Structural Steel Reuse as a Cost-Effective Carbon Mitigation Strategy

Abstract

New structures can be designed from existing steel elements at lower cost and with dramatically lower carbon emissions when compared to conventional steel structures. Steel building structures typically have the highest embodied carbon impacts when compared to masonry, wood, concrete, and reinforced concrete projects (De Wolf et al 2016). Designing with salvaged structural steel is a beneficial alternative for structural engineers to reduce embodied carbon in the built environment and implement life-cycle oriented and cost-conscious design of steel structures. However, there are still many barriers to designing with reused gravity elements in buildings at scale, such as the uncertainty surrounding element availability, and understanding which factors contribute to carbon emissions associated with reuse.

This thesis establishes more certainty about the supply of steel elements, quantifies potential carbon and cost savings, and identifies the variables that most impact such savings to better enable designing steel frames. This work first provides the context and terminology to connect structural systems to circular economy and reuse, and then outlines why reusing gravity beams and columns is particularly advantageous via a state-of-the-art overview of the steel value-chain. Next, a high-level material flow analysis is conducted for the U.S. structural steel market, indicating that the quantity of the existing steel heavy section scrap covers 140% of the demand for imports of steel. An LCA utilizing a comparative cut-off method is then performed and coupled with a cost estimation, which demonstrates a potential for around an 87% reduction in carbon emissions from steel reuse instead of recycling. Based on the findings of the partial LCA, an exploratory data analysis is then performed with both a stochastic sampling and nine real building projects to identify the variables most impacting carbon cost associated with reuse. Structural weight is found to have the greatest effect on reuse emissions, followed by number of elements, and then transportation distance.

Finally, this thesis explains the implications steel reuse has for stakeholders in the structural steel industry, including fabricators and engineer and design teams. In short, this thesis presents the case for steel reuse, and the intrinsic carbon, cost, and structural value it could have.