Keywords: finite element modelling, link finite element, gap finite element, boundary-interface conditions.

There are various causes and types of structural nonlinearity. One of many different classifications emphasizes two types of nonlinear structural behaviour: the so-called "smooth" and "rough" nonlinearity. One of the causes of "rough" nonlinear behaviour is the so-called "contact" nonlinearity. These nonlinear phenomena appear due to changes in structural systems according to "activation" or "deactivation" of boundary and/or interface conditions.

Contact nonlinearity appears through activation of new supports or deactivation of existing (usually translational) supports of the structural system resulting from displacements of the structural elements. The second type of contact problem can be caused by activation or deactivation of interfaces and changes in compatibility conditions of displacements between structural elements.

Formulation of adequate finite element models for rough nonlinearity is not only a formal or mathematical problem, but it requires knowing the causes of the discontinuity of nonlinear phenomenon. In some cases, the nonlinearity can make vulnerable the structural system integrity (i.e. bearing capacity, stability, serviceability and durability). For these nonlinear problems there are no common solutions and it is necessary to formulate special techniques for each specific case of nonlinear behaviour.

Modelling of boundary and interface conditions is very important step in the finite element approximation, because the real behaviour of the structural system depends on the real characteristics of supports and interfaces. There are no possibilities for automated modelling of boundary and interface conditions in finite element software. Therefore, it is very important for structural engineer to have good competency in the finite element technology and its software implementation.

In this paper, the basic principles of so-called "link" finite element, "gap" finite element and "nonlinear spring" finite element application in the modelling of civil engineering structures are explained. Theoretical considerations are outlined. Our basic intentions are giving advice and recommendation for gap-link-spring application. in finite element modelling.

As an illustration of the problems discussed, various numerical examples are given and analyzed. One of these is the modelling of beams prestressed by cables located out of the cross-section. High friction forces appear in the cable-column joint area, as an undesirable consequence. In order to decrease friction, rollers are usually installed in cable-column joint. Application of the "special" finite elements for modelling of this and similar problems are analyzed.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £140 +P&P)