Rihards Saknitis ARC6012 BSoAD
Technical Investigation Individual Report Rihards Saknitis Space and Form S15124521
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Technical Investigation Report
Cover Image: The Savill Building Model. Source: by author
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Contents Introduction Timber Gridshells; Precedent Study Material Constraints in the Design Process Understanding Material Characteristics Collaboration and Mutual Understanding in The Design and Construction Process Conclusion References
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Abstract This report analyses the use of material in design and construction, through the study of timber gridshells. Through precedent studies, model making exercises and design analysis, the links between material qualities, constraints and the manifestation of those in built design will be examined, with the aim to better understand the possibilities and opportunities in material driven design.
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Introduction This report will explore the relationship between designers, materials and the final built design. It will attempt to answer the following question: How can an understanding and use of material characteristics become a design driver, concept and philosophy for sustainable, affordable and successful designs, and what understanding and coordination of design processes is required between architects and engineers to achieve that? This question will be answered by exploring timber gridshell structures using precedent studies and model making exercises. Studying the development of strained timber gridshells, through the Mannheim Multihalle gridshell, Downland Gridshell and mainly focusing on the Savill Garden Visitor Centre gridshell, the report will explore the qualitative and quantitative aspects of the gridshell design, as well as reflect upon the design process, construction and collaboration between the parties involved in the production of the Savill Building.
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Figure 1: The Savill Building Interior. Source: by author The gridshell structure achieves long-spans, creating wast, organic, enjoyable spaces.
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Figure 2: Savill Building Roof Structure. Source: by author Strained Timber Gridshell
Figure 3: Savill Building Exterior. Source: by author
The struc tural ele ments are connecti ons. straight, achievin Figure 4: The Forum, University of Exeter. Source: Roynon(2017, 63)
g the sh ell curva ture
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Unstrained Timber Gridshell Figure 5: The Forum, University of Exeter. Source: Roynon(2017, 63)
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Timber Gridshells; Precedent Study A shell structure gains its strength, lightness and efficiency from its three-dimensional shape, which transmits compressive, tensile and shear stresses in the plane of its double curved surface. A gridshell is a structure, which maintains the structural behaviour of a shell structure, whilst distributing its surface material in strips, creating holes in the surface (Harris et al, 2008). The main quality of gridshells is that they can be constructed from materials which naturally are not shells, do not create double curved surfaces. Gridshells can be split into two kinds, based on what grid elements are used and how the structure is constructed. “Strained gridshells” (Adriaenssen et al, 2014: 89) are achieved by creating a grid of flat elements and bending it, to achieve strain in the structure. In the case of timber gridshells: flat straight pieces of timber are a laid in a lattice, bent to achieve a shell shape and braced to maintain shear stiffness. The other is an “unstrained gridshell” (Adriaenssen et al, 2014: 91), where the form of the structure is achieved either by using pre-bent structural elements, which are assembled to achieve a shell shape, or by using straight elements, which achieve the curvature in the nodal connections between them. These unstrained members can be prefabricated off-site using steel, aluminium, glulam and other materials, reducing cost and complexity of construction (Adriaenssen et al, 2014). The double timber gridshell is constructed by laying out either all four layers of laths or the first two layers of laths in a grid and fixing those at the overlaying points. These nodal connection points must allow for movement, mainly whilst shaping the grid into a shell structure, but also, after the structure has taken shape. This grid is then shaped to the shell shape, which has been done in a number of different ways. The gridshell is fixed to a stiff boundary to resist the structure flattening out. Whether constructed together with the first two layers or applied after shaping the structure, the second grid layer of laths is used to fix the shell into shape. The resulting structure optimally utilises the material qualities with its geometry (TRADA, 2008). Laths Bracing
Shear Blocks (not all gridshells)
Border Fixing
Figure 6: Double Timber Gridshell Elements Diagram. Source: by author
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Mannheim Multihalle; First of Its Size A culmination of Frei Otto’s experimentation with lightweight double curved structures, the Bundesgatenschau Multihalle gridshell can be considered the first large-scale gridshell design. A building of its time, in the devastated after WW2 Mannheim, Germany, was designed and built as an exhibition hall. As much a built design as an experiment, the Mannheim Multihalle has been the basis of strained gridshell designs that have followed, introducing methods of layering the lath lattices, and different methods of bracing and completing the gridshell at its edges. Modelled and designed physically, with scale structural models and hanging chain models, it merged geometry, structural engineering, material qualities and the architectural form and function into one. The design exhibited both the possibilities and the problems of the gridshell structure, and, although constructed as a temporary structure, the Multihalle still stands today (Liddell, 2015).
