Beam Elements: Element Types

Description

Beam elements in Straus7 are two-noded elements with an optional third node that can be used as a reference node to align the principal axes. In Straus7, the term "beam" can refer to any of the types in the general class of line elements, including spring-damper, truss, cutoff bar, point contact, user-defined, pipe and connection.

Element Types

The principal 3-axis of both of these elements is always coincident with the beam's axial direction (i.e., in the direction of the vector from Node 1 to Node 2). See Beam Elements: Local and Principal Axes.

Beam2

Two-node beam element.

The principal axis orientation in the 1 and 2 directions is assigned automatically and can be adjusted by using tools such as Align Tools: Beam Axes to UCS or Beam Attributes: Principal Axis Angle.

Beam3

Three-node beam element.

The two end-nodes are used in the same way as in the Beam2 element, with a third reference node used to align the direction of the element's principal 2-axis.

The reference node of the Beam3 element can also be used to define a quadratic line for the purpose of modelling and meshing. For example, Tools: Extrude can make use of the reference node in the Beam3 to extrude the beam into a curved quadratic plate element.

Beam Types

Spring-Damper

Carries axial force, shear and torque. Axial and twist behaviour can be either linear or nonlinear. The damper properties are used only in transient dynamic analysis.

Cable

A special element based on a catenary formulation. Its advantage is that it can have a length that is different from the distance between the nodes. In addition, the length can be varied during analysis to simulate post-tensioning effects.

Truss

The element provides axial stiffness, and optionally torque stiffness. No bending stiffness is included.

Cutoff Bar

An axial truss element, without bending or twist stiffness. In nonlinear analysis, different limits of tension and compression cutoff can be assigned for either brittle or ductile failure when these limits are exceeded.

Point Contact

Used to model a gap between two surfaces. There are four types of point contact elements:

Zero Gap

Provides stiffness only in compression, and only when the distance between the nodes to which it is connected becomes zero (the gap closes).
Normal Gap

Equivalent to zero gap except that the gap need not be closed before stiffness is provided. The contact activation point may be varied by the application of a pre-strain attribute.
Tension Gap

Similar to the normal type, but it also provides stiffness in tension (up to a specified value).
Takeup

Used to simulate a takeup or ratchet device. Such a device resists relative movement in either tension or compression, but permits relative movement in the opposite direction.

Beam

A conventional beam element with six degrees of freedom at each node: three translations and three rotations. The beam carries axial force, torque, shear forces and bending moments in its principal planes. Supports thin or thick beam formulations (see Beam Elements: Thin and Thick Beam Formulation).

User-defined

Provides a general format for the direct input of the beam stiffness matrix, defining the translational stiffness, [A], the rotational stiffness, [C], and the coupling between the translational and rotational stiffness, [B]. The values in the [A], [B] and [C] matrices can be derived computationally from a macro model of the special beam-like structure with unit translations and rotations applied sequentially at end 1 whilst keeping all others are zero.

Pipe

A special version of a circular hollow beam that can be straight, or curved as a segment of a circular arc. The pipe element, like the beam element, has six degrees of freedom at each node: three translations and three rotations. The pipe carries axial force, shear force, bending moment and torque. Internal and external pressure, and internal and external temperature, can be applied. The cross section of a pipe element is circular with only the external diameter and wall thickness required to define the pipe section.

Connection

A general stiffness element that allows each of the six values of stiffness to be independently defined between the two nodes. The connection element does not behave like a standard beam element.