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 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.

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.

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

• 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.
• 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.
• 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.
• 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.

Run this calculation

• Column Capacity Calculator
• Splice Connection Calculator

Related references

• K-Factor Guide
• Column K-Factor
• How to Verify Calculations
• column buckling equations
• effective length factor K
• connection design checklist
• Column Splice Reference
• Column base design example

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.