AASHTO’s LRFD Specifications for Foundation and Earth Retaining Structure Design
Download
1 / 43

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


  • 363 Views
  • Uploaded on

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.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'AASHTO s LRFD Specifications for Foundation and Earth Retaining Structure Design Through 2006 Interims and Beyond' - jeb


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Slide1 l.jpg

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 l.jpg
Existing Specifications Retaining Structure Design

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 l.jpg

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


Slide4 l.jpg

AASHTO LRFD Survey use LRFD for design of NEW structures by 2007.”

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


Slide5 l.jpg

Earthwork and walls: ASD use LRFD for design of NEW structures by 2007.”

Superstructure: LRFD

Substructure: LRFD/ASD

Foundations: ASD


Reasons for not adopting l.jpg
Reasons for Not Adopting use LRFD for design of NEW structures by 2007.”

  • 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 l.jpg
What is FHWA doing? use LRFD for design of NEW structures by 2007.”

  • Bridge Design examples.

  • NHI LRFD Training Courses.

  • FHWA Technical Assistance.

  • FHWA/ NCHRP Calibration efforts.

  • AASHTO Section 11 and 10 Revisions.


Bridge design examples l.jpg
Bridge Design Examples use LRFD for design of NEW structures by 2007.”

Concrete

Steel

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


Nhi lrfd training courses l.jpg
NHI LRFD Training Courses use LRFD for design of NEW structures by 2007.”

Course 130082A

LRFD for Highway Bridge Substructures and Earth Retaining Structures


Fhwa nchrp activities l.jpg
FHWA/ NCHRP Activities use LRFD for design of NEW structures by 2007.”

  • 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 activities11 l.jpg
FHWA/ NCHRP Activities use LRFD for design of NEW structures by 2007.”

  • 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 l.jpg
Revisions to Section 10 use LRFD for design of NEW structures by 2007.”

  • 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


Topics included l.jpg

Subsurface investigations use LRFD for design of NEW structures by 2007.”

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


Section 10 contents l.jpg

REORGANIZED, use LRFD for design of NEW structures by 2007.”

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 l.jpg
Section 10.4 Soil and Rock Properties use LRFD for design of NEW structures by 2007.”

Subsurface Investigations

Mayne, 2002

GEC 5

Sabatini, 2002


Section 10 4 soil and rock properties16 l.jpg
Section 10.4 Soil and Rock Properties use LRFD for design of NEW structures by 2007.”

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 l.jpg
Section 10.5 Limit States and Resistance Factors use LRFD for design of NEW structures by 2007.”

  • 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 l.jpg
Articles 3.4.1 and 3.11.8 use LRFD for design of NEW structures by 2007.”

Downdrag

  • Methods for computing

  • Load Factors

  • Use of minimum load factors clarified


Section 10 6 spread footings l.jpg
Section 10.6 Spread Footings use LRFD for design of NEW structures by 2007.”

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 footings20 l.jpg
Section 10.6 Spread Footings use LRFD for design of NEW structures by 2007.”

Hough method

Elastic Settlement of cohesionless soils


Section 10 6 spread footings21 l.jpg

Shear through overburden correction factor use LRFD for design of NEW structures by 2007.”

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 l.jpg
Section 10.7 Driven Piles use LRFD for design of NEW structures by 2007.”

Settlement of pile groups

4 new diagrams

From:

Hannigan (2005)


Section 10 7 driven piles23 l.jpg

P use LRFD for design of NEW structures by 2007.”

y

Section 10.7 Driven Piles

Qt

The P-y method specified for horizontal deflection

Mt

Ht


Section 10 7 driven piles24 l.jpg
Section 10.7 Driven Piles use LRFD for design of NEW structures by 2007.”

S

P

P

Original curve

Modified curve

Pm * P

y

D

P-multiplier (Pm)


Section 10 7 driven piles25 l.jpg
Section 10.7 Driven Piles use LRFD for design of NEW structures by 2007.”

Field determination of nominal resistance

Static load test

Dynamic load test


Section 10 7 driven piles26 l.jpg
Section 10.7 Driven Piles use LRFD for design of NEW structures by 2007.”

Static analysis methods

  • Nordlund – Thurman method added


Section 10 7 driven piles27 l.jpg
Section 10.7 Driven Piles use LRFD for design of NEW structures by 2007.”

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 piles28 l.jpg
Section 10.7 Driven Piles use LRFD for design of NEW structures by 2007.”

Requirements for driveability analysis have been added and clarified


Section 10 7 driven piles29 l.jpg
Section 10.7 Driven Piles use LRFD for design of NEW structures by 2007.”

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 l.jpg
Section 10.8 Drilled shafts use LRFD for design of NEW structures by 2007.”

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 shafts31 l.jpg
Section 10.8 Drilled shafts use LRFD for design of NEW structures by 2007.”

  • 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 shafts32 l.jpg
Section 10.8 Drilled shafts use LRFD for design of NEW structures by 2007.”

A + B

A + D

Total Resistance

B + C

A

Side Resistance

B

Resistance

C

D

QS

Tip Resistance

QP

Displacement


Conclusion l.jpg
Conclusion use LRFD for design of NEW structures by 2007.”


Future enhancements l.jpg
Future Enhancements use LRFD for design of NEW structures by 2007.”

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 enhancements35 l.jpg
Future Enhancements use LRFD for design of NEW structures by 2007.”

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 enhancements36 l.jpg
Future Enhancements use LRFD for design of NEW structures by 2007.”

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


Future enhancements37 l.jpg

H use LRFD for design of NEW structures by 2007.”

H

Future Enhancements

V

Pile head fixity

  • Connection details

  • Effects of axial loads


Future enhancements38 l.jpg

D use LRFD for design of NEW structures by 2007.”x

Dz

Future Enhancements

Serviceability limits

NCHRP 12-66

Due April 2006


What should i know and do l.jpg
What Should I Know and Do? use LRFD for design of NEW structures by 2007.”

  • 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 do40 l.jpg
What Should I Know and Do? use LRFD for design of NEW structures by 2007.”

  • 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 do41 l.jpg
What Should I Know and Do? use LRFD for design of NEW structures by 2007.”

  • Communicate your findings to AASHTO’s SubCommitteee members


Aashto section 11 l.jpg
AASHTO Section 11 use LRFD for design of NEW structures by 2007.”

  • Design specifications for:

    • Conventional gravity/semigravity walls

    • Non-gravity cantilevered walls

    • Anchored walls

    • Mechanically Stabilized Earth (MSE) walls

    • Prefabricated modular walls



ad