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Atlas TubeAtlas TubeWhere you can use this: Atlas Tube HSS Connections Hub onlyStatus: Beta · Region: US · Design codes: AISC 360-22, AISC Design Guide 24 (2nd ed.)

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What this calculator does

Designs HSS truss connections where branch members frame into a chord. The sheet auto-classifies the joint from geometry and force balance, so you do not have to know the joint type before you start, which is usually the case in real truss work. Supported classifications:

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Video walkthrough

Jason McNeil, PE, walks the calculator step by step, showing how it classifies connections from loading and geometry together and then runs the code checks. Useful if you design modified Warren trusses or work through K, T, Y and KT joints. There is also a shorter video on the overlapped round K connection.

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Inputting key properties

  1. Enter chord and branch sections and material strengths.
  2. Set the number of branches. Three branches plus a round chord shape is what unlocks the KT gap classification.
  3. Enter the connection geometry: branch angles, gap or overlap configuration, and the connection eccentricity.
  4. Enter weld type and size.
  5. Enter branch axial demands under ASD or LRFD, in factored or unfactored input mode.
Eccentricity is not optional for KT classification. The joint is classified from the branch sections and the eccentricity together, so leaving eccentricity at zero returns a “connection not supported” flag rather than a design. Enter the real eccentricity of your joint and the classification, and its calculations, appear automatically throughout the sheet.

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How KT joints are handled

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Gapped round KT

For a three-branch round HSS joint that classifies as a gapped KT, the sheet decomposes the joint into K1 and K2 gapped K sub-connections and designs each per AISC Design Guide 24, Section 9.6. Before running the capacity checks it verifies:
  • Vertical equilibrium of the three branch forces
  • Gap limits
  • Connection eccentricity
  • Chord and branch wall slenderness and width-ratio limits of applicability
Equilibrium outcomes and the KT gapped sub-connection assumptions are surfaced in the sheet rather than buried.

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Overlapped rectangular KT

Three-branch rectangular joints that classify as overlapped KT are designed in the same sheet. The calculator evaluates the overlap and applies the overlapped KT limit states used by the dedicated overlapped path, including chord plastification, branch local checks and weld strength. Connection diagrams show the overlapped three-branch layout.

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Reviewing the calculations

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Reading the results

Governing demand-to-capacity ratios per limit state, with the joint classification stated explicitly.

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Assumptions and exclusions

Joints falling outside the supported applicability limits are flagged as not supported, with warning notes explaining the gap. The sheet does not extrapolate beyond the code limits.