Overload response of flatbar frames to ice loads

ABSTRACT The paper presents the results of a focused study into the capacity and overload response of a wide range of simple flatbar frames. The work addresses a number of issues of current concern for ice class vessel design. While ice class rules have no formal requirements for overload response, concern for safety often leads designers and regulators to evaluate the full range of response to ice. This study examines the elasto-plastic response of simple frames to ice-like loads. This study is preliminary in nature, in that it only examines one frame type in one loading pattern and only examines the load-deflection response. Future work would need to examine a fuller range of parameters and issues. Nevertheless, the investigation explores a critical aspect of ice class frame design and takes one step towards a more comprehensive approach. A novel simple approach to the load is employed, in the hopes of creating a consistent and effective way to assess overload capacity. Typically, such investigations either apply a simple load patch or they use a much more realistic but complex technique of modelling the ice material as a failing solid in contact with the structure. In contrast to these approaches, this study employs a rigid indenter as a way to create an ice-like load, while maintaining simplicity and allowing the structure to exhibit realistic behaviour. The study uses LS-DYNA®, but could have used any explicit time-stepping finite element (FE) code. The results of the study show, not unexpectedly, that the overload response consists of a sequence of local plastic mechanisms. The results show that there are alternative failure paths, that depend on the specific local failures, that themselves depend on structural dimensions and material parameters.