Constructing Bridges and Walls

Part 4 - Superstructure

The superstructure is the part of the bridge that actually   spans the obstacle beneath the bridge. The superstructure consists of the following:

• Bridge Deck
• Structural Members
• Bridge Rail (Parapet)
• Aesthetic/Safety Features

The bridge deck is the roadway portion of the bridge. Most bridge decks are constructed using concrete reinforced with steel rebar. The bridge deck is supported by the structural members. The most common types of structural members are:

• Precast, Prestressed Concrete Bulb Tee Beams
• Precast, Prestressed Concrete I Beams
• Precast, Prestressed Concrete Box Beams
• Steel I-Beams and Girders

The structural members for the 28th/31st Avenue Connector Bridge are 54” tall Precast, Prestressed Concrete Bulb Tee Beams. Cross-braces, commonly referred to as diaphragms, are placed between the beams to help distribute vehicle loads and resist lateral loads.

Bridge rails (parapets) are an important safety feature of the bridge. Bridge rails are typically comprised of reinforced concrete. Their dimensions are chosen based on the design speed of the adjacent roadway.

Other features such as handrails, fences, sidewalks, lighting, and drainage devices can be added to the bridge for aesthetic or safety reasons depending on the site conditions of the bridge. The 28th/31st Avenue Connector Bridge incorporates a fence, lighting, two sidewalks and many additional aesthetic features.

Cross-section view of superstructure elements