Herein, a study on the hydrodynamic modelling of pontoon bridges is presented, with the Bergsoysund Bridge as a representative example. The model relies on the finite element method and linearized potential theory. The primary emphasis is placed on the stochastic response analysis within the framework of the power spectral density method. The quadratic eigenvalue problem is solved using a state-space representation and an iterative algorithm. The contribution of the fluid structure interaction to the overall modal damping is investigated. Response effects due to changes in the sea state are studied. A frequency independent approximation of the hydrodynamic coefficients is presented and discussed. (C) 2016 Elsevier Ltd. All rights reserved.