Column Splice Types per AISC Manual Part 14

AISC Manual Part 14 defines four categories of column splices, each with distinct load paths and detailing requirements:

  1. Bearing splice (direct bearing, milled ends): The column ends are milled to bear directly on each other (or on a division/filler plate). The axial compression load transfers through bearing of steel on steel. The splice plates and bolts carry tension from uplift or moment, shear, and serve as erection stability. This is the most common and most economical splice type, accounting for approximately 85% of all US column splices.

  2. Non-bearing splice (butt joint): The column ends do not bear on each other (typically when the upper and lower column sections differ in depth or series, making direct bearing impractical). The splice plates and bolts must transfer the full axial compression, tension, shear, and moment. This type requires significantly thicker plates and larger bolt groups.

  3. End-plate bolted splice: A welded end plate on each column segment is field-bolted together. Common for heavy W14 columns in high-rise construction where the end-plate provides a clean architectural floor line and the bolt group is concentric with the column centroid. Resembles a moment end-plate connection rotated 90 degrees.

  4. Welded splice (CJP groove weld): Full-penetration groove weld connecting the column segments directly. Used for architecturally exposed structural steel (AESS) where bolted splice plates would be visually intrusive, and for seismic moment frame columns requiring full moment transfer at the splice.

Bearing Splice Design — Axial Compression Transfer

In a bearing splice with milled ends, the compressive force transfers through direct bearing contact — no splice plates are needed for compression transfer. The AISC Specification requires:

  1. Milled bearing surfaces — The column ends must be milled to within 0.002 in. of true in accordance with AISC Code of Standard Practice Section 6.4. Milling ensures full contact area under compression, preventing local yielding or instability at the bearing interface.
  2. Division/filler plates — When the upper and lower column serial sizes differ (e.g., W14x145 above W14x311), a filler plate is shop-welded to the larger column to provide a continuous bearing surface. The filler plate thickness is typically 3/8 in. minimum with a width equal to the smaller column flange width.
  3. Splice plates designed for erection and unanticipated tension — Per the AISC Specification commentary, splice plates and bolts should be designed for a minimum tension of 25% of the column design axial compression for columns in braced frames, and 50% for columns in moment frames. This accounts for load reversal from wind uplift, construction sequence effects, and progressive collapse requirements.

Splice Plate Fastener Design:

The splice fasteners must transfer the lesser of:

For a W14x145 column carrying P_u = 620 kips (braced frame): Design tension for splice fasteners = 0.25 x 620 = 155 kips.

Using 7/8 in. A325-N bolts (phi Rn = 24.4 kips each): 155 / 24.4 = 6.4 bolts minimum per flange. Use 8 bolts per flange splice (4 per side of splice joint, 4 rows x 2 columns).

Non-Bearing Splice — Full Load Transfer

Non-bearing column splices require the splice plates to transfer the total compression, tension, shear, and moment. This dramatically increases plate thickness and bolt count.

Flange compression transfer: Use flange splice plates with a total gross area at least equal to the column flange area. For W14x145 (A_f = 15.5 in. x 1.09 in. = 16.9 in^2 per flange), use two side plates (one each side of the flange) with a combined area >= 16.9 in^2. Two 6 in. x 5/8 in. plates provide 7.50 in^2, which requires additional area.

Design rule of thumb: Non-bearing splice plates typically require plate areas 10-20% larger than the column flange area to account for bolt hole deductions and the eccentric load path through the bolts (the compression force must travel from the upper column flange, through the flange bolts, into the splice plate, back through the splice bolts, and into the lower column flange).

Column web splice: In a non-bearing splice, the web must also be spliced continuously to transfer the web compression and shear. Use web splice plates on both sides (double shear) with a combined shear area at least equal to the column web area. For W14x145 (d = 14.8 in., t_w = 0.680 in.), use two 10 in. x 3/8 in. web splice plates (A_web_plate = 10 x 0.375 x 2 = 7.50 in^2 vs column web shear area = 10.1 in^2; slightly undersized but typically acceptable for doubly symmetric W14 sections where the web carries minimal compression).

End-Plate Bolted Splice Design

End-plate column splices provide a clean, concentric bolted connection with no external splice plates projecting beyond the column footprint. Each column segment has an end plate shop-welded to the end (typically a CJP groove weld or fillet weld all-around), and the two end plates are field-bolted together.

End-Plate Thickness:

Per the AISC Manual Part 10 yield-line analysis (adapted from extended end-plate moment connection design): The required end-plate thickness is derived from yield-line mechanisms around the bolt pattern. For a column end plate with bolts inside the column flanges and web:

t_p_req = sqrt(4 M_u / (phi_b Fy Y)), where Y is the yield-line mechanism parameter from AISC Manual Table 10-4.

However, for typical W14 column splices, the required end-plate thickness from yield-line analysis is usually quite modest (1/2 in. to 5/8 in.) because the bolt lines are close to the column web and flange, minimising the yield-line mechanism length.

