SPTS − Spring element at point

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SPTS

Item Description Unit Default

NO REF TYPE

Spring number

number of 2nd reference point Type / direction of spring

CX, CY, CZ local X, Y, Z CXX, CYY, CZZ global X, Y, Z C explicit direction (DX, DY, DZ)

or direction to reference point

−

stiffness in axial direction transversal stiffness

X−component of explicit direction Y−component of explicit direction Z−component of explicit direction group number

number of stress−strain curve / material reference area

friction coefficient for lateral spring cohesion value for lateral spring dilatation value for lateral spring

[kN]₁₀₂₈ This record defines beddings or spring elements on a structural point. For a given structural point SPT multiple subsequent records of type SPTS can be entered allowing to create an arbitrary number of springs, which, for example, can be as-signed to different groups. Spring elements can be defined as beddings to a fixed support or relatively to another structural point.

The stiffness of a spring element can be basically defined with three parameters:

CA to CM. The first parameter CA describes an axial stiffness along the principal direction of the spring. The second parameter CQ describes a stiffness compon-ent acting in the whole plane perpendicular to the axial direction. Mechanically, this stiffness corresponds to two identical axial springs lying orthogonal to each other within the plane. Since the direction of these springs inside the plane can be chosen arbitrarily, this component is also denoted as isotropic lateral spring stiffness. The third parameter CM describes the rotational stiffness about the prin-cipal spring axis.

The axial and lateral spring stiffness as well as the nonlinear parameters CRAC, YIEL and COH are given as bedding stiffness per area (e.g. kN/m/m²). These stiff-ness values will be scaled by the given reference area AR, resulting in a spring element with point support stiffness (kN/m). If nothing is given for AR the stiffness values will be directly taken as point stiffness value.

A spring can have a number and can be assigned to a group. If the identifier of a second structural point is given at REF the spring is created between the given and the referenced structural point.

The direction of the spring can be defined as follows:

• Along the local coordinate system of the structural point

Each structural point contains a local coordinate system, which can be set explicitly at the structural point record SPT. By setting CX, CY, or CZ at parameter TYPE, the spring can be aligned to one of this local coordinate directions.

• Along one of the global X,Y,Z − coordinate axes

If CXX, CYY or CZZ is given at TYPE, the spring is oriented, indepenently of the structural point, toward one of the global X, Y, or Z− coordinate axes, respectively.

• Along an explicitly given direction vector at DX, DY, DZ

A spring can also be aligned arbitrarily by setting a direction at DX, DY, DZ.

• Distance between point and reference point

For a spring, connecting the point with a reference point, the direction to the reference point is taken as axial direction in the case, that no different settings have been given.

In the case that no direction is given at all, the spring is aligned with the local z−axis of the structural point.

Different stiffness values in lateral direction cannot be defined within one single record of type SPTP. However, multiple records can be given in order to create springs aligned perpendicular to each other. Using value lists, CADINP allows to handle this case efficiently. For example: SLNS TYPE CX,CY,CZ CP 1000.0, 2000.0, 3000.0 creates three orthogonal springs having each different stiffness values of 1000.0, 2000.0 and 3000.0, respectively.

Using the parameter PRE, prestress can be activated within the spring. In its initial position at rest, the spring already exerts a force or a moment (if only CM is given) into or about its direction. Prestress for the lateral component CQ cannot be defined.

At the parameters GAP, CRAC, YIEL, MUE, COH, DIL values like crack−, yield load or friction coefficients can be given in order to activate non−linear effects:

Prestress:

The failure and yield loads are shifted by the amount of the prestress.

Gap:

The spring transmits forces along its axis only after its deformation has ex-ceeded the gap.

Failure load:

Upon reaching the failure load the spring fails in both the axial and the lat-eral direction. The failure load is always a tensile force or a positive mo-ment.

Yield load:

Upon reaching the yield load, the deformation component of the spring in-creases in its direction, without a corresponding increase of the spring force.

Friction coefficient:

If a friction coefficient and/or a cohesion are input, the lateral spring can not sustain forces greater than:

Friction_coeff. · Compressive_force + Cohesion

For large tension forces or a failed axial spring (CRAC) the lateral force acts only if 0.0 has been input for both the friction coefficient and the cohe-sion.

General non−linear effects can be defined by referencing an arbitrary stress−

strain curve or a non−linear material at MNO. The number at MNO then refer-ences a work law or material which has been defined prior in AQUA. In the case that a material is being referenced, an influence area should be given at AR which scales the material bedding values accordingly in order to create the spring con-stants:

CP := Cb⋅AR [kN/m = kN/m²⋅m²/m]

CQ := Cq⋅AR

In the case that a dilatation value (DIL) is defined, a displacement in the lateral direction will generate a component in the axial direction.

See also: SPT