3/10/2013. Existing AASHTO Specifications. Application of the Load Resistance Factor Design Platform to Geotechnical Features (Fact and Fiction)

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1 Application of the Load Resistance Factor Design Platform to Geotechnical Features (Fact and Fiction) By Jerry A. DiMaggio, PE, D.GE, M.ASCE 1 Real Bio: Jerry A. DiMaggio, PE, D.GE, M.ASCE Pin Ball Machine Repairman 1yr Country Club Maintenance Foreman 5yrs Teamster 5yrs Father 34yrs Grandfather 2 years, 17 months, 1 month Civil Engineer (geotechnical and construction specialist) - 39yrs Husband 44yrs 2 Existing AASHTO Specifications Standard 18 th Edition LRFD now the 6 th Edition 3 1

2 History of AASHTO Code 1931 First US f standard specification for bridges (AASHO) 1973 LFD for steel and concrete bridge components (AASHO) 1986 First year any significant geotechnical guidance included in the code 1988 to 1993 Development of LRFD specifications for design and construction of highway bridges in US modeled after OHBDC $ F 1991 Provisions added to AASHTO Standard Specifications for Highway Bridges for design of drilled shaft foundations and soldier pile, anchored and MSE walls st Ed. of AASHTO LRFD Highway Bridge Design Specifications; 2nd Ed.: 1998, 3rd Ed.: 2004, 6th Ed.: Ceased updating AASHTO Standard Specifications for Highway p f Bridges as part of LRFD transition 2007 All Federal-funded structure design must use LRFD R-Q 4 What Changed with LRFD? f New philosophy of safety Limit states (strength, service, fatigue, extreme event) New load models (including new live load) New load and resistance factors based on reliability methods and calibrations $ F Introduce limit state-based provisions for foundation design and soil and rock mechanics Develop parallel commentary with design provisions Forced improved communication between structural, geotechnical and construction disciplines Forced geotechnical community to better understand, p loads, performance f requirements and conduct better geomaterial parameter assessments R-Q 5 The Good with LRFD f Few differences between ASD & LRFD Familiar design equations Familiar failure/performance criteria Strive to achieve comparable safety in structure and substructure components for RB calibration $ F Knowledge of statistics and reliability theory unnecessary to use LRFD Provides platform for rationally integrating performance data, site characterization and parameter selection into design Updated annually; not a cookbook, recognizes regional and local p f geology Sets a minimum standard of care for design and monitoring of geotechnical features R-Q 6 2

3 Geotechnical Features* A. Shallow Foundations (spread footings and mats) B. Deep Foundations (drilled shafts, driven piles and micropiles) C. Earth Retaining Structures (fill and cut) D. Soil Slopes (engineered fills and cuts) not addressed * The guidance in this webinar series is based on the AASHTO LRFD Specifications for bridges and structures but the concepts are applicable to all civil engineering facilities and industries. 7 Topics Included f Subsurface investigations Soil and rock properties Shallow foundations Driven piles Drilled shafts Microplies $ F Rigid and flexible culverts Abutments p f Walls (most types) R-Q Topics NOT Included Integral abutments Augercast piles Soil nails Reinforced slopes All soil and rock earthwork features ===================== There are also AASHTO LRFD CONSTRUCTION SPECS (driven, drilled and micropiles) 8 The Not So Good with LRFD f LRFD specification developed by and for bridge engineers; as such, the spec is based on a structural framework where -factors are lumped Geo-specialists work in an ASD world, so LRFD is unfamiliar and uncomfortable to many $ F Since 1st edition, numerous revisions have led users to question LRFD (why can t the code writers make up their minds?) Substructure implementation has lagged superstructure implementation and has often p been choppy f and confusing R-Q 9 3

4 Probability of Occurrence 3/10/2013 Reasons for Resisting LRFD Adoption f Human nature No perceived benefits Unfamiliarity with LRFD methods Lack of confidence in the computed results p f $ F Perceived errors and inconsistencies Specification that in some respects did not reflect current design practices Geotechnical practice is not as organized as structural practice R-Q 10 Sh i g i Q i R r = R n Q n f(g, ) R n g Q n Q R n R Q or R 11 Civil Engineering Design Platforms Allowable Stress Design (ASD) Working Stress Design (WSD) Load Factor Design (LFD) Ultimate Strength Design (USD) Load and Resistance Factor Design (LRFD) Limit State Design (LSD) Reliability Based Design (RBD) 12 4

