Experimental studies of load-bearing capacity and failure behavior of LNG cargo containment systems with multiple layers of insulation under heavy footprint loads

In the LNG carrier tank, cargo containment system (CCS) is used to maintain the cryogenic environment, prevent the leakage of LNG cargo and transfer the sloshing loads to the ship hull. During the construction phase of the LNG tank, the scaffold is placed directly on the top surface of the CCS to support the construction work at a higher position, and the heavy footprint load will be applied to the CCS by the scaffold. However, due to the multiple layers of various materials and complex junctions of adhesives, there is no direct or obvious indicator to assess the integrity of CCS under footprint loads. In this paper, the Mark III CCS consisting of plywood, polyurethane foam, and resin rope is chosen as the objective. Three experimental models of CCS were fabricated according to fabrication techniques. The compressive load was applied to the experimental model via a scaffold foot on four wooden blocks using a laboratory actuator. The applied load is gradually increased until the experimental model exhibits distinct deformations and failure features. In order to solve the difficulties of strain measurement on the porous foam, the digital image correlation system (DIC) is adopted to record the strain variation of the front surface during the entire experiment process. The tendency of the vertical stiffness of the experimental model to change can be clearly shown by the applied load and deformation curves. The failure process for each component of the CCS has been obtained according to the allowable strain requirements in the classification society's rules. The weakest regions of CCS have been found based on experimental results. Finally, the nonlinear finite element method has been applied to study the deformation and stress distribution of the experimental models under heavy vertical footprint loads. The maximum allowable deformation along the vertical direction has been proposed by introducing limit states. The conclusions of this paper can provide guidance for safety analysis of CCS design and fabrication.