Brooklyn Bridge Rehabilitation and Retrofit in New York City. Left image courtesy Wikimedia.

Brooklyn Bridge Rehabilitation and Retrofit



Transportation has been providing structural rehabilitation and retrofit services for this iconic New York bridge for more than 15 years.

(1) Approach Ramps Rehabilitation – In-depth inspection, BRPR, design, and PS&E for redecking ramp approaches, concrete deck on steel, and main approaches supported on brick arches. Transportation is providing plans, specifications, and estimates for the redecking of: five Brooklyn and two Manhattan steel approach structures (total length of 1,627 feet), 3,357 feet of ramp structures; and 1,300 feet of approach roadway supported on brick arches. The design encompasses the rehabilitation of the substructure for the approaches and ramps, lighting, striping, drainage, and maintenance of traffic. The assignment includes inspection of a portion of the suspension bridge towers, in-depth inspection of the bridge, and a bridge rehabilitation report.

(2) Franklin Square Truss Strengthening and Retrofit – Aesthetic retrofit of Roebling structure with structural steel arches to support the overloaded original trusses. The Franklin Square Bridge is part of the Manhattan approach to the historic Brooklyn Bridge. During an in-depth inspection of the bridge in 1992, Transportation studied the iron pin and link truss approach structure to determine the actual capacity of the truss under existing loads. Transportation analyzed the truss using the actual dead load and determined the truss to be severely overloaded. NYCDOT retained Transportation to perform the task of strengthening the truss to support the load. Transportation designed a retrofit that employed six structural steel arches to support the original iron trusses.

(3) Deck Replacement Design/Build – Emergency redecking of suspended spans, rehabilitation of 200 floor beams. Design, traffic maintenance, resident engineering and construction management. Transportation devised a unique design of grid deck splices for this fast track design-build project The project had an aggressive design and construction schedule of one year. In addition to the design of the grid deck, Transportation provided construction staging, MPTs, and construction support and inspection services during the construction phase. The bridge deck covers an area of about 210,000 square feet, including the 70,000 feet of stringers. The deck weight was another major problem addressed by Thornton Tomasetti, because any significant increase in weight might have reduced the capacity of the other structural components.

(4) Pedestrian Vibration Study – Study of pedestrian-induced vibrations on the Brooklyn Bridge with proposed mitigation. On August 14, 2003, one of the largest electrical power blackout in U.S. history struck a broad segment of the Northeast. In New York City, the massive pedestrian exodus from Manhattan via the historic Brooklyn Bridge led to reports of excessive vibrations on the structure. The NYCDOT retained Transportation to perform an investigation of the dynamic properties of the bridge, evaluate its vibrations when excessive pedestrian load is experienced, recommend procedures for guiding pedestrians in future events and determine whether mitigation measures are required. Pedestrian-induced vibrations have been observed on several pedestrian bridges worldwide where the pace of pedestrian marches is close to a certain natural frequency of the bridge. The Brooklyn Bridge is designed for vehicular loads. However, the bridge has many frequencies that fall within the frequencies generated by pedestrians walking/running, making it prone to pedestrian-induced excitations. Transportation is performing modal analysis, ambient vibration measurements and controlled vibration tests to identify experimentally natural vibration modes and evaluate the available structural damping; determining the bridge susceptibility to pedestrian loadings; and formulating recommendations for mitigation measures.

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