Column Splice — Engineering Reference

AISC 360 column splice types: bearing, bolted flange plate, welded. Flange force Pf=Mu/d, bolt/weld sizing, 50% axial minimum. Interactive calculator.

Overview

Column splices connect two column lengths end-to-end, typically located 4 feet above the finished floor level to provide erection clearance and working space. The splice must transfer axial compression, any net tension from load combinations, shear, and moment between the upper and lower shaft. AISC 360-22 Section J1.4 requires that splices in columns designed as part of the lateral-force-resisting system (LFRS) develop at least 50% of the available member strength.

The three common splice configurations are:

• Bearing splices — columns bear directly in contact (finished-to-bear or with filler plates). Flange splice plates transfer any net tension, moment, or erection loads. This is the most economical option for gravity columns.
• Bolted flange plate splices — bolted plates on each flange transfer axial force and moment. Used when bearing contact is not practical or when large column-to-column size transitions require thick filler plates.
• Welded splices — CJP groove welds connect the upper column flanges directly to the lower column or to splice plates. Common in moment frames and seismic applications where full member capacity must be developed.

Splice type comparison

Splice force requirements

For gravity-only columns (not part of the LFRS), the splice must resist the maximum net tension from factored load combinations and a minimum of the erection stability forces. Per AISC 360-22 J1.4(a), the splice need not develop any percentage of the column capacity if bearing contact is provided and all forces are compressive.

For LFRS columns, the splice must develop at least 50% of the required axial, shear, and flexural strength or the actual required forces, whichever is larger (AISC 360-22 J1.4(b)). In seismic applications per AISC 341, the splice requirements become even more stringent — typically 50% of the expected member capacity (R_y x F_y x A_g / 2 for tension).

The flange force for moment transfer is:

P_f = M_u / (d - t_f)

where d is the column depth and t_f is the flange thickness. Each flange plate or weld group must resist this force plus its share of axial load.

Bolt capacity for splices

Values use phi = 0.75. Bearing assumes F_u = 58 ksi (A36 plate), L_c >= 1.5d.

Flange force by column size

Pf = Mu / (d - tf). Deeper columns produce lower flange forces for the same moment.

Minimum splice requirements by system

Filler plate requirements

Per AISC J5.2: fillers thicker than 6 mm (1/4 in.) must be developed by extending the filler beyond the splice plate and adding bolts, or by using a cap plate.

Size transition details

Worked example — W14x82 to W14x68 splice

Given: Upper column W14x68 (A = 20.0 in^2, d = 14.0 in., b_f = 10.04 in., t_f = 0.72 in.), lower column W14x82. Required forces at splice: P_u = 450 kip (compression), M_u = 120 kip-ft, V_u = 15 kip. Gravity column (not part of LFRS). A36 splice plates, A325-N bolts.

1. Bearing check: Columns are finished-to-bear. 450 kip compression transfers directly. Bearing capacity = phi x 1.8 x Fy x A_contact. With full-contact bearing, this is satisfied by inspection.
2. Flange tension from moment: P_f = (120 x 12) / (14.0 - 0.72) = 108.4 kip per flange.
3. Net flange force: Each flange carries P_u/(2) = 225 kip compression from axial. Net = 225 - 108.4 = 116.6 kip compression on one flange, 225 + 108.4 = 333.4 kip compression on the other. No net tension, so bearing transfers all compression. Provide nominal splice plates for erection stability.
4. If wind uplift produces P_u = -60 kip (tension): Net flange force = -30 + 108.4 = 78.4 kip tension on the tension flange. Splice plate bolts must resist 78.4 kip. With 3/4 in. A325-N bolts at 17.9 kip/bolt, need 78.4/17.9 = 4.4 -> use 5 bolts per side.

Worked example — moment frame splice (SMF)

Given: W14x82 column, SMF per AISC 341. Upper and lower shaft same size. P_u = 350 kip (compression), M_u = 200 kip-ft, V_u = 25 kip.

Step 1 — Required splice capacity (AISC 341 D2.5b): Min. tension = 0.50 x R_y x F_y x A_g = 0.50 x 1.1 x 50 x 24.0 = 660 kip.

Step 2 — Flange force from moment: P_f = (200 x 12) / (14.31 - 0.855) = 177 kip per flange.

Step 3 — Net flange force (compression side): 350/2 - 177 = -2 kip (net tension possible under uplift combos). Check uplift combo separately.

