bridge-Spec_for_Foundation-Earth_Retaining_Structure_Design.ppt

7/30/2019 bridge-Spec_for_Foundation-Earth_Retaining_Structure_Design.ppt

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AASHTOs LRFD Specifications for

Foundation and Earth RetainingStructure Design

(Through 2006 Interims and Beyond)

Jerry A. DiMaggio, P.E.

Principal Bridge/Geotechnical Engineer

FHWA, Washington D. C.


2/43

Existing Specifications

Standard

17th

Edition

LRFD

3rd

Edition


3/43

AASHTO and FHWA

have agreed that allstate DOTs will use

LRFD for design ofNEW structures by

2007.


4/43

0-2-2

NE60%

MO

TN NCVA

WV80%

PA100%

NY50%

ME100%

IA5%

IL5%

KY

FL100%

GATX

13%

OK100%

KS50%

OH

WA100%

OR100% WI

CACO90%

SC50%

NJMACT

DEMD

VT5%

MN40%

MI

INUT

75%

ND

SD10%ID

100%WY

NMAZ

NV

MT35%

AR5%

LAMS AL

NHRI

0-24-100-2-2

NEMO

TN NCVAWVPA

NY

MEIA

ILKY

FLGA

TX

OK

KS OH

WAOR WI

CA

AASHTO LRFD SurveyMay 2005

CO

SC

VT

MN

MIINUT

NDSDID

WY

NMAZ

NV

MT

AR

LA MS AL

AK95%

AK

HI

PR q


5/43

Superstructure: LRFD

Substructure: LRFD/ASD

Foundations: ASD

Earthwork and walls: ASD


6/43

Reasons for Not Adopting

Human nature.

No perceived benefits.

Unfamiliarity with LRFD methods. Lack of confidence in the computed

results.

Perceived errors and inconsistencies. A specification that did not reflect

current design practices.


7/43

What is FHWA doing?

Bridge Design examples.

NHI LRFD Training Courses.

FHWA Technical Assistance. FHWA/ NCHRP Calibration efforts.

AASHTO Section 11 and 10

Revisions.


8/43

Bridge Design Examples

http://www.fhwa.dot.gov/bridge/lrfd/examples.htm

Concrete Steel


9/43

NHI LRFD Training Courses

Course 130082A

LRFD for HighwayBridge Substructuresand Earth Retaining

Structures


10/43

FHWA/ NCHRP Activities

NCHRP Project 12-66, Specifications forServiceability in the Design of BridgeFoundations

NCHRP Report 507, Load andResistance Factor Design (LRFD) forDeep Foundations


11/43

FHWA/ NCHRP Activities

Publication No. FHWA-NHI-05-052,Development of GeotechnicalResistance Factors and DowndragLoad Factors for LRFD FoundationStrength Limit State Design


12/43

Revisions to Section 10

Compiled by a Technical Expert Panel Review and input from A Technical

Working Group (TWG)

Accepted by AASHTO SubcommitteeT-15 in June 2005 in Newport, RhodeIsland

To be published in 2006 Interimhttp://bridges.transportation.org/?siteid=34&c=downloads

Attachments to Agenda Item 39 Section 3 revisions

Attachments to Agenda item 40 Section 10 revisions


13/43

Topics Included

Topics NOT Included


14/43

Section 10 Contents

10.1 SCOPE

10.2 DEFINITIONS

10.3 NOTATION

10.4 SOIL AND ROCK PROPERTIES

10.5 LIMIT STATES AND RESISTANCE FACTORS

10.6 SPREAD FOOTINGS

10.7 DRIVEN PILES

10.8 DRILLED SHAFTS

PROPERTY INFO

NO SIGNIFICANT CHANGE

UPDATED

UPDATED, CONSISTANT

REORGANIZED,NEW CONTENT

NEW CONTENT


15/43

Section 10.4 Soil and Rock Properties

GEC 5

Sabatini, 2002

SubsurfaceInvestigations

Mayne, 2002


16/43

Section 10.4 Soil and Rock Properties

Soil Strength

Soil Deformation

Rock Mass Strength Rock Mass Deformation

Erodibility of rock

10.4.6 SELECTION OF DESIGN PROPERTIES


17/43

Section 10.5 Limit States andResistance Factors

Resistance factors revised

Additional discussion on the basis for

resistance factors

Additional discussion of extreme event

considerations


18/43

Articles 3.4.1 and 3.11.8

Maximum Minimum

Piles, -method 1.4 0.25Piles, -method 1.05 0.30

Drilled Shafts, Oneill

and Reese (1999)

