User Area
> Advice
How To Use Single Joint Elements in Modeller
You may define a single joint by
selecting two points and assigning a point joint mesh attribute by dragging and dropping it from the
Attributes TreeView onto the model in the graphics window.
Alternatively, the mesh may be
assigned by selecting a set of points with your mouse and adding
it to the selection memory. Then separately select a second set of
points in normal selection and assign the point joint mesh. This will
create a series of joints between points paired between the selection
memory and normal selection. The order of points will be either
their point number (if
box selected) or the order that they have been picked one by one. If the option "Mesh from master to
slave" is ticked, then the points in normal selection
will become the 'Master' assignments to which material and
geometric attributes for the joint are then to be assigned.
More information on the
assignment of joint mesh can
be obtained in the help menu:
Help
> Help Topics > Contents > Modeller Reference
Manual > Chapter 5 : Model Attributes > Meshing >
Joint/Interface Element Mesh
This gives a case study
example. The following is a simple
step-by-step guide to the use of single joint elements.
- Generate a point feature at every position
that a single joint connection is required. Note that these points
must be active, i.e. used to define structural lines that are part
of the model geometry to be meshed.
- Either create a second structural
point or create a copy of the first point or points a short distance away.
- Define a point joint element mesh, specifying
an appropriate element type. 1 element division is
automatically applied. For a table of the recommended
choice of joint element with various structural element
types see:
Help
> Help Topics > Contents > Element
Reference Manual>Appendix L : Joint Element Compatibility
- Define a local coordinate dataset. For
linear analyses it is probably easiest to orientate it
in the global direction
(use Attributes > Local Coordinate > Cartesian > Rotate
and specify a zero angle)
- Assign the mesh to two
selected points, or with a set
of points in selection memory and a corresponding set
of points in normal selection. On the mesh
assignment form use the drop-down list to select the local
coordinate dataset. Don't assign the local coordinate
dataset directly to the points or any other connected
geometry features - this has a different effect and
purpose.
The local coordinate system is needed because the joint
elements and their stiffnesses work in local coordinates.
- Define a joint material, selecting the
appropriate number of degrees of freedom for the element
chosen (see the specific element details in the Element
Reference Manual for details). The columns in the form
correspond with the local coordinate system – first
column is local x-axis, second column, local y-axis etc.
- Assign the joint material to
the Master points. If there is a single joint at this
location you can simplify this procedure and assign the
joint material to both points.
- Assign a joint geometric
attribute if required. See the Element
Reference Manual to check if the joint element type
being used requires an eccentricity to be specified.
- Make the original point
and the copied points created in step 2 unmergable (Geometry
> Point > Make Unmergable).
- Move the points created in
step 2 to be coincident or near coincident to the
original points, such that the joints have zero or near
zero length.
In general there are two main issues to
consider in the use of joint elements
- The joint element The type of joint
element chosen controls what degrees of freedom will be
available. For example, to obtain a pin connection between
two beam elements in 2D use a JNT3 joint element whereas
for a full connection, use a JPH3 joint element. The Element
Reference Manual for each joint describes the degrees of freedom
associated with each joint
- The joint material The joint material
defines what stiffness/mass etc. will be associated with
each of the available joint degrees of freedom
|
