1 ARCHING ACTION IN CONCRETE BRIDGE DECKS Research at Queens University of Belfast Dr. Su Taylor Dr....

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ARCHING ACTION IN ARCHING ACTION IN

CONCRETE BRIDGE DECKSCONCRETE BRIDGE DECKS

Research at Queen’s University of BelfastDr. Su TaylorDr. Barry RankinProf. David ClelandProf. AE Long

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IntroductionIntroduction

• BackgroundBackground

• Previous researchPrevious research

• Changes to bridge designChanges to bridge design

• Recent laboratory and field testsRecent laboratory and field tests

• Comparison with existing standardsComparison with existing standards

• Future researchFuture research

• ConclusionsConclusions

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Background to researchBackground to research

Arching action or Compressive Membrane Action (CMA)

applied applied loadload

arching thrust

KKr r = = external external

lateral restraint lateral restraint stiffnessstiffness

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• laterally restrained slabs have inherent laterally restrained slabs have inherent strength due to in-plane forces set up as strength due to in-plane forces set up as a result of external lateral restrainta result of external lateral restraint

• external restraint occurs due to the slab external restraint occurs due to the slab boundary conditions boundary conditions

e.g. beamse.g. beamsdiaphragmsdiaphragmscontinuity of slabcontinuity of slab

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Midspan deflection

Ap

pli

ed

load

Arching Arching capacitycapacity

Bending Bending strengthstrengthfirst

cracking

Load vs. deflection for laterally restrained concrete slab

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Previous researchPrevious research

external external lateral lateral restraint, restraint, stiffness = Kstiffness = K

applied applied loadload

arching thrust

K,K, K,K,

LeLe

E, AE, A

Load, PLoad, P

Arching action and three-hinged arch analogy (Rankin, 1982)

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Clinghan’s bridge test modelClinghan’s bridge test model(Kirkpatrick et al, 1984)

8 Model Clinghan’s bridge deck slab

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Model Clinghan’s bridge deck slab failures loads (Kirkpatrick et al, 1984)

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Clinghan’s bridge load test

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Advantages from CMA in Advantages from CMA in bridge designbridge design

• NI bridge code amendment in 1986- reinforcement reduced from 1.7% to 0.6%T&B

• Improved durability and cost benefits

• BD81/02 – Highways Agency ‘Use of CMA in bridge decks’ is direct result of research at Queens University

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Calgary bridge

Canadian approachCanadian approach

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Calgary bridge –reinforcement detailno internal reinforcement

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Developments in UKDevelopments in UK

Majority of bridges RC

Advance knowledge of CMA:

• High strength concrete and fibres

• Reinforcement Single layer at mid-depth Fibre Reinforced Polymer (FRP’s)

• Goal: maintenance free deck slabs

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Beam and slab superstructuresBeam and slab superstructures

Total unit cost over service life

standard deck (normal durability)

CMA deck (normal durability )

CMA deck CMA deck (enhanced durability)(enhanced durability)

Un

it c

ost

Years in service

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Recent Laboratory testsRecent Laboratory tests

• Series of tests on full-scale slab strips typical of a bridge deck slab

• Variables were:

Concrete compressive strength

Reinforcement type and position

Boundary conditions

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Slab strips test load arrangement

Restraint, KRestraint, K

1425mm1425mmb=475mmb=475mmh=150mmh=150mmd=75 to 104mm d=75 to 104mm

KEY :KEY :

Fixed End & Longitudinal Fixed End & Longitudinal Restraint = F/E+L/RRestraint = F/E+L/R

Simple Support & Longitudinal Simple Support & Longitudinal Restraint = S/S+L/RRestraint = S/S+L/R

Simple Support = S/SSimple Support = S/S

18 Typical test set-up

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0 20 40 60 80 100

Concrete Cube Strength (N/mm^2)

0

50

100

150

200

250

300Fail

ure

Lo

ad

(K

N)

KKrr=197kN/mm=197kN/mmKKrr=410kN/mm=410kN/mm

BS5400 (F/E)BS5400 (F/E)

BS5400 (S/S)BS5400 (S/S)

F/E + L/R S/S S/S + L/R F/E + L/R

Summary of test results

Fai

lure

load

(k

N)

Fai

lure

load

(k

N)

