Bridge Lighting Brightens Miami Skyline

Bridges Article December 28, 2000
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The Miami skyline is a lot brighter due to the special architectural lighting of the award-winning Port of Miami/Dodge Island Bridge.

The bridge connects the largest cruise ship port in the world with downtown Miami. It provides unrestricted access over the coastal waterway to the growing Port of Miami, a vibrant center for the city's economy, bolstering the port's unique duel role as Òcruise capital of the worldÓ and providing for cargo shipping, which has a total annual impact on the local economy estimated at $5-6 billion a year. The bridge and roadways significantly aid the swift, efficient movement of as many as 40,000 vehicles a day currently passing to and from the Port of Miami.

The overall bridge length is 2,522 ft with approximately 1,356 ft of the structure over water and the remaining 1,166 ft over land. The width of the twin bridge is 106 ft 8 in. and the vertical clearance is 65 ft. Twin parallel structures provide three lanes of traffic, and were designed to accommodate possible future people-mover vehicles on the south side with two lanes of traffic. The westbound bridge provides two lanes of traffic plus a 9-ft-wide sidewalk on the north side.

From concept to final plans, the bridge was designed by the engineering firm of Beiswenger, Hoch and Associates (BHA), North Miami Beach, Fla. Construction of the bridge and final roadway was performed by Volker Stevin Construction Inc., based in southern Florida. The bridge pier footings within Biscayne Bay were constructed by Misener Marine Construction Inc. Tampa, Fla.

Award-winning design

From the design stage, aesthetics were a prime concern because of the bridge's proximity to the downtown Miami skyline, exposure to millions of international travelers and its unique location adjacent to the Bayside commercial development area.

A task force was formed by a joint agreement between the City of Miami Commission and the Metropolitan Dade Commission in August 1984 to monitor the design and construction of the bridge. The citizens' task force included three members appointed by the City of Miami Commission, three members appointed by the Dade County Commission and one member appointed by the governor. The task force, along with the Florida DOT, Dade County Public Works Department and the Port of Miami staff, was convinced that the new high-level bridge must convey a modern progressive image for Miami and Florida, particularly because this bridge was to be one of the most visible bridges in the state.

Four conceptual designs were developed by BHA for the new bridge structure. The task force endorsed the use of a long-span concrete design as the most aesthetically pleasing structure compatible with the downtown area of Miami. The bridge's piers align with the piers of a nearby railroad bridge. The bottom of the bridge's water-pier foundations are set 2 ft below the water level to conceal its pilings. The pier faces are rusticated with vertical grooves to break up the exposure of flat concrete, while corners are gradually splayed with flared tops to match the bridge's soffit width.

The Port of Miami Bridge was built as precast, double-cell concrete box girder, erected by the balanced cantilever method. Provisions also were made to incorporate an architectural lighting scheme. Conduits and fittings for lighting were embedded in box girders and in pier columns during construction. Resources Management International Inc. (RMI) participated in the design of the electrical system.

Since it was opened to traffic in March 1991, the bridge has received two awards. The Port of Miami Bridge was recognized with the Outstanding Concrete Structures Excellence in Concrete award in the category of public works, in 1992, by the Florida Concrete Products Association. In November 1994, the bridge was selected by the Federal Highway Administration for the Award of Excellence in the category of major structuresÑthe highest award in the agency's 1994 Biennial Awards Program.

Architectural lighting scheme

To develop a lighting scheme worthy of this award-winning bridge, BHA selected Wide-Lite, a Genlyte Co., based in San Marcos, Texas. The lighting company relies on Venture Lighting, Cleveland, to provide metal halide lamps.

For this project Wide-Lite recommended enclosed and gasketed metal halide floodlights based on three considerations. First, metal halide lamps offer greater efficiency and longer performance life compared to other light sources, and drastically reduce operating cost and heat generation.

Metal halide lamps are high-energy discharge electric arc lamps. The arc is contained, along with metal halide mixtures, in a quartz structure called an arc tube. The arc tube is housed in a heat-resistant, ultraviolet-light-absorbing quartz tube to protect it from the outside environment.

Tungsten electrodes, sealed through the ends of the arc tube, conduct electricity at high temperatures and vaporize the metal halide doses. The vaporization of these electrically excited doses produces the closest simulation to sunlight of all available lighting technologies.

Second, metal halide lamps render precise colors. They offer a wide range of lighting effects, from a ward incandescent-like amber to crisp daylight effects to intense vivid colors, which are generated by controlling the metal halide mixtures within the arc tube. The lamps do not require filters.

Third, the fixtures were selected based on their ability to perform in the harsh and corrosive marine environment. The floodlights are regularly used on oil rigs, ship docks and other harsh industrial areas. The floodlight fixtures feature: die-cast, low-copper content, marine-aluminum-alloy housings with integrally cast heated dissipating fins with a built-in aiming device; high-temperature gaskets to provide a weather-proof seal; cast-aluminum ballast bases for ease of mounting; high-purity anodized aluminum reflectors; and pre-wired grid-type mogul base sockets for precise alignment and easy lamp access. In addition, the housings for the floodlights are finished with a high-build, catalyzed eqoxy coating system, which provides chemical resistance to acids, alkalis, solvents, hydrocarbons, salts and water.

To complement the metal halide lamps and floodlight fixtures, bi-level lighting controls were specified. The bi-level controls feature a solid-state relay to detect and respond to changing conditions. For instance, the controls are set to reduce wattage during early morning hours to save energy. They also enable the lamps to smoothly and quickly respond without the lengthy re-strike periods.

Using this lighting system, six architectural lighting schemes were developed for lighting the piers and bridge superstructure. One representative span of the bridge was selected for the tests, which included two sets of piers. Out of the six lighting schemes, three were developed utilizing basic white lamps and three additional schemes were developed by BHA/RMI using blue lamps, or in combinations of blue and white lamps for the task force to review.

The three additional schemes include the following:

-- Lighting the north-south (narrower) face of the pier with blue lamps;

-- Lighting the east-west (wider) face of the pier with white lamps and north-south face of the pier using blue lamps; and

-- Utilizing white light across the superstructure section combined with lighting the east-west face of the pier with white lamps and the north-south face using blue lamps.

During the tests, the task force found that when the piers were lighted with the blue lamps on the narrower face only, the flared top piers with splayed chamfered and vertical rustication enhanced the bridge's appearance dramatically, and complemented the city's skyline.

As a result, 60 floodlight fixtures and metal halide lamps in wattages of 175,400 and 1,000 were strategically positioned to highlight the aspects of the bridge. The metal halide lamps will keep the Miami evening skyline bright and beautiful.

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