Practical Modelling of Joints and Connections

Most structures involve some form of jointing or connection. Traditional fabricated structures have used many thousands of bolts and rivets to connect components together in a continuous manner, in the case of ships and aircraft the total can run into millions.

Even today many structures rely on this type of technology – for example, the use of spot welds in a modern road vehicle. Significant discrete load paths are formed by lugs and pins, clips or similar connectors in many structures across a wide range of industries. Alternative forms of connection are welds joints and bonded joints. These may well exist as the sole means of load transfer or be supplemented by mechanical connections such as bolts or rivets.

The engineer is faced with an often difficult decision when attempting to simulate such connections and joints within a Finite Element Analysis (FEA). In many cases, the details of each individual connection can be ignored if an overall stiffness or strength assessment is to be made and the connection is assumed reasonably continuous. However, there may be doubts about the local flexibility and load paths developed with this assumption. It may be that the assessment of the local behavior of the connector is essential to the safety case. This would certainly be the case with main attachment fittings for example. In some cases, the interaction between the connectors and the surrounding structure is critical, as in the case of pre-loaded bolts and inter-rivet buckling.

Modeling of weld features to get a reasonable estimate of stress concentrations at the weld toe can be problematic; do we model with a fine detailed 3D model, or use a ‘hot spot’ type of approach?