Pile Eurocode

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

13

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

16

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