Design of Integrally-Attached Timber Plate Structures

Yves Weinand

• Publisher: CRC Press
• Year: 2021
• eBook ISBN: 9781000430592
• Edition: 1
• Topic: Arquitectura
• Subtopic: Diseño arquitectónico

Design of Integrally-Attached Timber Plate Structures outlines a new design methodology for digitally fabricated spatial timber plate structures, presented with examples from recent construction projects. It proposes an innovative and sustainable design methodology, algorithmic geometry processing, structural optimization, and digital fabrication; technology transfer and construction are formulated and widely discussed.

The methodology relies on integral mechanical attachment whereby the connection between timber plates is established solely through geometric manipulation, without additional connectors, such as nails, screws, dowels, adhesives, or welding. The transdisciplinary design framework for spatial timber plate structures brings together digital architecture, computer science, and structural engineering, covering parametric modeling and architectural computational design, geometry exploration, the digital fabrication assembly of engineered timber panels, numerical simulations, mechanical characterization, design optimization, and performance improvement.

The method is demonstrated through different prototypes, physical models, and three build examples, focusing specifically on the design of the timber-plate roof structure of 23 large span arches called the Annen Headquarters in Luxembourg. This is useful for the architecture, engineering, and construction (AEC) sector and shows how new structural optimization processes can be reinvented through geometrical adaptions to control global and local geometries of complex structures. This text is ideal for structural engineering professionals and architects in both industry and academia, and construction companies.

Chapter 1

Digitalization in innovative and sustainable timber construction

Yves Weinand

1.1TECHNOLOGICAL ADVANCEMENTS IN TIMBER CONSTRUCTION

The application of digital-driven tools in the design of spatial timber plate structures embodies both a vision of the future and an understanding of the past. It is inspired by the vision of building as an integrated planning process, where aspects of craft, technique, aesthetic, and structural engineering converge as they did just before the revolutionary ‘Age of Enlightenment,’ but this time using contemporary engineering methods and tools. This, in particular, demonstrates an act of creativity within the field of architecture and specific contemporary architectural approaches. The raw resource in question has innate qualities that can also satisfy the aesthetic and conceptual designs architects are interested in. The emerging tools in digital architecture, design software, and the digital drawing tool seen as an instrument to conceive architecture, have opened the way for broader digital technology applications, including technical nature. Technical advances that now lie within this context facilitate digital fabrication integration in ways that were unthinkable only a few years ago. Over the last two centuries, the predomination, first of steel, then reinforced concrete within research and applications in civil engineering and materials science, has opened a huge gap of missing research regarding timber as a structural material to be engineered. Our predecessors’ and carpenters’ intuitive knowledge during the 18^th century has been lost with the rise of the engineers who have not taken advantage of timber as a construction material, having a priori accorded it a lower level of importance than for steel and concrete.

Technical considerations are often treated as neutral data, which do not, or should not, greatly affect the initial creative design process of a given architect. The technique, construction methods, civil engineering, and static considerations are seen as almost unwelcome ingredients in a certain number of cases. Those supposedly neutral technical considerations are more often than not tackled at a later stage in the design process, compromising the genuinely interdisciplinary and fundamental quality that such research approaches could aspire to.

Timber construction research demands cross-cultural and interdisciplinary approaches involving architecture, civil engineering, and material science. But the timber construction industry itself has remained a particularly conservative and traditional one. The gradual replacement of timber by steel and concrete over the last 200 years has not helped improve new and contemporary timber construction applications from an architectural and civil engineering perspective. This radically new generation of timber structures can change the face of timber construction as an architectural form, both lifting it out of the classical image of traditional architecture and expanding the use of timber in constructions of contemporary character. The old-fashioned image of the “chalet’ and related vernacular architecture will be replaced by a contemporary interpretation of timber use in our constructions. It should establish timber as a modern, high-tech material that plays a central role in a society concerned with sustainability.

