HSS Connections Calculator

HSS truss and moment connection design per AISC Design Guide 24. Chord sidewall, punching shear, and local yielding limit state checks. Educational use only.

This page documents the scope, inputs, outputs, and computational approach of the HSS Connections Calculator on steelcalculator.app. The interactive calculator runs in your browser; this documentation ensures the page is useful even without JavaScript.

What this tool is for

Checking limit states for welded HSS-to-HSS connections: chord face plastification, chord sidewall failure, punching shear, and branch failure.
Screening connection adequacy for T, Y, X, and K-type HSS truss joints.
Understanding the sensitivity of HSS connection capacity to beta ratio (branch/chord width ratio) and chord stress ratio.

What this tool is not for

It does not design the welds between branch and chord members.
It does not handle multiplanar connections, moment connections, or through-plate details.
It does not check fatigue for cyclically loaded HSS joints.

Key concepts this page covers

chord face plastification
chord sidewall local yielding and crippling
punching shear of the chord wall
branch member effective width
beta ratio and its effect on connection capacity

Inputs and outputs

Typical inputs: chord and branch HSS sizes (width, depth, wall thickness), connection type (T, Y, X, K), branch angle, chord axial stress, and branch axial force.

Typical outputs: capacity for each limit state, controlling limit state, demand-to-capacity ratio, and whether the connection is adequate without reinforcement.

Computation approach

The calculator evaluates the applicable limit states from AISC 360 Chapter K and AISC Design Guide 24 for the specified connection geometry. Each limit state produces a nominal capacity that is factored by phi. The controlling limit state is the minimum capacity. The chord stress interaction function Qf reduces the connection capacity when the chord is under significant axial load or bending.

Frequently Asked Questions

What is the beta ratio and why is it critical for HSS connections? Beta is the ratio of branch width to chord width (Bb/B for rectangular HSS, Db/D for round HSS). When beta approaches 1.0 (branch nearly as wide as the chord), the connection is very efficient because the branch load transfers directly into the chord sidewalls. When beta is low (below 0.5), the load must be carried by chord face bending, which is much less stiff and strong. Connection capacity is highly sensitive to beta, and a small increase in chord size can dramatically improve the connection.

Why do HSS connections have different limit states than wide-flange connections? HSS members are closed hollow sections where the chord wall acts as both a beam and a plate that must resist local loads from branch members. The thin walls are susceptible to local failure modes (face plastification, sidewall yielding, punching shear) that do not occur in wide-flange connections where flanges are supported by the web. AISC Chapter K specifically addresses these HSS-specific limit states.

When is chord face plastification the controlling limit state? Chord face plastification governs for connections with low to moderate beta ratios (typically beta less than 0.85) where the branch load is resisted primarily by bending of the chord face. The capacity depends on the chord wall thickness, the beta ratio, and the chord stress level. This limit state is often the most restrictive for K-connections and T-connections with small branches on large chords.

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. Any calculations, outputs, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

The site operator provides the content "as is" and "as available" without warranties of any kind. To the maximum extent permitted by law, the operator disclaims liability for any loss or damage arising from the use of, or reliance on, this page or any linked tools.