Common Goal of ASD, LFD or LRFD Designs must be safe Capacity > Demand (or Demand < Capacity) Resistance > Load (or Load < Resistance) In LRFD the terms load and resistance are used 13 Resistance

5 Common Goal of ASD, LFD or LRFD Designs must be safe Capacity > Demand (or Demand < Capacity) Resistance > Load (or Load < Resistance) In LRFD the terms load and resistance are used 13 Resistance Factor For geotechnical features the resistance factor,, accounts for uncertainties in: Extent of subsurface investigation Variability of soil or rock properties (parameters) Accuracy and reliability of resistance prediction equations e.g., Terzaghi vs Meyerhof theories of bearing capacity Level and methods of construction monitoring (QC/QA) Consequences of failure Load Factor The load factor, g, accounts for uncertainties in Magnitude and direction of load(s) Location of application of load(s) Possible load combinations

Dial Gauge Jack Stressing Anchorage Fixed Base 16

Strength limit state Applies to strength and

Service limit state Applies to stress, deformation,

survival during once in a design-life events 4.

6 Dial Gauge Jack Stressing Anchorage Fixed Base 16 Primary Limit States AASHTO LRFD Article Strength limit state Applies to strength and stability during the design life 2. Service limit state Applies to stress, deformation, and cracking under regular operating conditions 17 Primary Limit States 3. Extreme event limit state Applies to structural survival during once in a design-life events 4. Fatigue limit state Applies to restrictions on stress range under repetitive live loading AASHTO LRFD Article

7 Definitions Extreme Event Limit States Limit states relating to events such as earthquakes, ice load, and vehicle and vessel collision, scour. Extreme event limit states relate to events with return periods in excess of the design life of the bridge or other structure. 19 LRFD (or LSD or RBD) Load Modifier (h i ) Load Effect (Q i ) Nominal Resistance (R n ) Sh i g i Q i R n Load Factor (g i ) Resistance Factor ( ) Factored Load Effect Factored Resistance 20 Maintaining separation between Q n and R n Q mean R mean f(r,q) Q n R n gq n R n g = Load Factor = Resistance Factor Q,R 21 7

8 What is Calibration? Calibration is the process of assigning values to resistance factors and load factors to quantify a chosen level of reliability LRFD Calibration can be achieved by Judgment Fitting with ASD Reliability theory Combination of above approaches 22 Establish g and by Fitting with ASD For DL and LL giqi gddl glll gd(dl/ll) g L FS Qi FS( DL LL) FS DL/LL 1 For DL only giqi gd( DL) g D FS Qi FS( DL) FS 23 AASHTO Definition of Reliability Index, b AASHTO (2007) defines reliability index as a quantitative assessment of safety expressed as the ratio of the difference between the mean resistance and mean force effect to the combined standard deviation of resistance and force effect. 24 8

9 AASHTO Definition of Reliability Index, b Assuming uncorrelated normally distributed probability distributed functions for R, Q and g, the Reliability Index, β, is as follows: Rmean Q b mean 2 s 2 R sq b Mean Std Dev 1 COV Reliability Index is also known as Safety Index because it is based on Safety Margin, i.e., R-Q 25 Calibration of b with P f β increases as P f reduces Need relationship between β and P f R b mean 2 sr Q s mean 2 Q F (1 P ) F -1 (1-P f ) is the value of the standard normal variate at the probability level 1-P f 1 f 26 Calibration of b with P f 27 9