End-Plate Bolt Design:

The bolts in an end-plate splice are concentrically loaded in pure shear (there is no moment on the bolt group because the splice is at the column centroid). This means:

The bolt count for end-plate splices carrying heavy column loads (500-1500 kips) can be high, which is why bearing splices are preferred for compression-governed columns. However, end-plate splices avoid external splice plates that project beyond the column footprint, an important consideration for architectural and fireproofing details.

Column Shear Transfer at Splices

Per AISC 360-22 and the AISC Seismic Provisions (AISC 341), column splices in moment frames and braced frames must be designed for the column shear demand at the splice location. The splice plates must develop:

  1. Panel zone shear (moment frames): The splice must transfer the column shear corresponding to the sum of the probable moments in the beams framing into the column above and below the splice. For CJP-welded splices, this is automatically satisfied; for bolted splices, the web splice plate bolts carry the shear.
  2. Braced frame column shear: The lateral load in a chevron or X-braced frame induces column shear equal to the unbalanced vertical component of the brace forces. At the splice location, the web splice bolts must transfer this shear.

For standard building columns in braced frames, the column shear is typically modest (5-15 kips), and a 3/8 in. web splice plate with 2 or 3 bolts per side is adequate. For moment frame columns, the shear demand can exceed 100 kips, and the web splice bolts must be designed accordingly.

Erection and Constructability

Column splice design must account for erection constraints:

  1. Erection aids: Bearing splices require temporary erection bolts, lugs, or drift pins to align the column segments before the permanent splice bolts are installed. The erection bolts should be designed for the self-weight of the upper column plus a construction wind load (typically 5 psf projected area).
  2. Column plumbness: AISC Code of Standard Practice Section 7.13 requires that individual column shipping pieces be within 1/8 in. of straight. At the splice, the out-of-plumb tolerance is 1:500 of the distance between splices. The splice detailing must accommodate this tolerance without forcing the splice plates.
  3. Splice location: Column splices in multi-storey frames are typically located 3-4 ft above the finished floor (top of steel), providing safe working access for ironworkers without requiring a ladder for every splice. The exact dimension is coordinated with the erector.
  4. Bolting access: For W14 and heavier columns, the web depth between flanges is approximately 10-12 in., providing adequate clearance for impact wrench access. For lighter columns (W8, W10), web splice access may require offset or channel-shape splice plates to clear the flange toes.

Frequently Asked Questions

What is the difference between a bearing and non-bearing column splice?

A bearing column splice transfers axial compression through direct steel-on-steel bearing of milled column ends. The splice plates and bolts carry only tension, shear, and erection loads. A non-bearing splice transfers all forces (compression, tension, shear, moment) through the splice plates and bolts because the column ends do not bear on each other. Bearing splices are substantially more economical (thinner plates, fewer bolts) and are the default choice unless the upper and lower columns differ significantly in size, the column is in net tension, or the architect requires a flush end-plate detail.

How many bolts are required in a typical W14 column bearing splice?

For a W14 column in a braced frame, the splice bolts are designed for 25% of the column axial compression per AISC commentary recommendations. For a typical 500 kip column at the splice: design tension force = 125 kips. Using 7/8 in. A325-N bolts (24.4 kips each), 6 bolts per flange provide 146 kips > 125 kips. The web splice requires 2-3 bolts per side for shear transfer. Total per column: approximately 14-16 bolts, compared to 28-32 bolts for a non-bearing splice carrying the same load.

Are column splices required to be moment-resisting per AISC 360?

For columns in braced frames (where lateral resistance is provided by bracing rather than frame action), column splices do not need to develop the full column moment capacity. The splice must be designed for the design moment at the splice location, which is typically the moment from frame notional loads or second-order effects. For columns in moment frames, AISC 341 (Seismic Provisions) requires that the splice develop the expected flexural strength of the smaller column section, or that the splice be located within the middle third of the clear height where moments from lateral loads are minimized under the assumed inflection point location.

When should an end-plate splice be used instead of bolted flange plate splices?

End-plate splices are preferred when: (1) the column is architecturally exposed and external splice plates would be visually undesirable, (2) fireproofing must be applied directly to the column face without cutting around splice plates, (3) the column footprint is the same above and below the splice (W14 above W14), and (4) the column axial load does not require an unreasonably large bolt count. The penalty is higher fabrication cost (shop-welded end plates) and a slightly heavier connection weight. For covered columns in standard building frames, bolted flange plate bearing splices are more economical.

Educational reference only. All design values are per AISC 360-22, AISC 341-22, and the AISC Steel Construction Manual 16th Edition. Verify column splice requirements against the project structural specification and the latest adopted building code (IBC 2024). Designs must be independently verified by a licensed Professional Engineer (PE) or Structural Engineer (SE). Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent professional verification.