1 / 43

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

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.

jeb
Download Presentation

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

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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 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.

  2. Existing Specifications Standard 17th Edition LRFD 3rd Edition

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

  4. 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

  5. Earthwork and walls: ASD Superstructure: LRFD Substructure: LRFD/ASD Foundations: ASD

  6. 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. 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. Bridge Design Examples Concrete Steel http://www.fhwa.dot.gov/bridge/lrfd/examples.htm

  9. NHI LRFD Training Courses Course 130082A LRFD for Highway Bridge Substructures and Earth Retaining Structures

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. Section 10.4 Soil and Rock Properties Subsurface Investigations Mayne, 2002 GEC 5 Sabatini, 2002

  16. 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!

  17. 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

  18. Articles 3.4.1 and 3.11.8 Downdrag • Methods for computing • Load Factors • Use of minimum load factors clarified

  19. 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

  20. Section 10.6 Spread Footings Hough method Elastic Settlement of cohesionless soils

  21. 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

  22. Section 10.7 Driven Piles Settlement of pile groups 4 new diagrams From: Hannigan (2005)

  23. P y Section 10.7 Driven Piles Qt The P-y method specified for horizontal deflection Mt Ht

  24. Section 10.7 Driven Piles S P P Original curve Modified curve Pm * P y D P-multiplier (Pm)

  25. Section 10.7 Driven Piles Field determination of nominal resistance Static load test Dynamic load test

  26. Section 10.7 Driven Piles Static analysis methods • Nordlund – Thurman method added

  27. 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

  28. Section 10.7 Driven Piles Requirements for driveability analysis have been added and clarified

  29. 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

  30. 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. 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)

  32. 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

  33. Conclusion

  34. 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

  35. 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. 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. H H Future Enhancements V Pile head fixity • Connection details • Effects of axial loads

  38. Dx Dz Future Enhancements Serviceability limits NCHRP 12-66 Due April 2006

  39. 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

  40. 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

  41. What Should I Know and Do? • Communicate your findings to AASHTO’s SubCommitteee members

  42. 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. LRFD Specifications for Foundation/ Earth Retaining Structure Design Questions?

More Related