A member hinge limits the internal forces and moments that are transferred from one member to others. Hinges can only be arranged at member ends, not at locations along the member.
Some member types are already provided with hinges: A truss, for example, does not transfer moments, and a cable member transfers neither moments nor shear forces. It is impossible to assign any hinges to such member types. The input is blocked.
Base
The Main tab manages the basic hinge parameters.
Coordinate system
A member hinge can be related to one of the following axis systems:
- Local member axis system x,y,z
- Global coordinate system X,Y,Z (optionally as a scissors hinge)
- User-defined axis system U,V,W
Generally, hinges are related to the local member axis system. However, scissor hinges (see the image Member Crossing) are only possible in the global or a user-defined axis system.
Hinge Conditions
The hinge conditions are divided into 'Translational' and 'Rotational' degrees of freedom. The former describe the displacements in the direction of the local or global axes; the latter describe the rotations about these axes.
To define a hinge, tick the check box for the respective axis. The check mark indicates that the member's displacement in or rotation about the corresponding direction is possible. The constant of the translational or rotational spring is then set to zero. You can adjust the 'Spring constant' anytime in order to model an elastic hinge. Enter the spring stiffnesses as design values.
In the 'Nonlinearity' column, you can specifically control the transfer of internal forces and moments for each component. Depending on the degree of freedom, suitable entries are available for selection in the list of nonlinearities.
Fixed if internal force is negative or positive
This allows you to control easily whether only positive or negative forces or moments are transferred at the member end. For example, a ux-hinge with a 'Fixed if positive N' nonlinearity has the effect that tension forces (positive) can and compression forces (negative) cannot be transferred at the member end. Thus, the hinge is effective for negative axial forces.
In the case of a local coordinate system, the internal forces and moments refer to the local xyz-member axis system.
When you select a different nonlinearity, you can define the parameters in the Partial Activity, Diagram, Friction or Scaffolding Diagram tabs.
Options
A 'Scissor hinge' is available in the global or user-defined coordinate system. This kind of hinge allows you to model intersections of continuous members.
Example
Four members are connected to a node. The members transfer moments in their "continuous direction", but not to the other member pair. Only axial and shear forces are transferred in the node.
Assign the hinge either to members 3 and 4, or to members 1 and 2. The other crossing member pair does not receive a hinge.
Partial Activity
The Partial Activity of a hinge component is available as a nonlinear property of the member hinge (see the image Selecting Hinge Nonlinearity).
Define the effect of the hinge for both the 'Negative Zone' and the 'Positive Zone'. The 'Type' list offers various criteria for the effectiveness of the hinge.
- Complete: Due to the hinge, displacement or rotation is possible to the full extent.
- Fixed from release displacement/rotation: The hinge is only effective up to a certain displacement or rotation. If the limit is exceeded, a fixed connection or restraint becomes effective.
- Tearing from release force/moment: The hinge is effective only up to a certain force or moment. If the limit is exceeded, the hinge fails and no longer transfers the internal force or moment.
- Yielding from release force/moment: The hinge is effective only up to a certain force or moment. If it is exceeded, the strains still increase, but not the internal force or moment.
- Spring ineffectiveness: In the case of a hinge with spring stiffness, the hinge component is not effective.
Most hinge types can be combined with a 'Slippage', which means that the hinge becomes effective only after a certain displacement or rotation.
Graph
The Diagram of a hinge component is available as a nonlinear property of the hinge (see the image Selecting Hinge Nonlinearity).
Define the number of definition points for the work diagram by entering the corresponding values in the 'Displacement' or 'Rotation' column. Then, in the 'Force' or 'Moment' column, you can assign the x-coordinates of the displacements or rotations with the hinge forces or moments.