Throgs Neck Bridge: Why did its deck deteriorate?

Rapid deterioration of the concrete roadway decks of the Throgs Neck Bridge approach viaducts was found to be due to secondary tensile and fatigue stresses brought on by deflection of the cantilever brackets supporting the decks under truck loading. The deck slabs were designed in accordance with Article 1.3.2 of the American Association of State Highway And Transportation Officials (AASHTO) Specifications. In these specifications, the authors say, no reference is made to the type of framing or stiffness of supporting steel members below the slab. Thus, the slabs were designed based on their span lengths between supporting, unyielding stringers, even though the cantilever brackets supporting the outside lanes cause the stringers to yield. The authors call for AASHTO to address in their specifications the condition of slabs on yielding cantilever supports.