Approccio sostenibile per invertire il processo di progettazione delle strutture in acciaio

Nell’ottica di favorire un utilizzo consapevole e sostenibile delle risorse destinate all’ambito della costruzione civile, l’esigenza di rinnovare le pratiche di design delle strutture in acciaio, considerando il fattore ambientale, è ormai imperativo. In questa ricerca, è proposta una nuova procedura per l’ottimizzazione strutturale basata sull’interazione di un famoso algoritmico evolutivo, conosciuto come Genetic Algorithm (GA), ed un noto problema matematico, Bin Packing Problem (BPP), con il quale è possibile ottenere il numero di tagli ottimali da effettuare su uno stock di materiale al fine di realizzare membrature metalliche per un edificio di nuova costruzione. La definizione della funzione obiettivo mostra un netto cambiamento del paradigma di ottimizzazione poichè a differenza degli approcci tradizionali, interamente basati sulla minimizzazione del peso strutturale, l’approccio proposto permette di abbattere i costi di produzione direttamente sull’acciaio acquistato dalla fabbrica riducendo gli sprechi dovuti alle procedure di taglio. Tale confronto verrà realizzato su un caso studio di particolare interesse per la comunità scientifica e professionale come una cupola geodesica realizzata mediante membrature tralicciate. I parametri di controllo del design, principalmente legati alle proprietà geometriche delle sezioni, muteranno dinamicamente durante il processo di ottimizzazione. Al termine di tale processo, adoperando l’approccio proposto dagli autori, si raggiunge un guadagno in termini di spreco di materiale di circa il 30% in meno rispetto agli approcci tradizionali di minimizzazione del peso strutturale. Conseguentemente, è altresì dimostrata una maggiore sostenibilità dovuto al risparmio del materiale adoperato. 

Optimizing structural design for material efficiency and waste reduction

In the last decades, the scientific community has been actively engaged in addressing the imperative of reducing the costs associated with structures through the strategic management of material selection, fabrication methods, and maintenance expenses. Within the context of structural optimization (SO), there has been a significant focus on the minimization of material costs, with the overarching goal of creating slender structures that optimize resource utilization. Conventional practice among researchers and practitioners in this field involves the optimization of structural design costs, while concurrently adhering to safety guidelines stipulated by relevant standard regulations.
It is noteworthy that a substantial portion of the expenditures can be attributed to material wastage resulting from the cutting process, particularly in the context of metal structures.

In other words, failing to incorporate a meticulously designed cutting strategy to reduce waste during construction can undermine the efficiency of cost optimization.
In the context of the solid waste stream, construction and demolition residues would comprise approximately 23% of the total volume. This translates to an annual production of over 100 million metric tonnes. Similar waste proportions have been reported in various other nations, cor- roborating the United States' estimates. A notable portion of this waste results from inefficient material utilization, representing an avoidable fraction of waste generation. Enhanced effi- ciency in material usage would consequently diminish the quantity of surplus materials, reduce unnecessary workmanship, and minimize the associated costs such as waste disposal and trans- portation fees. Certainly, effective resource utilization serves the greater global interest, extending beyond the immediate concerns of industrialists. Improper disposal of waste generated from stock-cutting operations can potentially contribute to environmental pollution, while unchecked wastefulness poses a significant risk to the exhaustion of our planet's invaluable resources.

Two different strategies exist for this problem: minimizing waste during fabrication or reusing materials from other structures. While the former approach has not received great attention among experts in the civil engineering field, it serves as a central focus of this research. The latter option has been extensively explored by Brütting et al. [6], who advocate for a circular economy model to reduce costs and environmental impact in construction. In this study, the length and number of predefined stock elements obtained from a previous structure are the design variables of the opti- mization. Hence, the geometry and topology of the structure are predetermined by the mechanical and geometric properties of available elements.

A new Mixed-Integer Linear Programming (MILP) formulation for discrete sizing and topology optimization of truss structures has been also recently proposed performing significantly better than all other formulations [7]. In their scientific endeavors, Brütting et al. also introduced a method to enhance the configurational efficiency of stock or kit-of-parts, enabling the reusing of its constituent elements across multiple structural contexts. This strategic consideration led to the proliferation of reusability within a stock of items across various structures, consequently result- ing in a further reduction of waste generation.

With the aim of minimizing waste, the Cutting Stock Problem (CSP) [8] is an essential research topic to focus on to reduce waste in the construction industry.

The innovative aspects introduced in the present study are focused on an optimization procedure aimed at minimizing structural waste, and to reduce the amount of material stock produced by the factory. This approach introduces a paradigm change considering constructability issues as cutting patterns during the production phase, contrasting with the conventional minimum-weight op- timization approach. The advantages of the adopted approach are expressed both in terms of mass savings (i.e. waste reduction) and Carbon footprint emission.

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La presente relazione è stata presentata in occasione del XXIX Congresso CTA, svoltosi a Milano il 26 e 27 settembre 2024.