On Modelling Of FRP Wrapped Steel CHS Joints

Abstract

The design of steel structures consisting mostly of Circular Hollow Sections (CHS) such as jacket structures and bridges is governed by fatigue loading due to the low fatigue resistance of the welded regions. A solution has been proposed where welding is completely avoided, thus eliminating the weakest factor of these structures. In this solution, joints are wrapped in FRP, which is bonded to the steel. Simple Finite Element (FE) models of these joints already exist. In this thesis, these models will be further developed in Abaqus for more accurate prediction of the behaviour of such FRP wrapped joints. A set of model and solver parameters will be established as a starting point formore detailed modelling of FRP wrapped joints with different geometry and static load conditions.

Because of large complexity of the models, and inclusion of many contact interactions, Abaqus/Explicit should be used to model such joints. The anisotropic nature of the FRP requires elements that are robust and able to handle this anisotropy. Also the complex, curved and layered geometry of the wrap requires elements that discretize a 3D volume. Without the use of user subroutines, continuum shell elements are the only elements that meet this requirement.

Prediction of the behaviour of axial joints was very accurate, although no unique set of input parameters for the Cohesive ZoneModel were found. This is because multiple failure modes occur at the same time, which makes the system very sensitive to some parameters and completely insensitive to other parameters. Prediction of more complex X-joints was not very accurate. This is mostly due to differences between the geometry of the model and the real life joint. The models did suffer from hourglass modes. Different methods of hourglass control had limited effect. It was found that as irregularity of the mesh increases, the effects of hourglass modes decreases. However, the effect of hourglass modes needs to be decreased further. A solution to do this is proposed at the end of this thesis.