Keywords: panel element, drilling stiffness, large element, panel, floor and wall.

This paper presents a panel element that can be large without compromising analysis results. The principles of finite element analysis require that the element size is sufficiently small, but for the reason of convenience of use, engineers and analysts sometimes like to use large size elements to simplify the modelling process and reduce the unwanted results. The panel element proposed in this paper can help alleviate this requirement conflict. The proposed panel element is developed based on the substructure principle and the panel element is meshed internally by smaller size shell elements. To the users, the panel element is just a four node large shell element capable of modelling a large physical object such as a wall and a floor by using one element. Internally in the finite element analysis solver, the panel element is meshed by smaller shell elements. Even though the panel element is meshed internally, not all the degrees of freedom (DOF) of the meshed model will be appear in the global analysis as the internal DOF will be condensed out of the panel element stiffness matrix. Because of this, the total number of DOF of a structural model can be significantly reduced by using the panel elements. Using panel elements is also very helpful in writing the parallel finite element analysis program because each panel element can be treated as a substructure and processed independently in different processors if they are available. There are also two other associated time saving benefits from using panel elements, one is the reduction of repetitive processes within one panel element because only one of the small shell elements in a panel element needs to be processed, the other associated benefit is the reduction of repetitive processes of panel elements in the whole structural model because it is very likely in a large structural model that there are many identical panel elements and only one of them needs to be processed. The large size nature of the panel elements also makes it possible to predict drilling stiffness more accurately. The drilling stiffness of shell elements is an issue that has not been solved satisfactorily to meet engineering requirements, but it is in great demand by engineering practice. The reason why the drilling stiffness has not been predicted satisfactorily is due to the fact that drilling stiffness not only depends on the properties of shell element itself, but also depends on the area that is used to apply the drilling moment. Using small shell elements cannot solve this problem as shell element sizes are normally too small. This paper recommends a method to calculate the drilling stiffness by taking the moment application area into account and the predicted drilling stiffness is more accurate than previously proposed methods.

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