1.2INNOVATIVE TIMBER CONSTRUCTION IN THE ARCHITECTURE, ENGINEERING, AND CONSTRUCTION (AEC) SECTOR

Using renewable and sustainable resources in Architecture, Engineering, and Construction (AEC) has become apparent in recent years. Within this context, interest in employing timber as a construction material has increasingly revived. Innovative timber-derived products, such as Laminated Veneer Lumber boards produced with the readily available type of woods, have emerged, and the use of such products is spreading.

This book's ambitious purpose is to develop the next generation of timber constructions made out of innovative engineered timber products at a building scale. It aims at the unprecedented exploration of advanced architectural geometry, engineering analysis, digital fabrication, prototyping, mechanical explorations, and construction of timber structures. Architectural production in recent years has been heavily focused on the digital outcome. With the growing development of computer-aided design (CAD) tools, architects have tried to integrate those new digital tools into their conception. For instance, one such conceptual trend has become known as‘blob’ architecture. But the way the architects use the latest digital tools has, until now, had more to do with the role of virtual representation than the role of fabrication. The structural productions derived from the new output of such digital tools have yet to address many formal issues from the digital design revolution on the civil engineering side. Civil engineering structures remain relatively conservative. New research concepts such as ‘structural morphogenesis’ have emerged recently from within interdisciplinary research environments. Still, the implications for physical and structural investigations constitutes an active part of the form-finding process have not been addressed yet. They need to be explored if such digital tools are to realize their true potential in the fields of architecture, design, and civil engineering.

The research being undertaken at the Laboratory for Timber Construction (IBOIS) at the Swiss Federal Institute of Technology (École Polytechnique Fédérale de Lausanne, EPFL) in Lausanne, Switzerland aims both to explore and to challenge the traditional relationship between engineering sciences and architectural conception. It is ultimately concerned with construction questions in ‘real’ space, as perceived and used by society. Therefore, we took an entirely different and unique perspective right from the beginning, devoting our attention to exploring in-depth how materialization and physical aspects of ‘real’ structures are related to their representations in the digital world. We seek to accomplish construction solutions that could be successfully disseminated throughout a construction market, meaning that the realization of unconventional structures at a reasonable cost must be an obligate goal. Developing specific and specialized digital tools appears to be increasingly necessary to pursue the many new questions arising from our ongoing research. A significant part of our approach is concerned with generating and linking together software that works on various levels, from tasks such as the creation of complex shapes to controlling and sizing finite elements and operating computerized numerical control machines (CNCs).

1.3SUSTAINABILITY ASPECTS AND TRANSDISCIPLINARY DESIGN METHODOLOGY IN ADVANCED TIMBER CONSTRUCTION

Timber is usually thought of as a ‘traditional’ material, and this is an advantage when it comes to socially legitimating more advanced research into complex shapes and free-form surfaces. Taking an interest in complex geometry from a (timber) construction point of view, instead of only a morphogenetic point of view, is a fundamentally different approach than blob architecture's ‘stylized mode’ phenomena, and the two should not be confused. Numerous recent buildings designed in the formalistic model of ‘blob’ architecture show a total lack of sustainable development awareness. This can be seen in the choice of construction materials, how difficult it is to maintain the structure's energy needs, and the high cost of material handling. In contrast, timber as a raw material for construction purposes certainly has a great future in the face of global sustainable development challenges.

In recent years, the necessity of using renewable resources and sustainable solutions in the building sector has become apparent, and timber has been promoted to the center of interest again. New timber-derived products, such as massif block panels, are emerging, and the use of such products has mostly increased over the past years. Their advantages are well-known, especially the low energy consumption for the production of building components (planks, boards, beams, etc.) and research into welded timber could, because of this, lead to exciting industrial opportunities. Savings in time and energy consumption are also notable in timber structure assembly and dismantling processes. However, we have observed that the challenges of sustainable development also concern the issue of architectural form. A fundamental challenge is: How can one integrate a process of formal and technological innovation within a sustainability perspective? A possible solution may lie in rethinking construction techniques and expanding the formal repertoire linked to wood use while affirming the ‘traditional’ values of timber construction. Together its technical, aesthetic, and environmental appeal can encourage an increase in the use of this material in contemporary construction and set the context through which this book should be understood.

