Case Study #4 – Composite Members

Deriving moments and shears for a box beam modelled as a set of plate finite elements can be complicated, as it is necessary transform and sum all the relevant forces at a section. Sam’s “Composite Member” feature makes it easy to get an answer to a simple question like "What is the total moment at a particular point?"

Take the simple case of a beam and a slab where the slab is modelled as a set of finite elements, and the beam is modelled as an offset beam element: to get a moment at any point it is necessary firstly to transform all the results into the same axis system, then to add the moments in the slab and beam and calculate the couple caused by the axial loads in the slab and the beam. It is far more complicated when analysing a box girder where the flanges and webs are modelled with plate finite elements.

Bestech have found a solution to this problem and we call it “Composite Members”. The engineer tells Sam that a Composite Member exists that is made up of various elements, for example, the slab elements and the beam elements of our first example. This is quick and simple to do with a few mouse clicks on one of Sam's graphics screens. Then Sam does all the necessary resolutions, transformations and summations and displays a simple moment or shear force diagram.

This technology underlies Sam’s ability to create influence surfaces for any effect for finite element models.