In the Netherlands there are many waterways where bridges or locks are situated within the navigation way of inland waterway vessels. To protect these civil structures from potential collision risks, protection structures are placed around them. In this research, a commonly used protection structure, the steel piled fender structure, is analyzed under impact events, followed by a comparison with the design methodology prescribed in the Dutch codes. In the Netherlands, design guidance is provided by the "Richtlijnen Ontwerp Kunstwerken", abbreviated as ROK. The ROK adopts a design formula for the required energy absorption capacity of fender structures from the EAU 2012. By applying the principle of work, the required energy absorption capacity can be converted into an equivalent static load that incorporates dynamic effects. This allows the soil-fender structure system to be designed using static analysis.

In this research, a triangular-shaped fender structure with fixed geometrical properties is examined. Additionally, the bow structure of a CEMT class IV ship is included to capture the interaction between the ship and the fender structure during impact events. The aim of this study is to obtain a transient response of the system, investigate the interaction between the ship, soil, and fender structure during dynamic impact events, and evaluate this against the design methodology prescribed in the Dutch codes.

To determine the transient response, two different models are developed. A simplified dynamic model based on linear beam theory is constructed. In this model, the problem is reduced to two-dimensional space, where the fender structure is modeled as a 2D frame partially supported by linear elastic foundations representing the surrounding soil. The ship's bow structure is simplified as a mass-spring system attached to the frame structure. Furthermore, a non-linear finite element model (NLFE) is developed in three-dimensional space. The NLFE model includes the full geometry of the fender structure of interest, with the ship's bow structure modeled up to the most frontal bulkhead, and the soil is represented by a series of non-linear discrete springs.

Before performing NLFE impact simulations that account for the full interaction between the ship, soil, and fender structure, an extensive sensitivity study was conducted on the individual models, showing expected behavior. Impact simulations performed during the sensitivity study were used to set up the impact configuration for the final head-on and oblique impact simulations, in which the ship, soil, and fender structure behave flexible simultaneously, allowing full interaction.

A comparison between the simplified model and the head-on impact simulation from the NLFE model revealed different peak responses. The response of the NLFE model was dominated by significant plastic deformations, resulting in larger peak displacements compared to the simplified model. However, during the initial stage of impact loading, dominated by elastic deformations, both models showed good agreement.

Finally, NLFE simulation results are compared to the design methodology prescribed in the Dutch codes. The energy absorption observed in the fender-soil system from the NLFE simulations is compared to the required energy absorption capacity according to the codes. For the head-on impact scenario, significant crushing of the ship's bow led to reduced energy absorption by the fender-soil system. In the oblique impact simulation, the NLFE model predicted higher energy absorption by the fender-soil system compared to the code requirements. There are numerous differences in modelling assumptions between the NLFE model and the method prescribed in the codes. Moreover, the NLFE model includes simplifications of the real-world problem that may lead to an overestimation of the absorbed energy by the fender-soil system. Therefore, extending the NLFE model by removing simplifying assumptions remains highly recommended.