5003 Lectures - Faculty of Engineering and Applied Science

E5003 - Ship Structures I 151
© C.G. Daley
For the 3 bar frame at left, we can define the
define local degrees of freedom for each member
using the same standard approach that was
described in Chapter 11. We will start from the
local element stiffness matrices and assemble the
full structural global stiffness matrix, just to
illustrate the process.
The local degrees of freedom follow the individual
members, while the global degrees of freedom are
all aligned to the Cartesian (x-y) system. The
other aspect is that global degrees of freedom refer
to nodes of a structure, rather than to ends of
members. This means that several member ends
can share a single set of degrees of freedom.
The matrices below show the local and global
versions of the stiffness matrix for beam 1. The
difference is the way the degrees of freedom are
defined. In this case the global degrees of freedom
are just versions of the local dofs.