External Pocket and Socket Connections for the Seismic Design of Alaska Bridges

Accelerated bridge construction (ABC) has gained momentum over the last several years due to the promise of rapid, robust construction. For Alaska, where the construction season is shorter than all other states, this is especially important. Numerous ABC connection options have been proposed in the literature as summarized by NCHRP 12-88 (Marsh et al., 2011). However, for the purpose of this research proposal, the most relevant connections are termed ‘Socket’ and ‘Pocket’ connections. Both will be described in more detail later. Recent research funded by AKDOT&PF at NCSU has resulted in the development of a rapidly constructible steel bridge system which uses grout and shear studs to connect bridge pile/columns to the cap-beam. The technique was shown to be tolerant of large construction errors, and robust for the seismic demands expected throughout Alaska. The design detail is now the recommended practice for Alaska DOT for construction of these bridge systems, which are employed for temporary (or semi-permanent) structures. A technique similar to that which was developed for steel bridge systems could be employed for reinforced concrete or reinforced concrete filled steel tube (RCFST) systems, the latter of which is the dominant form of construction for permanent bridges in Alaska. By adapting the grouted shear stud (GSS) connection to RCFST substructures, the benefits of rapid, robust construction could be extended to this class of bridges. RCFST or concrete columns would be placed in the usual manner in the field. A prefabricated assembly which consists of the cap beam and external socket would then be placed over the columns with the remaining gap filled with grout in the field. The proposed system would allow for significant construction tolerance, while also being robust against seismic forces. The design of the column to cap joint may also be simplified due to the lower strain levels that would exist in the joint as a consequence of elastic reinforcing steel which connects the column to the cap.