Simple Connections - the SCI Green Book explained - Product Development Engineers Ltd

✅ Full Title

“Simple Connections in Steel Frames: Design of Simple Joints to Eurocode 3”
Commonly referred to as the Green Book for simple connections.

Published by the Steel Construction Institute (SCI), it’s part of a set of authoritative guidance documents for structural steelwork design, particularly connection detailing, aligned with BS EN 1993-1-8 — the Eurocode 3 standard for design of steel structures.

🎯 What Are Simple Connections?

In steel structures:

A simple connection is a joint designed to transmit vertical shear and axial forces only.
Moment resistance is negligible — connections are assumed to behave as pinned.
The rotational stiffness of the connection is low enough that it does not restrain bending in the attached beams.

⚡ In reality:
Connections do have some moment capacity and stiffness, but for design simplicity, we treat them as ideal hinges (pinned) if they meet certain flexibility and capacity requirements.

🧠 Why the Green Book Exists

To give clear, practical design methods for simple steel connections.
To ensure designers can justify the simple assumption while staying compliant with Eurocode 3.
To provide standardised details, design models, and resistance calculation procedures for common connections.
Bridge the gap between theoretical codes and day-to-day engineering practice.

The Green Book standardises connection types and design checks to ensure consistency and safety.

🔍 What’s Inside the Green Book

✅ Typical Simple Connection Types Covered

Detailed illustration showcasing different types of simple steel connections, such as bolted end plates, fin plates, and cleat connections, essential for efficient and cost-effective structural steel design.

Flexible End Plate Connections
- Thin end plates bolted to columns.
Fin Plate Connections
- Single vertical plates welded to the column or beam and bolted to the beam web.
Double Angle Cleat Connections
- Angles bolted to both the beam and column or supporting member.
Web Angle Cleats
Top and Seat Angle Connections (rare now but historically important)
Extended End Plates
- Longer plates for lighter frames, but still simple category.

📚 Sections of the Green Book

Section	Content
Introduction	Theory of simple connections, Eurocode compliance
Connection Classification	How to define simple vs semi-rigid or rigid connections
Component Method Overview	SCI’s adaptation of Eurocode component-based method
Design Process	Step-by-step guide on designing simple joints
Worked Examples	Real design calculations with step-by-step walkthrough
Standard Details	Pre-approved standard connection configurations
Design Resistance Formulas	Equations for bolt shear, bearing, end plate bending, etc.
Bolt and Weld Detailing	Practical advice on bolt types, weld sizing, and detailing

🧩 Component Method (Eurocode 3)

The Green Book heavily relies on the Component Method from Eurocode 3 (EN 1993-1-8):

Breaks a connection down into individual components:
- Bolts in shear
- Plates in bending
- Welds in shear
- End plate bending
- Bolt bearing
Each component is assigned a design resistance.
The overall connection resistance is calculated by assembling these individual component strengths.

✅ This is much more rigorous than older, empirical BS 5950 designs — but the Green Book simplifies it for practical use.

📊 Example: End Plate Connection Design

For a Flexible End Plate Connection, you must check:

Bolt shear and bearing
End plate bending resistance
Weld strength
Column flange/web checks
Beam web checks

Equations look like:

Bolt shear resistance:

$F_{v,Rd} = \frac{f_u}{\sqrt{3} \gamma_M2} A_{bolt}$

Plate bending resistance:

$M_{pl,Rd} = \frac{f_y t^2}{4 \gamma_M0}$

where:

$f_u$ = ultimate tensile strength of bolt material
$f_y$ = yield strength of plate
$t$ = plate thickness
$\gamma_M0, \gamma_M2$ = partial safety factors for material strength

🚀 Benefits of Using the Green Book

Standardised, proven details — reduce design risk.
Saves time — ready-to-use connection types and calculation steps.
Eurocode 3 compliant — helps meet modern code requirements.
Improves design quality — encourages best practices for bolted and welded joints.
Worked examples — helps junior engineers learn connection design hands-on.

⚙️ Who Should Use It

Structural engineers working with steel frames.
Engineering consultancies preparing Eurocode-compliant designs.
Fabricators checking or verifying engineer-specified connections.
Engineering students studying practical connection design.

