The Basis tab manages the basic member parameters. If you select a check box in the 'Options' section, another dialog tab is usually added. There, you can define the details.
Member Type
The member type controls how internal forces can be absorbed or which properties are assumed for the member. Various member types are available for selection in the list.
Beam Member
A beam is a bending-resistant member that can transfer all internal forces. A beam member has no hinges at its member ends. This member type can be loaded by all load types.
Rigid Member
A rigid member couples the displacements of two nodes via a rigid connection. It thus basically corresponds to a coupling. This allows you to define members with very high stiffness, taking into account hinges that can also have spring constants and nonlinearities. Numerical problems rarely occur because the stiffnesses are adapted to the system.
Internal forces are output for rigid members if you activate the Results for Couplings in the Navigator - Results at the bottom of the 'Members' category.
The following stiffnesses are applied for rigid members:
| Axial stiffness E · A | 1013 · ℓ [SI unit] with ℓ = member length |
| Torsional stiffness G · IT | 1013 · ℓ [SI unit] |
| Bending stiffness E · I | 1013 · ℓ3 [SI unit] |
| Shear stiffness GAy / GAz (if activated) | 1016 · ℓ3 [SI unit] |
Rib Member
Ribs can be used to model T-beams (downstand beams). For this member type, the eccentricities and effective flange widths are taken into account in the FEM model.
Ribs are mainly suitable for reinforced concrete members, as the rib internal forces and cross-sections flow into the concrete design. A steel plate with a welded-on "rib" should be modeled as a surface with an eccentrically connected member.
The list provides several options for the 'Rib arrangement'.
A rib is generally an eccentrically arranged member. The eccentricity is automatically determined from half the surface thickness and half the member height. However, it can also be defined manually. The eccentricity of the rib increases the stiffness of the model. In a centric arrangement, the centroidal axis of the rib lies in the center of the surface.
The effective widths of the rib are to be defined in the 'Flange dimensions' section for the left and right side. Usually, the 'Automatic detection' setting can be kept, with which the program determines the two surfaces. If more than two surfaces meet at the line of the rib member, the defining surfaces must be specified manually.
There are various options for entering the integration widths b-y,int and b+y,int (see image New Rib): The widths can be entered directly or determined automatically from the member length with the options Lref / 6 and Lref / 8. They can also be determined according to the specifications of a standard, for example, according to 'EC2' Section 5.3.2.1.
The by,int values define the width of the surface or the integration area from which the internal forces are to be integrated. The by,eff values represent the cross-sectional width of the rib flange from the web center to the respective edge. By default, by,int and by,eff are set to the same value. However, you can define them separately by clicking the
button.
If nodes of the type 'Nodes on Member' have been defined, the rib can be defined in segments for the individual segments. If several segments are defined, the staggered width areas can be linearly connected via the 'Linear Distribution' table column to prevent large stiffness jumps in the rib member.
In 3D models, the effective widths have no influence on the stiffness, as the increased stiffness is taken into account by the eccentric member. However, the effective widths affect the distribution of the member and surface internal forces.
Truss Member
A truss member corresponds to a beam member with moment hinges at both ends. Additionally, the rotation about the longitudinal axis at the member start is released by a hinge φx. For this member type, bending and torsional moments from the member loads are output.
Truss Member (only N)
This type of truss member with stiffness E ⋅ A can absorb axial forces in the form of tension and compression. Only node internal forces are output. The member has a linear internal force distribution, provided no concentrated load acts on the member. No moment distribution that could arise due to self-weight or a line load is output. However, the node forces are calculated from the member loads, ensuring correct transfer.
Buckling-Restrained Brace
The Buckling-restrained brace type allows the modeling of a member with a steel core (flat steel or cruciform cross-section) and a concrete-filled casing in a square or round hollow section. It is used particularly in the USA for stiffening buildings at risk of earthquakes.
The steel core can move in the concrete casing without bond. Under compression, "micro-buckling" with high eigenmodes occurs because the casing prevents global buckling of the entire member.
Only the steel core is considered for the stiffness of the member; for the automatic self-weight, the concrete casing with the outer steel shell is also considered.
Tension Member
A tension member can only absorb tensile forces. The member type corresponds to a 'Truss Member (only N)' that fails under a compressive force.
The calculation of a framework with tension members is iterative: In the first step, the internal forces of all members are determined. If tension members receive a negative axial force (compression), another iteration step starts. The stiffness contributions of these members are no longer considered – they have failed. This process continues until no tension member fails. A system can become unstable due to the failure of tension members.
Compression Member
A compression member can only absorb compressive forces. The member type corresponds to a 'Truss Member (only N)' that fails under a tensile force. Failing compression members can lead to an unstable system.
