Karamba3D v2
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English 英文
  • Welcome to Karamba3D
  • New in Karamba3D 2.2.0
  • See Scripting Guide
  • See Manual 1.3.3
  • 1: Introduction
    • 1.1 Installation
    • 1.2 Licenses
      • 1.2.1 Cloud Licenses
      • 1.2.2 Network Licenses
      • 1.2.3 Temporary Licenses
      • 1.2.4 Standalone Licenses
  • 2: Getting Started
    • 2 Getting Started
      • 2.1: Karamba3D Entities
      • 2.2: Setting up a Structural Analysis
        • 2.2.1: Define the Model Elements
        • 2.2.2: View the Model
        • 2.2.3: Add Supports
        • 2.2.4: Define Loads
        • 2.2.5: Choose an Algorithm
        • 2.2.6: Provide Cross Sections
        • 2.2.7: Specify Materials
        • 2.2.8: Retrieve Results
      • 2.3: Physical Units
      • 2.4: Quick Component Reference
  • 3: In Depth Component Reference
    • 3.0 Settings
      • 3.0.1 Settings
      • 3.0.2 License
    • 3.1: Model
      • 3.1.1: Assemble Model
      • 3.1.2: Disassemble Model
      • 3.1.3: Modify Model
      • 3.1.4: Connected Parts
      • 3.1.5: Activate Element
      • 3.1.6: Line to Beam
      • 3.1.7: Connectivity to Beam
      • 3.1.8: Index to Beam
      • 3.1.9: Mesh to Shell
      • 3.1.10: Modify Element
      • 3.1.11: Point-Mass
      • 3.1.12: Disassemble Element
      • 3.1.13: Make Beam-Set 🔷
      • 3.1.14: Orientate Element
      • 3.1.15: Dispatch Elements
      • 3.1.16: Select Elements
      • 3.1.17: Support
    • 3.2: Load
      • 3.2.1: General Loads
      • 3.2.2: Beam Loads
      • 3.2.3: Disassemble Mesh Load
      • 3.2.4: Prescribed displacements
    • 3.3: Cross Section
      • 3.3.1: Beam Cross Sections
      • 3.3.2: Shell Cross Sections
      • 3.3.3: Spring Cross Sections
      • 3.3.4: Disassemble Cross Section 🔷
      • 3.3.5: Eccentricity on Beam and Cross Section 🔷
      • 3.3.6: Modify Cross Section 🔷
      • 3.3.7: Cross Section Range Selector
      • 3.3.8: Cross Section Selector
      • 3.3.9: Cross Section Matcher
      • 3.3.10: Generate Cross Section Table
      • 3.3.11: Read Cross Section Table from File
    • 3.4: Joint
      • 3.4.1: Beam-Joints 🔷
      • 3.4.2: Beam-Joint Agent 🔷
      • 3.4.3: Line-Joint
    • 3.5: Material
      • 3.5.1: Material Properties
      • 3.5.2: Material Selection
      • 3.5.3: Read Material Table from File
      • 3.5.4: Disassemble Material 🔷
    • 3.6: Algorithms
      • 3.6.1: Analyze
      • 3.6.2: AnalyzeThII 🔷
      • 3.6.3: Analyze Nonlinear WIP
      • 3.6.4: Large Deformation Analysis
      • 3.6.5: Buckling Modes 🔷
      • 3.6.6: Eigen Modes
      • 3.6.7: Natural Vibrations
      • 3.6.8: Optimize Cross Section 🔷
      • 3.6.9: BESO for Beams
      • 3.6.10: BESO for Shells
      • 3.6.11: Optimize Reinforcement 🔷
      • 3.6.12: Tension/Compression Eliminator 🔷
    • 3.7: Results
      • 3.7.1: ModelView
      • 3.7.2: Deformation-Energy
      • 3.7.3: Element Query
      • 3.7.4: Nodal Displacements
      • 3.7.5: Principal Strains Approximation
      • 3.7.6: Reaction Forces 🔷
      • 3.7.7: Utilization of Elements 🔷
        • Examples
      • 3.7.8: BeamView
      • 3.7.9: Beam Displacements 🔷
      • 3.7.10: Beam Forces
      • 3.7.11: Node Forces
      • 3.7.12: ShellView
      • 3.7.13: Line Results on Shells
      • 3.7.14: Result Vectors on Shells
      • 3.7.15: Shell Forces
      • 3.7.16 Results at Shell Sections
    • 3.8: Export 🔷
      • 3.8.1: Export Model to DStV 🔷
      • 3.8.2 Json / Bson Export and Import
    • 3.9 Utilities
      • 3.9.1: Mesh Breps
      • 3.9.2: Closest Points
      • 3.9.3: Closest Points Multi-dimensional
      • 3.9.4: Cull Curves
      • 3.9.5: Detect Collisions
      • 3.9.6: Get Cells from Lines
      • 3.9.7: Line-Line Intersection
      • 3.9.8: Principal States Transformation 🔷
      • 3.9.9: Remove Duplicate Lines
      • 3.9.10: Remove Duplicate Points
      • 3.9.11: Simplify Model
      • 3.9.12: Element Felting 🔷
      • 3.9.13: Mapper 🔷
      • 3.9.14: Interpolate Shape 🔷
      • 3.9.15: Connecting Beams with Stitches 🔷
      • 3.9.16: User Iso-Lines and Stream-Lines
      • 3.9.17: Cross Section Properties
    • 3.10 Parametric UI
      • 3.10.1: View-Components
      • 3.10.2: Rendered View
  • Troubleshooting
    • 4.1: Miscellaneous Questions and Problems
      • 4.1.0: FAQ
      • 4.1.1: Installation Issues
      • 4.1.2: Purchases
      • 4.1.3: Licensing
      • 4.1.4: Runtime Errors
      • 4.1.5: Definitions and Components
      • 4.1.6: Default Program Settings
    • 4.2: Support
  • Appendix
    • A.1: Release Notes
      • Work in Progress Versions
      • Version 2.2.0 WIP
      • Version 1.3.3
      • Version 1.3.2 build 190919
      • Version 1.3.2 build 190731
      • Version 1.3.2 build 190709
      • Version 1.3.2
    • A.2: Background information
      • A.2.1: Basic Properties of Materials
      • A.2.2: Additional Information on Loads
      • A.2.3: Tips for Designing Statically Feasible Structures
      • A.2.4: Hints on Reducing Computation Time
      • A.2.5: Natural Vibrations, Eigen Modes and Buckling
      • A.2.6: Approach Used for Cross Section Optimization
    • A.3: Workflow Examples
    • A.4: Bibliography
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On this page
  • Modify Beam
  • Activation status of beams
  • Bending stiffness
  • Height and Thickness of Cross-sections
  • Local and Global Eccentricity of the Beam Axis
  • Orientation of the Beam
  • Buckling property for cross section optimization
  • Buckling length in local beam directions
  • Second order theory normal force
  • Modify Shell
  • Height
  • Second order theory normal force

