Technical Guide - Timber Bridges - How to ensure their durability

Technical Guide - Timber Bridges - How to ensure their durability

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With the environmental concerns, the bridges owners rediscover timber construction and its cordial aspect.

In addition, the timber bridges are light and easy to erect: they thushave a strong potential of development, in particular for pedestrianbridges.

However, the durability of these structures is mainly based on thechoice of the right initial drawings who protect the wood. It is alsobased on the quality of maintenance.

Description

With the environmental concerns, the bridges owners rediscover timber construction and its cordial aspect.

In addition, the timber bridges are light and easy to erect: they thushave a strong potential of development, in particular for pedestrianbridges.

However, the durability of these structures is mainly based on thechoice of the right initial drawings who protect the wood. It is alsobased on the quality of maintenance. Moreover, in the event ofdemolition of a bridge whose wood were treated with chemicalpreservatives, the bridge owners are responsible for the producedwastes.

After the history of timber bridges, the guide published by Sétra :

* recalls the essential concepts on the anatomy and themechanical and physical properties of this material;

* presents the wood attackers and the methods used to preservewood, underlining the disadvantages of certain chemicalmethods;

* exposes the principal engineering drawings to ensure theprotection of timber structures;

* provides recommendations to the project managers toformalize a good choice of wood, to choose the treatments ofpreservation and the engineering drawings.

Sommaire

Synopsis

1. - General Presentation..............................................................................................................................................8

1.1. - WOOD: A LITTLE KNOWN MATERIAL TODAY............................................................................................... 8

1.2. - HISTORY OF TIMBER BRIDGES................................................................................................................... 10

1.2.1. – The first bridges.................................................................................................................................... 10

1.2.2. - Evolution of bridge construction and maintenance.......................................................................................... 11

1.2.3. - Durability, a forgotten design criterion......................................................................................................... 12

1.2.4. - An exception: timber bridges of Switzerland................................................................................................. 16

1.2.5. – Timber bridges of North America............................................................................................................. 17

1.2.6. - The return of wood.................................................................................................................................. 18

2. – Wood - The material ...........................................................................................................................................21

2.1. - GENERAL.................................................................................................................................................. 21

2.1.1 – Occurrence and availability....................................................................................................................... 21

Metropolitan Woods (or indigenous Woodsof Europe).............................................................................................. 21

The particular case of French Guiana......................................................................................................................... 22

The Northern woods.................................................................................................................................................. 23

Tropical woods........................................................................................................................................................... 23

2.1.2. – Sawn and reconstituted products............................................................................................................... 23

Sawing........................................................................................................................................................................ 24

Glued-laminated wood ( Glulam or glue-lam )............................................................................................................. 24

Industrial products “LVL, LSL and PSL”.................................................................................................................... 27

Panels......................................................................................................................................................................... 27

2.2. - ANATOMY OF WOOD................................................................................................................................. 28

2.2.1. – Untreated wood : a natural, living material................................................................................................. 28

2.2.2. – From the macroscopic to the microscopic...................................................................................................... 29

Wood is strong in both compression and bending....................................................................................................... 29

2.2.3. - Observation of the log.............................................................................................................................. 30

2.2.4. - The ligneous plan................................................................................................................................... 32

The ligneous plan of the coniferous trees.................................................................................................................... 33

The ligneous plan of leafy trees................................................................................................................................... 34

Ligneous plan and properties of wood......................................................................................................................... 34

2.2.5. - Cellular structure and chemical composition.................................................................................................. 36

2.3. - PHYSICAL PROPERTIES.............................................................................................................................. 37

2.3.1. - Wood and water..................................................................................................................................... 37

Wood moisture........................................................................................................................................................... 37

Drying........................................................................................................................................................................ 38

An anisotropic shrinkage............................................................................................................................................. 40

Influence of water on mechanical properties............................................................................................................... 44

2.3.2. - Behavior with respect to fire...................................................................................................................... 44

Flammability, reaction to fire....................................................................................................................................... 44

Stability with fire......................................................................................................................................................... 45

2.4. - MECHANICAL PROPERTIES OF WOOD........................................................................................................ 46