The collaborative approach of architects, civil engineers, mathematicians, and computer scientists in the IBOIS team has offered a unique blend of skills and insights that enabled us to reveal the potential for novel construction applications of a renewable resource. Our strategy of treating morphogenetic aspects and structural aspects on the same level is likely to produce exceptional structural solutions. While the focus of our studies applies specifically to timber, one should also consider the use of other materials and applications. Furthermore, the use of the many small pieces that interact in timber plate structures will be a factor of major importance in determining the probability of structure failure (global failure); the anatomy of timber as a natural, fiber-structured composite should be able to reach higher structural performances when local weak points can no longer affect global stability. This consideration led, in the past, to the invention of plywood. Since plywood is made out of several layers of timber sheets, the sum of those layers is stronger and more rigid or subject to less local failure than the same amount of material taken out of one naturally grown piece of wood. In plywood, the random placement of fiber-perpendicular layers plays a less critical role since they are covered with stronger layers. Taking advantage of this same principle on another scale, we intend to compensate such randomly appearing weak points – contained in a given timber fabric – by a multitude of adjacent and slightly more resistant members who will sustain each other like a fabric using its woven quality as its strength. This will raise the parameter characterizing a value we call ‘global failure ratio.’ A specific performance factor might be derivable that considers the natural anatomy of timber, which is a disadvantaged construction material in terms of the coefficient of the material defined in Eurocode 5.¹

With the discussion on global climate change in mind, it is more than obvious that there is a need to change our behavior in many ways. Alternative energy resources need to be made accessible and lower consumption of energy achieved. Here, a structure's production and energy consumption play an important role when it comes to timber, a renewable resource, and interesting building material that should be used more frequently. However, environmentally conscious behavior cannot be achieved by obtrusion only. To convince people to invest in environmentally friendly products and materials, these materials have to be attractive. In the past, this was a problem for sustainable architecture's popularity, which was mainly realized with timber as the building material. It has often had a rustic, primitive, and alternative touch, which, though attractive to some, was repellent to many other potential clients. To access the latter group, the design needs to be treated as a strict criterion. The method of contemporary and appealing architecture with timber is both feasible and necessary to become more widely used in construction.

1 European Committee for Standardisation (CEN) (2008) CEN-EN 1995-1-1:2005+A1 - Eurocode 5: Design of timber structures - Part 1-1: General - Common rules and rules for buildings. Brussels.

Traditional design and development of structures are primarily based on the concepts of stiffness and efficiency. They are substantially aimed at minimizing the bending of the structural components and generating structures that can be characterized as rigid and inflexible, avoiding elasticity. Disastrous failures of conventional structures (for instance, under conditions of seismic activity, unusually strong wind forces, or unusually heavy snowfall) are reason enough to suggest we must rethink these stiffness and efficiency paradigms to strike a new path in the conception of structures. Here, spatial timber plate construction, especially the way they are deployed, provides exciting perspectives. They offer high-resolution networks made of many individual components. Furthermore, they provide the advantage that singular element failure does not trigger the entire system failure. Such structures admit large deformation without rupture, a property that is highly unconventional for civil engineering structures. The use of such surface elements can also improve safety considerations concerning accidental fire. For instance, a traditional truss can be replaced by a multitude of surface elements (panels) that act socially, like a fabric (as described earlier), retaining the structure's overall integrity even when substantially damaged.

The goal is to improve and expand the uses of timber and timber-derived composites for applications in construction and design. Timber structures made out of simple rectilinear elements have essentially defined timber construction and carpentry for centuries. With new digital tools, timber construction could be transformed, allowing its introduction into a wide range of new applications. As shown by the various digital tools under development, other potentially physically achievable geometries and constructions may emerge first as virtual representations. Such developments introduce a new range of civil engineering challenges of interest in the field of timber construction.

