pile eurocode
DESCRIPTION
Pile designTRANSCRIPT
Eurocode 7 and New Design Challenges A Wee Scottish Bridge
Stuart Pennington
19 March 2013
UCL
2
• Ed ≤ Rd
• Challenges with pile design
3
Introduction
• New cable stayed bridge
• Specimen design
• Typically piers on pile groups, central tower on spread foundation
• Piles ≈ 3.0m diameter
4
Introduction
Made ground
Beach
Alluvium
Raised beach
Till
Fluvio-glacial
SST/XST/MST
Dolerite
Tuff
Limestone
5
Effects of Actions
Challenges
• Combinations and factors (y, g): numerous
• Set C (GEO Design Approach 1 Combination 2): forgotten
• Structural and geotechnical engineers: interaction
6
Effects of Actions - factors
ULS
SLS
7
Effects of Actions - factors
8
Effects of Actions
Challenges
• Combinations and factors (y, g): numerous
• Set C (GEO Design Approach 1 Combination 2): forgotten
• Structural and geotechnical engineers: interaction
9
Effects of Actions - interaction
Defines:
- characteristic actions
- combinations of actions
- partial factors (g)
- factors (y)
- construction tolerances
- serviceability criteria
Calculates:
- design actions
Defines:
- construction tolerances
- serviceability criteria
Designs:
- structure
Calculates:
- design resistances
- effects of actions
- global stability
- movement
Designs:
- geotechnical elements
STRUCTURES GEOTECHNICS
Earth
Loading
10
Resistance
Challenges
• Partial factors for accidental loading: not given
• Large diameter piles: calculation model
• Model factor: 1.2 or 1.4?
11
Resistance - factors for accidental loading
• Rc;d = Rb;k / gb + Rs;k / gs
• Rt;d = Rt;k / gs;t
12
Resistance - factors for accidental loading
• Maintain level of reliability
• Raccidental ≈ gACC-EN1992 / gPERM/TRAN-EN1992 . R4
• Others
Resistance Symbol Set
R4 with
ver. SLS
Raccidental
Base gb 1.7 1.5
Shaft gs 1.4 1.2
Shaft (tension) gs;t 1.7 1.5
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Resistance
Challenges
• Partial factors for accidental loading: not given
• Large diameter piles: calculation model
• Model factor: 1.2 or 1.4?
14
Resistance - large diameter piles
• Typical rock socket design:
- generally empirical
- socket friction (fs) = func{UCS}
- limited to diameter ≤ 1500mm
• For piles > 1500mm fs reduces with increasing diameter
• Rocket analyses:
- fs = func{c'i, f'i, fb, n, a, shi, Em}
15
Resistance - large diameter piles
• Reasonable agreement at 1.0m
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Resistance - large diameter piles
• Sensitivity analyses:
- socket friction influenced by several variables
- not possible to confirm influence of diameter from published data
- GI can’t directly determine socket roughness
• Hence:
17
Resistance
Challenges
• Partial factors for accidental loading: not given
• Large diameter piles: confidence in design
• Model factor: 1.2 or 1.4?
18
Resistance - model factors
19
Resistance - model factors
pile
20
Outcomes
• Manage geotechnical/structural interaction early on
• Complete simple checks - it’s easy to get lost in partial factors and combinations
• New partial factors ok but remember reliability
• Check your calculation model
• Be clear on what your pile test is testing
Outcomes