To promote accelerated bridge construction in seismic regions, a large-scale experimental investigation was conducted to examine the seismic sufficiency of precast concrete I-girders in integral bridge superstructures. Such structures are not frequently used in high seismic regions due to lack of design guides and overly conservative design approaches. A half-scale, 17.8 m (58.5 ft) long test unit modeling a portion of a prototype bridge incorporating a concrete column, ten I-shaped precast concrete girders, and an inverted-tee concrete cap beam was used to experimentally verify that precast concrete members employing accelerated construction techniques can be used in integral superstructures and provide excellent seismic performance. Comparison of an as-built girder-to-cap connection detail with an improved detail shows that the as-built detail in existing bridges will satisfactorily resist positive and negative seismic moments and allow plastic hinges to develop at the column tops, though this was not the original design intent. However, the improved detail, which exhibited excellent seismic moment resistance, is recommended for new bridges to avoid potential deterioration of the girder-to-cap connection.