20.5.1 Element end release

Product: ABAQUS/Standard

References

Overview

Element end release:

allows a rotational degree of freedom or a combination of rotational degrees of freedom to be released at one or both ends of an element or element set;
can be used in geometrically linear or nonlinear analysis; and
is available only for beam and pipe elements in ABAQUS/Standard.

Introduction

Element end release is used to model hinged connections (hinged in one, two, or three orthogonal directions) at one or both ends of the element. By releasing rotational degrees of freedom, an element end is allowed to rotate freely relative to the node about the chosen degrees of freedom. Any rotational degrees of freedom that are not released are shared with the node.

Element end release operates on the element local degrees of freedom. See “Beam element cross-section orientation,” Section 15.3.4, for a definition of the local axes (, , ) for beam-type elements. The rotational degrees of freedom affected by the release are the rotation about the local -axis, the rotation about the local -axis, and the rotation about the local -axis for beams in space. For beams in a plane, only the rotation about the local -axis is active (which coincides with rotations about the negative global -axis).

Equivalent MPCs

If only one rotational degree of freedom is released, the kinematic constraint is equivalent to MPC type REVOLUTE plus MPC type PIN between two nodes. If two rotational degrees of freedom are released, the kinematic constraint is equivalent to MPC type UNIVERSAL plus MPC type PIN. If all rotational degrees of freedom are released, the kinematic constraint is equivalent to MPC type PIN. See “General multi-point constraints,” Section 20.2.2, for details.

Identifying the element end involved in the release

Either element sets or individual elements can be specified for a release definition. Degrees of freedom can be released at the first, second, or first and second ends of an element. The first end of the element, S1, is node 1 on the element as defined by the element connectivity; the second end, S2, is the last node (node 2 or 3, as appropriate) on the element. See “Beam element library,” Section 15.3.8, for a definition of the node ordering for beam elements.

Identifying the local rotational degrees of freedom involved in the release

Rotation combination codes rather than degrees of freedom are specified to identify the rotational degrees of freedom involved in the release.

M1 refers to the rotation about the -axis,

M2 refers to the rotation about the -axis,

M1-M2 refers to a combination of rotational degrees of freedom about the -axis and the -axis,

T refers to the rotation about the -axis,

M1-T refers to a combination of rotational degrees of freedom about the -axis and the -axis,

M2-T refers to a combination of rotational degrees of freedom about the -axis and the -axis, and

ALLM represents a combination of all the rotational degrees of freedom (i.e., M1, M2, and T).

Input File Usage:	RELEASE element number or element set, element end ID, release combination code*
	For example, to release the rotational degree of freedom about the -axis at the first end of element 10 and all the rotational degrees of freedom at the second end of the element, use the following input: *RELEASE 10, S1, M1 10, S2, ALLM

Use with transformed coordinate systems

Transformations applied to released nodes (“Transformed coordinate systems,” Section 2.1.5) have no influence on the release. The release operates on the local degrees of freedom for the element.

Reading the data from an alternate input file

The data for a release definition can be contained in a separate input file.

Input File Usage:	RELEASE, INPUT=file_name*
	If the INPUT parameter is omitted, it is assumed that the data lines follow the keyword line.