‘Beam’ Tag

Concrete Bridge Substructure

Photo Credit: Karl Jansen

This is the underside of a concrete bridge. Technically, this is known as the substructure, or the part of the whole structure that supports the superstructure, or the roadway in this case. You can see nicely the beams and girders that run laterally and longitudinally under the bridge superstructure, and the massive columns that extends vertically down to the ground to provide the support. The substructure is an important element of every bridge.

Reduced Steel Beam Section

Photo Credit: Alex Mead

Seen here is a full moment connection between a beam and a column. Note the numerous welds, bolts, and stiffener plates required to get a full moment transfer from the beam to the column. The careful observer will also notice in this example that the beam is actually part of a plastic hinge inducing connection. This is evident by the reduced flange in the beam on the right side of the picture. This reduced section is purposely placed here to force the beam to form a plastic hinge in this location and draw the damaging plastic behavior into the beam away from the column. This connection is part of a strong column, weak beam design approach and allows the structure to absorb substantial amounts of energy in an event such as an earthquake without failing in a story collapse mechanism.