with both ANSYS® and the theoretical solution, before the versatility of the tool is demonstrated by analyzing the metal part in timber gridshell nodes. The results were satisfying and the tool can prove especially useful for early phase design and collaboration between diciplines.

Structural Analysis and Form-Finding of Triaxial Elastic Timber Gridshells Considering Interlayer Slips: Numerical Modelling and Full-Scale Test

Elastic timber gridshells are lightweight structures whose stiffness is highly dependent on multiple factors, such as boundary conditions and the semi-rigidity and eccentricity of the joints. Their structural analysis requires calibrated numerical models that incorporate all aspects influencing stiffness. Unfortunately, very little research on experimentally verified numerical models can be found. This paper focuses on the structural behaviour of a novel concept of triaxial elastic long-gridshells supported only on their short sides, called by the authors TEL-gridshells. First, the most relevant details of the construction process and the load test of a full-scale laboratory prototype are presented. Then, two finite element models for structural analysis and form-finding are proposed. Both are based on the modelling of the joints using a series of aligned couplings that allow the integration of the actual joint eccentricity and the interlayer slip by means of springs in all shear planes. The first model replicates the geometry of the prototype built from experimental measurements, focusing on stiffness calibration. The results of the load test are used to verify the proposed model and to analyse the most influential aspects on the stiffness of the structure. The second is a form-finding model that reproduces the construction process of the laboratory prototype, focusing on the residual stresses generated during the deformation process of the structural elements. From the numerical results, the structural behaviour of the prototype is discussed and some of the main aspects to be considered in the design and structural analysis of TEL-gridshells are established.

Inexpensive photogrammetry applied to displacement measurement of a gridshell

Gridshells are unexploited structures, over which lengths measurement are difficult to do due to their size and complex curvature. To deformation measurement on a timber gridshell beam and on an entire gridshell, we used an affordable photogrammetry system that consisted of a consumer-level camera, a tripod, a mast with a gimbal to elevate the camera, a laptop, and two photogrammetric software: PhotoModeler Scanner and Metashape. The beam was subjected to a bending test, and the gridshell was loaded with 105 kg of dead load per node on its five central nodes. The maximum error in the measurement was 1.26 mm on the beam and 3.45 mm on the gridshell, which corresponded to 0.77 ‰ error relative to the span of the beam and 0.41 ‰ relative to the length of the gridshell. Three-dimensional models obtained through the proposed method serve as dimensional data with a uniform error around the object.

Structural Models Based on Minimal Surfaces and Geodesics

This article presents the results of research carried out with respect to the geometric, formal and structural adaptation of minimal surfaces. These surfaces were discretized into strips developable on geodesic curves, and then used for the construction of timber gridshells. For this project, both physical and virtual models derived from the same geometric models were used. The objective was to demonstrate the validity of the use of models and the transformation that modelling is undergoing due to the use of digital tools, both software and hardware. These include, on the one hand, drawing and analysis software and, on the other, digitally controlled fabrication tools. This research focuses specifically on the design and construction of the Scherk Pavilion, a space where the results of various experiments in which the common factor was the use of models was transferred to a real scale.

Computational analysis of hygromorphic self-shaping wood gridshell structures.

Bi-layered composites capable of self-shaping are of increasing relevance to science and engineering. They can be made out of anisotropic materials that are responsive to changes in a state variable, e.g. wood, which swells and shrinks by changes in moisture. When extensive bending is desired, such bilayers are usually designed as cross-ply structures. However, the nature of cross-ply laminates tends to prevent changes of the Gaussian curvature so that a plate-like geometry of the composite will be partly restricted from shaping. Therefore, an effective approach for maximizing bending is to keep the composite in a narrow strip configuration so that Gaussian curvature can remain constant during shaping. This represents a fundamental limitation for many applications where self-shaped double-curved structures could be beneficial, e.g. in timber architecture. In this study, we propose to achieve double-curvature by gridshell configurations of narrow self-shaping wood bilayer strips. Using numerical mechanical simulations, we investigate a parametric phase-space of shaping. Our results show that double curvature can be achieved and that the change in Gaussian curvature is dependent on the system’s geometry. Furthermore, we discuss a novel architectural application potential in the form of self-erecting timber gridshells.

Innovative design and construction of a permanent elastic timber gridshell

This paper presents a new elastic timber gridshell built to cover a wood storage area at the Timber Engineering Laboratory of the University of Santiago de Compostela in Spain. It is the first permanent elastic timber gridshell to be built in the country and the first in the world to be made of Eucalyptus globulus Labill. It includes various novelties for timber gridshells, such as a long-shell structural concept supported only on its short sides and the use of a third direction of bent laths to give the shell in-plane shear stiffness. Several research and development concepts have been implemented by the authors in this new gridshell. The design and structural analysis processes, experimental research for the development of 24 m long laths without mechanical joints, structural details and information about the construction method are described.

Mallas elásticas de madera - Estructuras con un diseño integrado

Una malla estructural de madera es un tipo especial de estructura que establece un nuevo marco para la construcción
 ligera. Es posible crear una amplia variedad de formas y geometrías, garantizando así una enorme libertad arquitectónica. Sin embargo, dada la variedad de formas y la complejidad que pueden presentar es necesario utilizar diferentes herramientas e información para avalar este complejo proceso.
 