2.4.1. - Mechanical properties.............................................................................................................................. 46

Density....................................................................................................................................................................... 46

Orthotropism............................................................................................................................................................. 46

Rheology of wood....................................................................................................................................................... 48

Factors influencing performance................................................................................................................................. 49

2.4.2. - Dynamic Damping................................................................................................................................. 49

2.4.3. - Classification of solid wood....................................................................................................................... 49

Methods..................................................................................................................................................................... 49

Singularities of wood................................................................................................................................................... 52

2.4.4. - Creep................................................................................................................................................... 53

2.5. - DURABILITY.............................................................................................................................................. 53

2.5.1. - Aggressors............................................................................................................................................ 53

Fungi.......................................................................................................................................................................... 53

Insects........................................................................................................................................................................ 55

Marine borers............................................................................................................................................................. 57

Sun and rain................................................................................................................................................................ 57

2.5.2. - Preservation........................................................................................................................................... 57

General principle........................................................................................................................................................ 57

Classes of employment (standard EN 335).................................................................................................................. 60

Natural durability according to wood type................................................................................................................... 60

Natural durability and class of employment................................................................................................................. 61

Impregnability............................................................................................................................................................. 62

2.5.3. – Preservation treatments........................................................................................................................... 63

Products..................................................................................................................................................................... 63

Implementation.......................................................................................................................................................... 64

Requirements of penetration and retention.................................................................................................................. 65

Guarantees.................................................................................................................................................................. 66

2.5.4. - Finishes................................................................................................................................................ 67

Protective coatings...................................................................................................................................................... 67

Varnishes and paint.............................................................................................................................................. 67

Other finishes............................................................................................................................................................. 68

3. - Use of chemical preservatives: regulations and management at end of life ................................................69

3.1. -RESPECT OF CONSTRAINTS RELATED TO HEALTH AND THE ENVIRONMENT.............................................. 69

3.2. – PRESERVATION TREATMENTS FOR CLASS OF EMPLOYMENT 2................................................................... 69

3.3. – PRESERVATION TREATMENTS FOR CLASSES OF EMPLOYMENT 3, 4 AND 5................................................. 69

3.4. - REGULATIONS APPLICABLE TO TREATED WOOD,CONCERNING THE USE OF TOXIC PRODUCTS................. 70

3.4.1. - General regulation context........................................................................................................................ 70

3.4.2. – Regulation situation of traditional chemical treatments................................................................................... 71

Arsenic salts (CCA)..................................................................................................................................................... 71

Pentachlorophenol (PCP)............................................................................................................................................ 71

Creosote..................................................................................................................................................................... 72

3.4.3. - Alternative treatments............................................................................................................................. 72

Woods treated at high temperature.............................................................................................................................. 72

Substitutes for CCA.................................................................................................................................................... 73

3.5. - REGULATIONS CONCERNING TREATED WOOD WASTE:.............................................................................. 73

3.5.1. - Demolition of old structures...................................................................................................................... 73

3.5.2. - Treated wood waste: classification and nomenclature....................................................................................... 73

Wood treated with CCA or creosote: a waste classified as dangerous......................................................................... 73

3.5.3. – Channels of waste treatment:.................................................................................................................... 74

Particular case of wood waste contaminated by xylophagous insects (Article 10 of the decree of October 2, 1992)............... 75

3.5.4. - Obligation of the building owner, producer of waste........................................................................................ 75

3.6. - CONCLUSION............................................................................................................................................ 77

4. - Design of engineering structures in wood..................................................................................78

4.1 - Types of structures adapted to wood..........................................................................................78

4.1.1. - Principles of use of wood in bridges ................................................................................................ 78

Timber bridges and heavy vehicle traffic................................................................................................................... 78

General design principles............................................................................................................................................ 78

Importance of association of wood and other materials.............................................................................................. 79

4.1.2. - Various structures.................................................................................................................................. 81

Arch bridges............................................................................................................................................................... 81

The composite timber-concrete bridges....................................................................................................................... 83

Farm bridges............................................................................................................................................................... 86

Lattice beam bridges................................................................................................................................................... 87

