development of a slab-on-girder wood-concrete … · development of a slab-on-girder wood-concrete...

DEVELOPMENT OF A SLAB-ON-GIRDER WOOD-CONCRETE COMPOSITE HIGHWAY BRIDGE

International Conference on Timber Bridges 2013

Las Vegas, NV

September 2013

Andrew Lehan David Moses

Development of a Slab-on-Girder Wood-Concrete Composite Highway Bridge

Andrew Lehan, Delcan & David Moses, Moses Structural Engineers

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THE ``PROPOSED CONCEPT``

• Slab-on-girder bridge superstructure • Vehicular bridge • Applied loads as per the Canadian Highway Bridge Design Code • Designed for spans ranging from 10 m – 30 m in 5 m increments



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THE NEED FOR A WOOD-CONCRETE COMPOSITE BRIDGE?

• Wood bridges are rare in Canada in spite of a large forestry industry

• Advancements in material technology afford longer span opportunities for wood bridges:

Ultra-high performance fibre-reinforced concrete

External unbonded post-tensioning

• Slab-on-girder bridges are common in Canada

• Cast-in-place concrete is scarce in many remote regions

Roadway cross-section valid for:

1) an undivided local rural road with a speed limit of 100 km/h

2) an undivided urban collector road with a speed limit of 80 km/h

ROADWAY CROSS-SECTION



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STRUCTURAL CROSS-SECTION



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• Four double-T modules • Eight glued-laminated girders • 110 mm thick ultra-high performance fibre-reinforced concrete deck • Composite action between deck and girders • Longitudinal and transverse post-tensioning

PRESTRESSING CONCEPT



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Longitudinal Tendon Profile

Tendon Deviator End Buttress

DIAPHRAGMS



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• Cast monolithically with deck slab • Improve live load distribution between girders • House transverse post-tensioning ducts &

anchorages

CONSTRUCTION SEQUENCE



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Stage 1

• Erect modules

Stage 2

• Stress transverse & longitudinal tendons

Stage 3

• Construct curbs & barrier

• Pave deck

ULTRA-HIGH PERFORMANCE FIBRE-REINFORCED CONCRETE St

ress

Strain εc

fc'

0

0

Stre

ss

Strain εt

ft'

0 0

fcr

εcr

Cracking Strength = 7.0 MPa

Ultimate Tensile Strength = 14.6 MPa Ultimate Compressive Strength = 120 MPa



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Benefits: • Allows for slender slab, unlike conventional concrete • High tensile strength precludes most passive reinforcement • Very low permeability (enhances durability) • Excellent freeze-thaw resistance (enhances durability)

Behaviour in Compression Behaviour in Tension

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COMPOSITE ACTION

• Proposed concept is a partially-composite system



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LONGITUDINAL SHEAR CONNECTOR



Lo

ad

Displacement

Idealized Connector Behaviour

Span % Composite Action

10 m 87%

15 m 92%

20 m 95%

25 m 96%

30 m 87%

• Idealized behaviour is supported by experimental evidence

• Nearly full composite action is attainable

SUMMARY OF THE PROPOSED CONCEPT



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Span Depth Span-to-Depth Ratio

10 m 0.56 m 17.9

15 m 0.76 m 19.7

20 m 0.91 m 22.0

25 m 1.11 m 22.5

30 m 1.26 m 23.8

SLAB-ON-CPCI-GIRDER BRIDGES



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TYPICAL CROSS-SECTION

COMPARISON TO SLAB-ON-CPCI-GIRDER BRIDGES

0

2

4

6

8

10

12

10 15 20 25 30 35

kN

/m

2

Span (m)

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

10 15 20 25 30 35

m3/

m2

Span (m)

Superstructure Weight

Volume of Cast-in-Place Concrete

14

16

18

20

22

24

26

10 15 20 25 30 35

Sp

an

-to

-De

pth

Ra

tio

Span (m)

Slenderness

Legend

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Proposed Concept

CPCI Girder Bridges



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CONCLUSIONS RELATIVE TO SLAB-ON-CPCI-GIRDER BRIDGES

1) The Proposed Concept is half as heavy • Less expensive foundations • Less expensive transportation of materials to site • Lesser inertial forces during seismic event

2) The Proposed Concept uses much less cast-in-place concrete • Shorter duration of on-site construction • Likely more durable

3) The Proposed Concept is much more slender • Greater structural efficiency • Less approach fill and shallower fill retaining structures

development of a slab-on-girder wood-concrete … · development of a slab-on-girder wood-concrete...

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