1.25 0.35

Downdrag Methods for computing

Load Factors

Use of minimum load factors clarified


19/43

Section 10.6 Spread Footings

Eccentricity provisions clarified

B= B 2eB

L= L 2eLQ = P/(B L)

ML M

B

LB

eB eL

BL

P

q

Applies togeotechnical designfor settlement and

bearing resistance


20/43


Hough method

Elastic Settlement ofcohesionless soils

vo

vvoc

'

'log

C'

1HH


21/43


qn = c Ncm + DfNqm Cwq + 0.5 B Nm Cw

NOMINAL RESISTANCE

Nc sc ic Nq sq dq iq N s i

Shape Correction Factors

COHESIONUNIT WEIGHT

DEPTH WIDTH

Bearing Capacity FactorsInclination FactorsShear through overburden

correction factor

Water table correction

Settlement correction factors removed


22/43

Section 10.7 Driven Piles

Settlement of pile groups

4 new diagrams

From:

Hannigan (2005)


23/43


Ht

Qt

Mt

P

y

The P-y method specified

for horizontal deflection


24/43


P

y

Pm * P

P

Spacing (S) Row 1 Row 2 Row 3

3D 0.7 0.5 0.35

5D 1.0 0.85 0.7

P-multiplier (Pm

)D

S


25/43


Field determination of nominal resistance

Static load test Dynamic load test


26/43


Static analysis methods

Nordlund

Thurman methodadded


27/43


Static analysis methods

Primary use is for pile length estimation

for contract drawings Secondary use for estimation of downdrag,

uplift resistance and scour effects

Should rarely be used as sole means ofdetermining pile resistance


28/43


Comp Str

ksi

30

20

10

Ult Cap

200

400

600

800

kips

0 160 320 480 Blows/ft

4.0

8.0

12.0

16.0

ft

Stroke

Tens Str

ksi

Requirements for

driveability analysishave been added and

clarified


29/43


10.7.3.2 PILE LENGTH ESTIMATES FOR

CONTRACT DOCUMENTS

10.7.6 Determination of minimum pile

penetration


30/43

Section 10.8 Drilled shafts

Refers to driven piles section where possible

Downdrag

Group settlement

Horizontal displacement (single and group)

Lateral squeeze Water table and buoyancy

Scour

Group resistance (cohesive soil only) Uplift (group and load test sections)

Buckling

Extreme event limit state


31/43


Static analysis methodsfor soil and rock have

been updated

Consideration of both

base and side

resistance in rock is

now included

ONeill and Reese (1999)


32/43


A + B

QP

QS

Displacement

Resistance

Side Resistance

Tip Resistance

Total Resistance

B

CD

A

A + D

B + C


33/43

Conclusion


34/43

Future EnhancementsOverall stability

Weight is both a load and a resistance

Service limit state (should be strength

limit state) +

WTWT

WT WT

N N

T T

T T

l l

cl cl

N tan f N tan f


35/43

Future Enhancements

Inclination Factors Ignored by many practicing engineers

Based on small scale tests and theory

Effect of embedment (Df) Resistance factors are for vertical load

Q

Df


36/43

Future Enhancements

Nominal bearing resistance of rock

Very little guidance available

CSIR Rock Mass Rating System proposed

CSIR developed for tunnel design

Includes life safety considerations and

therefore, margin of safety May be conservative


37/43

Future Enhancements

Pile head fixity

Connection details Effects of axial loads

H H

V


38/43

Future Enhancements

Serviceability limits

NCHRP 12-66

Due April 2006

x

z


39/43


40/43


41/43


42/43

AASHTO Section 11

Design specifications for:

Conventional

gravity/semigravity walls Non-gravity cantilevered walls

Anchored walls Mechanically Stabilized Earth

(MSE) walls

Prefabricated modular walls


43/43

LRFD Specifications for

Foundation/ Earth RetainingStructure Design

Questions?

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