Strut frame bridges...................................................................................................................................................... 89

Suspension bridges or stayed...................................................................................................................................... 92

Composite timber- steel bridges................................................................................................................................. 93

4.1.3. - Examples of footbridges........................................................................................................................... 94

Vaires footbridge........................................................................................................................................................ 94

Ajoux footbridge......................................................................................................................................................... 94

Footbridge at Saint-Jorioz........................................................................................................................................... 95

Footbridge in Grigny.................................................................................................................................................. 95

Bridges with full side beams........................................................................................................................................ 97

4.2. – DISEASES AND CAUSES OF DAMAGE........................................................................................................ 100

4.2.1. – Lack of drainage and ventilation............................................................................................................ 100 6Sealing...................................................................................................................................................................... 100

Wood badly ventilated............................................................................................................................................... 100

Assembly trapping water........................................................................................................................................... 101

Flat surface............................................................................................................................................................... 102

4.2.2. - Solar Aggression and humidity gradient.................................................................................................... 102

4.2.3. - Other causes........................................................................................................................................ 103

4.2.4. - Maintenance........................................................................................................................................ 104

4.3. - CONSTRUCTIVE PROVISIONS................................................................................................................... 105

4.3.1. - General Rules...................................................................................................................................... 105

4.3.2. - Covered bridges.................................................................................................................................... 105

4.3.3. - Boarding............................................................................................................................................. 106

Boarding arrangements............................................................................................................................................. 107

Protective hoods....................................................................................................................................................... 108

Protection of the end wood............................................................................................................................. 110

Handrail.................................................................................................................................................................... 111

4.3.4. - Joints................................................................................................................................................. 113

Some rules about joints............................................................................................................................................. 113

Ventilation of wood.................................................................................................................................................. 116

Joining using supports............................................................................................................................................... 118

Water traps............................................................................................................................................................... 119

4.3.5. - Flooring decks..................................................................................................................................... 119

Wood flooring.......................................................................................................................................................... 120

Bituminous flooring.................................................................................................................................................. 120

4.4. - CHOICE OF WOODS................................................................................................................................. 122

4.4.1. - Wood in class of employment 2................................................................................................................ 122

Parts concerned........................................................................................................................................................ 122

Woods usable........................................................................................................................................................... 122

Treatments................................................................................................................................................................ 122

4.4.2. - Wood in class of employment 3................................................................................................................ 122

Introductory remark.................................................................................................................................................. 122

Parts of structure concerned...................................................................................................................................... 122

Woods usable........................................................................................................................................................... 122

4.4.3. – Special case of boarding......................................................................................................................... 123

Generalities............................................................................................................................................................... 123

Woods with sufficient natural durability.................................................................................................................... 123

Durability conferred by treatment............................................................................................................................. 123

4.4.4. - Wood in class of employment 4 and 5....................................................................................................... 124

Parts concerned........................................................................................................................................................ 124

Types of wood usable............................................................................................................................................... 124

4.4.5. – Summary table of choice of woods............................................................................................................ 125

5. – Help for writing order...................................................................................................................................... 126

5.1. - DEFINITION OF THE ORDER.................................................................................................................... 126

5.1.1. - The program of the structure................................................................................................................... 126

5.1.2. - Qualification of the company................................................................................................................... 127

5.1.3. – Project Management............................................................................................................................. 127

5.1.4. - External Control................................................................................................................................. 127

5.2.1. - Documents to be supplied by the contractor................................................................................................. 128

5.2.2. - Plan of quality assurance (PAQ)............................................................................................................ 128

5.2.3. – Execution procedures............................................................................................................................ 130

5.2.4. - Constructive Provisions.......................................................................................................................... 130

5.2.5. – Regulation texts and calculations............................................................................................................ 131

5.2.6. - Forces, stresses, justifications................................................................................................................... 131

5.3. - SOURCE, QUALITY AND PREPARATION OF MATERIALS............................................................................. 131

5.3.1. – Wood material.................................................................................................................................... 131

Types of wood.......................................................................................................................................................... 131

Wood humidity......................................................................................................................................................... 132

Mechanical classification........................................................................................................................................... 132

