Extended End Plate — Overview

The extended end plate moment connection is the most common rigid connection in European steel frames. The end plate projects beyond the beam tension flange, allowing an additional bolt row above the top flange that significantly increases the lever arm and moment capacity.

Key Features

• End plate extends 80-120 mm beyond beam flanges
• 3-4 bolt rows: 1 above tension flange, 1-2 at tension flange, 1 at compression flange
• Rigid or semi-rigid classification per EN 1993-1-8 Clause 5.2
• Suitable for moment-resisting frames in EN 1993-1-1 Clause 5.2.2.2
• Capacity range: 100-800 kN·m (typical IPE 300-600, S355)

The Component Method — EN 1993-1-8 Clause 6.2.3

The component method decomposes the connection into basic components, each with its own force-deformation characteristic:

The lowest resistance of each zone is assembled into the design moment resistance M_j,Rd. This is then classified as rigid, semi-rigid, or nominally pinned per Clause 5.2.

T-Stub Model — Tension Zone (Clause 6.2.4)

The tension zone is modelled as equivalent T-stubs representing the column flange and the end plate in bending. The effective length l_eff depends on the bolt row location:

Three Failure Modes (Table 6.2):

Mode 1 is ductile and preferred. Mode 3 is brittle — increase end plate thickness or reduce bolt spacing to force Mode 1 or 2.

Column Web Panel Shear — Clause 6.2.6.1

The column web panel resists the shear developed by the moment couple between the tension and compression forces. For a double-sided connection:

V_wp,Ed = (M_b1,Ed / z_1) + (M_b2,Ed / z_2) - V_c,Ed

Where z is the lever arm and V_c,Ed is the column shear at the joint.

Design resistance (unstiffened):

V_wp,Rd = 0.9 × f_y,wc × A_vc / (√3 × γ_M0)

If V_wp,Rd is insufficient, provide supplementary web plates (doubler plates) or diagonal stiffeners.

Worked Example — IPE 400 Extended End Plate to HEB 260

Step 1 — T-Stub Resistance per Bolt Row

Row 1 (extended, above tension flange): m = 40 mm, e = 45 mm, n = min(1.25 × 40, 45) = 45 mm M_pl,Rd per unit length = 0.25 × 20² × 355 / 1.00 = 35,500 N·mm/mm

l_eff (non-circular) for individual bolt row = 2 × (π × 40 + 45) = 341 mm

Mode 1: F_T1,Rd = 4 × 35,500 × 341 / (40 × 1000) = 1,211 kN Mode 2: F_T2,Rd = (2 × 35,500 × 341 + 45 × 2 × 203.3) / ((40 + 45) × 1000) = 312 kN Mode 3: F_T3,Rd = 2 × 203.3 = 406.6 kN (F_t,Rd M24 10.9 = 203.3 kN per bolt)

Row 1 governs at Mode 2: F_T,Rd = 312 kN

Row 2 (inner row): Mode 2 governs similarly: F_T,Rd ≈ 298 kN

Step 2 — Bolt Row Force Distribution

The total tension force must equal the compression force:

ΣF_T,Rd = F_T,Rd,row1 + F_T,Rd,row2 = 312 + 298 = 610 kN

Lever arm z = distance from compression flange centre to tension force centroid: z = (312 × 455 + 298 × 385) / 610 = 420.8 mm

Step 3 — Moment Resistance

M_j,Rd = ΣF_T,Rd × z = 610 × 0.4208 = 256.7 kN·m

Step 4 — Column Web Panel Shear Check

V_wp,Ed for single-sided connection (no opposite beam): V_wp,Ed = M_j,Rd / z = 256.7 / 0.4208 = 610 kN

V_wp,Rd (HEB 260, S355) = 706 kN > 610 kN — OK (no doubler plate required)

Step 5 — Connection Classification

Per EN 1993-1-8 Clause 5.2.2:

• Rigid if S_j,ini ≥ 25 × EI_b / L_b
• For a 6 m beam span: S_j,ini = 65,000 kN·m/rad > 25 × 210,000 × 23,130 × 10⁴ / 6000 = 20,165 kN·m/rad — Classified as RIGID

Stiffener Requirements

Column Web Stiffeners in Tension (Clause 6.2.6.3)

Transverse stiffeners are required when the column web tension resistance is less than the applied flange force:

F_t,wc,Rd = ω × b_eff,t,wc × t_wc × f_y,wc / γ_M0

If F_t,wc,Rd < F_T,Rd (total tension from bolt rows), provide full-depth stiffeners.

