Massachusetts Bay Transportation Authority, Charles/MGH Station
The structure for the Massachusetts Bay Transportation Authority (MBTA) Charles Street/MGH Station included a 1914 riveted steel, through-girder viaduct that carries two tracks of the MBTA’s Red Line transit system. As part of the complete rebuilding and reconfiguring of the station, the contractor needed to remove an existing pier supporting the viaduct. SGH designed a load-transfer system that could be installed and utilized within the single weekend shutdown permitted by the MBTA.
The existing pier supporting the viaduct had a reinforced concrete stem supporting a steel-hammerhead cap beam. The new supports consisted of steel moment frames integrated into the architecture of the new station.
SGH designed a structural jacking system and procedures to allow transfer of the total dead load reactions of two viaduct spans from the existing hammerhead pier onto the new steel frames on either side of the pier. For the design, we carefully considered the loads and deflections imposed on the existing and proposed structures and allowed for precise, but practical, limits on the total deflections of the viaduct superstructure.
SGH provided nearly continuous observation of the process to help the contractor carry out a safe transfer of loads. The contractor successfully completed the work within the permitted time frame and met the allowable deflection limits so that the MBTA could resume regular Red Line operations on Monday morning.