Figure 7: The Mannheim Multihalle. Source: Drew (1976, 140)
Time of Construction: 1974/75 Location: Mannheim, Germany Engineer: Frei Otto Architects: Carlfried Mutschler and Winfried Langer Span: 60x60m, longest span 85m, height 20m Layers of Laths: 4 Lath Size: 50x50mm Lath Material: Canadian hemlock Cladding Material: PVC-Coated polyester fabric Bracing: Twin 6mm cables every 6th node Boundary Type: Laminated Timber, Cable, Concrete, Arches Nodal Connection: Bolts with slots in laths for movement. Erection: Pushed up from below (Drew, 1976)
Downland Gridshell; UK First Designed as an archive store for tools and artefacts and a workshop for restoration and training, the Downland gridshell of the Weald and Downland Open Air Museum was the first gridshell of its type in Britain. Using locally sourced materials and workforce the gridshell fits into the nature of its context and uses it, its energy, for heating and water. The building is “environmentally sustainable” (Cullinan Studio, 2002: 3), meaning it has a fraction of the embodied carbon of an equivalent structure done in concrete or steel. In the construction of the Downland Gridshell, the laths were made by finger jointing shorter bits of timber and connecting these with a steel bracket that allows for movement in the connection nodes of the lath grid (Cullinan Studio, 2002).
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Figure 8: Downland Gridshell Interior. Source: Cullinan Studio (2002)
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Time of Construction: 2002 Location: Near Chichester, West Sussex, UK Engineer: BuroHappold Engineering, Green Oak Carpentry Company Architects: Cullinan Studio Span: 48m long, 11-16m wide Layers of Laths: 4 Lath Size: 50x35mm Lath Material: Green Oak Cladding Material: Cedar Cladding, Strips of Polycarbonate Bracing: Timber Rib Laths (Triangulated) Boundary Type: Timber Nodal Connection: Steel Brackets Erection: Flat, lowered to shape by gravity
Savill Building; Report Precedent The Savill Building is the largest strained gridshell structure in the UK. Unlike other gridshells, the building’s shell structure does not finish at the ground and is instead connected at its edges to a steel tubular ring beam. Designed and functioning as entrance and a visitor centre to the Windsor Great Park, the raised gridshell allowed one façade of the building to be entirely glazed achieving panoramic views of the Savill gardens (Glenn Howells Architects, 2008). The construction sequence of this gridshell was unique, as it shaped the first layer of laths in two directions first, connecting those allowing rotation. Then shear blocks were added, which increased the section size of the gridshell, allowing to use thinner timber sections, whilst remaining structurally stable. On top of that, the second layer of laths was added, together with the birch plywood bracing, fixing the structure to its shape and completing it. The sourcing of timber was done locally, in clients, Crown Estates, owned forests, which was then processed and classed by skilled carpenters. The joining of the shorter timbers and laying out of the gridshell structure was done on-site by a crew of specially trained carpenters. This achieved an environmentally sustainable, clean and efficient construction (Harris et al, 2008).
Figure 9: The Savill Building Under Construction. Source: GHA (2008)
Time of Construction: 2006 Location: Windsor Great Park,Berkshire, UK Engineer: BuroHappold Engineering, Green Oak Carpentry Company, EngineersHRW Architects: Glenn Howells Architects Span: 90x25m Layers of Laths: 4 Lath Size: 80x50mm Lath Material: Larch Cladding Material: Oak Bracing: Birch Plywood Boundary Type: Steel Tubular Ring Beam Nodal Connection: Bolts Erection: Flat, lowered and raised to shape with scaffolding
Rihards Saknitis Technical Investigation Report Figure 10: The Savill Building West Elevation. Source: GHA (2008) The Savill Buidling exhibits a clear connection of architectural concepts(in yellow), architectural elements (in cyan) and structure (in magenta) which are inseparable in the full experience of the building.