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  1. 3: In Depth Component Reference
  2. 3.1: Model

3.1.10: Modify Element

Previous3.1.9: Mesh to ShellNext3.1.11: Point-Mass

Last updated 3 years ago

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“Modify Element” is a multi-component which can be applied to shell-, beam- and truss elements. Use the drop-down list at the bottom of the component to select the type.

By default Karamba3D assumes the cross-section of beams to be steel tubes with a diameter of 114mm and a wall-thickness of 4mm. Use the “ModifyElement”-component with “Element Type” set to “Beam” to set the beam properties according to your choice. Fig. 3.1.10.1 shows how this can be done. There are two variants for using the “Modify Element”-component:

  1. Insert it in front of the “Assemble”-component and let element objects flow through it (see e.g. the modification of beams in fig. 3.1.10.1). By default the “ModifyElement”-component leaves all incoming elements unchanged. Several “ModifyBeam”-components may act consecutively on the same beam.

  2. Create a stand-alone element-agent that can be fed into the “Elem”-input of the “Assemble”-component. The input-plug “ShellId” or “BeamId” let you select the elements to be modified. Use regular expressions to specify groups of elements.

Modify Beam

These element properties can be modified:

Activation status of beams

Bending stiffness

Beams resist normal forces and bending moments. Setting the “Bending”-input of the “ModifyElement”-component to “False” disables the bending stiffness and turns the corresponding beam into a truss. There exist reasons that motivate such a step:

  • Connections between beams that reliably transfer bending and normal force are commonly more expensive than those that carry normal force only. The design of connections heavily depends on the kind of material used: rigid bending connections in wood are harder to achieve than in steel. Yet rigid connections add stiffness to a structure and reduce its deflection. Therefore you are always on the safe side if you use truss elements instead of beams.

  • For slender beams i.e. beams with small diameter compared to their length the effect of bending stiffness is negligible compared to axial stiffness. Just think of a thin wire that is easy to bend but hard to tear by pulling.

  • Abandoning bending stiffness reduces computation time by more than half for each node with only trusses attached.

