Studio Banana TV interviews Pedro Pablo Arroyo, author of the Pucan Road bridge in Shanghai.
Project requirements and constraints
The bridge must solve a problem of accessibility between a consolidated edge of the city, whose boundary is formed by Herbin Road, and a newly created neighborhood, separated 50 meters from each other by the Dianpu River, which crosses the area from east to west. Very near the bridge, the new urban planning scheme defines the position of a future Catholic church, designed by the Sancho-Madridejos architecture office.
The interpretation of the context, composed of references to Chinese tradition and the physical conditions of the site, together with the expression of the structural performance, will generate the design of the bridge.
Urban insertion of the proposal
Learning from the marvelous bridges of the Suzhou gardens, we decided to join both sides of the river with a path whose bent axis integrates the access flows and visually emphasizes the location. The most logical sites for the bridge ramps on each shore are extended diagonally out over the river until capturing a horizontal plane that looks straight towards the church. This dynamic visual relationship creates a spatial tension that activates the projected square between the two constructions.
Structural solution adopted
The load-span relation recommends the use of a metal truss, which we activate three dimensionally in order to resist the strong torsion stress associated with the support-less winding shape of the bridge.
The different conditions of support on the concrete ramps symbolize the spatial contrast existing between the two access shores. The bridge rests on a simple support at the edge of the narrow and traffic-laden Herbin Road on the northern side. In contrast, the structure is firmly held by a stiff connection on the southern side near the large and peaceful square. The asymmetric elevation of the bridge is the result of the overall diagram of bending moments. In turn, the steel structural elements gradually become denser according to the diagram of shear stress.
As a result, the visitor walks through a sequence of spaces that dilate and contract in relation to the exterior, creating different nuances and sieves.
General constructive characteristics
Due to the geometry of the structure and the complex resolution of the junctions, all the profiles are put together with steel flanges. The joints were transported from the workshop to the site, and were assembled on the southern shore. Finally, two cranes deposited the complete beam on the ramps. Except for those located at critical points of the structure, the vast majority of the trusses are open H-sections. Because they are painted white and cast in shadow by the structure, the bridge is perceived by our eyes as thin and light.
As in the Chinese bridge building tradition, we also wanted our bridge to be a protected space over the water. For this pupose, we covered the roof and floor planes with two independent wooden skins which are supported minimally on the steel structure, thus contributing to the magical structural balance of the bent shape of the bridge. The wood is pine which has been heat treated to avoid the green hues associated with the most commonly used chemical processes.
The wooden slats are placed in the direction of the maximum slope of the roof planes for rapid evacuation of the rain onto the river. Drainage of the basin, which would otherwise form at the southern end of the bridge, is made by a precise cut, a scarless wound; a detail inspired by the canvases of the painter Lucio Fontana.
Lighting of the structure
The relationship of the bridge with the different lighting conditions is one of the most important features of the project. During the day, the wooden roof acts as a projector of the reflections of the sun on the water. The vertical steel meshes are the most prominent features, with he shadows of one flange over the other and the shadows of the profiles over the wooden floor. At night, the ceiling scatters the light from the artificial lighting situated in the space between the structure and the roof. Under the stars, the cloud of indirect light transforms the bridge into a lamp floating on the river.
This is not (only) a bridge
The bridge is architecture over the water, a room of the city over the river instead of a mere means across it. We wanted other uses of the space to be as important as those based on strictly engineering reasons.
Indeed, the bridge is now a playground for children, a house for the sun, a clock of shadows, a fish jumping into the water, a balcony for lovers, a machine of dreams…
