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20/05/2008 LimitState:GEO launch & technology briefing - ICE London
11/04/23 geo1.0
LimitState:GEOLimitState:GEOEurocode 7Eurocode 7
Colin Smith MA(Cantab) PhD
Director & LimitState:GEO Product Manager, LimitState Ltd
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
Contents
Eurocode 7a. Introduction
b. LimitState:GEO functionality
c. Examples
11/04/23 geo1.0
Eurocode 7
Introduction
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
• Eurocode 7 has been under development since 1980.
• Use of Eurocode 7 will be mandatory in the UK in 2010.
Eurocode 7
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
Soil properties: cu = 70 kN/m2, = 20 kN/m3
Example – footing design
G
D
B Geometry: D = 0.75m, B = 1 m
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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)
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
Factor on load = 1.35
Design Combination 1G
D
B Factor on cu
= 1.00
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
Factor on load = 1.00
Design Combination 2G
D
B Factor on cu
= 1.4
c.f. Gfail = 278 kN/m for Combination 1
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
• 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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
11/04/23 geo1.0
LimitState:GEO
functionality
Load type specification
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
Scenario solutions
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
11/04/23 geo1.0
Examples
Analysis
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
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.
20/05/2008 LimitState:GEO launch & technology briefing - ICE London
11/04/23 geo1.0
Thank you for listening