Skip to main content

Video 4 Course Guide: Cross-Sections & Materials

This guide demonstrates how material selection directly influences structural performance and utilization in Karamba3D by testing timber, steel, and concrete under identical load conditions, followed by automated cross-section optimization.

1. Modulus of Elasticity (E) and Stiffness​

By reusing identical beam geometry and loading conditions, material selection is isolated as the single testing variable:

  • Modulus Value (E): Represents real-world material stiffness in structural calculations.
  • Relative Stiffness: Steel exhibits a significantly higher stiffness ($E$) compared to timber.
  • Custom Material Definitions: Material property values can be sourced online for specific species of wood or alloys and plugged directly into Grasshopper material components.

2. Shared Setup and Script Structure​

Although the Grasshopper canvas contains many wires, the workflow isolates variables across parallel branches using a single base beam setup:

  1. Load Magnitudes and Reference Points: Defines the force inputs and point coordinates at the top of the canvas.
  2. Dimension Sliders: Control global beam geometry (length, width, and cross-section dimensions) across all material branches.
  3. Material Property Inputs: Feeds material values into individual Cross Section components to define beam geometry and stiffness.
  4. Element Conversion: Converts curves/lines into Karamba elements (LineToBeam) with linked cross-section definitions.
  5. Analysis Pipeline: Routes elements through Assemble Model → Analyze → ModelView / BeamView → Utilization → Panel.
  6. Multi-Segment Outputs: The beam is divided into three distinct segments, generating three separate utilization readings in the output panels.

3. Comparing Timber, Steel, and Concrete​

When applying an identical load across identical beam spans, lengths, widths, and cross-section shapes, each material yields distinct utilization levels:

MaterialUtilization RatioStructural Characteristics & Trade-offs
Timber~0.866Highest utilization under load. Less structurally strong than steel or concrete, but provides desirable aesthetic and visual qualities.
Steel~0.03Extremely low utilization. Very structurally sound and stiff, but comes at a higher material cost.
Concrete~0.42Mid-range utilization. Highly common structural material; performs well under compression but is brittle and weak in shear/tension (fails when pulled).

4. Automated Cross-Section Optimization​

The Optimize Cross Section component automatically selects the most efficient beam profile from a library of candidate cross-sections based on a target utilization ratio.

Optimization Pipeline​

  1. Base Assembly: Assign an initial profile (such as an I-section) to the beam lines, convert them to elements, and assemble the base model.
  2. Target Utilization Slider: Connect a slider to define the precise target utilization (e.g., targeting a ratio of 0.60).
  3. Candidate Selection & Toggles: Supply candidate lists of cross-sections across material types (steel, timber, concrete). Boolean toggles enable or disable specific sections from the pool (e.g., toggling an item list count between 11 and 12 profiles).
  4. Optimization Solving: Route the merged candidate list and assembled model into the Optimize Cross Section component.
  5. Deconstructing Output: Pass the optimized model output into Disassemble Model, Disassemble Elements, and Disassemble Cross Section components to reveal which section profile was selected.

Demonstration Behaviors​

  • Setting a target utilization of 0.02 causes Karamba to select a Steel 10x5.3 section.
  • Increasing the target utilization to 0.60 causes the component to select a different, lighter steel profile to closely match the higher target efficiency.
  • Adjusting target thresholds and candidate libraries causes Karamba to automatically evaluate and switch between concrete, steel, or timber profiles.

Component Reference​

ComponentRole in Workflow
Material PropertiesDefines material stiffness ($E$ value) from physical lookups.
Cross SectionAssigns geometric shapes, dimensions, and material properties to beam sections.
Optimize Cross SectionSolves for and selects the ideal cross-section from a candidate pool to match a target utilization.
Disassemble (Model / Elements / Cross Section)Deconstructs the optimized structural model to extract and read the specific profile selected by Karamba.