📚 Recent Editions and Versions

The original Green Book was aligned with BS 5950 (British Standards).
The modern editions (post-2005) are aligned with EN 1993-1-8 (Eurocode 3).
New versions keep evolving to include:
- Preloaded (HSFG) bolt connections
- Stainless steel considerations
- Simplified moment-rotation curve classifications

🏆 Summary

The SCI Green Book for Simple Connections provides a clear, efficient framework for the design of pinned steel connections that comply with Eurocode 3, making life easier for practicing engineers while ensuring the reliability and safety of steel structures.

📚 Worked Example: Flexible End Plate Connection Design

✅ Problem Statement

Design a flexible end plate connection between an I-section beam and a column:

Beam: UB 406×178×54 (Universal Beam)
Design shear force $V_{Ed}$ : 90 kN
Design moment at face of column: Assume negligible (since it’s a simple connection)
Bolts: Grade 8.8 M20 bolts (nominal diameter = 20 mm)
End Plate: S275 steel (mild steel with $f_y = 275 \text{ MPa}$ )

Design according to Eurocode 3 (EN 1993-1-8) using Green Book methodology.

🧠 Step 1: Design Assumptions

Since this is a simple connection:

Primary force to resist: shear.
Connection should not provide significant moment resistance — keep it flexible.

Assume:

4 bolts in a standard rectangular arrangement (2 rows of 2 bolts).
End plate welded to beam web and flanges.
Bolts in double shear.

🔢 Step 2: Bolt Shear Capacity

Design shear resistance of one bolt:

$F_{v,Rd} = \frac{f_u}{\sqrt{3} \gamma_{M2}} A_s$

Where:

$f_u = 800 \text{MPa}$ (Grade 8.8 bolts)
$\gamma_{M2} = 1.25$ (Partial factor for bolts in shear)
$A_s = 245 \text{mm}^2$ (Tensile stress area of M20 bolt)

Thus:

$F_{v,Rd} = \frac{800}{\sqrt{3} \times 1.25} \times 245 = 90,446 \text{N} = 90.45 \text{kN}$

Since the bolts are in double shear, the capacity doubles:

$F_{v,Rd,,\text{double shear}} = 2 \times 90.45 = 180.9 \text{kN}$

🔢 Step 3: Shear Check

Total resistance for 4 bolts:

$V_{Rd} = 4 \times 180.9 = 723.6 \text{kN}$

Applied design shear:

$V_{Ed} = 90 \text{kN}$

✅ Check:

$V_{Rd} = 723.6 \text{kN} > V_{Ed} = 90 \text{kN}$

The bolts are adequate in shear.

🔢 Step 4: End Plate Bending Check

Assume the plate acts like a cantilever fixed at the bolts.

Maximum moment on end plate per unit width:

$M = \frac{V_{Ed} \times e}{2}$

Where:

$e = 40 \text{mm}$ (distance from bolt centerline to plate edge)

$M = \frac{90,000 \times 40}{2} = 1.8 \times 10^6 \text{Nmm}$

Design bending resistance per mm width:

$M_{pl,Rd} = \frac{f_y}{\gamma_{M0}} \times \frac{t^2}{4}$

Where:

$f_y = 275 \text{MPa}$ (steel yield strength)
$\gamma_{M0} = 1.0$ (partial factor for yielding)
$t$ = thickness of end plate

Rearranging to solve for $t$ :

$t = \sqrt{\frac{4 \times M_{Ed}}{f_y}}$

$t = \sqrt{\frac{4 \times 1.8 \times 10^6}{275 \times 10^6}} = \sqrt{0.02618}$

$t \approx 5.12 \text{mm}$

Practical minimum thickness — round up to 10 mm for fabrication robustness.

🔢 Step 5: Weld Check

Welds attach the end plate to the beam web and flanges.

Assume 6 mm fillet welds both sides of the web and flanges.

The standard weld capacity $(f_{vd})$ can be verified, but typically a 6 mm fillet weld is sufficient to resist the shear demand.

📈 Step 6: Final Check Summary

Component	Check	Status
Bolt Shear	90.45 kN per bolt × 2 shear planes	✅ OK
Bolt Group	723.6 kN total vs 90 kN applied load	✅ OK
End Plate Bending	10 mm thickness adequate	✅ OK
Weld Capacity	6 mm fillet weld sufficient	✅ OK

🏆 Final Design

4 × M20 Grade 8.8 bolts in double shear
10 mm S275 end plate
6 mm continuous fillet welds top, bottom, and web
Clear and robust connection suitable for simple, pinned behavior

✅ Meets the assumptions and requirements of the SCI Green Book for Simple Connections and Eurocode 3.

