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# HSS to HSS Splice Connection (End Plate)
> Design bolted end plate column splices between HSS members for axial, moment and shear, with AISC 341-22 seismic capacity design checks.
**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:** Released, with features in beta · **Region:** US, CA · **Design codes:** AISC 360-22, AISC 341-22
The AISC 341-22 seismic checks are released. Round end plate moment and square/rectangular shear limit states are in beta.
## What this calculator does
Designs and checks a bolted end plate splice between two HSS columns, under combined axial load, moment and shear, to AISC 360-22. Both single and double end plate arrangements are supported, with automatic sizing and optimisation routines.
Two end plate geometries are available as presets, and the coverage differs between them.
| Preset | Geometry | Axial | Shear | Moment | Seismic |
| ------------------------------ | ---------------------------------------------- | ----- | ---------- | ---------- | --------------------------- |
| Round end plate | Circular plate on round HSS | Yes | Yes | Yes (beta) | SFRS combinations supported |
| Square / rectangular end plate | Rectangular plate on square or rectangular HSS | Yes | Yes (beta) | Yes | Not yet supported |
All three combinations are now covered on the round preset: axial and shear, axial and moment, or axial and shear and moment together.
## Inputting key properties
1. **Select the HSS column section and grade** for both sides of the splice.
2. **Choose the end plate preset**, round or square and rectangular, and whether the splice uses a single or double end plate.
3. **Choose the bolt layout type.** Square and rectangular end plates offer **bolts on two sides** or **bolts on four sides**. For the four-side layout the total bolt count is `2 * (n_bolts_ep_x + n_bolts_ep_y)`.
4. **Enter the end plate geometry:** diameter or width and depth, thickness, and grade.
5. **Enter bolt size, grade and spacing.** Short-side and long-side spacing inputs are validated to fit within the column.
6. **Enter the weld size.**
## Applying loads
Enter axial, moment and shear demands either as individual load types or pre-factored.
### Shear direction on rectangular columns
Rectangular columns carry a diagram in the Applied Loads section letting you select whether shear acts on the **short face** or the **long face** of the column.
This is not cosmetic. The face you pick changes which column walls carry the shear, and therefore the results of several column limit states. Set it to match your framing rather than leaving the default.
### Combining axial and moment on round end plates
When you enter both a tensile axial load and a moment on a round end plate, the calculator computes an **effective tensile demand**: the applied tension plus the additional tension induced by the bending moment, resolved around the bolt circle.
Every tensile limit state is then checked against that effective demand rather than the raw axial load, including tensile yielding, the bolt checks, the end plate classification, and the weld checks. Where there is no moment, the checks run against tension or compression as normal.
Entering a moment on a round end plate displays an in-sheet beta message. All limit states are implemented; the feature is in quality assurance.
### Seismic capacity design (AISC 341-22)
Enable **Seismic Design Checks** when the splice sits in a seismic force-resisting system. Ordinary load combinations are not sufficient there: AISC 341 requires capacity-based demands tied to the expected strength of the column.
With seismic enabled:
* Supply seismic load cases as individual load inputs. The horizontal seismic effect must already be amplified by the overstrength factor, and the vertical seismic component entered separately. Factored-load entry is disabled while seismic is active so the overstrength combination is applied explicitly.
* For **square and rectangular** HSS columns carrying moment, the required column flexural strength is taken as the greater of the load-combination moment and the moment developed by the expected flange-splice tension acting over the column depth, per the AISC 341-22 column-splice flange provisions.
* For **round** HSS columns, which have no flanges, the seismic moment requirement correctly reduces to the load-combination demand alone.
The capacity-design flange-splice strength and the required column flexural strength are shown as intermediate outputs so the basis of the demand is visible.
## Reviewing the calculations
### Column
| Limit state | Reference |
| ------------------------------------------------------------------------------------- | ---------------------- |
| Tensile yielding and rupture | AISC 360-22 J4.1, J4.3 |
| Shear yielding, from the shear force, buckling factor and gross area subject to shear | AISC 360-22 G |
| Flexural yielding capacity (round sections) | AISC 360-22 Eq. F8-1 |
| Local buckling, compact / noncompact / slender classification | AISC 360-22 Chapter F |
| Tensile yielding and flexural yielding interaction | AISC 360-22 Chapter H |
### Bolts
| Limit state | Reference |
| -------------------------------------------------------------------------------------------------------------- | ---------------------- |
| Bolt tension capacity, per bolt and for the group | AISC 360-22 J3.7 |
| Bolt shear capacity, nominal shear stress on the bolt area, per bolt and for the group | AISC 360-22 J3.7 |
| Combined tension and shear: a shear stress is estimated and used to compute a reduced nominal tensile strength | AISC 360-22 J3.7, J3.9 |
### End plate
| Limit state | Reference |
| ------------------------------------------------------ | --------------------------------------- |
| Prying action | AISC Steel Construction Manual |
| Shear yielding (using Fy) and shear rupture (using Fu) | AISC 360-22 J4.2 |
| End plate thickness adequacy and flexural check | AISC 360-22, elastic section properties |
### Moment capacity of the connection (round end plates)
Two capacities are computed using the empirical formulations of Packer (2023):
1. Bolt capacity of the connection under moment
2. End plate moment classification capacity
The **lower of the two governs** and is reported as an interaction index.
### Welds
Checked to AISC 360-22 J2.4. The available strength runs three separate checks: axial alone, shear alone, and the resultant combining both. Where tension and moment coexist, the resultant is built from the effective tensile load.
## Assumptions and exclusions
SFRS load combinations are currently limited to the round end plate preset. The seismic treatment has not yet been validated for square and rectangular geometry.
* Uses elastic section properties.
* The moment capacity formulation for round end plates follows Packer (2023) rather than a codified AISC procedure. Check it is acceptable to your reviewer.
## Related
* [HSS to HSS splice gusset connection](/docs/connections_hub/calculators/hss_to_hss_splice_gusset)