Optimum design of low environmental impact structures through component reuse

Load-bearing systems (structures) in buildings and infrastructure contribute to a significant share of adverse environmental impacts (EI) because of resource- and energy-intensive fabrication. A currently overlooked circular economy strategy to reduce EI is to reuse structural components over multiple service cycles, which avoids resource use, energy for reprocessing, and waste. To apply reuse, the design process is fundamentally different to conventional practice: employing reused elements involves solving an inverse process whereby the structure layout (topology and geometry) is a result of available element characteristics (cross-sections and lengths). This thesis proposes a new computational workflow to enable design through reuse in structural engineering.

Discrete structural optimization techniques are formulated to design reticular structures (trusses and frames) that make best use of a stock of reclaimed elements (linear bars and beams). The objective is the minimization of EI through optimizing stock element assignment and structure topology subject to ultimate and serviceability limit states. The structure EI is quantified through Life Cycle Assessment (LCA) which includes process impacts for building deconstruction, reconditioning, and transport of reclaimed elements. The design process is formulated as a Mixed-Integer Linear Programming problem which produces global optima, and thus it allows rigorous benchmarking between solutions obtained by varying stock compositions and LCA parameters. In addition, geometry optimization is carried out in sequence with assignment optimization to improve further the structure performance and to reduce cut-off waste. The proposed method is applied to typical engineering structures including roof trusses and multi-story building frames subject to statistically simulated and realistic stocks inventoried from deconstructed buildings. Results show that solutions made from reused steel elements have an up to 60% lower EI compared to minimum-weight solutions made of recycled steel elements. An LCA parametric study shows that long transport distances for reclaimed elements are only marginally important, whereas machine operation during deconstruction has a significant influence on EI. This study concludes that a combination of reused and new elements leads to structures with the least EI.

To further extend the application range of component reuse, another method is formulated to synthesize a kit of parts comprising linear bars and spherical joints that can be assembled to form non-modular structures of diverse layouts. Multiple structure geometries are optimized simultaneously with the kit-of-parts composition (number of elements, dimensions, cross-sections). The method is implemented as an interactive design and fabrication workflow which has been successfully applied to build three pavilion-scale prototypes. Results show that reusability of the same set of components for multiple structures requires only half the components compared to one-off construction.

In summary, this thesis lays out the foundation for optimum design of structures through component reuse and it provides new benchmarks of attainable EI reductions compared to structures made of new components. The significant EI reduction obtained through applying the proposed workflow fosters a broader implementation of reuse strategies in research and practice.

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

Optimization Formulations for the Design of Low Embodied Energy Structures Made from Reused Elements

Jan Friedrich Georg Brütting, Corentin Jean Dominique Fivet, Gennaro Senatore

The building sector is one of the major contributors to material resource consumption, greenhouse gas emission and waste production. Load-bearing systems have a particularly large environmental impact because of their material and energy intensive manufacturing process. This paper aims to address the reduction of building structures environmental impacts through reusing structural elements for multiple service lives. Reuse avoids sourcing raw materials and requires little energy for reprocessing. However, to design a new structure reusing elements available from a stock is a challenging problem of combinatorial nature. This is because the structural system layout is a result of the available elements’ mechanical and geometric properties. In this paper, structural optimization formulations are proposed to design truss systems from available stock elements. Minimization of weight, cut-off waste and embodied energy are the objective functions subject to ultimate and serviceability constraints. Case studies focusing on embodied energy minimization are presented for: (1) three roof systems with predefined geometry and topology; (2) a bridge structure whose topology is optimized using the ground structure approach; (3) a geometry optimization to better match the optimal topology from 2 and available stock element lengths. In order to benchmark the energy savings through reuse, the optimal layouts obtained with the proposed methods are compared to weight-optimized solutions made of new material. For these case studies, the methods proposed in this work enable reusing stock elements to design structures embodying up to 71% less energy and hence having a significantly lower environmental impact with respect to structures made of new material.

Springer International Publishing AG, part of Springer Nature2018

Zürich Stadtspital Triemli Personalhäuser – Resource assessment of structural elements

Maléna Bastien Masse, Julie Rachel Devènes, Corentin Jean Dominique Fivet, Célia Marine Küpfer

The Triemli Personalhäuser are three equal 15-story buildings located on the Zürich Triemli Stadtspital campus and erected between 1964 and 1969. Cast-in-place reinforced concrete (RC) slabs and walls form the building cores and their surrounding corridors. The rooms are arranged around these cores. The load-bearing intermediate walls, made of prefabricated masonry, support thin precast slabs used as permanent forms. A RC layer is cast over these precast slabs and connects the room slabs with the cast-in-place slabs of the corridors and cores. The self-supporting facade consists of precast RC panels. The City of Zürich plans the deconstruction of these three buildings, thus making available a large amount of RC elements composing the structure and the facades of these buildings. Little-known and rarely implemented, the reuse of concrete elements from obsolete buildings in new projects is a sustainable approach that promotes a circular economy. When reusing, the components of obsolete buildings are carefully dismantled without being crushed. They are then cleaned, possibly repaired or trimmed, and reused without many transformations in a new project, maintaining their shapes, technologies, and mechanical properties. In addition to maintaining the embodied energy and history of the reused components, reuse allows the construction industry to reduce demolition waste, greenhouse gas emissions, and material consumption. This report is a preliminary resource assessment and aims at inventorying and assessing all structural elements of the Triemli Personalhäuser, focusing on their potential value for reuse. Both precast and cast-in-place RC elements are included. They are part of the load-bearing structure or are self-supporting such as the precast facade elements. The proposed methodology allows identifying all properties needed to evaluate the potential for reuse of an element: geometry, material properties, current condition, aesthetics, accessibility, resistance, future durability and environmental impacts. After reviewing available reports and drawings on the buildings, onsite visits are carried out to complete the information and visually inspect the structural elements. During the inspection, the elements are assessed with regards to their suitability for reuse and their condition is classified into a five-grade scale. The investigations are completed with destructive and non-destructive testing of the material properties. Together, Buildings A, B and C are made up of approximately 7 000 m3 of materials constituting their load-bearing system, with approximately 2 500 m3 of precast concrete, 3 400 m3 of cast-in-place concrete and 1 100 m3 of masonry. Of this total, approximately 4% of the volume is dropped from the analysis due to the bad condition of the elements, namely the balcony slabs, the roof slab, and the external stairs. The other elements are in a good or acceptable condition and ae inventoried and analysed in detail. The inventoried elements are divided into 5 categories: (1) facade elements; (2) slab elements; (3) wall elements; (4) column elements; and (5) staircases. Each of these categories are subdivided into a certain number of element types for which a complete factsheet is prepared, including pictures, drawings and useful information on their condition. The volume and weight of each element types are given, as well as their share of the total material volume. The embodied global warming potential (in kgCO2eq) for fabrication and demolition of the elements is also calculated. The results of the investigation on material properties confirm sufficient compressive strength for all elements. The carbonation depths measured on the cores are lower than the cover thickness of the reinforcement. Thus, the concrete is not carbonated in the reinforcement areas and the risk of corrosion is kept low, insuring a good durability of the elements. This document should serve as a base for designing and planning future reuse applications for the concrete elements extracted when deconstructing the Triemli Personalhäuser. The information presented here will help the planners to prioritize the reuse strategy on the elements in the best conditions, with the largest volume share and thus with the largest embodied global warming potential.

EPFL2022