Use of precast substructure in accelerated bridge construction (ABC) has been gaining popularity due to its advantages over traditional cast-in-place (CIP) construction. When using vertical precast members (e.g., columns and piles) in bridge substructure construction, they must be connected to the adjoining members (e.g., bent cap, pile cap, and abutment) reliably. To accomplish this goal and promote ease of construction, the preformed socket connection has been suggested. This connection is established by inserting the vertical precast member inside a preformed socket in the precast adjoining member and filling the socket with non-shrink, high-strength grout. Using specimens that modeled the full-scaled connection interfaces, this paper experimentally evaluates the side shear strength of preformed socket connections with various connection parameters. Test results show that side shear mechanism in the preformed socket connections can provide significant resistance, facilitating transfer of large vertical loads. This paper also includes recommendations for the socket connections and appropriate stress limits.