To date, structural analysis has not been widely applied to timber construction as it has to steel or concrete construction. The proposed use of planar structural elements and curved linear elements made out of timber-derived products will introduce timber in constructions, such as public buildings where architectural and aesthetic considerations are deemed to be of strong cultural importance. In the product sector of fills, insulations, and claddings, high-performance, economically attractive ready-to-build-systems, and design objects can be developed from the basic principles described in this book. Other architecture applications are also possible but have not yet been sufficiently developed for industrial applications. For example, one might envisage the industrial production of new classes of timber-derived products, such as woven timber walls and timber composites. Meanwhile, the recent acquisition of a 3D digital scanner allows for precise identification of specific trees and locks and a detailed prescription of their natural anatomy. This enables us to create a link between a particular selection of trees and a specific architectural design or form, avoiding any intermediate geometrical calibration, thus increasing timber profitability by at least 50 percent.

Switzerland has a long tradition in timber construction. The renowned education of carpenters and joiners, the guaranteed craftsmanship, the transfer of know-how from generation to generation, and identifying with the timber as construction and finishing material still build on this long-term experience. The ecological principles and the awareness for the environment (insulation and energy saving) have more and more impact in Switzerland, where the use of timber as a building material is considered an excellent thing to do. The future goal is to use even more timber and timber-based products in residential and commercial buildings. A good variety of timber is available as a local and renewable resource and transferred into high-quality timber products.

Traditional constructions can still be admired, particularly in alpine and rural areas and modern architecture relying on new materials, modern fabrication, and alternative construction methods present in Switzerland. Among other central European countries, Switzerland plays a leading role in the planning and constructing multistory buildings following state-of-the-art design and fire safety concepts, fulfilling the latest earthquake requirements, and using modern (prefabrication) construction methods. New materials and innovative combinations of materials allow for interesting solutions as prefabricated timber concrete composite floors.

Thanks to the ‘open’ concept of the Swiss design code for timber structures (SIA 265: Timber Structures²) and Eurocode 5 for the European Union and the UK, many new ideas could still be realized in prototype solutions, further developed, and finally brought on the market. Recent timber bridges for foot/bicycle traffic, heavy road traffic, and large warehouses and dome structures demonstrate outstanding and state-of-the-art structural timber engineering.

2 Swiss Standard SN 505 265 (SIA 265): Timber Structures.

The quality of the materials and construction today are high and must be maintained. In most cases, integral solutions are offered in terms of modular, prefabricated elements in the field of (multistory) constructions. The connection details, facade systems, windows and doors, thermal insulation, and even interior finish are incorporated into the prefabricated elements before the construction begins on site. In time, productions with rationalized (not necessarily fully automated) production, with immediate delivery on-site for fast construction, have been consolidated. Computer planning, cutting centers, or even robot manufacturing will play an essential role in the different stages of drafting, detailing, fabrication, and planning, minimizing the difference between a one-off design and a serial product. Such techniques make it possible to reintroduce long-forgotten, expensive-to-produce carpentry techniques, such as dovetail connections, which allow for the exact production of any desired architectonic shape and to achieve any prefabrication degree. Given the significant use of timber in construction and a desirable market for timber and timber-based products, there is a vast potential to attract the AEC sector to present their latest engineering, architecture, construction, and research developments.

This book is primarily centered around the use of wood-wood integral connections in timber plate structures. Particular attention is put on the design of form-active surface structures with engineered timber panels. A wide range of geometries ranging from simple configurations to complex forms is essentially investigated. These forms typically lie in the category of spatial structures. In particular, in essence, these structures are an arrangement in 3D space made of planar timber panels. While timber panels can differ in shape and size, they interface with their respective neighboring elements through angular connections. Despite traditional timber-frame structures where timber plates were considered a secondary structural element, in the new design framework for spatial structures, timber plates play a primary role in the load-bearing mechanism.

One of the significant benefits of designing self-supporting, surface-active structures with timber plates is that it offers a sustainable construction by bene...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication Page
• Contents
• Foreword by Hanif Kara
• Preface
• Acknowledgments
• 1 Digitalization in innovative and sustainable timber construction
• 2 Structural design methodology in Integrally-Attached Timber Plate structures by Aryan Rezaei Rad and Petras Vestartas
• 3 Case studies in Integrally-Attached Timber Plate structures: From prototypes and pavilions to large-scale buildings
• 4 Design optimization in timber plate structures
• Index