D-Spline | Gijs Joosen

D-Spline is a 150m motorway overbridge crossing for pedestrian and cyclists connecting the Vijfhoek district with the old city center of Deventer. A single curve spanning the N348 expressway and the Overijssels Kanaal in Deventer. An elegant spline that captures the essence of the span in one fluid gesture.

The Design & Construct tender was awarded to Dura Vermeer and ONL [Oosterhuis_Lénárd] based on a fixed budget and clear aesthetics. Converging and diverging curves form the base of the architectural design. On both ends the curves emerge from the landscape, slowly transforming to the required height of the railing and bridge deck.

By introducing a fold line in the main profile of the bridge the shape interacts with light and shadow. The surface aimed at the sky will reflect the light in a different way than the surface aimed at the road. The Powerlines play their part to enhance the impression of fluid motion and give the bridge its slender character. At night the impression is inverted as the bottom surface is illuminated from floor spots embedded in the landscape. The LED lighting of the deck is embedded in the railing as to omit the need for lamp posts.

We have chosen a single, robust material for the design of the bridge to emphasize the simplicity of the design. Guardrails, deck, landings and supports are all made of concrete and painted with a white anti-graffiti coating. A combination of production techniques enabled an amazing design to operation time of less than 12 months.

The spline curve that defines the design has a continuously variable radius. As a result not a single section of the bridge is the same. This adds an extra level of complexity to the design process. The molds are CNC [computer numerically controlled] produced, this enables us to use in-situ concrete for the bridge deck, precisely following the curvature of the design.