Seismic and wind investigation for the RFK Bridge in Manhattan. Model courtesy Boundary Layer Wind Tunnel Laboratory at The University of Western Ontario.
Weidlinger Transportation, which became a Thornton Tomasetti practice in September 2015, was the lead firm in a joint venture with TY Lin to conduct a seismic investigation for the Robert F. Kennedy (RFK) Bridge and a wind study for its suspended spans. The work included an evaluation of the seismic and wind design in current and past projects to determine any additional retrofit needs. Retrofit concepts that are consistent with the seismic performance criteria of the structural components and that meet applicable code requirements were developed. The scope also included a review of the seismic performance of the bridge’s nonstructural life-safety systems, such as fire standpipes, fire pumps, elevators, and bridge lighting/electrical systems.
The RFK Bridge consists of many bridge structures, including:
• The Queens Approach Viaduct
• The Suspended Spans
• The Wards Island Viaduct
• The Randall’s Island Viaduct
• The Bronx Toll Plaza
• The Bronx Kills Truss Spans
• The Bronx Approach
• The Manhattan Toll Plaza
• The Harlem River Lift Bridge
• The Manhattan Approach
A Critical Bridge
The RFK Bridge is a major link between Manhattan, Queens, and the Bronx, and is a critical bridge for seismic evaluation and design. In accordance with the NYCDOT Seismic Guidelines, which have been used for TBTA bridges, critical bridges must be analyzed for two levels of seismic hazard (500-year and 2,500-year return periods) and they must meet the performance criteria for each level. These performance criteria aim to ensure the survival of the bridge after a safety-level (2,500-year) event, with all damage to be of a repairable nature. The requirements for function-level (500-year) events specify that no structural damage may occur to primary elements and only minimal damage to all other elements is permitted.
Applying Modern Analysis Techniques to a Historic Bridge
The RFK Bridge was designed in the 1930s, when wind-load design criteria were not fully developed. The collapse of the Tacoma Narrows Bridge in 1940 led to renewed research in bridge aerodynamics. Extensive research and wind tunnel testing have yielded a much deeper understanding of wind effects on structures. The modern approach to the evaluation of wind effects includes the combination of wind climate studies, wind tunnel testing of scaled models and finite element analysis. Our investigation applied this modern approach to the suspended spans of the RFK Bridge to identify any retrofit needs.
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