Concrete compressive strength (N/mmConcrete compressive strength (N/mm22))

20 HSC - F/E + L/R model post-failure

topside

severe crushing in compression zone

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0 20 40 60 80 100 1200

50

100

150

200

250

Fai

lure

load

(k

N)

Fai

lure

load

(k

N)

Concrete compressive strength (N/mmConcrete compressive strength (N/mm22))

Comparison Phase 1 results with theory

proposed methodproposed method

F/E + L/R (S1-S5)S/S + L/R (S8)

BS5400 (F/E)BS5400 (F/E)

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Bridge model testsBridge model tests

• Final series of tests on one-third scale bridge deck models

• HSC with variables of:

lateral restraint stiffness reinforcement (type & amount)

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Applied line load

Applied load, PkN

SECTION

Support beam

50mm

PLAN

Typical one-third scale bridge deck model

bb = 100, 150, 200mm

24 Typical reinforcement details

25 Typical test

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0 0.2 0.4 0.6 0.8 1 1.2 1.40

50

100

150

200

250

Third scale bridge model test results - effect of reinforcement

conventional bars T&Bconventional bars Cunbonded bars Cfibres only (1%)F

ailu

re lo

ad (

kN

)F

ailu

re lo

ad (

kN

)

% reinforcement% reinforcement

Two wheel loads45 units HB (ULS)

trend

line

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Third scale bridge model test results – varied restraint to slab

50 100 150 200 2500

50

100

150

200

250

Fai

lure

load

(k

N)

Fai

lure

load

(k

N)

Edge beam width (mm)Edge beam width (mm)

BS5400 shear capacity

BS5400 flexural capacity

conventional bars T&B in slab

QUB capacity

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Corick BridgeCorick Bridge

29 Deck slab reinforcement

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Test panel arrangement

A1 B1

A2

C1

C2B2

D1

D2

F2

F1

E2

E1

Cen

tre

rein

forc

e-m

ent

T &

B

rein

forc

e-

men

t0.5%C 0.25%C 0.5%C reinforcement

0.6%T&B reinforcement

= testing order

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Typical test arrangement

2000mm1500mm

T1 T2 T3 T4 T5

hydraulic jack 300mm steel plate

32 Typical test set-up

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Typical test set-up: deck underside

centreline and span of test panel

T1 T2 T4T3

midspan of test panel

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app

lied

load

(k

N)

app

lied

load

(k

N)

midspan deflection (mm)midspan deflection (mm)

max. wheel load (45units HB)

=span/4250=span/4250

2m test panels- comparison of midspan deflections

0

100

200

300

400

500

0 0.5 1 1.5 2 2.5

A1B1C1D1E1F1

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app

lied

load

(k

N)

app

lied

load

(k

N)

crack width (mm)crack width (mm)

wheel load (45units HB)

2m test panels- comparison of crack widths

0

100

200

0 0.1 0.2

A1B1C1D1E1F1

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CMA in FRP Reinforced BridgesCMA in FRP Reinforced Bridges

• Series of tests on full-scale slab strips

• FRP and steel reinforcement compared

• variables:

boundary conditions

concrete strength

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Preliminary results on GFRP slabsPreliminary results on GFRP slabs

In simply supported slabs • service behaviour of GFRP poor • ultimate strengths similar

In laterally restrained slabs • GFRP & steel slab behaved

similarly in service• GFRP slabs higher ultimate

capacities

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Test results for full scale laterally restrained slab strips

0

50

100

150

200

250

300

0 20 40 60 80 100 120

Experimental:L/R + Steel

Experimental:L/R + GFRP

predicted strength from arching theory

Fai

lure

load

(k

N)

Fai

lure

load

(k

N)

Concrete compressive strength (N/mmConcrete compressive strength (N/mm22))

BS predictions

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ConclusionsConclusions• Degree of external restraint and concrete

strength influence capacity

• deflections up to 45 units HB wheel load were independent of %As

• crack widths up to 45 units HB wheel load were substantially narrower than BS limits

• strength of panels with centre reinforcement in excess of ultimate wheel load

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• Structural benefits of CMA well understood

• CMA incorporated in Ontario & UK codes

• Improved strength/serviceability less problems for assessment

• Arching phenomenon has potential for substantial economies

Concluding remarksConcluding remarks