Three Peaks and Wallies of The Building
View Towards The Garden
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Steel Ringbeam
Gridshell Structure
Steel Supports
Glazed Elevation
Oak Cladding
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Material Constraints in the Design Process Any material can be characterized by a list of its physical constraints. These can be used as a design limitation or a design driver. The way a material is procured, what size elements can be achieved from it, how the material behaves when it is under different forces, its environmental behaviour, its look and feel, even image, meaning. These are design parameters, which are inherent with any construction material and are apparent among the slightest investigation, the experience of the material (DeLanda, 2004). The understanding and use of these material parameters in design and construction have varied through time and trends. With the rise of CAD (computer-aided design) and use of NURBS (Non-uniform rational basis spline) systems when modelling and designing buildings, the material is often a means to achieve a digital shape, rather than what shapes the design. Designs which freely cut, bend, cast materials to create any form imaginable, are almost synonymous with 3D computer modelling. To counteract that, an understanding of material values and nature is needed, and It has to be applied in a parametric system, where the material characteristics, parameters affect the spatial, programmatic, architectural and structural parameters and vice versa (Cabrinha, 2008). The strained timber gridshell is a true and clear example of the bottomup approach to designing with material values in consideration. These structures have been experimented with by Frei Otto and his many physical models, and are still designed and constructed as much physically as digitally. The Savill building design began, with learning from a previous gridshell, with sourcing quality local timber, with working with carpenters and engineers with experience of designing gridshells, which were crucial to a successful final product (Roynon, 2017).
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Figure 11: Downland Gridshell Laths Lowered Into Place The four layers of laths where connected in a flat lattice in by Gravity. Source: Cullinan Studio (2002) metal brackets laid out on adjustable scaffolding. Then the laths lowered into the designed shape a couple of centimeters per day, where those were fixed to the timber boundary.
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Figure 12: Savill Building Card Model Experiment. Source: by author The first sketch model our group did was constructed at a 1:50 scale. A model of the Savill Building at a 1:50 scale. The card lath With a single layer of grid and card, the shell shape did not stay. grid failed to keep the desired shell shape, due to the limited stiffness of the model making material. Desired curvature The lessons learned from this model were: the lath lengths need to drawn in cyan and magenta. be fixed, the material stiffness is crucial, four layers of laths are
needed to fix the shape.
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Understanding Material Characteristics Through several model-making exercises, the material qualities, constraints and requirements, and construction sequence for a stable gridshell were explored. Based on the precedent of the Savill Visitor Centre gridshell a study was carried out using varied materials and construction sequences. The first attempt was a thin card model at a 1:50 scale. Only one of the wings of the Savill Building was modelled, with the aim of showing the double curvature of the gridshell surface. Because of a limited amount of information about the finished building and lack of stiffness in the model making material, this model failed to keep the shell shape and caved in. The card laths could not hold their weight and the result could almost be described as something resembling a hanging chain model, a reversed gridshell structure. Based on these findings, further models were constructed using 1.5mm thick aeroply, at about 3mm width, which was found to be a suitably accurate scaleOsacenco, representation the Denisa-Nicole Ed Revans, Richard Robinson,of Rihards Saknitis laths used in the Savill Building. First, a grid of scaled laths was laid out and fixed with wire, to retain some flexibility in the nodes of the lattice. This created a highly flexible plane which could be formed into double-curved surfaces easily. From this, a wing of the Savill Building was constructed again.
Figure 13: we Aeroply Grid.lath, Source: The second sketch model constructedLath was an aero-ply single gridby model. We to explore the freedom of forming shellamount structures,of Thegot lath lattice achieves vast however, as this was a single layer grid, it would flatten out.
author shapes and spaces, with its ability to freely bend and distribute forces in the shell surface.
