Integrally attached timber folded surface structures

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...

Component reuse in structural design: emerging practices and tools for the circular economy

Jan Friedrich Georg Brütting, Corentin Jean Dominique Fivet, Jonas Warmuth

Structural engineers play an increasing role in ensuring the transition towards a more sustainable construction sector: a) they are responsible for the design of the most resource- and energy-intensive part of buildings and infrastructure, and b) they regularly interact with architects, contractors, and clients, and hence are full stakeholders in the overall decision process. Traditionally, structural engineers follow two paths to reduce structure environmental impacts: 1) minimizing the volume of material, and 2) adopting low impact (e.g. low carbon) materials. A third strategy that has recently re-emerged in practice and research is the reuse of structural components over multiple service cycles, which allows drastically reducing raw material use, reprocessing energy, and waste. Therefore, employing reuse strategies in structural design has considerable potential to reduce structure environmental impacts further. Although reuse is not new, systematic adoption in practice implies an important paradigm shift: rather than manufacturing components after the structural system has been designed, the system must be synthesized from a stock of available components. The first part of our contribution provides an overview of historic and contemporary structures that efficiently reuse structural components. It also highlights the influence of component reuse on the structural design process. The second part presents a new computational tool for the conceptual design of structures from a stock of reclaimed elements. The tool combines Combinatorial Equilibrium Modelling, graphic statics, efficient Best-Fit heuristics, and Life Cycle Assessment to explore different design options in a user-interactive way and with almost real-time feedback. The method applicability is demonstrated through a realistic case study for the design of a complex 3D spatial structure made of reclaimed structural elements originating from deconstructed buildings in Switzerland. Results show that structures made of reused elements have a significantly lower environmental impact than solutions made of new material only. Link to the video: https://youtu.be/VCyD1yqXH8w

fib2021

Reuse in Architecture & Structural Design

Jan Friedrich Georg Brütting

Introduction The construction industry has an extensive impact on the global environment and will be facing three big challenges in the next decades: reducing its resource consumption, decreasing its energy use, and limiting its waste production. This is even more crucial, considering global population growth and increasing urbanization. Consequently, a shift of paradigm from a linear economy of make-use-dispose, towards a circular economy that advocates closed loops within the service life of materials and components is required. Recycling currently is the common strategy to make use of obsolete materials; however, it involves energy for reprocessing (e.g. melting steel scrap). Instead, direct reuse of components close to their original form has the potential to reduce environmental impacts further because sourcing additional raw material is avoided and only few energy is spent for transformation [1]. In the case of buildings and infrastructures, load-bearing systems contribute the most to the embodied environmental impacts. This is because of their big mass and energy intensive construction process. These observations suggest that reusing structural elements has large potential to reduce the environmental footprint of building structures. Reused components may consequently have a longer service life than the systems to which they initially belonged and disassembled buildings become a mine for new constructions. This idea is of course not a today’s invention, but has found application already far in the past as well as in recent building projects. Before industrialization, most building materials were sourced locally and reuse of building materials and components was the rule because it was more cost and time efficient than new production [1]. The scarcity of building materials had to be considered in design and construction. A classic example is the reuse of bricks throughout the Roman and Greek eras or in post-war times. Remarkable are also the stone columns of the Great Mosque of Cordoba, Spain, which were reused from nearby Roman and Visigoth ruins to support Moorish double arches (Fig. 1a). More recently, the steel structure of the BedZED project in London (Fig. 1b) was constructed from 90 % locally reclaimed elements [2]. Many other contemporary case studies in which bricks, timber, or steel elements have been reused are reported in [1] and [2]. An outstanding structure is the London Olympic Stadium (Fig. 1c), whose roof truss incorporates 2000 tons of steel pipeline tubes reused from a nearby development project [3]. At smaller scale, a strained grid-shell pavilion made of reclaimed skis has been built by the researchers at EPFL’s Structural Xploration Lab (Fig 1d). Recently this environmental-aware architectural and structural design is evolving. In addition, governments have understood the potential of circular economy and circular design. For instance, the European Commission has issued an EU action plan for the circular economy in order to reduce waste and landfill. Research While historic and contemporary projects, especially in Europe, highlight the environmental, time or cost benefits of building with reclaimed (structural) elements, many technological challenges remain. Buildings have to be carefully disassembled, which is often only possible for steel or wooden structures that are joined with reversible connections, or when elements can be cut and member ends are reshaped to fit new settings. Further, the quality and structural capacity of reclaimed elements has to be ensured. Under these assumptions, this research focuses on the standpoint of composing building structures from a stock of reclaimed elements. This entails reversing the conventional design process. The constrained availability of elements dictates the layout (topology and geometry) of the designed structure due to the a-priori set geometric and mechanical properties. The design shifts towards a “form follows availability” paradigm [1]. Structural optimization methods, which traditionally seek best performing structural systems under given boundary conditions, can be extended to integrate and facilitate element reuse in structural design. This research uses the combination of combinatorial optimization and form-finding methods to design reticulated structures from a given stock of reclaimed elements [4], where: 1) available elements are grouped by material, structural capacity and dimensions, 2) an optimal assignment of a subset of stock elements into a structural system is performed, and 3) the structure geometry is optimized. Generally, the assignment step 2) minimizes the structural weight to optimally utilize the available element capacities, whereas the geometry optimization step 3) is carried out to match truss geometry and available element lengths. This method is applied to optimize truss systems subject to differently composed stocks. In each case, varying cross section sizes or element lengths result in a different outcome of the designs. Figure 2 (a) shows a typical roof truss design, which is loaded at the top chord and is used as the initial topology for the introduced optimization method. The obtained layout for the case of using Stock A is reported in Fig. 1b. This stock consist of elements with 3.00m length which are n = 4 times available for each of the six cross-section groups. The use of the stock is indicated by the superimposed magenta colored bars on top of the grey ones. Due to limitations of the stock to 3.00 m elements only, the truss layout contains two arrays of three almost equilateral triangles. For the truss made from Stock B, which is composed of equivalent cross section groups but with variable element lengths, the found geometry is shallower and vaulted. In both cases, the geometry optimization allows to use most of the stock members with their full length. The exploration of these case studies concludes that the availability of elements has a significant influence on the final structural design as well as its structural performance. For example, if an insufficient amount of elements with small cross-sections is available, the structure will be oversized (i.e. the capacity of available members is not utilized) and environmental savings are diminished. Conclusion The proposed optimization and form finding method renders a first step towards facilitating the design with reused elements where the outcome is not as predictable as in the well-established conventional structural design process. Future research will extend this method towards different structural typologies such as bending and frame systems. Further, the question of customized connection details enabling the joining of stock elements has to be addressed.

2018

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.