A Contribution to the Design of Textile Reinforced Concrete Structures

The reduction of green-house gas emissions is one of the global challenges that our society is facing and the production of cement plays a major role because concrete is the most used material worldwide. For every 1000 kg of cement produced, 900 kg of CO2, are released in the atmosphere. In addition, for structural concrete, the generous concrete cover, prescribed by current codes of practice, yields to robust but also to relatively heavy and massive members.

Textile Reinforced Concrete (TRC) is a novel building material made of high-strength fabrics embedded in a fine grained mortar matrix. The implementation of non-corrosive reinforcement materials allows to reduce drastically the concrete cover requirements. That empowers to cast extremely thin-walled structural elements and to reduce the structural dead-load up to 90 % (with respect to conventional Reinforced Concrete). In addition to substantial material savings associated to the structure and its foundations, low-clinker-content cements can be used, since no passivation of the reinforcement is required. That, reduces further the environmental footprint and allows to build more sustainable load-bearing structures. Despite its advantages, TRC is hardly implemented in current engineering practice. On one hand there is a lack of design regulations, but on the other, there is also a shortage of construction experiences. With the aim to promote the widespread of TRC, this work addresses both hurdles at three different levels of analysis:

First, the tensile response of TRC is investigated by means of an extensive experimental programme. It includes, tests on bare fabrics, the plain mortar and composite tension ties. On the basis of the experimental observations and the coaxial ring analogy, a mechanical model has been derived, allowing to predict the deformation capacity and resistance in a unified manner. That is fundamental to understand the effects of fabric-coating, impregnation, tie- and load introduction length on the load-bearing behavior at a micro-level.

More complex loading conditions have been investigated at a meso-scale. Full-scale load tests of thin-walled flanged members have been instrumented with external photogrammetric measurements. These have allowed to validate and adapt the Elastic-Cracked-Stress-Field approach for TRC linear members. The method allows to model beam- and discontinuity regions in a comprehensive manner as well as predicting the response under serviceability conditions and at failure in a unified way, while accounting for both, bending and shear.

Finally, the application potential of TRC is addressed at a macro-level. Starting from previous ferrocement works, different formworking materials, casting methods and connections of thin walled members have been explored. The obtained results have been condensed to design, build and erect a full-scale, demountable, prototype pavilion within a three-weeks workshop.

Eventually, a proper architectural language has been derived for light-weight structures made of thin-walled TRC members. The structural design can be performed in a comprehensive manner with the Elastic-Cracked-Stress-Field approach, while the resistance of the composite can be estimated with the coaxial ring model. That contributes to the development of code-like prescriptions for TRC and its future implementation in common construction practice for sustainable structures.

Re:Crete - A Footbridge made of Reused Concrete Blocks

Maléna Bastien Masse, Jan Friedrich Georg Brütting, Julie Rachel Devènes, Corentin Jean Dominique Fivet, Célia Marine Küpfer

Today, concrete is the most widely used construction material worldwide. Strong, versatile, durable, and vector of economic development, this exceptional material is also the principal cause of greenhouse-gas emissions, material depletion and waste generation by the construction industry. Hence, reusing concrete elements extracted from obsolete building structures has large potential to significantly reduce the environmental impact of construction. To demonstrate the potential of such an unusual strategy for bridge construction, this paper shows the construction of the Re:Crete arch prototype. It is made of 25 reclaimed concrete blocks connected through post-tensioning to create a 10-m span arch. The complete design-and-build workflow of the prototype is presented, including the structural design of the arch, the sourcing of the reusable concrete elements and the assembly. The Re:Crete arch prototype mechanical properties and environmental impact are assessed through non-destructive investigation, load testing and Life-Cycle Assessment. The results show that the reuse of concrete blocks leads to a comparable structural behaviour as a similar arch made of new or recycled concrete, with an environmental footprint reduced by more than 70%.

Asociación Española de Ingeniería Estructura2022

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

Can timber lower the environmental impact of tall buildings?

Catherine Elvire L. De Wolf, Corentin Jean Dominique Fivet

The building sector is responsible for 30% of anthropogenic greenhouse gas (GHG) emissions (UNEP, 2009). Recent energy efficiency measures have helped reduce the operational carbon related to the use phase of the building, but a lack of industry attention hinders the reduction of embodied carbon related to the rest of its lifecycle: material extraction, transport, construction and demolition. Tall buildings are an evident solution to fight urban sprawl and hence reduce transportation emissions. In addition, the volume-to-surface ratio lowers the need for heating and thus reduces the use of operational energy. However, the challenge with current tall buildings is their inherent need for more structural materials. Research is needed to achieve structural efficiency in tall buildings by reducing the material quantities and choosing low carbon materials. For example, we can use mass timber to achieve skyscrapers that sequester carbon. Major engineering companies have studied the possibility of constructing timber skyscrapers. A new timber tower construction technique was recently validated, using reinforced concrete only for the connections. In composite structures, materials are used where they are most needed by combining their best qualities such as fire safety, high strength, and low density. This allows structural engineers to design using less material. This paper makes two contributions: it discusses the challenges of assessing the embodied carbon of timber materials and it characterizes the specificities of tall timber systems with built case studies.

Taylor & Francis Group2019

Reuse in Architecture & Structural Design

Jan Friedrich Georg Brütting

2018