McDonough

The existing south stretch of Lake Shore Drive, between McCormick Place and Hyde Park, is cordoned between Lake Michigan and the Metra tracks. Isolated from neighboring buildings and sparsely lacking architectural themes, an opportunity is created to beautify this setting with a dramatic signature structure.

The proposed bridge utilizes a structurally innovative support system, which motorists and pedestrians will find interesting and appealing. Nautical themes and terminology are used to develop these forms and elements:

Towers, visually reminiscent of sailboat masts, support the bridge on opposite sides of the bridge in "chairs".

Cables, hung from the "masts" in a fan-like pattern, reminiscent of a sail, support the center of the bridge in a sling-like "cradle". The cables are intentionally slung under the superstructure, to emphasize the nature of the cable support. This particular cable arrangement was chosen, in lieu of other methods of support, such as hidden post-tensioning.

The bridge curves from side-to-side, in serpentine fashion, adding to the visual rhythm of the structure.

The structural logic of this form will support the visual logic of the form. Viewers from the road will notice and appreciate the unusual method of support. The nautical analogies will quickly become apparent, yet are sophisticated. Pedestrians and bicyclists on the bridge will enjoy the curvilinear symmetry of the bridge deck and unobstructed views of the Chicago skyline.

POTENTIAL HISTORICAL SYMBOLISM OF BRIDGE:
The location of this bridge, next to the Douglas Memorial, provides an opportunity to metaphorically relate a structural form to an important time in history. The Lincoln-Douglas Debates, prior to the Civil War, signify America's greatest time of tension, a time of opposing values. The inclined towers are symbolic of strong individuals struggling with all their might, backs arched, outstretched arms pulling ropes, for the values they believe in and trying to influence the connections between the way things are and promises of the Constitution. Looking at the bridge in symbolic contexts may allow an opportunity for giving this bridge a special name. Names such as "The Constitution Bridge" or "The Lincoln-Douglas Bridge" come to mind.

IMPORTANT CONNECTION OF NEIGHBORHOODS TO THE LAKE:
Since the middle of the 19th Century, the railroad and subsequently Lake Shore Drive, have obstructed and limited the access of pedestrians and cyclists to the wonderful enriching environment of the lake shore. This bridge will be an important connection for neighborhoods to the lake shore. The bridge provides ease and frequent access to areas previously obstructed or remote and will be an important connection to the Douglas Memorial.

CONSTRUCTION AND ENGINEERING ISSUES:
This structure can be described as a cable-stayed bridge, although it is not a typical cable-stayed bridge. There have been other bridges with one-sided supports constructed or envisioned throughout the world, but these differ in concept from this proposal. The difference in this proposal is a unique cable weaving pattern.

This proposal uses a cable weaving pattern that traverses the structure, supporting the bridge between the masts. The spans measured from mast-to-mast are on the order of 250 feet. Beams will span continuously 125 feet from the masts to cables between spans. This arrangement will introduce certain torsional and lateral bending characteristics into the framing system that will need to be addressed in the structural design.

We envision that this structure can be built with conventional bridge materials. Ordinary curved steel plate girders or box beams can be fabricated and erected. The deck can be constructed from precast concrete off-site, and erected and connected to the girders using bolts. The cables would consist of external post-tensioning tendons, typically used for precast segmental bridges. Many of the bridge's structural elements would use standard Department of Transportation (DOT) details.

Although the structural support system is unusual, the design appears feasible and not too out the ordinary. A space frame analysis would be required, to determine forces, which is a standard procedure. Particular emphasis would be needed to address the issues of twisting and vibration, as these are issues relevant to the design of any cable supported structure.