Emergence of Semi-Integral Bridges

At the 73rd TRB Annual Meeting in January 1994 the paper “Semi-Integral Bridges: Movements and Forces” was presented. It described the attributes, limitations, and peculiarities of a presumably new bridge concept developed by the Ohio Department of Transportation. That presentation elicited a comment from an attendee at the TRB meeting about recent research on a Washington State bridge, a bridge that was later found to be based on this same concept except that it predated Ohio’s earliest prototype by more than 10 years. This discovery of the Washington State experience provoked a state and province inquiry about semi-integral bridge construction, an inquiry that revealed the startling fact that fully 26 state transportation departments have constructed one or more of these structures; some departments have been constructing them for more than 20 years, and two departments have been constructing them for at least 40 years. Another surprising indication of semi-integral bridge experience was the discovery that the design of more than 80 percent of bridges built by two departments are based on the semi-integral concept. Because semi-integral bridges are deck-jointless bridges that can be designed to operate well within usual stress limits, because they are suitable for most moderate-bridge-length applications, because they can be designed to resist the destructive effects of rigid pavement growth and earthquakes, and because so many departments have achieved favorable performance with them, it appears that interest in semi-integral bridges will continue to increase, as will their numbers. However, since the stability of some semi-integral bridges depends to a great extent on composite backfill-structure interaction, future applications of this innovative bridge concept will depend to a great extent on the development of suitable soil-structure interaction research to provide the necessary experimental background to guide future designs.