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PD 06687 — Concrete Structures Eurocode UK National Annex Background and Design Recommendations Standard Series (PD 6687)
Background to the UK National Annexes and Recommendations for the Design of Structures to Eurocode 2 (Published Document series)
📐 PD 6687 is a British Standards Institution (BSI) “Published Document” (PD) series providing background documents and design recommendations for the application of Eurocode 2 (BS EN 1992 series) for concrete structures in the UK. The series is the responsibility of BSI Technical Committees B/525/2 (Structural use of concrete) and B/525/10 (Bridges). This batch collects two parts: Part 1 (PD 6687-1:2010) is the background to the UK National Annexes to BS EN 1992-1 and BS EN 1992-3, and Part 2 (PD 6687-2:2008) is the recommendations for the design of structures to BS EN 1992-2.
💡 The Eurocodes are developed by CEN (European Committee for Standardization); the UK determines national parameter values through National Annexes. PD 6687 is the key document explaining the background of these national parameters and providing non-contradictory complementary information (NCCI) for practical application.
1. Series Overview and Positioning 📌
PD 6687 targets UK structural engineers using Eurocode 2, providing explanatory background of National Annex parameters, design recommendations and supplementary rules. The parts serve different sub-parts of Eurocode 2: Part 1 covers BS EN 1992-1 (buildings) and BS EN 1992-3 (liquid retaining/containing structures), and Part 2 covers BS EN 1992-2 (bridges).
This batch contains the following two parts:
| Document | Subject | Edition | Companion standard | Core content |
|---|---|---|---|---|
| PD 6687-1:2010 | Background to the UK National Annexes to BS EN 1992-1 and BS EN 1992-3 | 2010 | BS EN 1992-1-1, 1-2, BS EN 1992-3 | Background of National Annex parameters, materials/crack width, detailing for particular situations, structural appraisal and temperature effects |
| PD 6687-2:2008 | Recommendations for the design of structures to BS EN 1992-2 | 2008 | BS EN 1992-2 (bridges) | Bridge design basis, materials, durability, structural analysis, ultimate/serviceability states, reinforcement detailing and external prestressing |
⚠️ Part 1 and Part 2 target “buildings/liquid-retaining structures” and “bridges” respectively. Select by structure type and do not mix; PD 6687 provides complementary information and recommendations and does not replace the mandatory clauses of Eurocode 2.
2. National Annex Background (Part 1) 🔧
Part 1 explains the background of the parameter values in the UK National Annexes to BS EN 1992-1 and BS EN 1992-3, with supplementary recommendations:
- Materials and reinforcement: gives the distribution of reinforcement yield strengths, concrete stress-strain relationships (for different loading durations) and explanations of average compressive-zone stress and centroid position, providing background for material partial factors and design curves.
- Crack width calculation: lists typical crack-width calculation cases (e.g. non-rectangular tension zones) for design verification.
- Detailing (Annex B): detailing rules for particular situations, such as frame corners and corbels with strut-and-tie models.
- Structural appraisal and testing (Annex C): guidance for appraisal and testing of existing structures.
- Temperature effects (Annex D): creep coefficient multipliers for concrete heated prior to loading.
This part helps engineers understand why the National Annex chooses particular parameter values, enabling correct application of Eurocode 2.
3. Bridge Structure Design Recommendations (Part 2) 🌉
Part 2 gives non-contradictory complementary information (NCCI) and design recommendations for BS EN 1992-2 (concrete bridges):
- Design basis and materials: structural analysis, material properties and design assumptions.
- Durability and cover: concrete cover and durability requirements.
- Ultimate limit state design: bending, shear, punching and crack control, with limiting strain distributions and shear reinforcement design increment guidance.
- Serviceability limit state: stress limits, crack width and deflection control.
- Detailing and prestressing: effective height, limiting stress ranges, minimum spacing of post-tension ducts and minimum radius of curvature of tendons.
- Precast and external prestressing: additional rules for precast elements and externally prestressed structures.
In bridge design, fatigue (stress range) and prestressing detailing are key; Part 2 provides specific numerical recommendations for these.
💡 Engineering note: PD 6687’s “recommendations” (should) differ from the Eurocode’s “requirements” (shall). Design should first satisfy the mandatory Eurocode 2 requirements, then optimise and check with PD 6687; never rely on PD 6687 alone without executing the Eurocode.
4. Engineering Practice Points ⚙️
- 🔍 National parameters: when using UK National Annex parameters, consult PD 6687-1 to understand the background and ensure correct parameter selection.
- 🔧 Cracks and durability: check crack width and cover per Parts 1 and 2 to satisfy durability and serviceability.
- 📊 Bridge fatigue: check reinforcement stress ranges in road bridges against the Part 2 limits to control fatigue cracking.
- 📋 Structural appraisal: for existing concrete structures, appraise and test per Annex C of Part 1.
5. Frequently Asked Questions ❓
❓ Q: What is the relationship between PD 6687 and Eurocode 2?
A: PD 6687 is the background document and design recommendations for the UK National Annexes to Eurocode 2 (BS EN 1992), providing explanation and complementary information (NCCI), but it does not replace the mandatory clauses of Eurocode 2.
A: PD 6687 is the background document and design recommendations for the UK National Annexes to Eurocode 2 (BS EN 1992), providing explanation and complementary information (NCCI), but it does not replace the mandatory clauses of Eurocode 2.
❓ Q: How to choose between Parts 1 and 2?
A: Part 1 is for buildings and liquid-retaining structures (BS EN 1992-1, 1992-3); Part 2 is for bridges (BS EN 1992-2). Select by structure type.
A: Part 1 is for buildings and liquid-retaining structures (BS EN 1992-1, 1992-3); Part 2 is for bridges (BS EN 1992-2). Select by structure type.
❓ Q: Why are National Annex parameters so important?
A: The Eurocodes give permissible parameter ranges; the National Annex determines the specific values used in the UK. These parameters (e.g. material partial factors, load combinations) directly affect design results and safety, and PD 6687 explains their background.
A: The Eurocodes give permissible parameter ranges; the National Annex determines the specific values used in the UK. These parameters (e.g. material partial factors, load combinations) directly affect design results and safety, and PD 6687 explains their background.
🔍 Q: How is crack width checked?
A: Calculate per the Eurocode 2 crack-width formulae (including the typical cases given in Part 1) and compare with the limit; for bridges, apply the Part 2 stress-range and crack-control recommendations as needed.
A: Calculate per the Eurocode 2 crack-width formulae (including the typical cases given in Part 1) and compare with the limit; for bridges, apply the Part 2 stress-range and crack-control recommendations as needed.