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AASHTO’s LRFD Specifications for Foundation and Earth Retaining Structure Design (Through 2006 Interims and Beyond) PowerPoint PPT Presentation


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AASHTO’s LRFD Specifications for Foundation and Earth Retaining Structure Design (Through 2006 Interims and Beyond). Jerry A. DiMaggio, P.E. Principal Bridge/Geotechnical Engineer FHWA, Washington D. C. . Existing Specifications. Standard 17 th Edition. LRFD 3 rd Edition.

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AASHTO’s LRFD Specifications for Foundation and Earth Retaining Structure Design (Through 2006 Interims and Beyond)

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AASHTO’s LRFD Specifications for Foundation and Earth Retaining Structure Design

(Through 2006 Interims and Beyond)

Jerry A. DiMaggio, P.E.

Principal Bridge/Geotechnical Engineer

FHWA, Washington D. C.


Existing Specifications

Standard

17th Edition

LRFD

3rd Edition


“AASHTO and FHWA have agreed that all state DOT’s will use LRFD for design of NEW structures by 2007.”


AASHTO LRFD Survey

May 2005

AK

AK

95%

WA

WA

MT

MT

ND

ND

100%

MN

MN

35%

ME

ME

40%

100%

SD

SD

OR

OR

VT

VT

ID

ID

WI

WI

10%

5%

100%

100%

NY

NY

MI

MI

WY

WY

50%

NH

IA

IA

0

-

24

-

10

NE

NE

5%

0

0

-

-

2

2

-

-

2

2

MA

PA

PA

60%

IL

IL

100%

OH

OH

IN

IN

RI

UT

UT

5%

NV

NV

CO

CO

CT

MO

MO

75%

KS

KS

WV

WV

90%

NJ

50%

80%

KY

KY

VA

VA

CA

CA

DE

MD

OK

OK

TN

TN

NC

NC

AR

AR

100%

AZ

AZ

NM

NM

SC

SC

5%

50%

MS

MS

AL

AL

GA

GA

TX

TX

LA

LA

13%

HI

FL

FL

100%

Full Implementation

¢

PR

50-90% Partial Implementation

¢

26-50% Partial Implementation

¢

11-25% Partial Implementation

¢

1-10% Partial Implementation

¢

No Implementation

q


Earthwork and walls: ASD

Superstructure: LRFD

Substructure: LRFD/ASD

Foundations: ASD


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.


What is FHWA doing?

  • Bridge Design examples.

  • NHI LRFD Training Courses.

  • FHWA Technical Assistance.

  • FHWA/ NCHRP Calibration efforts.

  • AASHTO Section 11 and 10 Revisions.


Bridge Design Examples

Concrete

Steel

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


NHI LRFD Training Courses

Course 130082A

LRFD for Highway Bridge Substructures and Earth Retaining Structures


FHWA/ NCHRP Activities

  • NCHRP Project 12-66, Specifications for Serviceability in the Design of Bridge Foundations

  • NCHRP Report 507, Load and Resistance Factor Design (LRFD) for Deep Foundations


FHWA/ NCHRP Activities

  • Publication No. FHWA-NHI-05-052, Development of Geotechnical Resistance Factors and Downdrag Load Factors for LRFD Foundation Strength Limit State Design


Revisions to Section 10

  • Compiled by a Technical Expert Panel

  • Review and input from A Technical Working Group (TWG)

  • Accepted by AASHTO Subcommittee T-15 in June 2005 in Newport, Rhode Island

  • To be published in 2006 Interim

http://bridges.transportation.org/?siteid=34&c=downloads

  • Attachments to Agenda Item 39 Section 3 revisions

  • Attachments to Agenda item 40 Section 10 revisions


Subsurface investigations

Soil and rock properties

Shallow foundations

Driven piles

Drilled shafts

Rigid and flexible culverts

Abutments

Walls (All types)

Integral abutments

Micropiles

Augercast piles

Soil nails

Reinforced slopes

All soil and rock earthwork features.

