Which of the following is NOT a primary member in a typical Two girder bridge?

In a typical two-girder bridge configuration, the primary members are specifically designed to bear the loads and provide structural support. Girders, floor beams, and stringers all play critical roles in this structure.

Girders serve as the main horizontal support members, directly carrying loads from the deck or roadway. The floor beams are connected to the girders and typically support the stringers, which, in turn, support the bridge deck. The interaction among these elements is essential for maintaining the integrity and stability of the bridge as it accommodates various loads.

Shear keys, on the other hand, do not function as primary structural members in the same sense. Instead, they are typically used to connect structural elements and help maintain positional stability, particularly in situations requiring alignment and load transfer. Therefore, while shear keys play a role in the overall design, they do not fall under the category of primary members in the same way that girders, floor beams, and stringers do. This distinction makes the option relating to shear keys the correct answer to the question, as it identifies an element that supports rather than forms the primary framework of a two-girder bridge.