Section of woods and tolerances...............................................................................................................................132

Adhesive................................................................................................................................................................... 133

Tropical woods......................................................................................................................................................... 133

Chemical interaction with metal................................................................................................................................ 133

Receiving.................................................................................................................................................................. 133

Requirements, implementation.................................................................................................................................. 134

7Certificates, attestations............................................................................................................................................. 134

Finish....................................................................................................................................................................... 134

5.4. – EXECUTION OF THE WORK..................................................................................................................... 135

5.4.1. - Execution and assembly of the wooden structure.......................................................................................... 135

5.4.2. - Tests of the structure............................................................................................................................. 135

5.4.3. - Internal control.................................................................................................................................... 135

5.4.4. - External control................................................................................................................................... 135

5.5. - THE UNIT AND CONTRACT PRICE SCHEDULE (CPS)................................................................................. 135

5.5.1. - Price of framework................................................................................................................................136

5.5.2. - Price of boarding.................................................................................................................................. 136

5.5.3. - Price of pedestrian flooring...................................................................................................................... 136

5.5.4. - Price of on-site assembly......................................................................................................................... 136

5.5.5. - Steel Price for assemblies........................................................................................................................ 137

5.5.6. - Price of protective coating........................................................................................................................ 137

5.5.7. - Price of tests........................................................................................................................................ 137

5.6. - FOLLOW-UP OF THE STRUCTURE............................................................................................................. 137

5.7. - SUMMARY: WHO DOES WHAT?................................................................................................................. 139

6. - Appendices ......................................................................................................................................................... 140

6.1. - LEXICON................................................................................................................................................. 140

6.2. - CLASSIFICATION PROCEDURE OF THE AUTHORIZED SUBSTANCES........................................................... 143

6.3. - EUROPEAN AND FRENCH REGULATIONS: HEALTH, ENVIRONMENT AND BIOCIDES DIRECTIVE............. 144

6.4. - PRINCIPAL PRODUCTS USED FOR WOOD PRESERVATION IN FRANCE, AND REGULATIONS........................ 147

6.5. – WASTE CLASSIFICATION PROCEDURE..................................................................................................... 148

Structure of the classification of waste....................................................................................................................... 148

6.6. - DANGEROUS WASTE...............................................................................................................................151

Components which make waste dangerous ................................................................................................ 151

Properties that make waste dangerous....................................................................................................... 152

6.7. - HOW TO FILL IN AN INDUSTRIAL WASTE FOLLOW-UP FORM (BSDI)......................................................... 154

6.8. - REGULATION RELATING TO WASTE......................................................................................................... 156

6.9 – STANDARD SECTIONS.............................................................................................................................. 157

6.10 - BIBLIOGRAPHICAL REFERENCES............................................................................................................. 158

PRINCIPAL STANDARDS.................................................................................................................................... 158

Vocabulary.................................................................................................................................................... 158

Safeguarding of wood........................................................................................................................................ 158

Classification.................................................................................................................................................. 160

Manufacture and tolerances................................................................................................................................161

Joints............................................................................................................................................................ 161

Adhesives...................................................................................................................................................... 162

Tests and measurements.................................................................................................................................... 162

Surface coatings............................................................................................................................................... 163

Panels........................................................................................................................................................... 163

DTU............................................................................................................................................................ 164

Waste regulations............................................................................................................................................ 164

6.11 - GUIDES AND OTHER TECHNICAL DOCUMENTS....................................................................................... 165

6.12. - TABLES OF THE FIGURES AND TABLES................................................................................................... 167

6.13. - TABLE OF THE PHOTOGRAPHS............................................................................................................... 169

6.14. - USEFUL ADDRESSES OTHER THAN SÉTRA.............................................................................................. 172

Détails
Catégorie de produit
Ouvrage
Numéro ISRN
EQ-SETRA--07-ED40--FR+ENG
Editeur
Cerema (ex-Setra)
Auteur collectif
Cerema
Date de parution
Nombre de pages
173 pages
Langue de la publication
Anglais
Type d'auteur
Oeuvre collective
Paiement 100% sécurisé
Livraison dans le monde entier