Topics Included

Topics NOT Included


REORGANIZED,

NEW CONTENT

NEW CONTENT

PROPERTY INFO

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

NO SIGNIFICANT CHANGE

UPDATED

UPDATED, CONSISTANT


Section 10.4 Soil and Rock Properties

Subsurface Investigations

Mayne, 2002

GEC 5

Sabatini, 2002


Section 10.4 Soil and Rock Properties

NEW!

10.4.6 SELECTION OF DESIGN PROPERTIES

  • Soil Strength

  • Soil Deformation

  • Rock Mass Strength

  • Rock Mass Deformation

  • Erodibility of rock

NEW!


Section 10.5 Limit States and Resistance Factors

  • Resistance factors revised

  • Additional discussion on the basis for resistance factors

  • Additional discussion of extreme event considerations


Articles 3.4.1 and 3.11.8

Downdrag

  • Methods for computing

  • Load Factors

  • Use of minimum load factors clarified


Section 10.6 Spread Footings

Eccentricity provisions clarified

B′ = B – 2eB

L′ = L – 2eL

Q = P/(B’ L’)

Applies to geotechnical design for settlement and bearing resistance


Section 10.6 Spread Footings

Hough method

Elastic Settlement of cohesionless soils


Shear through overburden correction factor

Shape Correction Factors

Inclination Factors

Bearing Capacity Factors

Section 10.6 Spread Footings

NOMINAL RESISTANCE

COHESION

UNIT WEIGHT

DEPTH

WIDTH

qn = c Ncm +  Df Nqm Cwq + 0.5  B Nm Cw 

Nc sc ic

Nq sq dq iq

N  s  i 

Water table correction

Settlement correction factors removed


Section 10.7 Driven Piles

Settlement of pile groups

4 new diagrams

From:

Hannigan (2005)


P

y

Section 10.7 Driven Piles

Qt

The P-y method specified for horizontal deflection

Mt

Ht


Section 10.7 Driven Piles

S

P

P

Original curve

Modified curve

Pm * P

y

D

P-multiplier (Pm)


Section 10.7 Driven Piles

Field determination of nominal resistance

Static load test

Dynamic load test


Section 10.7 Driven Piles

Static analysis methods

  • Nordlund – Thurman method added


Section 10.7 Driven Piles

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 of determining pile resistance


Section 10.7 Driven Piles

Requirements for driveability analysis have been added and clarified


Section 10.7 Driven Piles

NEW!

NEW!

10.7.3.2 PILE LENGTH ESTIMATES FOR CONTRACT DOCUMENTS

10.7.6 Determination of minimum pile penetration


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


Section 10.8 Drilled shafts

  • Static analysis methods for soil and rock have been updated

  • Consideration of both base and side resistance in rock is now included

    O’Neill and Reese (1999)


Section 10.8 Drilled shafts

A + B

A + D

Total Resistance

B + C

A

Side Resistance

B

Resistance

C

D

QS

Tip Resistance

QP

Displacement


Conclusion


Future Enhancements

Overall stability

  • Weight is both a load and a resistance

  • Service limit state (should be strength limit state)

WT

WT

N tan f

N tan f

cl

l

cl

l

T

N

T

WT

N

WT

T

T


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


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


H

H

Future Enhancements

V

Pile head fixity

  • Connection details

  • Effects of axial loads


Dx

Dz

Future Enhancements

Serviceability limits

NCHRP 12-66

Due April 2006


What Should I Know and Do?

  • Become familiar with BOTH the AASHTO standard specifications and LRFD specs.

  • Develop an understanding of your agency’s current design practice


What Should I Know and Do?

  • Develop and compare results for SEVERAL example problems with LRFD and YOUR standard design practice

  • Translate your current practice to an LRFD format


What Should I Know and Do?

  • Communicate your findings to AASHTO’s SubCommitteee members


AASHTO Section 11

  • Design specifications for:

    • Conventional gravity/semigravity walls

    • Non-gravity cantilevered walls

    • Anchored walls

    • Mechanically Stabilized Earth (MSE) walls

    • Prefabricated modular walls


LRFD Specifications for Foundation/ Earth Retaining Structure Design

Questions?


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