david iles

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22 - 23 November, 2010 Institution of Civil Engineers Bridge Design to Eurocodes - UK Implementation

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Page 1: David Iles

22 - 23 November, 2010Institution of Civil Engineers

Bridge Design to Eurocodes - UK Implementation

Page 2: David Iles

Design illustration – steel-concrete composite bridge design

David IlesThe Steel Construction Institute

Page 3: David Iles

SCI Bridge Design Guides

• Succession of guides over 20 years

• Capture best practice advice• Complemented by worked

examples • Now includes guidance on

use of the Eurocodes• Examples in separate book

Page 4: David Iles

SCI Bridge Design Guides

• Worked examples – P357• Same format as previous

examples to BS 5400• Covers the major stages of

detailed design

• This paper presents an overview of some aspects revealed during preparation

Page 5: David Iles

Scope of the paper

• The examples• Preamble to design verification• Design effects• Global analysis• Design verification of beams• Design of connections

Page 6: David Iles

The examples - 1: Multi-girder bridge

2-span bridge (28 m + 28 m) carrying 2-lane roadWith integral abutments

Page 7: David Iles

The examples - 1: Multi-girder bridge

28000 28000

500 5001000 1000

3700 37003700

marginalstrip

marginalstrip

2000 20007300

1100

Page 8: David Iles

The examples - 2: Ladder deck bridge

3-span bridge (24.5 m + 42 m + 24.5 m)

Page 9: David Iles

The examples - 2: Ladder deck bridge

4200024500 24500

500 5001000 1000marginal

stripmarginal

strip

2500 25007300

11700

varies1200 to 2200

Page 10: David Iles

Preamble to design verification Documentation

• The Eurocodes – at least 14 Parts needed!– EN 1990– Eurocode 1 (4 Parts)– Eurocode 2 (2 Parts)– Eurocode 3 (6 Parts)– Eurocode 4 (1 Part)– Eurocode 7 (1 Part) (for integral bridges)

• National Annexes (NAs)– One for each Part

Page 11: David Iles

Preamble to design verification Documentation

• Published Documents (PDs)• Non-contradictory complementary information (NCCI)• Not forgetting …

– Execution standards and product standards (notably EN 1090-2 for steel)

Page 12: David Iles

Preamble to design verification Design basis

• EN 1990– Sets out basis for limit state design– Defines design situations & combinations of actions– Similar in principle to BS 5400-1 but much more

extensive• Terminology - Eurospeak

– Actions, Effects, Verification, Execution• Symbols

– Such as: Q,1 ψ0 Qk ; NEd ; Mb,Rd

– Clear differentiation - avoids confusion and error

Page 13: David Iles

Preamble to design verification Material properties

• Material properties defined in:– EN 1992-1-1 for concrete– EN 1993-1-1 for steel

• Eurocode 4 refers back to Eurocodes 2 and 3 for properties … but:– potential confusion over design value of concrete

strength– shrinkage and creep depend on ‘age at first loading’

Page 14: David Iles

Design effects Actions

• Self-weight – dimensional variability• Traffic loads

– lanes– UDL– Tandem system– Fatigue vehicle

• Thermal actions– large F on thermal effects– care needed in design effects for integral bridges and

expansion joints

Page 15: David Iles

Design effects Global analysis

• Elastic global analysis for bridges• Analysis should take account of shear lag

– Effective widths given in Eurocodes 3 and 4– Not needed if using FE model with shell elements

• First order analysis for effects in members– Consideration of LTB may require elastic buckling

analysis

Page 16: David Iles

Design effects Global analysis - example 1

• 3D FE model (beam and shell elements) gave:– Effects during construction stages– Effects due to gr1 and gr5 combinations of traffic loads– Effects due to soil pressures on endscreen walls

Page 17: David Iles

Design effects Global analysis - example 2

• 3D FE model (beam and shell elements) gave effects:– On main girders and cross girders– Due to construction and traffic loads

Page 18: David Iles

Design verification of beams

• Eurocode 3 sets out separate verifications for:– Cross sections– Buckling resistance of members

• Eurocode 4 refers back to Eurocodes 2 and 3– Adds assessment of stage construction– Gives rules for shear connection

Page 19: David Iles

Design verification of beams Resistance of cross sections

• Eurocode 3 defines 4 classes of cross section in bending and under axial compression– 1 & 2 similar to compact– 3 similar to non-compact– 4 non-compact with web not fully effective

• Shear resistance of slender web defined in EN 1993-1-5– Uses a different partial factor for design strength

• Bending-shear interaction only considered for the cross section

Page 20: David Iles

Design verification of beams Resistance of cross sections

• M-V interaction on cross sections

0

500

1000

1500

2000

2500

3000

3500

0 5000 10000 15000 20000

Moment (kNm)

Shea

r (kN

)

M f,RdM pl,Rd

M el,Rd

V bw,Rd

V b,Rd

V pl,Rd

Page 21: David Iles

Design verification of beams Buckling resistance

• Reduction factor applied to cross section resistance• Requires non-dimensional slenderness • Value of only given in relation to Mcr

• Options are:– elastic buckling analysis– simple rules derived from ‘effective length’

LTλ

LTλ

Page 22: David Iles

Design verification of beams Buckling resistance

• Common set of buckling curves

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0 0.5 1 1.5 2 2.5 3

Slenderness

Redu

ctio

n fa

ctor

Page 23: David Iles

Design verification of beams Buckling resistance

• Verification during construction– Buckling mode for paired girders

Page 24: David Iles

Design verification of beams Buckling resistance

• Verification for in-service stage– Consider bottom flange adjacent to support

• General method in EN 1993-2:– Treat bottom flange and part of web as a strut– can allow for variation of M

and V

– and for flexible lateral restraint

Page 25: David Iles

Design verification of beams Restraint of slab in ladder decks

• In mid-span region, slab in compression susceptible to buckling– Cross girders must provide stiff restraint– Slab must be checked as strut

• No explicit rules in Eurocodes– Guidance is available

Page 26: David Iles

Design verification of beams Longitudinal shear connection

• Rules given in EN 1994-2• Studs to EN ISO 13918 are 10% less strong than

BS_5400 studs but design resistance is similar• The SLS requirement is almost always automatically

satisfied when ULS is OK• When using 3D modelling, take care in evaluation of

shear flow, because axial force varies along span

Page 27: David Iles

Design of connections Bolted connections

• Now using preloaded bolts to EN 14399– Similar properties and preload

• Connection of cross girders– Difficult to determine forces on individual bolts

(notch ignored)

250 mm

725 mm

(notch ignored)

250 mm

725 mm

Page 28: David Iles

Design of connections Welded connections

• Procedures similar to those for design to BS 5400• Directional method looks complex

– can be rationalized– then as easy as the simple method

• Weld sizes expressed in terms of throat thickness rather than leg length– be careful when specifying

Page 29: David Iles

Conclusion

• Preparation of the examples revealed no major difference (from those to BS 5400)

• Terminology is slightly different but rather more precise

• The Eurocodes are comprehensive but this means extensive documentation

• There are no simple rules for ‘effective length’ of buckling

• There is no indication that the structure need be any heavier (than if designed to BS 5400)

Page 30: David Iles

Thank you for listening