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By connecting the two sets of lath grids with shear blocks in-between, a rigid, stable grid shell was achieved. The construction sequence of this model closely resembled that of the Savill Building, however, a ring beam was not used, and the structure had to be braced with string, which was removed as the fourth layer of laths was applied and the Osacenco, structure Denisa-Nicole Ed Revans, Richard Robinson, Rihards Saknitis gained stiffness.
Denisa-Nicole Os
Figure 15: The Savill Building Model. Source: by author After the application of four lath layers and shear blocks the gridshell model became strong and only needed bracing for when loads were applied to the surface.
The third sketch model was the first model to achieve the shell form. With four layers of ply laths and shear blocks employed at a 1:50 scale the model represented one of the ends of the building. The third sketch model was the first model to achieve the shell form. With four layers of ply laths and shear blocks employed at a 1:50 scale the model represented one of the ends of the building.
Figure 14: Aeroply Lath Grid. Source: by author The scaled laths where connected at the nodal connections with soft wire to allow movement and slight rotation when shaping the flat grid into a shell shape.
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Finally, a 1:50 model of the highest peak of the Savill Building was constructed with the edges of the model dipping and creating the double curvature of the structure. This model was constructed in the same sequence as the Savill Gridshell, beginning with a scaled scaffolding system. Over that, grids of laths with shear blocks sandwiched between were formed and trimmed at edges. These were connected to a scaled steel ring beam on the two facades of the model. This achieved a structurally sound model, which held up with forces applied.
Figure 16: The Savill Building 1:50 Model. Source: by author A third of the Savill Building was modeled to achieve the doubble curvature of the gridshell surface.
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Figure 17: The Savill Building 1:50 Model. Source: by author
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The model came to demonstrate the structural, architectural, visual, interior qualities of the Savill Gridshell, amongst other things, creating interesting light and shadow effects. Perhaps, the model speculates, what the interior space could have been, if the gridshell was not braced with plywood exclusively.
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Figure 18: The Savill Building 1:50 Model; Ring Beam. Source: by author The ringbeam collects and distributes the loads to the concrete base of the Savill building
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These exercises successfully explored and presented how the ability of wood to bend and remain stiff is key to a successful strained timber gridshell, and how simple design elements can contribute to the stability of a structure. It also demonstrated the importance of an accurate construction sequence.
Figure 19: The Savill Building 1:50 Model. Source: by author
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Collaboration and Mutual Understanding in The Design and Construction Process Over the number of design and construction stages of the Savill building, different parties had to collaborate and guide the production process of the building. The idea for a gridshell structure for the Savill Garden Visitor Centre came from Glenn Howells Architects as part of a design competition submission. As they presented the Downland Gridshell as a gridshell precedent to the Crown Estates, who had set up a design competition for the Savill Building, and now own and manage the building, it was decided that this would be the most suitable kind of structure for the location. The architectural vision was a flowing form, which resembles the tree line of the park, with a large opening towards the gardens. A sketch and a competition visual were handed over to BuroHappold Engineering, who had worked on the important preceding gridshells before the Savill Building, having formed out of the Frei Otto Mannheim Multihalle team. At this stage, the design was meant to be a gridshell but was far from being resolved, having been modelled for the competition digitally and with little regards to material constraints. BuroHappold Engineering worked with Green Oak Carpentry Company, who had worked on the Downland Gridshell to locally source and prepare the timber, and EngineersHRW, who were the clients appointed engineers and worked on other solutions than the gridshell roof in the project. The design resolution of the gridshell was a seeking of a structure that would achieve the architectural vision, whilst being a gridshell. One of the issues was the unusual border to the gridshell which could not end at the ground, because of the architectural vision of the view of the park and the site topography. The steel ring beam installed was designed to keep the structure slim whilst being stable. To create the spaces imagined by Glenn Howells Architects the Savill Building is unusually flat, for a gridshell. Ultimately, a gridshell on this site might not have been the most viable option, and other structural solutions might have achieved a more successful and pure design. The problem might have arisen from not fully understanding the type of structure when picking a gridshell as the competition-winning design (Roynon, 2017). The specificity of the gridshell requires a complete understanding of the engineering, carpentry and the material to achieve a qualitative architectural space. The structure utilises material and geometry to a level, where a disregard of either would result in an unachievable structure. Rather poetically, the kind, size and visual appearance of the timber used becomes an inseparable part of the architectural experience, but also the structural stability. Because of its complexity and unique construction sequence, the gridshell becomes or at least has proven to possibly be a sustainable structure (Cabrinha, 2008).