Column Web Stiffeners in Compression (Clause 6.2.6.2)

Required when the column web crushing resistance is insufficient:

F_c,wc,Rd = ω × k_wc × b_eff,c,wc × t_wc × f_y,wc / γ_M0

Practical Rules for HEB Columns with IPE Beams

For IPE 400 (400 mm deep) to HEB 260 (260 mm deep): ratio = 1.54 > 0.75 — stiffeners required.

Frequently Asked Questions

What is the difference between flush and extended end plate moment connections?

A flush end plate terminates at the beam flange levels (plate depth equals beam depth), while an extended end plate projects beyond the beam tension flange by 80-120 mm. The extension accommodates an additional bolt row above the top flange, increasing the internal lever arm by 15-30% and the moment capacity by 40-70%. Extended end plates are used for rigid moment frames; flush end plates suit semi-rigid frames or smaller moments.

How does the component method differ from traditional moment connection design?

The component method (EN 1993-1-8 Clause 6.2.3) decomposes the connection into independent basic components (column flange, end plate, bolts, column web), determines each component's resistance and stiffness, and assembles them into a bi-linear or tri-linear moment-rotation curve. Traditional methods treat the connection as a single entity with empirical formulas. The component method provides a consistent, mechanics-based approach valid for any configuration and allows optimization of individual components.

When are column web doubler plates needed for extended end plate connections?

Column web doubler plates (supplementary web plates) are needed when the column web panel shear resistance V_wp,Rd is less than the shear demand from the moment couple. Per Clause 6.2.6.1, the shear area is increased by adding a plate welded to the column web. The doubler plate thickness is typically 0.6-0.8 × column web thickness. As a rule, for single-sided extended end plate connections where the beam depth exceeds the column depth, doubler plates are almost always required.

What is the rotational stiffness classification per EN 1993-1-8?

EN 1993-1-8 Clause 5.2.2 classifies connections by stiffness: rigid (S_j,ini ≥ k_b × EI/L_b where k_b = 8 for braced frames or 25 for unbraced), semi-rigid (0.5EI/L_b < S_j,ini < k_b × EI/L_b), and nominally pinned (S_j,ini ≤ 0.5EI/L_b). Extended end plate connections to column flanges with 20+ mm end plates and preloaded bolts typically achieve rigid classification for braced frames. For unbraced (sway) frames, rigid classification is harder to achieve and may require thicker plates or haunched beams.

Related Pages

• EN 1993 End Plate Connection → — T-stub model and flush end plates
• EN 1993 Shear Connection → — Fin plate and web cleat
• EN 1993 Moment Frame → — Moment frame design
• EN 1993 Bolt Torque Chart → — EN 14399 preload values
• All European References →

Educational reference only. Design per EN 1993-1-8:2005 Clause 6.2 and Table 6.2. T-stub effective lengths per Clause 6.2.4. Bolt row forces per Clause 6.2.7. Verify all components independently. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification by a qualified structural engineer.

Design Resources

Calculator tools

• End Plate Moment Connection Calculator
• Bolted Connection Calculator
• Steel Column Calculator
• Weld Capacity Calculator

Design guides

• EN 1993-1-8 Bolted Connection Worked Example
• Moment Connection Worked Example
• Bolted Connection Checklist
• Beam Design Worked Example
• Steel Connection Calculator Guide

Reference pages

• EU End Plate Connection
• UK Moment Connection
• EU Moment Frame