Friction support

Definition, application

Support nonlinearity is nonlinear functionality which can be apply on any type of supports. These features can simulate special nonlinear behaviour of supports. For taken into account it is necessary to perform nonlinear analysis.

Where to find it

In project data dialog in part 'Functionality' it is necessary to switch ON 'Friction support/Soil spring'. After that in support properties there are several new possibilities which can be set for any degree of freedom.

When inserted into the model, a friction support (friction defined in Y and Z direction) is marked with the following symbol (remember that in order to see the symbol, view parameters must be adjusted to show model data).

$image\frictionSupportSymbol.gif$

Possibilities

From reaction	The user may select the reaction that defines the force pushing against the support.
C flex	Stiffness of the support. This stiffness applies ONLY until the friction force is exceeded.
mju	Coefficient of friction. If friction of X / Y / Z or XY / XZ / YZ type is selected, one mju value must be input. If friction of X+Y / X+Z / Y+Z type is selected, two mju values must be input.
Independent	If simple friction (X, Y, Z) is defined in two directions, this option is available. It specifies that friction in one direction is independent on the friction in the other direction.

From reaction

X, Y, Z

The final limit force can be calculated from the reaction in a specified direction. If a support in X-direction is being defined, it can be said that the friction force should be determined from the reaction calculated in either Y or Z direction.

XY, XZ, YZ

The final limit force can be calculated as a compound friction. Only one of the stated options is offered for each direction. E.g. if a support in X-direction is being defined, it can be said that the friction force should be determined from the reactions calculated in Y and Z direction. The friction force is calculated from the following formula:

$image\frictionFormula1.gif$

X+Y, X+Z, Y+Z

The same as above can be said here. Different procedure is however used to calculate the limit force. E.g. for friction support in X-direction the following formula is employed:

$image\frictionFormula2.gif$

Note: Friction can be input in one or two directions. It is not possible to define friction in all three direction otherwise the "thrust" could not determined.

Note: Composed friction (e.g. YZ or Y+Z) can be input in one direction only.

Note: Option Independent friction is available ONLY if simple friction (X, Y, Z) is defined in two directions.

Limitations

- only for node supports

Supported members

Table of supports, for which it is possible to set nonlinearity in project.

Type of support

Support - in node

Support - point on beam

Example

Let’s assume a plane XY and a support that can slide on it in any direction with a friction.

X	friction
C flex x	1E5
mju x	0.20
from reaction	Z
Y	friction
C flex y	1E5
mju y	0.55
from reaction	Z
Z	rigid (or press only)
Independent friction	YES

Let’s assume a pipe in a borehole in X-direction.

X	friction
C flex x	1E5
mju x	0.20
from reaction	YZ
Y	flexible
stiff y	5E5
Z	flexible
stiff z	3.5E6