Tan House Footbridge: Designing with repurposed steel, from early design stages to fabrication

Tan House Footbridge was a collaboration between Network Rail, WSP UK and Format Engineers. The use of repurposed steel has been central to the design process, made possible by creative digital techniques that facilitated a refinement of structural typology to match the available stock of previously unwanted material. The use of generative digital methods permitted an iterative and flexible design process that allowed any material and embodied carbon savings arising from different options to be tracked at each step towards fabrication. The collaboration is a good illustration of how to achieve carbon reduction by making informed early design decisions. The bridge was designed, detailed and fabricated between February 2022 and October 2024. At the time of writing, the authors believe Tan House to have the lowest embodied carbon of any footbridge which Network Rail has constructed on a live site. An internal Network Rail/design team study has determined that Tan House is considerably lower in CO2 than the Network Rail standard Series 400 steel rail bridge. It is testament to the fact that a bespoke and site-appropriate design does not have to be costly in capital expenditure or embodied carbon. This article describes the workflow used to deliver the bridge and shares lessons learned by the team on the use of repurposed/reclaimed material within the design and procurement process.