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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 86
Edited by: B.H.V. Topping
Paper 131

Some Aspects of Finite Element Structural Modelling using a Link Finite Element

D. Kovacevic and R. Folic

Civil Engineering Department, Faculty of Technical Sciences, University of Novi Sad, Republic of Serbia

Full Bibliographic Reference for this paper
D. Kovacevic, R. Folic, "Some Aspects of Finite Element Structural Modelling using a Link Finite Element", in B.H.V. Topping, (Editor), "Proceedings of the Eleventh International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 131, 2007. doi:10.4203/ccp.86.131
Keywords: finite element modelling, structural modelling, link element, boundary-interface conditions.

This paper explains the main principles of the application of so-called "link" finite elements (link FE) in the finite element method (FEM) modelling of civil engineering structures. The concept, application field and some numerical aspects of the link FE are discussed.

Modelling of boundary-interface conditions is an important step, because the real behavior of a structural system strongly depends on the real supports-connections state. The structural designer must have a good knowledge of FEM technology and its software implementation.

There are two ways of numerical modelling of the boundary conditions of a FE system:

  • numerical modeling by "skip" and
  • numerical modeling by "restraint".
The "skip" approach is applicable for zero value degrees-of-freedom (DOF) in support and it is not universal. This approach implies the "deletion" of a row and a column of the global stiffness matrix of the FE system for zero DOF.

The "restraint" approach is more comprehensive than the previous and demands numerical forbidding or permission of a specific DOF by transformation of the global stiffness matrix of the FE system.

The term "single-joint restraint" is often in use for boundary conditions, because the restraint is applied to the joint of the FE system with regard to the support. The so-called "multi-joint restraint" is in use for the definition of the restraint between two or more FE system joints (interface condition). A typical example for a "multi-joint restraint" is the modelling of a slab-beam connection.

As an illustration of the previous consideration some numerical examples are given, using the AxisVMRFEM software. The first example shows the possibility of modelling a composite beam. The second example shows the differences in plate behaviour if:

  • the connection is aligned to the axes (the beam axis is in the midplane of plate) and
  • the connection is aligned to the top surface (the top surface of the plate coincides with the top surface of the beam).
The third example shows the behaviour of a so-called "sandwich-plate", i.e. a composite plate formed by three layers: steel foils (top and bottom face) and polystyrene foam core (between the steel foils). The fourth example is an illustration of modelling a reinforced plate. The FE model of the plate consists of: a shell FE for modelling the concrete, a beam FE for modelling the steel bars, a link FE for modelling the steel-concrete bond and a link FE for modelling the connection between the slab and the rib part of the plate.

This paper emphasized the importance of modelling the boundary and interface conditions in FEM structural analysis. By convenient choice of the link FE stiffness parameters it is possible to obtain the behaviour of different structural systems (with-without shear stiffness, with-without flexural stiffness, etc.).

The link FE are successfully available for the modeling of reinforced concrete structural elements, eccentrically connected structural elements, cross-sections created by different materials, composite plates, etc.

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