Graeme Walker Design Illustration Concrete

7/29/2019 Graeme Walker Design Illustration Concrete

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22 - 23 November, 2010

Institution of Civil Engineers

Bridge Design to Eurocodes- UK Implementation


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Design Illustration Concrete Bridge Design

Graeme Walker, Gifford

Paul J ackson, Gifford


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Introduction

Design example prepared for the Concrete BridgeDevelopment Group

Precast, prestressed beam and slab bridge selected todemonstrate as many aspects of the codes as possible

Follows UK NAs and PDs, but makes clear the sourceof all information


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Scheme Design

2 span integral bridge, each span 20m long

7.3m wide c/way + 2m wide footways either side

Superstructure 8 standard precast, pretensioned concrete Ybeams with a 160mm deep in-situ RC deck slab; in-situ diaphragmsat abutments and pier

Substructure precast concrete piles with pile caps


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Actions

Permanent Actions

- Self weight

- Differential settlement- Differential shrinkage

Variable Actions- Wind

- Thermal

- Traffic Loads


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Traffic Loads

Positioning of the notional lanes does not have to correspond to the

position of the lane markings on the bridge. Instead, the lanes & the

remaining area are posit ioned to create the most severe load effects foreach element under consideration.

Division of carriageway into notional lanes

Carriageway width w = 7.30 m

Width of notional lanes w1 = 3.00 m

Number of notional lanes n1 = 2

Width of remaining area wr = 1.30m


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Traffic Loads Load Model 1

a) A double axleloading, referred to astandem system, or TS.

b) A uniformly

distributed load (UDL).

Normal traffic in EN 1991 is represented by (LM 1),which is the equivalent of HA loading in BD 37.

For each lane, LM1 consists of 2 parts:


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LM3 represents Abnormal Vehicles. The UK NAdefines a series of load models.

The vehicles are applied in the worst position and arecombined with LM1 loads at their frequent values.

4.0m

180kN 180kN 100kN

1.6m 4.4m

Direction of TravelDirection of Travel

165kN 165kN 165kN 165kN 165kN

1.2m 1.2m 1.2m 1.2m

OverallVehicleW

idth

0.35m

0

.35m

3.0m

3.0m

165kN 165kN 165kN 165kN 165kN

1.2m 1.2m 1.2m 1.2m

OverallVehicleW

idth

0.35m

0

.35m

3.0m

3.0m

OverallVehicleW

idth

0.35m

0

.35m

3.0m

3.0m

165

kN

165

kN

165

kN

165

kN

1.2m 1.2m 1.2m

Critical of1.2mor

5.0mor

9.0m

Critical of1.2mor

5.0mor

9.0m

SV 196


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Lanes and remaining area interchangeable for worsteffect

1,3m

Lane 1

Lane 2

Remaining Area

3m

3m

UDL = 0,61 X 9,0 =5,5kN/m2

TS Axle = 1,0 X 300 =300kN

UDL = 2,2 X 2,5 =5,5kN/m2

TS Axle = 1,0 X 200 =200kN

UDL = 2,2 X 2,5 =5,5kN/m2 No TS


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Lanes and remaining area interchangeable for worsteffect

SV/SOV normally replaces lane 2 (or 3+), not lane 1

1,3m

Lane 1

Lane 2

Remaining Area

3m

3m

Frequent value of LM1

Frequent value of

LM1

Frequent value of LM1

SV / SOV


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Global Design at SLS

As for most prestressed structures, SLS criteriagoverned

3 checks were required:

- Decompression (near tendons)

- Crack widths (elsewhere + in RC)

- Stress limits


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Decompression

For XD (chloride) exposure, decompression limit ischecked for the frequent load combination

All concrete within the minimum cover distance of thetendons remain in compression


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Decompression

DecompressionCheck requiredhere! (if a tendon)

Beam section showing strand position


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Decompression

Same design to BS 5400 resulted in a similar level ofprestress

Same design to EN 1992 but with no chloride exposure

allowed a 25% reduction in prestress


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Transfer and Tendon Arrangement

Tendon or rebar?

Beam section showing strand position


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Design at ULS

Flexural design differs little from BS 5400-4

More shear reinforcement required for prestressedmembers

However, interface shear governed in the designexample

(B12 @ 75mm c/f B12 @ 250mm adjacent to supports)


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Fatigue

Method 1

Cumulative fatigue damage due to the predicted cyclicload history of the structure calculated

Impractical for most structures


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Fatigue

Method 2 Simplified method

Not applicable to tendons Calculate stress range due to cyclic portion of the

frequent load combination

Allowable to EN 1992-1-1 = 70 MPa

Allowable to PD for this case = 85 MPa

Stress range under frequent load = 128 MPa

50% increase in reinforcement required over pier


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Fatigue

Method 3 Damage Equivalent Stress Range

Applicable to bars and tendons

Stress range calculated under a special load model

Stress range multiplied by factors reflecting site specificinfluences to give damage equivalent stress range

Stress range under fatigue load model 3 = 96 MPa

Damage equivalent stress range = 140 MPa

Permissible stress range = 141 MPa

No additional reinforcement required


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Conclusion

Prestressed sections designed to EN 1992 comes outvery similar to those designed to BS 5400 for normal

structures

Same design to EN 1992 but with no chloride exposure

allowed a 25% reduction in prestress

Documents

Graeme Walker Design Illustration Concrete