EN 1995-2 Timber Bridges

Oslo May 2. 2018

CEN TC250 SC5

WG6 (Convenor Kjell Arne Malo)

2

Topics with Priority

• Issues not covered in EN 1995-1-1 Buildings

1. Fatigue loading and resistance

2. Prestressed laminated timber deckplates (stress-laminated)

3. Durability, Detailing and Water Management

4. Timber-Concrete Composites bridges

5. Pedestrian bridges and human induced vibrations

3

1. Fatigue, resistance

-1 0 1 2 3 4 5 6 7 8

Log N

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1.1

f ma

x

R=0.1

Multiple dowel

connection axially

loaded

4

Effect of stress ratio (or mean stress)

Source Type of loading RA

(experimental)

A

(EN1995-2)

Malo et al

(2006)

Dowelled

connections (Nordic

Pine glulam)

0.1 0.066 0.079

-1 0.098 0.111

Malo et al (2006)

ത𝜎𝑚𝑎𝑥 ≈ 1 − 𝐴 ∙ log10𝑁

Introduction · European Standards · Fatigue lives of WBP/Connections · Deformation/Damage - Conclusions

5

Stress range vs max stress

• Steel – stress range:

𝛾𝐹𝑓Δ𝜎𝐸,2 ≤Δ𝜎𝑐

𝛾𝑓

• Wood – max stress:

𝜎𝑑,𝑚𝑎𝑥 ≤ 𝑘𝑓𝑎𝑡 ∙𝑓𝑘

𝛾𝑀,𝑓𝑎𝑡

6

Fatigue life – mean stress, stress ratio

• Stress and Strength based on stress range

• implies

– Strength independent of mean stress (or R)

𝜎𝑚𝑒𝑎𝑛 =1

2𝜎𝑚𝑎𝑥 + 𝜎𝑚𝑖𝑛 =

1

2𝜎𝑚𝑎𝑥 1 + 𝑅

𝑅 = Τ𝜎𝑚𝑖𝑛 𝜎𝑚𝑎𝑥

1

2 1mean

R

R

Δ𝜎 = 𝜎𝑚𝑎𝑥 − 𝜎𝑚𝑖𝑛

σa =1

2𝜎𝑚𝑎𝑥 − 𝜎𝑚𝑖𝑛 =

1

2𝜎𝑚𝑎𝑥 1 − 𝑅

7

𝜅 =𝜎𝑑,𝑚𝑎𝑥 − 𝜎𝑑,𝑚𝑖𝑛

𝑓𝑘𝛾𝑀,𝑓𝑎𝑡

≤ 𝜅𝑙𝑖𝑚

Type of loading or joint Limit value of ratio κ

members in compression parallel or

perpendicular to grain0.60

members in bending or tension 0.20

members in shear 0.15

connections with dowels 0.40

connections with nails 0.10

other connections 0.15

𝜎𝑑,𝑚𝑎𝑥 ≤ 𝑘𝑓𝑎𝑡 ∙𝑓𝑘

𝛾𝑀,𝑓𝑎𝑡

𝑘𝑓𝑎𝑡 = 1 −1 − 𝑅

𝑎 ∙ 𝑏 − 𝑅∙ log10 𝑁

Type of loading or connections a b

Compression parallel or perpendicular to

grain2.0 9.0

Bending or tension 9.5 1.1

Shear 6.7 1.3

Connections with dowels (d ≤ 12 mm) 6.0 2.0

Connections with nails 6.9 1.2

Unlimited fatigue strength if:

Fatigue life assessment (S-logN):

𝐴 =1 − 𝑅

𝑎 ∙ 𝑏 − 𝑅Slope of S-logN line:

Fatigue verification according to EN 1995-2 (informative)

ത𝜎𝑚𝑎𝑥 = 1 − 𝐴 ∙ log10 𝑁

8

“Cyclic” Fatigue,

wood is anisotropic material

• Different slopes

of S- logN curves

for different:

– fastener types

– stress situation

9

WOOD

Slope of the fatigue curves: Depends on R

ത𝜎𝑚𝑎𝑥 ≈ 1 − 𝐴 ∙ log10 𝑁

𝐴 =1 − 𝑅

𝑎 ∙ 𝑏 − 𝑅

𝑅 = Τ𝜎𝑚𝑖𝑛 𝜎𝑚𝑎𝑥

10

“Static” Fatigue

• Interaction ?

– Static fatigue

(strength

reduction with

duration of

load (DOL)

11

Fatigue strength

• Interaction ?

– Static fatigue (DOL: Duration Of Load)

– Cyclic fatigue (Number of cycles)

• Models for interaction ?

– Linear like Miner Palmgren

– Nonlinear incremental damage model

12

Fatigue and load models timber bridges

• Effect of mean stress and Load models in EN 1991-2?

• Load combination, cyclic and static fatigue?

• Mean stress or stress ratio?

• How to count and combine different stresses and

cycles?

– Rainflow or similar methods

– Miner Palmgren?

13

2. Prestressed laminated timber

deckplates (stress-laminated)

14

Stress laminated decks

• Functional requirements of systems

• Special effects:

– Prestressing and long term properties

– Friction

– Computations

15

3. Durability, detailing and water

management

Timber Bridge buillt 1988

DEMOLISHED

16

Trondheim, Norway

• Buillt 1861

17

Durability and detailing

1. Water management on covered or non-covered

timber bridges

2. Protection and preventive measures for weather or

humidity exposed constructions

3. Ventilation measures for dehumidification of timber

bridges

4. Monitoring and maintenance of timber bridges

Wooden bridge decks – edge details

• Stress-laminated timber decks

• Asphalt wearing surface on top

• Waterproof layer

• Edge details

• Ventilated panels along sides

19

4. Timber Concrete Composite Bridges

• General rules in buildings (in-house)

• Add bridge specific parts

– Weather exposed structures (moisture, creep)

– Fatigue

20

5. Pedestrian bridges and human

induced vibrations

• General Requirements in EN 1990

• General Pedestrian Load models in EN1991-2

• Guidelines for calculation of fundamental frequencies in

EN 1995-2 Timber Bridges

• Damping Properties in EN 1995-2 Timber Bridges