Opportunities and Challenges for the. Friday September 24,

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1 LRFD Facts and Misconceptions: Opportunities and Challenges for the Micropile il Community Friday September 24, 2010 By Jerry A. DiMaggio, PE, M.ASCE 1

2 Bio: Jerry A. DiMaggio Pin Ball Machine Repairman 1 yr Country Club Maintenance Foreman 5 yrs Teamster 5 yrs Father 32 yrs Civil Engineer (Geotechnical Specialist)-37 yrs Husband 41 yrs Retired Principal Bridge Eng., Geotechnical National Program Manager FHWA, Washington D.C. (September 2008) Currently: SHRP 2 Implementation Manager, TRB, The National Academies, Washington D.C. Currently: Private Civil Engineering, Construction and Business Development Consultant 2

3 LRFD Micropile Community Issues/ Topics Brief History of AASHTO Specifications and Evolution of LRFD LRFD Basics and Advantages and Limitations Available LRFD Resources and training (professional and academic institutions) Calibration Methods, techniques and limitations ***Current LRFD issues for micropiles: factored loads, load test failure criteria, structural design, maximum factored stresses, process for AASHTO LRFD updates OTHERS? *** 3

4 i i Q i R r = R n i = Load modifier (eta) i = Load factor (gamma) Q i = Force effect R r = Factored resistance = Resistance factor (phi) R n = Nominal resistance 4

5 Webinar References Primary References: AASHTO (2010) 5 th Edition Section 10 Foundations Sections 3 Loads and Load Factors FHWA (2006) Soils and Foundations 2 volumes (1,056 pages; Free download at) The micropile design process is discussed in detail in Micropile Design and Construction (Sabatini, et al., 2005). List of info sources provided at end Legend: AASHTO: American Association of State Highway and Transportation Officials FHWA: Federal Highway Administration i ti 5

6 AASHTO - Section 10 Outline Article Topic Webinar # 10.1 Scope 10.2 Definitions 10.3 Notation ti 10.4 Soil Properties and Materials Limit States and Resistance Factors 5, 6, 7, 8, 9, 10, Spread Footings Driven Piles Drilled Shafts Micropiles 7 Refer to Section 3 for Loads and Load Factors 1-2 6

7 Micropile Foundations Topic Slides General (Section 3, Section 10.4, ) 1) Limit States and Resistance Factors Service Limit State Strength Limit State Extreme Event Limit State C Corrosion and ddeterioration ti The sequence of Article 10.9 in AASHTO 7

8 AASHTO Table DC Use One of These at DD a Time DW EH EV LL ES IM Load EL CE Combination PS BR CR PL Limit State SH LS WA WS WL FR TU TG SE EQ IC CT CV STRENGTH LIMIT EXTREME EVENT I γ p /1.20 γ TG γ SE II γ p /1.20 γ TG γ SE III γ p /1.20 γ TG γ SE IV γ p / /1.20 V γ p /1.20 γ TG γ SE I γ p γ EQ II γ p I / /1.20 γ TG γ SE II /1.20 SERVICE LIMIT III /1.20 γ TG γ SE IV / FATIGUE - LL, I IM & CE only II

9 Load Factors for Permanent Loads, AASHTO Table S O 3412 p Type of Load, Foundation Type, and Method Used to Calculate Downdrag Load Factor Maximum Minimum DC: Component and Attachments DC: Strength IV only DD: Downdrag Piles, Tomlinson Method Piles, Method Drilled shafts, O Neill and Reese (1999) Method DW: Wearing Surfaces and Utilities EH: Horizontal Earth Pressure Active At-Rest AEP for anchored walls N/A EL: Locked-in Construction Stresses EV: Vertical Earth Pressure Overall Stability 1.00 N/A Retaining Walls and Abutments Rigid Buried Structure Rigid Frames Flexible Buried Structures other than Metal Box Culverts Flexible Metal Box Culverts and Structural Plate Culverts with Deep Corrugations ES: Earth Surcharge

10 Figure C , 2 Typical Application of Load Factors Bearing Sliding and Eccentricity 10

11 AASHTO Section 10.4 Soil and Rock Properties 4.1 Informational Needs 4.2 Subsurface Exploration 4.3 Laboratory Tests 4.4 In-situ Tests 4.5 Geophysical Tests 4.6 Selection of Design Properties 11

12 Table Geotechnical Resistance Factors of Axially Loaded Micropiles Limit State Method/ Ground Condition Side Resistance (Bond Resistance): Presumptive Values Resistance Factor 0.55 (1) Compression Resistance of Tip Resistance on Rock O Neill Single Micropile, and Reese (1999) 0.50 stat Side Resistance and Tip Resistance Load Test Values in Table , but no greater than 0.70 Block Failure, bl Clay 0.60 Presumptive Values 0.55 (1) Uplift Resistance of Single Micropile, up Tension Load Test Values in Table , but no greater than Group Uplift Resistance, ug Sand & Clay 0.50 (1 ) Apply to presumptive grout-to-ground bond values for preliminary design only in Article C

13 Table Structural Resistance Factors for Axially Loaded Micropiles Section / Loading Condition Resistance Factor Pile Cased Length Pile Uncased Length Tension, TC 0.80 Compression, CC Tension, TU 0.80 Compression, 0.75 CU CU 13

14 Pile Structural Resistance Concrete ( ) Steel ( ) Axial Comp. = 0.75 Axial = Flexure = 0.9 Combined Shear = 0.9 Axial= Flexure = 1.0 Shear = LRFD Specifications Steel Article for noncomposite piles and Article6951forcompositepiles composite piles Concrete Articles and Potential for buckling should be as in Article

15 Static Load Test: Failure Definition Load nt X ttleme Se X= B/120 Pile top settlement 15

16 LRFD Micropile Community Issues/ Topics Brief History of AASHTO Specifications and Evolution of LRFD LRFD Basics and Advantages and Limitations Available LRFD Resources and training (professional and academic institutions) Calibration Methods, techniques and limitations ***Current LRFD issues for micropiles: factored loads, load test failure criteria, structural design, maximum factored stresses, process for AASHTO LRFD updates OTHERS? *** 16

17 Accelerating solutions for highway safety, renewal, reliability, and capacity $630 Million in Highway Transportation R&D Jerry A. DiMaggio, P.E., M.ASCE SHRP2 Implementation Manager, TRB 17

18 SINCE THE 1500 s THE NAME and FAMILY DIMAGGIO HAS REPRESENTED THE VERY BEST IN COFFEE, BASEBALL AND GEOENGINEERING AND GEO-CONSTRUCTION EXCELLENCE! 18

19 LRFD Facts and Misconceptions: Opportunities and Challenges for the Micropile il Community THANK YOU! By Jerry A. DiMaggio, PE, M.ASCE