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Here also the problem of the gridshell arises with its uniqueness and absolute parameters. An architectural vision can be of a gridshell, but it has to cease to be a vision and become a design process at that exact moment, for the design not to become a compromise of other ideas, and truly exhibit and utilise the qualities of a gridshell. This has also limited the number of gridshells constructed, as clients are inspired by the experience of a gridshell but intimidated by the production of one. Here the collaboration between architects, engineers and ultimately: the construction material must be most effective to achieve a gridshell (Roynon, 2017).
Figure 21: The Savill Building Plan. Source: by author
The gridshell is unusually lifted, to achieve a wide view of the park and circulation through the centre of the building (in blue). Figure 20: The Savill Building Exterior. West Entrance. Source: by author
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Figure 22: The Savill Building Exterior. East Entrance. Reconstruction. Source: by author
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Conclusion The strained timber gridshells are interconnected systems of material, design, structure and all that these encompass. The material and the utilisation of it, the timber, is the key element of the timber gridshell structure, the geometry shaping the laths, and the timber realising the geometry and making it structural. Because of the complexity of material understanding and construction, the strained gridshells constructed so far have exhibited a design philosophy with regard to the construction material and environmental sustainability. Gridshells have also proven to be challenging and imperfect, with highly skilled professionals, experimentation and innovation involved in the production of each strained gridshell, with the engineerarchitect relationship exceptionally active and collaborative. The strained gridshell is an example to how, with research, knowledge, innovation, close collaboration and mutual understanding between architects, engineers, contractors and clients, the building material can be the concept, the structural design, the architectural form, expression and the function of a successful building.
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References: Adriaenssen, S., Block, P., Veenendaal, D. and Williams, C., eds. (2014) Shell Structures
for Architecture. Form Finding and Optimization. Abingdon: Routledge. Cabrinha, M. (2008) Gridshell Tectonics. Material Values Digital Parameters. In:
Silicon + Skin: Biological Processes and Computation. 28th Annual Conference of the Association for Computer Aided Design in Architecture (ACADIA), Minneapolis 16-19 October 2008. Fargo: ACADIA, pp. 118-124. Cullinan Studio (2002) Downland Gridshell. [pdf] London: Cullinan Studio. Available at: http://cullinanstudio.com/uploads/documents/DownlandGridshell_CaseStudy.pdf [Accessed 13th December 2017]. DeLanda, M. (2004) Material Complexity. In Neil Leach, David Turnbull, and Chris Williams, Digital Tectonics. London: Wiley-Academy Press. Drew, P. (1976) Frei Otto: Form and Structure. London: Crosby Lockwood Staples. Glenn Howells Architects (2008) Savill Building. Available at: https://glennhowells. co.uk/ [Accessed 29th October 2017] Harris, R., Haskins, S., Roynon, J. (2008) The Savill Garden gridshell: design and
construction. The Structural Engineer, 86(17), pp. 27-34. Liddell, I. (2015) Frei Otto and the Development of Gridshells. Case Studies in Structural
Engineering, 4(2015)/ 39-49. Available at: https://www.sciencedirect.com/science/ article/pii/S2214399815300011 [Accessed 12 December 2017]. Roynon, J. (2017) The Savill Building. ARC6012 Technical Investigation. BA Architecture, School of Architecture and Design, Birmingham City University, 13 November [lecture notes taken by Rihards Saknitis] TRADA Technology (2008) Case Study-The Savill Building, Windsor Great Park. High Wycombe: TRADA Technology.