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Introduction
The New Tacoma Narrows Bridge is a pair of motorway suspension bridges, featuring a truss deck structure, which are often taken together to refer to Tacoma Narrows. The 2007 Narrows Bridge addition is parallel and adjacent to the 1950 Narrows Bridge, which in turn replaced the collapsed original Tacoma Narrows Bridge. The materials of construction mainly include steel wire and reinforced concrete. The new structure was built to accommodate greater traffic flow. According to WSDOT, the bridge was first started in 2002 with building the caissons, followed by the towers, the toll plaza and finally the new bridge superstructure and suspension system. The project was officially completed in 2008. As it spans the Puget Sound, the caissons account for 100’ scour potential. The towers are 510 feet high. The New Tacoma Narrows Bridge is a good example of structural art, due to its graceful, minimalist form coupled with a structural integrity derived from its initial failures.

Scientific
The New Tacoma learns the lesson of its ancestor’s failure. In the original design, the hyper flexible deck had little lateral resistance to wind force and thus exhibited sinusoidal flutter caused by “negative damping” of oscillatory motion*. This “self-excitation” of the deck was greatly reduced in the new design, because the reinforced towers are slightly to moderately splayed (the 1950’s design is still fairly linear), because the deck has stiffening trusses, and because the parallel bridges are generally more aerodynamic. At 510 feet high, the concrete towers have enough sag to support heavy load forces. Finally, the structure has sound foundation design, with deep, scour-resistant caissons. Thus, the New Tacoma Narrows Bridge succeeds from a scientific and efficiency standpoint – it is structurally sound.

Symbolic
But the structure does not sacrifice aesthetics for stability and permanence. Each bridge is gracefully slender, with notably splayed reinforced concrete towers that feature two sets of symmetric, simple cross-like horizontal members. In addition, the main cables are thin yet durable steel wire, leaving wide swaths of open area. The steel aspect of the structure is further minimized with a simple steel truss design, symmetrical diagonal members that meet at the center of each chord member and contact a vertical member, which help smoothly transfer compressive and tensile forces respectively. This makes a predominately steel structure less intrusive to its natural surroundings. Therefore, the New Tacoma Narrows Bridge succeeds from a structural art perspective.

Social
It also succeeds from a symbolic aesthetics perspective – it’s a graceful, airy design that has served as a cautionary tale for multiple generations of civil engineers. It argues for a simple beauty but not at the cost of a sound design. Moreover, as a bridge that has consistently been one of the top five longest suspension bridges throughout seven decades of existence, it has become symbolic of the Washington area and even, arguably, the Pacific Northwest region. The New Tacoma Narrows Bridge is also a social and economic success. The 1950’s bridge currently carries over 90,000 cars daily, and the 2007 addition adds three 12’ traffic lanes and a bike lane. Also, the towers and caissons have been designed for a second deck, of either road or light rail, which will likely be added in the future, as well as a toll plaza. In addition, the 2007 bridge was finished ahead of schedule and under budget. Thus, the bridge serves a pragmatic social and economic purpose, increasing commerce through greater traffic flow and tolls.

Conclusion
In conclusion, the New Tacoma Narrows Bridge succeeds as an example of structural art, because it manages to combine a slender, graceful design without sacrificing structural integrity.