Orthotropic Deck Fatigue Investigation at Triborough Bridge, New York

The Triborough Bridge connects the boroughs of Manhattan, Queens, and the Bronx in New York City. The bridge has suspended spans with a total length of 2,700 ft (823 m). The existing concrete deck is being replaced with an orthotropic steel deck to reduce the overall dead load. Before deck replacement, a prototype steel orthotropic deck was installed on the main span for a length of 120 ft (36.6 m). About 300 strain gauges were installed at critical locations to investigate the fatigue strength under static and dynamic loads of the AASHTO fatigue truck and under normal traffic. The strain gauge testing was done in three phases, and structural refinements were made to the deck system between phases. Traffic monitoring was conducted for the most critical locations over a 30-day period during Phase III. The results from three phases of the strain gauge testing, including influence lines and traffic monitoring data, were used to calculate fatigue stress ranges and the fatigue life for each detail. In addition to strain gauge testing, a finite element analysis of the orthotropic deck was performed with loading criteria set by AASHTO load and resistance factor design. The results from the finite element analysis were compared with the results obtained from the strain gauge testing. It was concluded that the heavy trucks on the bridge cause fatigue stresses higher than what had been anticipated by AASHTO. The investigation assisted in modifying the design to obtain a longer service life for the deck system under heavy-truck traffic.