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# 4.20 Member Nonlinearities

General description

Member nonlinearities can be used to represent nonlinear relations between forces (or moment) and strains in members.

Some nonlinear properties can already be specified when defining the member type: A tension member, for example, is a truss for which the strain increases proportionally with the tension force, but whose strain may rise under compression without a verifiable force being required for it.

In principle, member nonlinearities can be assigned to any type of member. Of course, combinations have to make sense. A compression member with the design criterion "Failure under compression" would cause problems during the calculation. Member nonlinearities are therefore not allowed for tension members, compression members, buckling members, and cable members, as well as for members with cross-sections of the type Dummy Rigid.

Table 4.9 Member nonlinearities

Failure under tension

The member cannot absorb tensile forces.

Failure under compression

The member cannot absorb compressive forces.

Failure under tension
with slippage

The member cannot absorb tensile forces.
Compressive forces are not absorbed until the slippage ux is overcome.

Failure under compression
with slippage

The member cannot absorb compressive forces.
Tensile forces are not absorbed until the slippage ux is overcome.

Slippage

The member only absorbs axial forces after having exceeded a strain or shortening by the value ux.
Please note: A line refinement on a member with Slippage causes an internal member division into small member parts. The slippage criterion is applied to each of these partial members.

Tearing under tension

The member absorbs compressive forces without limitation, but fails if tensile forces exceed Nto.

Yielding under tension

The member absorbs compressive forces without limitation, but only a maximum tensile force of Nto.
If the strain increases, the tensile force remains constant in the member.

Tearing under compression

The member absorbs tensile forces without limitation but fails if compressive forces exceed Nfrom.

Yielding under compression

The member absorbs tensile forces without limitation, but only a maximum compressive force of Nfrom.
If the strain increases, the compressive force remains constant in the member.

Tearing

The member fails when the compressive force Nfrom or the tensile force Nto is reached.

Yielding

The member starts to yield if the compressive force Nfrom or the tensile force Nto is reached: If the strain increases, the force remains constant.

Plastic hinge

If a plastic design force is reached on a location of the member, a plastic hinge for the internal force is formed there.
The internal forces must be entered as absolute values. For components of internal forces not resulting in plastifications, you have to enter high values.