In the Netherlands many deep building pits, created by sheet-pile walls, tensile piles and underwater concrete, have been used. An underwater concrete floor is necessary to prevent water leakage. Up till now only limited flexural tensile stresses are allowed in the concrete floor. However, a new design code for underwater concrete allowed cracking in the floor. Consequently, the floor can be made less thick. In order to investigate the flow of forces three different FEM-models have been used. The models consist of beam, shell or volume elements. The differences in results based on the models were very small with respect to the linear elastic analysis. However, the non-linear analysis showed larger differences. Not only the load factor was lower but also the failure mode was different in the FEM-model based on the volume elements compared to the other two models.