Buckling Member
A buckling member corresponds to a 'Truss Member (only N)' that absorbs unlimited tensile forces but only compressive forces up to the critical force. For Euler case 2, this force is determined as follows:
This member type can often be used to avoid instabilities that arise from the buckling of truss members in a nonlinear calculation according to second-order or large deformation analysis. Replacing these (realistically) with buckling members increases the critical load in many cases.
Cable Member
A cable can only be subjected to tension. This allows cable chains to be analyzed by an iterative calculation according to the large deformation analysis, taking longitudinal and transverse forces into account.
Cables are suitable for models where large deformations with corresponding changes in internal forces can occur. For simple bracing, such as on a canopy, tension members are perfectly adequate.
Reinforcement Bar
This member type allows you to model slack steel reinforcements in the FE model of a reinforced concrete element. For example, discontinuity regions based on the strut-and-tie model (tension and compression strut for corbels, beams with openings) can be investigated.
The reinforcement bar has an automatic connection function to other elements such as members or surfaces if it is physically located within the element. Like the Truss Member (only N), a reinforcement bar only has tangential stiffness. Nonlinear material behavior is not yet possible.
In the 'Settings' section, a slack reinforcement is set as the member type. Other reinforcement bar types are available if the Tendons add-on is activated.
In the 'Master Objects' section, assign the members or surfaces in which the reinforcement bar lies. Use the
button for this. You can then automatically connect the reinforcement bar to the master object using the
button.
Cable on Pulleys
This cable member type also only absorbs tensile forces and is calculated according to cable theory (large deformation analysis). A cable member on pulleys, however, can only be defined on a polyline that has at least three nodes. This member type is therefore suitable for flexurally slack tension elements whose longitudinal forces are guided through the model via deflection points. An application example is a pulley block.
In contrast to a normal cable member, only displacement in the inner nodes in the longitudinal direction (ux) is possible. The member must therefore not be loaded by member loads acting in the local y or z direction. Only displacements ux and axial forces N are considered.
At the inner nodes of the polyline, it is irrelevant whether a nodal support exists or whether the member is connected to another structure: The entire system of the cable member is analyzed over the length of the polyline.
Result Beam
The result beam is suitable for integrating surface, solid, or member results into a fictitious member. This allows you, for example, to read the resulting shear forces of a surface for the masonry design.
The line of a result beam can be placed anywhere in the model. The result beam requires neither a support nor a connection to the model. However, a cross-section must be assigned to enable a design. No loads can be applied to a result beam.
In the 'Integrate Stresses and Forces' section, select the type of result beam to define the geometric shape of the integration area. In the 'Parameters' section, you can then define the dimensions. They are related to the line of the member in its centroid.
In the 'Include Objects' section, define the surfaces, surface cells, solids, and members whose results are to be considered during integration. Alternatively, select 'All' objects and then exclude certain elements in the 'Excepted from Inclusive Objects' section.
Result Line
The result line is suitable for integrating surface, solid, or member results in a line. This line can be placed anywhere in the model.
The principle corresponds to a Result Beam. However, you do not need to assign a cross-section. In the 'Cross-section' tab, you can read the length of the line and, if necessary, rotate the line for the result display; it has no further function.
Load Transfer
This member type allows loads to be applied to objects that are connected to the member at end or intermediate nodes. The member itself has no stiffness. You can define the criteria for the load transfer in a new tab.
Load transfer is currently performed using the stripe method. The loading of the load transfer member – member load or node load of the Force, Moment, or Mass type – is transferred proportionally to the nearest common structural objects. These are, for example, supported nodes, members, nodes of surfaces, or supported lines.
If the self-weight of the member is to be considered, you can define the member weight in the 'Parameters' section.
In the 'Loaded Objects' section, the numbers of the nodes to which the member load is transferred to the adjoining objects are specified. If not all of these nodes are relevant, you can exclude certain nodes in the 'Without Effect on' section.
Virtual Joist
This member type allows you to apply the cross-section properties for Open Web Steel Joists, which the Steel Joist Institute has stored in so-called "Virtual Joist" tables. These Virtual Joist profiles represent equivalent wide flange beams that closely approximate the chord area, effective moment of inertia, and weight. The joist is thus replaced by a member with a virtual cross-section. This allows complex supporting units, such as a truss girder, to be simulated in the overall system.
In the list, select the 'Series' of the virtual joist.
You can then define the exact type in the 'Virtual Joist' list.
The
button in the 'Cross-section and Material' section allows you to import the virtual joist from the cross-section library.
Surface Model
This member type is primarily suitable for modeling cellular and castellated beams or local cross-section reductions such as openings for utility lines in the member model. The member is converted into a surface model in which the Member Openings are arranged according to user specifications. However, the member is retained. The following conditions must be met:
- The cross-section represents a standardized or parameterized thin-walled profile with a web.
