Where you can use this: Atlas Tube HSS Connections Hub and Calcs.comStatus: 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
Inputting key properties
- 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). - Enter the steel grade.
- Enter the concrete compressive strength (
f'c) and unit weight. - Enter the column height (
L) and effective length factor (K). - Enter the position of supports or brace locations.
- Enter the load eccentricity.
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.
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
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
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
- Bending is treated as uniaxial.
- The round preset assumes plain concrete with no longitudinal reinforcement in the core.