Owing to the growth in human population, the land-scarce island countries and countries with long coastline are expanding their horizon to ocean environment through very large floating structures (VLFS) for different purposes as these are cost-effective, environment-friendly and can be manufactured easily. VLFS applications include floating airports, artificial islands, mobile offshore base and Mega-Float and are built using Pontoon-type or semi-submersible-type structures. In these types of structures, because of its large size, elastic deformations are more important than their rigid body motions. In this paper, hydroelastic behaviour of a barge Pontoon-type VLFS under various water depths is investigated. Analysis is based on three-dimensional linear hydroelastic theory to obtain the wave-induced hydroelastic response of the structures in the frequency domain. For solving this coupled fluid-structure interaction problem, the modal expansion method and the dry normal modes of vibration is commonly used for the floating structure. The structure is modelled using PATRAN [1], and the hydroelastic analysis is carried using HYDRAN-XR software. Responses in regular wave in the vertical mode at salient point along the length of the VLFS are presented for various wave headings and frequency. Vertical displacements at both edges of the structures and at the centre portion are found. Response for the six water depth conditions has been examined, and the observed results emphasize that vertical displacements are dominant in deep water conditions in relative to the shallow water conditions. Results also suggest that horizontal displacement is significantly higher in shallow water conditions. © Springer Nature Singapore Pte Ltd. 2019.