 El presente trabajo explora la interacción entre la información y las diferentes herramientas utilizadas por arquitectos e ingenieros durante el proceso de diseño y construcción de una malla elástica de madera, presentando un caso de estudio real con 42m2 (6,5mx6,5m), después de la elevación, construida con la intención de explorar el diseño y el proceso constructivo junto con métodos de integración de “form finding”. En el trabajo, los objetivos de optimización tanto del arquitecto como del ingeniero se realizan sobre el mismo caso de estudio. Se presentará el proceso de diseño y se describirá la construcción de la malla elástica.

Numerical methods for post-formed timber gridshells: Simulation of the forming process and assessment of R-Funicularity

A nonlinear staged construction analysis is adopted here to simulate the forming process of timber gridshell. In this respect, particular attention is paid to the modelling of the cylindrical joints connecting the orthogonal laths. Cylindrical joints enable the initially flat lattice to be formed into a doubly curved gridshell shape; therefore, accurate modelling of the joints’ mechanical behaviour is a crucial aspect when simulating the forming process of timber gridshells.Another important parameter influencing the gridshell shape is the orientation of laths making up the initially flat lattice. Using an equivalent continuum definition, the final geometry of the gridshells, obtained from different laths orientations, is analysed in here to assess how laths orientation affects the structural shape in terms of funicularity. The Relaxed Funicularity Ellipse method presented in Gabriele et al. (2018) is used for such purpose.

Design of Canary Wharf Elizabeth line station and Crossrail Place oversite development

Canary Wharf was the first station on the Elizabeth line to be constructed, and the first to be let as a design-and-build contract, with developer Canary Wharf Group. Innovative design and construction techniques enabled the station box to be completed four months ahead of the development programme. Construction of the Crossrail Place retail and leisure oversite development (OSD) proceeded concurrently with that of station. The OSD included a number of features aimed at increasing future flexibility for the developer and tenants. A timber gridshell roof completes the development, partially covering a large roof garden that is open to the public. The OSD opened in May 2015, nearly four years ahead of the planned station opening.

A numerical and experimental approach to cold-bent timber-glass composite elements

The current rise of wooden constructions, which is encouraged by a strong trend towards sustainability of our buildings, also engenders innovation in facade design and materials. Timber-glass composite elements are a novel interpretation of the structural sealant glazing concept aiming at a reduction of the carbon footprint of facades by using materials from renewable resources. Already available facade systems based on the principle of timber-glass composite construction are applied in curtain walls, which is a rather conventional way. This paper assesses the feasibility of cold bended timber-glass composite elements to widen the scope of possible applications to curved or freeform surfaces such as timber grid shells. Cold bending appears an efficient way to adopt the flat element to a non-regularly shaped substructure. The twisting from an initial undeformed to a deflected state leads to permanent stresses in the glass as well as in the adhesive joint, the adapter and the screwed connection. Numerical models of a rectangular and a square-shaped timber-glass composite element help to understand the mechanical reactions in the individual components and the joint. The virtual components are deflected on one corner while the other three remain in plane. The cold bending of such elements is additionally assessed in life-size experiments. Shape and size correlate to those used in the numerical models to enable a validation of the virtual model. The derived stresses and time-depended deformations of the deflected test specimens yield a better understanding of the structural behavior and design of timber-glass composite elements.

Production phases and market for timber gridshell structures: A state-of-the-art review

Timber gridshell is a structure with a doubly curved shape that is made of grid timber laths. Gridshell structure can be a solution of interest in modern free-form structures that are environmentally sustainable. However, there is a lack of academic research focusing on the potential markets and the production stages based on this construction technology. The aim of this literature review is to investigate the gridshell structure to identify its global production process, as well as the partners involved in the architectural examples studied. A review of both peer-reviewed scientific articles and grey literature resources (e.g., magazines, web pages, etc.) was conducted to gather information about timber gridshells. The design examples found were categorized as small, medium, and large gridshells. The categorization is based on the size and level of complexity of the design examples. Production phases and partners involved in the design and construction of these structures were identified for each category. Furthermore, the motivations and barriers to using gridshell designs in construction, and the potential market segments were determined.

Production Phases and Market for Timber Gridshell Structures: A State-of-the-Art Review

Timber gridshell is a structure with a doubly curved shape that is made of grid timber laths. Gridshell structure can be a solution of interest in modern free-form structures that are environmentally sustainable. However, there is a lack of academic research focusing on the potential markets and the production stages based on this construction technology. The aim of this literature review is to investigate the gridshell structure to identify its global production process, as well as the partners involved in the architectural examples studied. A review of both peer-reviewed scientific articles and grey literature resources (e.g., magazines, web pages, etc.) was conducted to gather information about timber gridshells. The design examples found were categorized as small, medium, and large gridshells. The categorization is based on the size and level of complexity of the design examples. Production phases and partners involved in the design and construction of these structures were identified for each category. Furthermore, the motivations and barriers to using gridshell designs in construction, and the potential market segments were determined.

Digital tools and experimentations for structures realised with the active bending

The research presented in this paper deals with the experience gained by a Research Unit from DiARC Naples on the topic of active bending structures, in the specific domain of timber post-formed gridshells. The design of specific digital tools aimed at controlling architectural and construction issues of such structures can be considered as one of the most important achievements to guarantee the buildability of these lightweight and ecological structures. So far, the research group experimented the design and construction of more than 10 among pavilions and full-scale prototypes of timber gridshells. This paper traces the method to design elastic gridshells starting from their form in a strict relationship with construction issues, with the aim at freeing the initial concept stage under the surveillance of buildability and allowing the implementation of the bespoke tools as well as of the construction methods.