SUMMARYThe response of an open high-pressure pipeline containing moving liquid to horizontal seismic loading is investigated. The problem of the interaction between the pipe and the liquid inside it is solved after thorough kinematic analysis, involving two-stage application of the Coriolis theorem. The basic axial loading on the pipeline is also taken into account. As a result, the equation of motion of an arbitrary one-span part of the pipeline under seismic loading is obtained. The harmonic balance is used to find the solution. As an illustration to the theory a numerical example is given with the data of a real water power station pressure pipeline under a past earthquake record.