A description is given of the parametric study done to evaluate the structural behavior of the replacement steel orthotropic deck planned for the Bronx—Whitestone Bridge in New York City. A principal objective was to analyze the deck details for stress ranges that indicated sensitivity to fatigue cracking. On the basis of the analysis findings, important modifications were made to the preliminary deck design. These changes were primarily to reduce the maximum stresses in the diaphragms and ribs around the diaphragm cutouts—locations that traditionally have been prone to cracking, as observed on orthotropic decks on other bridges. After the completion of the deck design, a full-scale prototype deck measuring 48 by 37 ft was fabricated and subjected to a series of laboratorycontrolled fatigue tests. Proper boundary conditions and loading procedures were created to produce stress ranges similar to those in the full bridge model. Laboratory test results correlated well with the computed stress ranges and demonstrated that the deck had outstanding fatigue resistance and could readily provide the 75-year design service life specified for the orthotropic deck.

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In the past decade, the performance-based method has been applied to the seismic evaluation and retrofit of bridges. Suspension bridges are not covered by AASHTO specifications. Therefore, project-specific performance criteria are required. Suspension bridges are mostly critical bridges and generally need to be analyzed for two levels of seismic hazards: function (e.g. 500-year return period); and safety (e.g. 2500-year return period). In addition, the analysis methodology including site-response analysis and soil-structure interaction analysis will generally be required for suspension bridges. Seismic retrofits following the performance-based approach are usually more cost-effective than those derived from the force-based approach.