Passionate people generate great bridge installation with parametric models

The bridge installation project was approached in the same way as any other – pulling together a team with relevant expertise, brainstorming ideas, analysing and developing them.

With little over a month to develop and manufacture the design, our computational designers led engineers from our Transport and Buildings teams to consider several key project criteria: the bridge was to support a model train running between two stands (in reference to the Holmestrand Mountain Station project), it needed to be light and easily demountable enough for us to carry from London to Copenhagen, build in an afternoon, break down in an hour and then return back to London (for later re-assembly in our home office). We also wanted it to form an interactive part of the conference rather than merely being a static display piece.

For the interactive element, the team decided to allow people to clad the bridge with business cards folded to a specific 3D form. By the end of the second day, the slotted bridge surface was packed with business cards.

Project manager Sarah Ord said: “This project shows that having the right mix of people with a passion for a common goal can generate great design in a short period of time.”

Design of the overall structure progressed rapidly through several brainstorming meetings, based around a flexible parametric Grasshopper model. After the examination of several options the design settled on a timber shell/arch structure as an aesthetically pleasing, lightweight, robust solution. The team was influenced by Ramboll's extensive experience in bridge engineering, timber structures such as Dalston Lane, and the TRADA pavilion computational design project, which featured the benefits of rapid manufacture and assembly.

Throughout the development of the bridge the team ensured that the design was robust enough to stand and carry the applied loads. The geometry was exported to and analysed in MIDAS to make sure the design was structurally feasible and to guide further refinement of the form and material thicknesses. At the same time, the team used preliminary laser cut samples of sections of the bridge to physically test the manufacturing process and connection detail design.

The team wanted to make the bridge quick to take apart and re-assemble by avoiding adhesives or mechanical fixings. The resulting connections were designed as simple slotted plates, held in place laterally by a matching slot in one of the plates they joined and restrained laterally by small standard ‘U’-shaped clips, all cut from the same 6mm plywood as the rest of the structure.

The Grasshopper model was used to determine cutting patterns for each connector and panel. The nature of the shell form meant that the angle between each panel (per quarter of the structure) was different. Due to the variety of panel shapes and sizes two separate arrangement algorithms were used to determine slot placement and the best panel arrangement.

Ramboll’s Ollie Wildman said: “The use of parametric modelling and rapid prototyping and manufacture released the team’s time to concentrate on the creative design of the bridge through swift iterations. Designing and building the bridge in one month would not be possible without this approach”.

As foundation design is a key component of any project, the team designed two pedestals to support the feet of the bridge. As an arch, the natural reaction of the structure under load was to try and push outwards. To resist these thrusts without having to tie the base of the arch, these pedestals contained hidden compartments to conceal bottles of water which were procured on-site and provided the necessary ballast.

Ramboll has a track record in developing digital techniques which enable us to challenge traditional typologies with complex geometry and evolve economic solutions for the built environment. For example: Vanke Pavilion façade with hundreds of ceramic tiles in different shapes and sizes, covering a unique structural form; and Tate Modern Extension with its one-of-a-kind geometry and a remarkable brick façade.

Ramboll also has world class bridge engineering expertise and is currently involved in all three major estuary crossing projects currently under construction in the UK: The Queensferry Crossing, New Wear Crossing; and The Mersey Gateway.