To achieve sustainability goals, the Dutch government is striving toward a circular economy, which necessitates changes in the building and construction sector—responsible for 34% of global carbon dioxide emissions in 2022. Steel production contributes significantly, accounting for 7.2% of global greenhouse gas emissions. Reuse, a key strategy within the circular economy, holds great potential but remains underutilized in infrastructure projects. This research investigates the feasibility and environmental impact of reusing a Rijkswaterstaat bridge, addressing the central question: What are the feasibility and environmental implications of reusing the Keizersveerbrug, a steel truss bridge, on an object-level basis, as assessed through a comprehensive case study design process?

A donor structure file, following the technical guideline NTA 8713 for the reuse of steel elements, is developed to assess the feasibility of reusing the Keizersveerbrug. A visual inspection confirms that the bridge is in good condition, with minimal corrosion and damage. The truss bridge aligns well with the design criteria of the new application, allowing for multiple feasible design options for both the approach ramps and the main span. An evaluation based on environmental impact, user comfort, and integration into the surroundings leads to a preliminary design. This design incorporates three 100-meter truss bridge elements from the donor structure, with adaptations including a new deck and a fresh paint layer.

An environmental impact assessment, conducted using Environmental Product Declarations and in accordance with NEN-EN 15804+A2, demonstrates significant environmental cost savings. When considering all life cycle stages, a reduction of 0–66% is observed, while excluding life cycle stage D results in a 25–60% reduction compared to variants constructed from other materials. Additionally, this research adapts the traditional design cycle to integrate reuse considerations, providing a structured approach for engineers addressing the challenges of reusing steel bridges. These findings underscore the potential of reuse to contribute to sustainable infrastructure that aligns with the principles of a circular economy.

Rapid developments of both new (digital) fabrication techniques and innovative software facilitate the possibility to design, check and construct objects with great complexity and uniqueness without a large price tag. After new techniques slowly entered the field of architecture, the next step is to apply them in civil engineering to design load-bearing structures, dealing with a large number of load cases, outdoor conditions and strict safety requirements.

The application of digital fabrication in civil engineering is examined through a case study: the design of a pedestrian frame bridge made of timber using CNC-milling techniques. In this research a strong focus is on the design, optimisation, detailing and testing of the connections.

This research demonstrates that the combination of a reciprocal gridshell structure in combination with interlocking joints (lap joints) is particularly suitable for digital timber fabrication since a stable system can be obtained without the use of fasteners. The uniqueness of all connections and the strong relation between them makes the design process complex. Nevertheless, with the help of digital design tools like Grasshopper and evolutionary it is possible to deal with a large number of parameters with a complex relation between them.

Additionally lab tests were carried out to get insight in the shear capacity of notched members. The tests show that the verification method for notched members in Eurocode 5 does not accurately predict the shear strength when hardwood is applied. Additional research on the fracture energy of hardwood is required to propose an improved calculation method. Furthermore, the tests have shown that the application of rounded edges and screws as reinforcement significantly improve the shear capacity of notched members. It is therefore always advised to apply rounded edges, if possible in combination with screws.

All in all, the case study has shown that it is possible to design a load bearing free-form gridshell timber structure on both global and connection level, using the advantages of digital design and fabrication techniques.