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

Abstract

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.

A BIM-Based Framework and Databank for Reusing Load-Bearing Structural Elements

“…The Intergovernmental Panel on Climate Change (IPCC) reminds us that we face significant risks with global warming of 1.5 • C and more [1], which seems to be looming if growth keeps its current pace. In this context, the building sector is a major contributor to three environmental hazards: resource depletion, energy consumption and waste generation [2][3][4][5]. The building sector is the main emitting sector able to improve the global environmental impacts significantly, according to the United Nations Environment Program (UNEP SBCI) [6].…”

“…EE during the construction phase is the amount of energy used for the extraction of raw materials, the production and transport of building components as well as the building construction and end-of-life (EOL). Moreover, EC refers to the associated GHG emissions [3]; the operating energy during the operation phase as energy consumption and associated operational carbon emissions during the use phase of buildings (heating, cooling, etc.). The average value of EE is 50% of the total primary energy demand [14].…”

“…Most of the literature focuses on waste management, which shows a great interest in reducing the construction and demolition waste (CDW) generated by the construction sector as it represents around 40% of the waste produced [17]. Cai et al [18] and Lismont et al [19] explained that in Europe, about 25-30% of the waste result from the building sector amounting to 870 million tons annually and Brütting et al [3] estimated this share at more than a third of the waste. Meanwhile, we face stricter disposal and landfill regulations, and fewer landfills are available [20].…”

“…Thus, building structures generate a large amount of CDW [2]. Besides, in a post-disaster context (earthquakes and other natural disasters, war) the implementation of a reuse process not only makes it possible to limit the generation of waste but also to respond to a health and human emergency [22,23].Furthermore, load-bearing systems have a major impact among building components because of their material and energy-intensive manufacturing process [3]. Load-bearing systems represent the most substantial part of EE [24,25], with 39% according to Marzouk et al [26], and 50% and above of the total building embodied impact also called embodied carbon for Kaethner et al [27] and Veselka et al [28].…”

“…Furthermore, load-bearing systems have a major impact among building components because of their material and energy-intensive manufacturing process [3]. Load-bearing systems represent the most substantial part of EE [24,25], with 39% according to Marzouk et al [26], and 50% and above of the total building embodied impact also called embodied carbon for Kaethner et al [27] and Veselka et al [28].…”