> ## Documentation Index
> Fetch the complete documentation index at: https://calcs.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Concrete-Filled HSS Column
> Design round, square and rectangular concrete-filled HSS composite columns to AISC 360-22 and Design Guide 6.
**Where you can use this:** [Atlas Tube HSS Connections Hub](https://connectionshub.atlastube.com/login/organisations?src=CALCSDOCS) and [Calcs.com](https://app.calcs.com/login?src=calcsdocs)
**Status:** Beta · **Region:** US · **Design codes:** AISC 360-22 Chapter I, AISC Design Guide 6 (2nd ed.)
## What this calculator does
Sizes and checks concrete-filled HSS composite columns, taking a section from classification all the way through to a combined bending and axial check, for both LRFD and ASD from one set of inputs.
Composite behaviour makes this fiddly by hand. The section has to be classified as compact, noncompact or slender, and the axial and bending classifications will not always agree. The available strengths then come from different methods depending on that class, and the interaction diagram has to be built up point by point before any combined check can run. Faced with that effort, engineers often fall back to a spreadsheet that is hard to audit, or sidestep composite behaviour entirely and design the bare steel tube, which throws away the concrete's contribution and oversizes the column.
## Supported sections
| Section | Method | Notes |
| -------------------------- | ------------------------------------------------------------------------------------------------------- | -------------------------------------------------- |
| Round HSS | Follows DG 6 Example 2.7 | Plain concrete core, no longitudinal reinforcement |
| Square and rectangular HSS | Plastic Stress Distribution Method, DG 6 Cl. 2.5.6, concrete stress coefficient C2 = 0.85 per Eq. I2-9b | Separate flange and web slenderness limits |
| Built-up box sections | As above | |
## Inputting key properties
1. **Set the column type**, then select the section. Pick a catalog HSS, or define a custom section by outside width (`B_c`), depth (`H_c`) and plate thickness (`t_c`).
2. **Enter the steel grade.**
3. **Enter the concrete compressive strength** (`f'c`) and unit weight.
4. **Enter the column height** (`L`) and effective length factor (`K`).
5. **Enter the position of supports or brace locations.**
6. **Enter the load eccentricity.**
Cross-section diagrams and the compression, moment and shear results build as you go, along with the interaction diagram.
## Applying loads
Enter either individual loads or factored loads directly.
* **Individual loads.** The calculator generates the load combinations and reports the governing axial force, moment and shear.
* **Factored loads.** Enter demands you have already factored.
You can also enter a factored lateral distributed load, and choose whether to include the column self weight.
Serviceability deflection is only calculated when individual load inputs are used. Select factored loads and the deflection check disappears, because factored demands carry no service-level equivalent. If deflection matters to your design, enter individual loads.
### Design criteria
A design criteria section shows the design code driving the load combinations and lets you set the deflection limit and the short-term deflection limit, against either a span ratio or an absolute value.
## Reviewing the calculations
### Section classification
Compact, noncompact or slender, evaluated separately for axial (Section I2) and bending (Section I3) against the Table I1.1a and Table I1.1b limits, with the maximum permitted slenderness enforced. Round sections classify on the diameter to thickness ratio; rectangular sections on separate flange and web limits. This classification controls the design path for every strength check that follows.
### Capacities
| Check | Reference |
| --------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------- |
| Composite section properties and plastic axial compressive strength | AISC 360-22 Chapter I |
| Axial compressive strength, including length reduction through the buckling curve | AISC 360-22 Cl. I2.2b |
| Axial tensile strength, from the steel and any reinforcement | AISC 360-22 Cl. I2.2c |
| Flexural strength | AISC 360-22 Cl. I3.4b |
| Shear strength | AISC 360-22 Cl. I4.2, concrete shear coefficient `K_c` conservatively taken as 1.0 |
| Short-term deflection | Against a span ratio or absolute limit |
The flexural section exposes its working: the flexural stress block geometry and the first yield flexural segment properties are shown as intermediate outputs, then used to compute the plastic moment, the yield moment and the nominal flexural strength.
For round sections, the composite first yield moment is worked out from the stress blocks in Commentary Figure C-I3.8b: steel at yield, a triangular concrete block at 0.70 f'c, and the neutral axis placed so there is no net axial force.
### Interaction
| Case | Equations |
| ------------------------------ | --------------------------------------------------------------------------- |
| Compact sections | H1-1a and H1-1b |
| Noncompact or slender sections | I5-1a and I5-1b, coefficients from Table I5.1 |
| Rectangular sections | Both the Cl. I1.2 plastic distribution method and Cl. I1.5(b) are evaluated |
The interaction diagram is built from the Manual Table 6-4 anchor points A through E, giving both the design envelope and the allowable envelope.
The combined check separates compression and tension behaviour so the correct axial capacity is used: the equations adjust when the column is in tension rather than compression.
## Reading the results
The summary reports the governing results and the design strengths for axial, flexure and combined interaction, alongside the interaction diagram. The calculator picks the correct code path on its own based on how the section classifies and which design method you are using.
## Assumptions and exclusions
Out of scope and remaining the engineer's responsibility: connection limit states, ACI 318-19 reinforcement detailing (cover, spacing, ties), and AISC Section I6 force transfer at load introduction points.
* Bending is treated as uniaxial.
* The round preset assumes plain concrete with no longitudinal reinforcement in the core.
## Related
* [WF beam to concrete-filled HSS moment connection](/docs/connections_hub/calculators/wf_to_concrete_filled_hss_moment)