End Plate Connection — Engineering Reference

Extended end plate moment connection design — AISC DG4/16, 4E and 8ES configurations, yield line bolt force model, plate thickness, and column-side checks.

Overview

An end plate moment connection consists of a plate welded to the end of a beam and bolted to the face of a supporting column flange. Unlike clip-angle or shear-tab connections that transfer shear only, end plate connections develop the full or partial moment capacity of the beam, making them a primary choice for moment-resisting frames. AISC Design Guide 4 (DG4) and Design Guide 16 (DG16) provide the detailed design procedures used in North American practice.

End plate configurations are classified by the number and position of bolt rows:

• 4E (Four-bolt extended unstiffened) — two bolts above and two bolts below the tension flange, extended end plate, no stiffener.
• 4ES (Four-bolt extended stiffened) — same as 4E but with a vertical plate stiffener welded between the end plate and the beam flange, increasing the plate's bending resistance.
• 8ES (Eight-bolt extended stiffened) — four bolts above the tension flange (two rows of two) and four bolts below, with stiffener. Used for heavy moment connections.
• Flush end plate — bolts are entirely within the beam depth. Lower moment capacity but simpler to fabricate and suitable for wind-moment frames.

Yield line theory for plate thickness

End plate design per AISC DG4/DG16 uses yield line analysis to determine the required plate thickness. The yield line pattern depends on the bolt layout, the distance from the bolt centerline to the beam flange (p_f), and the plate width (b_p). The required end plate thickness is:

t_p = sqrt(2 x M_u / (phi_b x F_yp x Y_p))

where M_u is the factored beam moment, phi_b = 0.90, F_yp is the end plate yield strength, and Y_p is the yield line mechanism parameter from the applicable DG4/DG16 table. Y_p is a function of the bolt geometry (s, p_f, p_b, g) and the plate width.

Bolt force model

The bolt force in the tension zone is not simply M_u / (n x d). Because the end plate flexes, prying action increases the bolt tension. DG16 accounts for this using the split-tee analogy: each bolt row is modeled as a T-stub in which the plate acts as the T-stub flange. The bolt force including prying is:

B = T + Q

where T is the applied tension and Q is the prying force. When the plate is thick enough to prevent prying (the "thick plate" condition), Q = 0 and the bolt force equals the applied tension. When the plate is thin, Q can increase the bolt force by 30% or more.

Worked example — W18x50 beam, 4E configuration

Given: W18x50 beam (d = 18.0 in., b_f = 7.50 in., t_f = 0.57 in.), M_u = 250 kip-ft, end plate F_yp = 50 ksi, A325 bolts 3/4 in. diameter, bolt gage g = 5.5 in., p_f = 1.75 in. (distance from flange face to first bolt row centerline), b_p = 9.0 in.

1. Yield line parameter Y_p: For a 4E configuration, Y_p = (b_p/2) x [h_1 x (1/p_f) + h_0 x (1/s)] + 2/g x [h_1 x (p_f + s)]. Using h_1 = 15.68 in., h_0 = 17.43 in., s = 3.5 in.: Y_p = 138.2 in.
2. End plate thickness: t_p = sqrt(2 x 250 x 12 / (0.90 x 50 x 138.2)) = sqrt(6000/6219) = 0.98 in. Use t_p = 1.0 in.
3. Bolt tension: Flange force = 250 x 12 / (18.0 - 0.57) = 172 kip. Per bolt (4 bolts in tension) = 172/4 = 43.0 kip. A325 3/4 in. bolt available tension = phi x F_nt x A_b = 0.75 x 90 x 0.4418 = 29.8 kip. Not adequate — need 7/8 in. bolts (phi x R_n = 40.6 kip) or add bolt rows.

Code comparison — end plate connections

Column-side limit states

The column must be checked for several limit states caused by the concentrated flange forces from the end plate:

• Column flange bending — the column flange acts like a T-stub loaded by the bolt tension. If the column flange is too thin, stiffening with continuity plates is required.
• Column web yielding (AISC J10.2) — the beam compression flange force can yield the column web directly opposite. R_n = F_yw x t_w x (5k + l_b).
• Column web crippling (AISC J10.3) — at concentrated compression loads, the column web can buckle locally.
• Column panel zone shear (AISC J10.6) — the moment couple from the beam creates a shear force in the column web panel. R_v = 0.60 x F_y x d_c x t_w for single-sided connections. Doubler plates may be needed.

Common mistakes to avoid

• Ignoring prying action — using T = M/(n x lever arm) without the DG16 prying model can underestimate bolt forces by 30% or more, leading to bolt fracture.
• Wrong bolt position — the distance p_f from the beam tension flange to the first bolt row is critical. Values outside the DG4 recommended range (typically 1.5 to 2.0 in.) produce unreliable yield line solutions.
• Omitting column-side checks — even when the end plate and bolts are adequate, the column flange may be too thin or the panel zone may be overstressed. Continuity plates and doubler plates are frequently required.
• Using flush end plates for large moments — flush configurations have limited moment capacity because all bolts are within the beam depth. For moments exceeding about 60% of the beam plastic moment, extended configurations (4E or 8ES) are generally required.
• Not checking the weld to beam flange — the CJP or fillet weld connecting the beam tension flange to the end plate must develop the full flange force. Undersized welds at the tension flange are a fracture-critical failure mode.

Run this calculation

• Section Properties Database
• Beam Calculator

Related references

• Steel Connection Design
• Bolt Capacity Table
• Plate Weight Reference
• How to Verify Calculations
• moment frame design
• structural bolt grade reference
• weld group properties
• steel connection capacity calculator
• weld capacity for connection design
• Steel girder-to-column connections
• Connection Types
• End Plate Calculator

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.