ARC Wildlife Competition winner announced

The winner of this contest to design a prototype wildlife bridge in Colorado has been announced: HNTB with Michael Van Valkenburgh & Associates.

When I previously covered the competition finalists, I noted that this design was my favourite, because the structural form is both easy to erect and readily adaptable to different geometries. The bridge has the elevation of a portal frame, but functions as a three-pinned arch, with the two halves of the portal propped against each other at the crown.


Each precast concrete element is in the form of a hyperbolic paraboloid (hypar) shell, which provides high stiffness while being of low weight, hence easy to erect without requiring unduly heavy craneage. The size can be readily amended and multiple units stacked side-by-side to create differently sized wildlife crossings.


The jury report [PDF] makes interesting reading, stating that the winner:

"combined brilliantly an overarching focus on wildlife habitat, behavior, and viability with a practical intelligence regarding the making of such a work of infrastructure. The scheme marries well a simple elegance with a brute force. It effectively recasts ordinary materials and methods of construction into a potentially transcendent work of design."

Clearly, they were looking for something practical and modest rather than an architectural statement in its own right.

I wonder whether the winning design has wider applications than just for use in building wildlife bridges. For example, could it substitute for the precast con-arch system sometimes used to cheaply span watercourses, but which lacks the ideal profile for spanning roads and railways? The challenge is in getting the formwork adaptable for precasting a wide range of geometries, and I'm not entirely convinced by the simple diagrams provided above (click on any image for a larger version).

I-70 Wildlife Bridge Finalists Announced

Five finalists have been announced in the ongoing contest to design a wildlife bridge over the I-70 Highway in Colorado. The original shortlist featured 36 entrants.

I've provided a short note below each entry summarising the structual form, but there is much more information on each design at the competition website.

Balmori Associates (New York)
with StudioMDA, Knippers Helbig Inc., David Skelly, CITA, Bluegreen, John A. Martin & Associates, and David Langdon

This design involves a series of transversely laminated timber "plates" which are sculpted to give an organic form underneath. It's clearly the contribution of Knippers Helbig as there's a family resemblance to their Margaretengürtel design.

The Olin Studio (Philadelphia)
with Explorations Architecture, Buro Happold and Applied Ecological Services

The Happolds influence is apparent in the structural form, which is a weathering steel diagrid (Happolds being known for their expertise in gridshell roofs). Overall, it's shaped as a hyperbolic paraboloid, or hypar (also known as the "pringle"), which provides stiffness through curvature rather than depth.

Janet Rosenberg & Associates (Toronto)
with Blackwell Bowick Partnership, Dougan & Associates, and Ecokare International

Structurally, this is the least interesting design, featuring a timber and plastic composite deck used to support fibreglass composite screens. Some of the images make the decking look a little like a scaffold platform.

Michael Van Valkenburgh & Associates / HNTB Engineering (New York)
with Applied Ecological Services, Inc.

Hypars are clearly flavour of the month, because HNTB have also used them in this design, although in a very different way to the Happold entry. The bridge has a series of precast concrete ribs, each of which is made up of a thin concrete shell in hypar form. L-shaped ribs are propped against each other to form three-hinged arches, which would be both lightweight and stiff. The ease of erection, and adaptability to different spans and geometries, make this one my favourite, although architecturally it's less spectacular.

Zwarts & Jantsma Architects (Amsterdam)
with OKRA Landscape Architects, IV-infra and Planecologie

Finally, here's another hypar, this time in the form of an in-situ concrete shell. Thin shells of this type are rarely used in bridge construction, partly because they perform well when subject to evenly distributed loads, and less well against concentrated loads. A wildlife bridge, with its plentiful earth fill, is a rare case where the geometry makes sense. However, in-situ concrete is problematic, and the designer has had to illustrate a complex temporary cable net, suspended on stays, to support the formwork. This might add an unwelcome cost as well as cause greater highway disruption than some of the alternatives.

ARC Wildlife Crossing Competition Shortlist announced

The ARC International Wildlife Crossing Competition has announced five shortlisted design teams, chosen from 36 entrants, to go forward to the contest's second stage. I've covered the competition here previously: entrants are to design an innovative wildlife crossing over Interstate Highway 70 in Colorado, USA.

The shortlisted teams are:

• Balmori Associates (New York), with StudioMDA, Knippers Helbig Inc., David Skelly, CITA, Bluegreen, John A. Martin & Associates, and David Langdon
• Janet Rosenberg & Associates (Toronto), with Blackwell Bowick Partnership, Dougan & Associates, and Ecokare International
• Michael Van Valkenburgh & Associates (New York), with HNTB and Applied Ecological Services
• The Olin Studio (Philadelphia), with Explorations Architecture, Buro Happold and Applied Ecological Services
• Zwarts & Jantsma (Amsterdam), with OKRA Landscape Architects, IV-infra and Planecologie

Details of the second stage competition process are available on the ARC website. They seem to have a well-informed jury (including Marc Mimram), and reasonable prize money, although much of that will be eaten up by the need for entrants to deliver a physical scale model of their concept.

The organisers are very keen to promote innovative use of materials, so it will be interesting to see what emerges in January when the winning design is to be announced.

North American Wildlife Crossing Structure Design Competition

Here's an interesting bridge design competition.

Vail Pass, on the I-70 in Colorado, has been chosen from 22 possible locations as the site for a prototype wildlife bridge. Designers are asked to come up with a structure which can carry wildlife while being more economic than a typical highway bridge (see artist's impression, vaguely reminiscent of the CZWG / Mott MacDonald Mile End Park bridge in the UK).

As well as protecting the wildlife and bridging the ecological divide created by the highway, the bridge is also there to protect motorists. Organisers estimate the average cost of a critter-vehicle collision to be $6,617 for deer, $17,483 for elk, and $30,760 for moose, although those look a bit on the low side to me (having had a friend hospitalised for several weeks after a collision with a deer). They do reckon the annual cost to the American economy to be about US$8bn.

Go to the ARC Competition website for more information, although as yet there are no dates, rules or information on the cash prize. There's no funding in place to actually build the bridge yet, but organisers hope the competition will raise the concept's profile sufficiently to raise funding.