Structural elements
The structures contain two basic types of elements: Joints (nodes) and members. Joints are divided into absolute and relative ones.
Absolute joints
Absolute joints are spaceless points in a plane, that represent individual connections of structural members. The position is given by absolute (aren't depending on any other object) coordinates in global coordinate system.
Absolute joints in "Fin 3D" have six degrees of freedom (3 movements and 3 rotations), any of these degrees can be eliminated by support (or reduced by spring support). The supports can be defined both in the global coordinate system or in the coordinate systems of joints.
Absolute joints in "Fin 2D" have three degrees of freedom (2 movements and 1 rotation), any of these degrees can be eliminated by support (or reduced by spring support). Joint supports can be defined in the global coordinate system or according to the joint rotation.
Members
The members are structural elements that connect joints in the structure. From geometric point of view, members are oriented line segments given by two joints. The member has reference beginning and end joints. The axis 1 of local coordinate system is defined by the orientation of the line from beginning to end joint.
Cross-sectional and material characteristics have to be assigned to any member. The cross-sectional characteristics may be defined with the help of the pre-defined database, manually or with the help of external program (programs "Section" or "Sector"). In a similar ways, material characteristics may be specified.
Next attribute is the member type. Two basic types are included: "Beam" and "Beam on elastic subsoil". The "Beam" is the fundamental member type locally supported in joints, "Beam on elastic subsoil" is the member, that is supported along the whole length by a subsoil (e.g. foundations).
The connection at the beginning and end is given by end conditions. Both connections have 6 degrees of freedom (3 movements and 3 rotations) in "Fin 2D" or 3 degrees of freedom (2 movements and 1 rotation) in "Fin 2D". Any of these degrees can be switched on/off or converted into spring connection. When switching off, the occurrence of mechanism may appear.
The advanced characteristics are marked as "Special" in the software. These characteristics contain the consideration of shear effect on deformation, excluded tension or compression, warping parameters at the reference joints. These parameters are described in the chapter "Special member characteristics".
Relative joints
Relative joints aren't given by the coordinates in the global coordinate system. They have the position specified relatively to the reference member. The position on member is given by the distance from the beginning or end joint of the member. The distance may be specified in length unit (metres) or in a proportional unit. The joints may be placed between beginning and end joints of the member or may lie outside this segment and extend the member length.
The relative joints may be supported in the same way as absolute joints. The identical is also number of degrees of freedom. The supports may be specified both in the global coordinate system and in the coordinate systems of joints.
The relative joints are used for connections of members to the point placed on the other member (typically connection of webs to chords). They may be also used for display of results in given position.
Scissor joint is a special type of relative joint, as it has two reference members. The position of such joint is given by the intersection of these reference members. This joint creates hinged connection of intersecting members.