Step 4 — Flange splice plate design: Required plate area for tension: 660 kip / (phi x F_y) = 660 / (0.90 x 36) = 20.4 in^2. Two flange plates: each 10 in. x 1-1/8 in. = 11.25 in^2 per plate x 2 = 22.5 in^2 > 20.4.

Step 5 — Bolts per flange plate: 660 / 2 = 330 kip per flange. 330 / 22.5 (A490-X 3/4" in double shear) = 14.7 -> 16 bolts (4 rows of 4).

Step 6 — Web splice: V_u = 25 kip. Web splice plate 1/2 in. x 6 in. Two plates. phi x V_n = 1.0 x 0.60 x 36 x 2 x 0.5 x 6 = 129.6 kip >> 25 kip. Use 4 bolts per side.

Splice location guidance

Code comparison — column splice requirements

Key design considerations

• Column size transition — when the upper column is significantly smaller, a bearing plate (butt plate) or filler plates are needed. Web fills must be provided when the web offset exceeds 3 mm to prevent load eccentricity.
• Erection stability — even compression-only splices need at least two bolts per plate for erection safety. Check that the erection bolts can resist a lateral load of 2% of the axial load as a minimum erection force.
• Splice location — standard practice places the splice 4 ft above the floor. This keeps the splice in a region of low moment for gravity frames. In moment frames, the splice should be at the inflection point if possible, typically near mid-height.
• Depth difference — when column depths differ (e.g., W14x82 to W12x65), a cap plate welded to the lower column or shim plates accommodate the change. This detail requires careful shop drawing coordination.
• Finish-to-bear contact — AISC requires that bearing surfaces be milled or saw-cut to a flatness tolerance of 1/16 in. in any 12-inch length. Verify the fabricator's finishing method meets this tolerance.

Common mistakes to avoid

1. Ignoring the 50% rule for LFRS columns — gravity column splices can be designed for actual forces only, but LFRS columns require 50% of the available strength. Misclassifying a column as gravity-only can produce an under-designed splice.
2. Forgetting net tension in uplift cases — wind or seismic load combinations frequently produce net column tension. If the splice is designed only for compression bearing, uplift separates the joint. Always check all load combinations for net tension.
3. Undersized filler plates — when fillers exceed 6 mm (1/4 in.) thickness, AISC J5.2 requires them to be developed by extending the filler beyond the splice plates or by adding additional bolts. Undeveloped fillers reduce the bolt group capacity.
4. Not detailing for web shear transfer — in moment frame splices, web splice plates are needed to transfer the column shear V_u. Omitting the web splice in a moment frame splice is a common drafting error that can have serious consequences.

Frequently asked questions

What is the 50% rule? AISC 360 J1.4(b) requires that splices in LFRS columns develop at least 50% of the required strength for axial, shear, and flexure. This is a minimum capacity floor, not the actual design forces.

Where should column splices be located? Standard practice is 4 ft above the finished floor. This provides erection clearance and places the splice in a low-moment region for gravity frames.

What is finish-to-bear? Columns machined flat on their ends so they transfer compression through direct steel-to-steel contact. AISC requires flatness within 1/16 in. per 12 in. length.

When do I need filler plates? When the upper and lower column flange widths or thicknesses differ. Fillers over 1/4 in. thick must be developed per AISC J5.2.

Can I weld a column splice in the field? Yes, but field welding requires careful quality control. Demand-critical welds in seismic systems require 100% UT inspection. Bolted splices are preferred for field connections.

What is the difference between a partial and full penetration splice weld? A PJP (partial joint penetration) weld develops only part of the member capacity. A CJP (complete joint penetration) weld develops the full capacity of the connected material. SMF and IMF column splices require CJP welds.

Run this calculation

• Column Capacity Calculator
• Splice Connection Calculator

Related references

• Column Buckling Curves
• Column K-Factor
• Connection Types
• Connection Checks
• Bolted Connections
• Base Plate Design
• Steel Grades
• Effective Length
• How to Verify Calculations

Disclaimer

This page is for educational and reference use only. It does not constitute professional engineering advice. All design values must be verified against the applicable standard and project specification before use. The site operator disclaims liability for any loss arising from the use of this information.

Design Resources

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Design guides

• Column Capacity Worked Example
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• EN 1993-1-1 Column Buckling Worked Example
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Reference pages

• Shear Tab