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An important share of building environmental impacts is embodied in load-bearing structures because of their large material mass and energy-intensive fabrication process. To reduce substantially material consumption and waste caused by the construction industry, structures can be designed and built with reused elements. Structural element reuse involves: element sourcing and deconstruction, reconditioning and transport. As these processes also generate environmental impacts, reuse might not always be preferred over new construction. This paper presents a method to design reticular structures with minimal environmental impact made from reused and new elements. The formulation given in this paper is based on a combination of Life Cycle Assessment (LCA) and discrete structural optimization. The LCA carried out in this work accounts for impacts generated from sourcing reclaimed elements to the assembly of the structure. Structural optimization is subject to stress constraints on element capacity and deflection limits for serviceability. Typical loading scenarios are considered. The method is applied to the design of three single-span steel trusses of different topology subject to 100 simulated stocks of reusable elements that have varying cross-sections and lengths. Benchmarks against minimum-weight solutions made solely from recycled steel show that this method produces structures with up to 56% lower environmental impact. Depending on stock availability, the lowest environmental impact is achieved through a combination of reused and new elements.
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, cutoff 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.
This paper presents optimization methods to design frame structures from a stock of existing elements. These methods are relevant when reusing structural elements over multiple service lives. Reuse has the potential to reduce the environmental impact of building structures because it avoids sourcing new material, it reduces waste and it requires little energy. When reusing elements, cross-section and length availability have a major influence on the structural design. In previous own work, design of truss structures from a stock of elements was formulated as a mixed-integer linear programming (MILP) problem. It was shown that this method produces solutions which are global optima in terms of stock utilization. This work extends previous formulations to stock-constrained optimization of frame structures subject to ultimate and serviceability limit states hence expanding the range of structural typologies that can be designed through reuse. Fundamental to this method is the globally optimal assignment of available stock elements to member positions in the frame structure. Two scenarios are considered: (A) the use of individual stock elements for each member of the frame, and (B) a cutting stock approach, where multiple members of the frame are cut from a single stock element. Numerical case studies are presented to show the applicability of the proposed method to practical designs. To carry out the case studies, a stock of elements was inventoried from shop drawings of deconstructed buildings. Results show that through reusing structural elements a significant reduction of embodied greenhouse gas emissions could be achieved compared to optimized structures made of new elements.
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