Element End Release

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.

The following topics are discussed:

Introduction
Identifying the element end involved in the release
Identifying the local rotational degrees of freedom involved in the release
Use with transformed coordinate systems
Reading the data from an alternate input file

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. You must be careful not to release a given degree of freedom at a node for all elements that share that node; otherwise, the node has no stiffness for that degree of freedom and Abaqus/Standard issues zero pivot warning messages.

Element end release operates on the element local degrees of freedom. See Beam element cross-section orientation for a definition of the local axes ( $n_{1}$ , $n_{2}$ , t) for beam-type elements. The rotational degrees of freedom affected by the release are the rotation about the local $n_{1}$ -axis, the rotation about the local $n_{2}$ -axis, and the rotation about the local t-axis for beams in space. For beams in a plane, only the rotation about the local $n_{1}$ -axis is active (which coincides with rotations about the negative global z-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 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 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 $n_{1}$ -axis,
M2: refers to the rotation about the $n_{2}$ -axis,
M1-M2: refers to a combination of rotational degrees of freedom about the $n_{1}$ -axis and the $n_{2}$ -axis,
T: refers to the rotation about the t-axis,
M1-T: refers to a combination of rotational degrees of freedom about the $n_{1}$ -axis and the t-axis,
M2-T: refers to a combination of rotational degrees of freedom about the $n_{2}$ -axis and the t-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 $n_{1}$ -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) 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.