- The material of the cross-section is based on an isotropic linear-elastic material model.
For the 'Surface Model' member type, the member exists as both a member and a surface object. The geometric properties are identical; both models have the same centroid. The display is controlled in the Navigator - Display via the entry Model → Basic Objects → Members → Surface Model or the
button in the toolbar.
The FE mesh of the surface model is generated automatically; it cannot be influenced currently. The surface model is used for the static calculation. Both the member results are then available for evaluation (as for a Result Beam, where the stresses of the member partial surfaces are integrated into member internal forces) and the surface results. The control can also be made here via the Navigator - Display or the
button.
The design of a surface model member in the add-ons is performed with the member internal forces and the member cross-section.
As can be seen in the image above, several rigid members are created at the member ends of a surface model member. They connect the surface model to the end nodes of the adjoining members. This ensures the correct transfer of the internal forces to the 1D objects. If several surface model members are adjacent to each other, these coupling members are generated for each member.
In this case, define a Force Eccentricity on the cross-section for the member load. The load is thus realistically applied at the cross-section edge and is also retained in the surface model.
Stiffness
With this member type, you can use a member with user-defined stiffnesses. The stiffness parameters are to be defined in the 'New Member Stiffness' dialog (see chapter Member Stiffnesses).
Coupling
A coupling member is a virtual, very stiff member with rigid or hinged member ends. Four options are available for coupling the degrees of freedom of the start and end nodes as 'Rigid' or via a 'Hinge'. Couplings can be used to model special situations for force and moment transfer. The axial and shear forces or torsional and bending moments are transferred directly from node to node.
Spring
A spring member offers the possibility of modeling linear or also nonlinear spring properties with definable effective ranges. For a spring member, you only need to define the member length Lz in the 'Cross-section' tab, not a cross-section: The stiffness of the member results from the spring parameters that you define in the 'New Member Spring' dialog (see chapter Member Springs).
Damper
A damper corresponds in principle to a spring member with the additional property 'Damping Coefficient'. This member type expands the possibilities for dynamic analyses according to the Time History Analysis.
As with a spring member, you only need to define the member length Lz in the 'Cross-section' tab, not a cross-section. The stiffness of the member results from the spring parameters that you define in the 'New Member Spring' dialog (see chapter Member Springs). You can control the damping properties via the damping coefficient X.
Options
In this section, you can define further member properties via the check boxes.
Nodes on Member
With one or more nodes on the member, you can divide the member into segments without dividing the member (see chapter Nodes).
Hinges
You can arrange hinges on a member to control the transfer of internal forces at the end nodes (see chapter Member Hinges). For certain member types, the input is locked because internal hinges already exist. You can assign hinges separately to the 'Member start i' and the 'Member end j'.
Eccentricities
Eccentricities offer the possibility of connecting the member eccentrically at the end nodes (see chapter Member Eccentricities). You can assign eccentricities separately to the 'Member start i' and the 'Member end j'.
Supports
You can assign a support to the member that is effective over its entire length. The degrees of freedom and spring stiffnesses are to be defined in the support conditions (see chapter Member Supports).
Transverse Stiffeners
Transverse stiffeners on the member have an influence on the warping stiffness of the member. They affect the calculation with torsional warping taking into account seven degrees of freedom (see chapter Member Transverse Stiffeners).
Member Openings
Member openings affect the cross-section properties and the internal force distribution. They are relevant for the 'Surface Model' member type. Chapter Member Openings describes how you can define the type and position of the openings.
Nonlinearity
You can assign a nonlinearity to the member. The nonlinear properties are to be defined as member nonlinearities (see chapter Member Nonlinearities).
Result Intermediate Points
With result intermediate points, you can control the table output of the results along the member. The division points are to be defined in the 'New Member Result Intermediate Point' dialog (see chapter Member Result Intermediate Points).
End Modifications
With end modifications, you can graphically adapt the geometry of the member at its ends. This allows you to prepare overhangs, shortenings, or bevels for the rendered display.
'Extension': You can define an 'Extension' for the member start and the member end each. A negative value Δ acts as a shortening.
'Slope': With a slope, you can bevel each member end. Slope angles about the two member axes y and z are possible. A positive angle causes a clockwise rotation about the respective positive axis.
Activate Load Transfer
The check box allows the load of the member to be distributed – independently of the stiffness of the member – using a load transfer. Thus, the member is effective in the model through its stiffness. The distribution of the load to the neighboring objects, on the other hand, is controlled via the parameters that you can define in the Load Transfer tab.
Deactivate for Calculation
If you select this check box, the member including loading is not considered in the calculation. In this way, you can investigate how the structural behavior of the model changes when certain members are not effective. The members do not need to be deleted; the loads are also retained.
