Numerical modelling techniques for predicting the hull girder ultimate strength under cyclic bending moments based on model tests

Ships voyaging in severe sea conditions are subjected to cyclic extreme bending moments arising from wave loads, which may result in the ultimate strength reduction. The test approach with continuous cyclic bending moment loading and replaceable test sample, as well as the numerical method with reasonable modelling configurations, was addressed for predicting the hull girder ultimate strength. Two four-point bending experiments, including one-time and cyclic bending moment loads with three and four cycles before and after structural collapse, were designed to investigate the box girder ultimate strength. The continuous uniaxial tension compression of the loading actuator could be transformed into continuous cyclic hogging-sagging bending moment, which could avoid the dangerous and difficult turning over of test samples. Furthermore, eleven respective nonlinear finite element analyses were adopted to conduct parametric studies on the progressive collapse behaviours of small-scale box girder and full-scale hull girder, which included geometrical range, solution type, element type, loading time and material model. After comparison, the reliable finite element modelling techniques using the dynamic explicit method were identified to account for transient effects and avoid convergence issues in the iterative procedure, which could reach the balance between acceptable ultimate strength results and computation resources under extreme wave bending moments.