Bridges to Nowhere – for now
Pedestrian bridges, often called foot bridges, have been both separate from and part of vehicular bridges. As separate structures they were often constructed in rural or wilderness areas tied to trails rather than roads and were designed with a rustic look.
However, pedestrian bridges associated with urban areas are in demand now and often include bicycle usage. As shown by the three bridges presented here, the reduced scale of urban bridges and their proximity to human beings and nature no longer call for a rustic design.
Despite the fact that these three bridges have gained praise and publicity, the present economic downturn has given them uncertain futures. Hence the title “Bridges to Nowhere—for now.”
THE ST. PATRICK’S ISLAND BRIDGE, CALGARY, CANADA
The St. Patrick’s Island Bridge in Calgary was designed in 2009 by Endres Ware* and Ammann & Whitney**, as a gateway to the activities of the island’s Centenary Park. The two-part bridge will also frame views of Calgary and the Rocky Mountains.
The bridges connect to a central platform located where they meet on a mound of earth to be constructed on a site in Centenary Park. The rendering shows a curved path on a mound leading to a ramp lifted up and attached by some of the cables to another land form behind the main pier. The bridges’ low arches, also visible in the rendering, rise just high enough above the underlying flood plain to avoid possible flooding but will not block views of the surroundings.
The bridges’ structure allows the weight of the concrete decks to be carried by a series of main cables running up to the two masts from which backstay cables transfer the deck’s weight back to the ground.
The two separate cable-stayed bridges, one longer than the other, span the Bow River flowing by the city of Calgary.
The masts are bent to reduce their height. The main cables are strung evenly along the length of the masts; the backstay cables, gathered near their tops, are “harped”, meaning that the cables have different lengths. They cables splay from the top of the mast downward and extend to the adjacent bridge, which reduces the amount of force necessary for their anchorage and allows the bridges to brace each other horizontally.
The bridges appear to bow to their respective destinations, the city and the neighborhoods on the riverbanks. One hopes that users from both places will be able to respond with their feet to their salutes in the not too distant future.