The superstructure includes all structural elements located above the bridge bearings, such as the deck, girders, trusses, and railings. Its primary function is to resist and safely transmit traffic and environmental loads (wind, snow, thermal expansion) down to the substructure.
A hidden killer. For steel superstructures, the engineer must check the stress range (max stress – min stress) over 75,000+ cycles. Certain connection details (like welded attachments) have a finite "fatigue life." The handbook provides the AASHTO fatigue categories (A through E'). bridge engineering handbook superstructure design