LimitState:GEO Eurocode 7

20/05/2008 LimitState:GEO launch & technology briefing - ICE London

19/04/23 geo1.0

LimitState:GEOLimitState:GEOEurocode 7Eurocode 7

Colin Smith MA(Cantab) PhD

Director & LimitState:GEO Product Manager, LimitState Ltd


Contents

Eurocode 7a. Introduction

b. LimitState:GEO functionality

c. Examples

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Eurocode 7

Introduction


• Eurocode 7 has been under development since 1980.

• Use of Eurocode 7 will be mandatory in the UK in 2010.

Eurocode 7


Eurocode 7 moves away from:• working stresses,• overall factors of safety,to:• limit state design approach,• partial factors,• unified approach.

Eurocode 7

It introduces a range of separate checks:

• Ultimate Limit States (ULS)

• Serviceability Limit States (SLS)

Eurocode 7

EQU : loss of equilibriumSTR : failure of the structureGEO : failure of the groundUPL : failure by upliftHYD : hydraulic heave


In the UK the checks against failure in the ground (GEO) and in the structure (STR) must be checked using ‘Design Approach 1’ which specifies 2 calculations :

Design combination 1 Design combination 2

Eurocode 7


Different factors are applied if loads are:

• Permanent• Variable• Accidental

Different factors are applied if loads are:

• Favourable• Unfavourable

i.e assist or resist collapse (this may not be clear at outset)

Loads


Partial FactorsEC7 DC1 EC7 DC2 Conventional

bearing capacityBS8002 (Retaining walls)

Permanent unfavourable load 1.35 1.0 1.0

1.0

Variable unfavourable load

1.5 1.3 1.0 1.0

Permanent favourable load

1.0 1.0 1.0 1.0

c' 1.0 1.25 1.0 1.2

tan' 1.0 1.25 1.0 1.2

cu 1.0 1.4 1.0 1.5

Overall F.O.S N/A N/A 2.5 – 3.0 N/A


Soil properties: cu = 70 kN/m2, = 20 kN/m3

Example – footing design

G

D

B Geometry: D = 0.75m, B = 1 m


Soil properties: cu = 70, = 20 kN/m3

Example – footing design

G

D

B Geometry: D = 0.75m, B = 1 m

Gfail/B = 5.14 cu + D = 375 kN/m (unfactored)


Design Combination 1 Factors are primarily placed on the loads and the soil properties are unfactored.

Factor on: Permanent load = 1.35 Variable load = 1.5

Usually controls failure in the structure

Design Combination 1


Factor on load = 1.35

Design Combination 1G

D

B Factor on cu

= 1.00


Gfail = 278 kN/m = (5.14 x 70 + 0.75 x 20) / 1.35

Design Combination 2 Factors are primarily placed on the soil properties and loads are unfactored. Factor on: c = 1.25 tan = 1.25 cu = 1.4 Usually controls failure in the ground.

Design Combination 2


Factor on load = 1.00

Design Combination 2G

D

B Factor on cu

= 1.4

c.f. Gfail = 278 kN/m for Combination 1


Gfail = 272 kN/m = 5.14 x (70/1.4) + 0.75 x 20

• Different factors are applied for different ULS cases

• The purpose of the partial factors is to ensure the probability of failure is sufficiently low.

Partial Factors


• Multiple ULS cases (e.g. GEO, STR, UPL) each with own set of partial factors

• Use of multiple load types (Permanent, Variable, Accidental)

• Favourable/unfavourable to be defined

and…

EC7 Challenges

• Different failure modes to be checked (e.g. local/global, sliding/bearing etc)

• Drained / undrained cases to be checked


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LimitState:GEO

functionality

Load type specification


Multiple scenarios

• Choose to solve one or many scenarios in one go

• Select partial factor sets

• Set long term / short term (drained/undrained) solution mode


Scenario solutions


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Examples

Analysis


Analysis

• At this stage, LimitState:GEO was used to analyse the problem as described in the previous slides

(Hands on demo of software)

Conclusions

• LimitState:GEO has been designed to maximise ease of use with Eurocode 7:

Permanent, variable and accidental load specification Unfavourable/favourable load specification User can specify any partial factor set Multiple scenarios can be solved together

• The new unified approach in Eurocode 7 makes use of generic ULS analysis software such as LimitState:GEO directly applicable to all geotechnical problem types.

• Flexible approach makes it easy to utilise partial factors from other design codes.


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Thank you for listening

LimitState:GEO Eurocode 7

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