Wednesday, April 07, 2010

AE 19: Structural Decoration

A couple recent bridge designs make me wonder about the symbiosis of structure and decoration in designing for long spans. Engineering expression in bridges certainly isn't new, but the traditional means of expression have been elements like arches, beams, and suspension cables. Think of the Brooklyn Bridge without its cables, its structural expression. As impossible as ignoring the Gothic stonework of its piers. But the two bridges below, and other recent examples, merge architecture and engineering to create unique expressions where the lines between structure and decoration have disappeared.

[Yale Hill House Bridges | image source]

First is the to-be-realized Yale Hill House Bridges by Pelli Clarke Pelli Architects and Guy Nordenson and Associates. The latter describes the design of the two bridges as such:
Each pedestrian bridge consists of two 3ft 6in steel plate girders which comprise the primary structure of the bridge as well as its railings. The plate girders have 1/4in-thick corrugated, perforated webs. The corrugation depth or "amplitude" of the web is trapezoidal in plan and varies between 2in and 6in across the span to enhance the structural stability of the web and to brace the top compression flange of the girder. The corrugation, therefore, allows for a thinner web and less bracing material. The corrugation also creates a varying pattern of light and shadow when the girders are viewed at an angle. The perforations in the web are diamond-shaped to generate a lattice-like appearance that recalls the original wood lattice canal bridges designed by a local architect Ithiel Towne in 1820. The perforations also help to reduce the weight of the structure.
[Yale Hill House Bridges | image source]

So what looks like a decorative guardrail is in fact a structural member, and an important one in that its shape and perforation increase performance and reduce weight from additional members that are now deemed unnecessary. And of course these pieces create dramatic effects for fairly small bridges.

[Bridge, La Roche-sur-Yon | image source]

Another design merging architecture and engineering, spotted at ArchDaily, is a footbridge recently completed in Roche-sur-Yon, France by Bernard Tschumi Architects and Hugh Dutton Associates (HDA Paris). They describe the bridge as such:
The intention...was to demonstrate an integration of an original structural system with an architectural concept developed from urban scale research of neighborhood identity and carried through the expression of the minutest details.
[Bridge, La Roche-sur-Yon | image source]

The bridge is experienced as a walk through a lattice-like tube. From the exterior it reads like a solid tube or an ethereal object, depending on ones relationship to the bridge. (Check out the PDF press release for many more images.) HDA was responsible for the engineering on the project, though their role as local architects probably aided in fusing the two usually distinct realms of architecture and engineering.

I think this apparent trend of engineering merging with architectural surfaces and decoration is not limited to bridges, much less pedestrian ones. It's found in buildings of many types, though what is special here is the openness that is possible with footbridges; space only needs to be contained for safety not for climate-control. Space then flows through the bridge openings, designed as much for structural performance as for formal appearance.