Trusses only take axial forces. Therefore they do not prevent the nodes they are connected to from rotating. In case that only trusses attach to a node, Karamba3D automatically removes its rotational degrees of freedom. Otherwise the node could freely rotate which is a problem in static calculations. As soon as one beam with bending enabled connects to a node the node has rotational degrees of freedom. Bear this in mind when the “Analysis”-component turns red and reports a kinematic system. Transferring only axial forces means that a truss reduces a node's movability in one direction. A node that is not attached to a support has three translational degrees of freedom. Thus there must be three truss elements that do not lie in one plane for a node to be fixed in space.

Height and Thickness of Cross-sections

“Height” – which in case of circular tubes is equivalent to the outer diameter D – and wall-thickness of a cross-section influence a beams axial and bending stiffness. Karamba3D expects both input values to be given in centimeter. The cross-section area is linear in both diameter and thickness whereas the moment of inertia grows linearly with thickness and depends on D3D^3D3 for e.g. full rectangular sections and on D2D^2D2 for e.g. I-profiles and box sections. So in case of insufficient bending stiffness it is much more effective to increase a beams height (or diameter) than increasing its wall thickness.

Local and Global Eccentricity of the Beam Axis

Orientation of the Beam

Buckling property for cross section optimization

Buckling can be turned off for cross section optimization. This lets you simulate pre-tensioned, slender elements without having to really pretension them. The necessary pretension force is roughly the negative value of the largest compressive axial normal force of all load cases.

Buckling length in local beam directions

Second order theory normal force NIIN^{II}NII

Axial normal forces influence the stiffness of a beam in second order theory (Th.II) calculations. If compressive they lower, in case of tension they increase its bending stiffness. Think of a guitar string which vibrates at a higher frequency (i.e. is stiffer) under increased tension. In Karamba3D the normal force which impacts stiffness -NIIN^{II}NII- is independent from the normal force which actually causes stresses in the cross sectionNNN. This enables one to superimpose second order theory results on the safe side by choosing NIIN^{II}NII as the largest compressive forceNNNof each beam.

Modify Shell

Height

Sets a uniform cross section height throughout the shell.

Second order theory normal force NIIN^{II}NII

As for beams, NIIN^{II}NIIfor shells specifies the in-plane normal force which impacts stiffness in case of second order theory calculations. It is a force per unit of length assumed to be of same magnitude in all directions.

When input “Active” is set to false the corresponding beam is excluded from further calculations until “Active” is reset to true. See section for an alternative way of setting a beam's activation state.

Karamba3D bases deflection calculations on the initial, undeformed geometry. Some structures like ropes are form-active. This means that when a rope spans between two points the deformed geometry together with the axial forces in the rope provide for equilibrium. This effect is not taken into account in Karamba3D first order theory (Th.I.) calculations. In such a case only the bending stiffness of the rope (which is very small) keeps it from deflecting indefinitely. One way to circumvent this lies in using a truss instead of a beam-element when doing first order analysis. The second possibility would be to reduce the specific weight of the rope to zero (see further below). The third possibility would be to start from a slightly deformed rope geometry and apply the external loads in small steps where the initial geometry of each step results from the deformed geometry of the previous one (see section ).

The input-plugs “EcceLoc” and “EcceGlo” serve to set the eccentricity of the beam-axis with respect to the connection line between its endpoints. Both expect a three dimensional vector. “EcceLoc” refers the eccentricity to the local, “EcceGlo” to the global coordinate system. Eccentricities of beams can also be defined via the “Eccentricity on Beam”-component (see section ).

Lets you define the orientation of a beam. Works analogously to the orientate-beam-component (see section ).

For doing cross section optimization it is necessary to know a beam’s buckling length. Karamba3D approximates it using the algorithm described in section . For cases of system buckling this approximation does not lie on the safe side. The input-plugs “BklLenY”, “BklLenZ” and “BklLenLT” allow to specify the buckling length of a beam for its local Y- and Z- axis respectively as well as for lateral torsional buckling. When specified, these values override those from the buckling length calculation of Karamba3D. The value “lg” sets the distance of transverse loads from the center of shear of the cross section. It defaults to zero. Positive values mean that the loads point towards the shear center and thus act destabilizing for lateral torsional buckling. The property “lg” influences the beams utilization with respect to lateral torsional buckling according to Eurocode 3.

3.1.5
3.5.4
3.3.7
3.1.14
3.5.8
44KB
Modify_Element.gh
28KB
LocalCooSys_I.gh
34KB
LocalCooSys_II.gh
33KB
Beam_Modifier.gh
28KB
Shell_Modifier.gh
Fig. 3.1.10: Modification of the default element properties