📚 Where Simple Connections Are Used

Simple connections are one of the most common types of joints in structural steelwork. They’re designed to transmit shear forces and axial loads only — no significant moments. They are treated as pinned connections in structural analysis.

✅ Typical Applications for Simple Connections

1. Steel-Framed Buildings

Beams-to-Columns:
In low- to mid-rise buildings, simple beam-to-column connections are typical. They transfer shear and avoid building up unwanted moments that would complicate design.
Floor Beams:
Secondary beams (joists) connected to primary beams using fin plates or flexible end plates.
Bracing Systems:
Where members primarily carry axial loads, pinned connections are simple and economical.

2. Industrial Structures

Warehouses, Factories, and Sheds:
Portal frames are often designed with pinned bases and rigid (moment) joints at the eaves — but the secondary steel (like purlins, side rails) uses simple connections.
Pipe Racks:
Lightweight frames that support piping — simple connections reduce fabrication and erection costs.

3. Bridges

Deck Beams to Girders:
In composite or steel bridges, floor beams are often connected simply to the main girders to allow rotation and avoid moment restraint.
Temporary Structures:
Where ease of assembly and disassembly is critical, pinned/simple connections are practical.

4. Temporary and Modular Structures

Exhibition halls, stages, scaffolding:
Modular steelwork often relies on simple, fast-to-install connections that allow easy dismantling — pinned behaviour is ideal.

5. Retrofit and Repair Work

Strengthening Projects:
Adding new members to existing frames — simple shear connections are less invasive to install and avoid overloading old columns.

🧠 Why Use Simple Connections?

Ease of Fabrication:
Simpler to fabricate — fewer welds, standard bolts, less material.
Ease of Erection:
Faster to assemble on-site — just bolt together, no need for site welding or complex alignment.
Economical:
Lower material and labour costs.
Predictable Behaviour:
Structural analysis is simpler — assumptions about pinned joints match reality well for simple structures.
Safety:
Reduces the risk of unintended moment build-up, which could cause brittle failure.

⚠️ Limitations

Cannot resist moments — not suitable where frame stability depends on moment-resisting joints (e.g., seismic design, tall frames needing lateral stiffness).
May require additional bracing or moment frames elsewhere in the structure for global stability.

🏗️ In Summary

✅ Simple connections are the backbone of standard steel-framed buildings, industrial structures, and economical construction.
They allow efficient load transfer with minimum cost and complexity — especially where moment resistance is not critical.

📚 For Further Information

For deeper guidance on designing simple connections and ensuring compliance with structural codes such as Eurocode 3 and SCI Green Books, it’s essential to consult the latest design manuals and connection guides.

For more information on how Eurocode 3 is applied see: Eurocode 3.

To download your own copy of the book, see: Green Book Simple Connections.

For further detail on all of Product Development Engineers Ltd’s design services see: PDE’s Design services.

If you need expert assistance with structural design, connection detailing, or code compliance, Product Development Engineers Ltd offers specialist services in:

Structural connection design
Engineering calculations
Finite Element Analysis (FEA)
Design validation and certification

✅ Get in touch today to discuss how we can help bring confidence and compliance to your next project.

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Simple Connections – the SCI Green Book explained

✅ Full Title

🎯 What Are Simple Connections?

🧠 Why the Green Book Exists

🔍 What’s Inside the Green Book

✅ Typical Simple Connection Types Covered

📚 Sections of the Green Book

🧩 Component Method (Eurocode 3)

📊 Example: End Plate Connection Design

🚀 Benefits of Using the Green Book

⚙️ Who Should Use It

📚 Recent Editions and Versions

🏆 Summary

📚 Worked Example: Flexible End Plate Connection Design

✅ Problem Statement

🧠 Step 1: Design Assumptions

🔢 Step 2: Bolt Shear Capacity

🔢 Step 3: Shear Check

🔢 Step 4: End Plate Bending Check

🔢 Step 5: Weld Check

📈 Step 6: Final Check Summary

🏆 Final Design

📚 Where Simple Connections Are Used

✅ Typical Applications for Simple Connections

1. Steel-Framed Buildings

2. Industrial Structures

3. Bridges

4. Temporary and Modular Structures

5. Retrofit and Repair Work

🧠 Why Use Simple Connections?

⚠️ Limitations

🏗️ In Summary

📚 For Further Information

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