An example of the use of Eurocodes in An example of the use of Eurocodes in the design of underground metro the design of underground metro

structuresstructures

Tony Gee and PartnersTony Gee and Partners

David BeadmanDavid Beadman

Presented byPresented by

British StandardsBritish Standards

••

EurocodesEurocodes

EurocodeEurocode 77Retaining wall designRetaining wall design

Temporary construction stages

Case C /DA1 Comb 2

Case B /DA1 Comb 1

1.01.351.0Effects of actions

Lesser of 0.5m or 1/10th of the depth below the last prop

0Over-dig allowance

1.251.01.0Partial factor on soil friction (tan �’)

1.61.01.0Partial factor on soil shear strength (cu/c’)

Ultimate loadcasesServiceability loadcase

Design parameters

Cases B and C Design Approach 1 Combinations 1 and 2

Temporary construction stages

Design Approach 1 Combinations 1 and 2

Cases B and C

Stage 1 Install retaining wall

Stage 2 Excavate and construct roof

Stage3 Excavate and construct waling beam

Stage 4 Excavate to formation level

Case C / Design Approach 1 Combination 2Case C / Design Approach 1 Combination 2

Stage 4 Excavate to formation level

Design only critical for final excavation stageDesign only critical for final excavation stage• Only necessary to

check the stability of each construction stage

• Actually analysed the full construction sequence

Case B / Design Approach 1 Combination 1Case B / Design Approach 1 Combination 1

Design critical at intermediate stagesDesign critical at intermediate stages

Stage 1 Install retaining wall

Stage 2 Excavate and construct roof

Stage3 Excavate and construct waling beam

Stage 4 Excavate to formation level

Serviceability Limit State (Serviceability Limit State (crackwidthcrackwidth limit)limit)

EurocodesEurocodes

• Principles (P) general statements and definitions – no alternatives

• Application Rules – examples of generally recognized rules that follow the Principles and satisfy their requirements

EurocodeEurocode 77Geotechnical Design Report (GDR)Geotechnical Design Report (GDR)

-1000

-500

0

500

1000

1500

2000

2500

3000

3500

4000

Time

Load

Kn

EurocodeEurocode 7 7 –– Observational MethodObservational Method

EurocodeEurocode 7 7 –– Observational MethodObservational Method(2)P The following requirements shall be

met before construction is started:• Establish limits of behaviour• Assess range of possible behaviour• Plan monitoring• Review monitoring• Plan contingency

EurocodeEurocode 7 7 –– Observational MethodObservational Method

Temporary Prop

EurocodeEurocode 22

Rules for Buildings

Piles require some special attention for buildability

EurocodeEurocode 22

Analysis programs unavailable

Spreadsheets written and checked

Comparison between BS5400 and the Comparison between BS5400 and the

Metro SpecificationMetro Specification

0.2mm0.25mmMaximum crack width

90mm75mmMinimum cover for structures cast against the ground

50mm35mmMinimum cover for durability for retaining wall members, as concrete cast in non-aggressive ground

fck=30N/mm2fcu=35N/mm2Concrete grade

100 years120 yearsDesign life

Metro Specification

BS5400Requirements

Retaining wall structureRetaining wall structure

Ground Conditions:

Made ground

Glacial till

Limestone

Retaining wallRetaining wallHard soft Secant piles

above the limestone.750mm dia. soft piles1180mm dia. hard piles at

1450mm c/c.

1060mm dia. Contiguous piles within the limestone with grout pipes between the piles.

EurocodeEurocode 22Crack width calculationCrack width calculation

Station crossStation cross--sectionsection• Structure hung from

roof

• Large fixed-end moments

EurocodeEurocode 22Lapping of barsLapping of bars

• Principle – not permitted to lap bars greater than 32mm diameter. (Not satisfied)

Equivalent perimeter of bundle = 40 x (2 + �) = 206mm

Number of bars in bundle:

(Assume 40mm diameter bars)

Two:

Equivalent diameter of a single bar = 56mm

Perimeter of equivalent bar = 56.6 x � = 178mm

EurocodeEurocode 22Equivalent diameter of bar bundlesEquivalent diameter of bar bundles

Equivalent perimeter of bundle = 40 x (3 + �) = 246mm

Number of bars in bundle:

(Assume 40mm diameter bars)

Three:

Equivalent diameter of a single bar = 69.3mm

Perimeter of equivalent bar = 69.3 x � = 218mm

EurocodeEurocode 22Equivalent diameter of bar bundlesEquivalent diameter of bar bundles

• Bundles of equivalent diameter greater than 55mm not permitted (Application Rule)

EurocodeEurocode 22Equivalent diameter of bar bundlesEquivalent diameter of bar bundles

• Bundles to be considered as notional bars for purposes of crack-width calculation (Application Rule)

Use of Use of EurocodesEurocodes

• Consistent design approach• Common design language between the

different nationalities• Enabled the use of the Observational

Method

Use of Use of EurocodesEurocodes

• Learning curve• Development of design tools• Use of EC7 checklists• Incomplete suite of new codes

Use of Use of EurocodesEurocodes