Member Hinges

A member hinge limits the internal forces that are transferred from one member to other members. Hinges can only be arranged at the member ends, not at locations along the member.

Some member types are already equipped with hinges: a truss member, for example, does not transfer any moments, and a cable member transfers neither moments nor shear forces. You cannot assign hinges to such member types. The input is locked.

Dialog Box "New Member Hinge"

Basic

The Basic tab manages elementary 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 scissor hinge)
• User-defined axis system U,V,W

As a rule, the hinges are related to the local member axis system. Scissor hinges (see image Member crossing), however, are only possible in the global or a user-defined axis system.

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Selecting Hinge Nonlinearity 

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Fixed if internal force negative or positive

This allows you to easily control whether only positive or negative forces or moments are transferred at the member end. A u_x hinge with the nonlinearity 'Fixed if N positive', for example, means that tensile forces (positive) but no compressive forces (negative) are transferred at the member end. For negative axial forces, a hinge is thus effective.

In the case of a local coordinate system, the internal forces are related to the local xyz member axis system.

If you select a different nonlinearity, you can define the parameters in the Partial activity, Diagram, Friction, or Scaffolding diagram tabs.

Options

The 'Scissor hinge' is available in the global or user-defined coordinate system. This allows you to model the crossing of continuous members.

Example

Four members are connected at a node. The members transfer moments in their "continuation direction," but not to the other pair of members. Only axial and shear forces are transferred at the node.

Member Crossing with Scissor Hinge

Assign the hinge either to members 3 and 4 or to members 1 and 2. The other crossing pair of members is not assigned a hinge.

Partial Activity

The Partial activity of a hinge component is available as a nonlinear property of the member hinge (see image Selecting hinge nonlinearity).

Defining Partial Activity of Hinge

Define the activity of the hinge for the 'Negative zone' as well as for the 'Positive zone'. In the 'Type' list, various criteria are available for selecting the effectiveness of the hinge.

• Complete: The displacement or rotation is fully possible through the hinge.
• Fixed from release displacement/release rotation: The hinge is only effective up to a certain displacement or rotation. If exceeded, a rigid connection or restraint becomes effective.
• Cracking from release force/release moment: The hinge is only effective up to a certain force or moment. If exceeded, the hinge fails and no longer transfers the internal force.
• Yielding from release force/release moment: The hinge is only effective up to a certain force or moment. If exceeded, the strains increase, but the internal force no longer does.
• Spring failure: For a hinge with spring stiffness, the component of the hinge is not effective.

Most hinge types can be combined with a 'Slippage', whereby the hinge only becomes effective after a certain displacement or rotation.

Diagram

The Diagram of a hinge component is available as a nonlinear property of the hinge (see image Selecting hinge nonlinearity).

Defining Stiffness Diagram

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Friction

In the 'Nonlinearity' list, four options are available for defining the friction of a translational hinge as a function of another hinge component (see image Selecting hinge nonlinearity).

Defining Friction Coefficients

The transferred hinge forces are set in relation to the axial or shear forces acting in another direction. Depending on the selection in the 'Basic' tab, the friction depends on only one or on two internal forces. The following relationship exists between the hinge friction force and the axial force or shear force:

Plastic

Plastic hinge properties are important for pushover analyses. For the Plastic option of a nonlinear hinge component, four options are available (see image Selecting hinge nonlinearity):

• Bilinear
• Diagram
• FEMA 356 | Rigid
• FEMA 356 | Elastic

1. banner.textyield' and 'δ / δ_yield' or 'φ / φ_yield', define the parameters of the plastic zones. For a value of M_y / M_y,yield of, for example, 1.27, the cross-section begins to yield once the plastic moment is exceeded. If 127% of the ultimate limit state is exceeded, the member fails. The plastic limit internal forces are determined automatically from the cross-section properties of the member. The member length affects the stiffness calculation of the plastic hinge. As a rule, it is automatically recognized from the lengths of the members to which the hinge is assigned. If necessary, you can specify a 'User-defined member length' for the hinge. ==== Acceptance Criteria ==== In the lower section, you can define the limit values of the yielding criteria that are to apply to the safety of the building. For steel components, these are regulated, for example, in Table 5-5 of the ASCE standard FEMA 356 [[#Refer [1]]]. For a value of φ / φ_yield of 6.000, the critical value for 'life safety' is reached as soon as the plastic deformations become six times greater than those that occur when the yield strength is reached. The ranges of the acceptance criteria are also shown in the diagram. For one of the two plastic FEMA options, the acceptance criteria are preset according to the specifications of the US standard. If required, you can adjust them by selecting the 'User-defined' check box. HIDDENSTART_IMAGE_E12A5412284A4B7E8D39F251CE13D9EC_HIDDENEND In the list, define the 'Component type'. The acceptance criteria for primary and secondary components are regulated in [[#Refer [1]]] Table 5-5. The technical article [[#/de/support-und-schulungen/support/knowledge-base/001783 Plastic hinges in RFEM 6]] describes how to use a plastic hinge for a pushover analysis. #banner.tipThe acceptance criteria are also displayed in color for the member internal forces (see image HIDDENSTART_EXTBOOKMARK_03A056E82226408F9D04A4C461B135CA_HIDDENEND). This allows you to quickly check in which plastic zone the results lie. #/ scaffoldingDiagramInnerTubeTab">

Scaffolding Diagram

The Scaffolding diagram of a hinge component is available as a nonlinear property of the hinge (see image Selecting hinge nonlinearity). This allows you to model the mechanical effect of a plugged tube connection with an inner tube stub between two members. The substitute model transfers – depending on the compressive state at the member end – the bending moment via the pressed outer tube and, due to positive locking, additionally via the inner tube stub.

You can describe the hinge properties separately in the 'Scaffolding diagram | Inner tube' and 'Scaffolding diagram | Outer tube' tabs.

Defining Scaffolding Diagram for Outer Tube

1. banner.text@For the nonlinearity type 'Scaffolding | Nφ_yφ_z', the translational component u_x is coupled with the rotational components φ_y and φ_z.
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The options presented in the Diagram section are available for defining the parameters.