Seismic response of buried socket pipelines with typical cross connections

The joint type and cross connection pattern of buried pipelines have a significant impact on the seismic responses of pipeline structures. As the seismic deformation and stress of pipeline cross are determined by the structural types of branch pipelines, a finite element model for straight branch pipelines is firstly established to investigate the joint displacement and relative pipe-soil displacement of ductile iron pipelines (DIP) with flexible socket rubber joints and cast iron pipelines (CIP) with rigid joints under seismic wave propagation. Then, the seismic responses of pipeline connections using cross-shaped, T-shaped, L-shaped and double-T-shaped cross connections are analyzed, where the pipe cross is connected to the branch pipelines using the socket or flange joints. Furthermore, the effects of joint types on the seismic responses of pipeline cross connections are evaluated. The results show that for the straight pipelines with different types of joints, the peak joint displacement of the DIP with flexible joints is larger than that of the CIP with rigid joints. When the pipe cross is connected with the socket joints, the peak joint displacement of the pipelines with double-T-shaped cross is slightly smaller than that of the pipelines with cross-shaped and T-shaped connections. When the pipe cross is connected using the flange joints, the DIP with flexible joints adjacent to the flange joints exhibits a larger joint displacement and is prone to tensile failure, while the CIP with rigid joints adjacent to the flange joint experiences greater axial compressive force and is prone to compressive failure. At the cross of double-T-shaped pipelines, the responses of the socket joints adjacent to the flange joints are significantly larger than those of the cross-shaped and T-shaped connections.