10 AASHTO Table Load Combination Limit State STRENGTH LIMIT EXTREME EVENT SERVICE LIMIT FATIGUE - LL, IM & CE only DC DD DW EH EV ES EL PS CR SH LL IM CE BR PL LS WA WS WL FR TU TG SE Use One of These at a Time EQ IC CT CV I γp /1.20 γtg γse II γp /1.20 γtg γse III γp /1.20 γtg γse IV γp /1.20 V γp /1.20 γtg γse I γp γeq II γp I /1.20 γtg γse II /1.20 III /1.20 γtg γse IV / I 1.50 II Selecting a Load Combination Limit State Load Combination Primary Application I Normal vehicles, no wind II Special or permit vehicles Strength III Locations where wind exceeds 55 mph IV Very high DL to LL ratios V Normal vehicles with wind I Crack width in concrete, etc. Service II Steel structures only III P/S concrete structures only IV P/S concrete structures only Extreme I Includes earthquake Event II Includes ice and collision Fatigue I/ II Fatigue vehicle only AASHTO LRFD Article Load Factors for Permanent Loads, g p AASHTO Table 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 1.35 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

11 Loads Factors for Permanent Loads Selected to produce max./min. total extreme force effects For maximum force effects, loads that reduce maximum force effects should be factored by minimum load factor AASHTO Identify Controlling Load Combinations and Factors Sliding at Strength I Limit State 32 Article Topic AASHTO Section 10.4 Soil and Rock Properties Informational Needs Subsurface Exploration Laboratory Tests In Situ Tests Geophysical Tests Selection of Design Properties 33 11

12 AASHTO - Section 11 Outline Article Topic 11.1 Scope 11.2 Definitions 11.3 Notation 11.4 Soil Properties and Materials 11.5 Limit States and Resistance Factors 11.6 Abutments and Conventional Retaining Walls 11.7 Piers 11.8 Non-gravity Cantilevered Walls 11.9 Anchored Walls Mechanically Stabilized Earth Walls Refer to Section 3 for Loads and Load Factors 34 AASHTO Section 10.7 Driven Piles Article Topic General Service Limit State Design Strength Limit State Design Extreme Event Limit State Design Corrosion and Deterioration Minimum Pile Penetration Driving Criteria for Bearing Drivability Analysis Test Piles 35 Comparison of LRFD and ASD Geotechnical approaches for Structural Foundations and Earth Retaining Structures Same Determining resistance Determining deflection Different Comparison of load and resistance Separation of resistance and deflection NEW IN LRFD Additional design equations New load computation methods Deformation based analysis for extreme events Significantly expanded commentary and guidance for designers 36 12

Structural Loads Geotechnical Bridge Deck New Fill Lateral Squeeze Soft Soil Consolidating Due to Fill Weight Downdrag Bearing Stratum See FHWA Soils and Foundation Manual (2006) for more information

13 Structural Loads Geotechnical Bridge Deck New Fill Lateral Squeeze Soft Soil Consolidating Due to Fill Weight Downdrag Bearing Stratum See FHWA Soils and Foundation Manual (2006) for more information on geotechnical loads Refer to AASHTO Section 3 and Tables and for loads and load factors 37 Strength Limit State Driven Piles ARTICLE Axial compression resistance for single piles Pile group compression resistance Uplift resistance of single piles Uplift resistance of pile groups Pile punching failure in weaker stratum Single pile and pile group lateral resistance Constructability, including pile driveability 38 SPECIAL DESIGN CONSIDERATIONS Negative shaft resistance (downdrag) Lateral squeeze Scour Pile and soil heave Seismic considerations 39 13

STRENGTH LIMIT STATES Axial Driven Assess Driveability

HAVE PILE DAMAGE WHEN: The Pile Falls Over After Driving!

13 Pile Structural Resistance Concrete (5.5.4.2) Axial Comp. = 0.

9 LRFD Specifications Steel (6.5.4.2) Axial = 0.5-0.

14 STRENGTH LIMIT STATES Axial Driven Assess Driveability Structural Flexure Shear Geotechnical Axial YOU KNOW YOU HAVE PILE DAMAGE WHEN: The Pile Falls Over After Driving! 41 Structural Resistance Factors Pile Structural Resistance Concrete ( ) Axial Comp. = 0.75 Flexure = 0.9 (strain dependent) Shear = 0.9 LRFD Specifications Steel ( ) Axial = Combined Axial= Flexure = 1.0 Shear = 1.0 Timber ( and.3) Compression = 0.9 Tension = 0.8 Flexure = 0.85 Shear =

Service Limit State Checks Global Stability Vertical and Horizontal Displacements 43 10.

15 Service Limit State Checks Global Stability Vertical and Horizontal Displacements LIMIT STATES AND RESISTANCE Strength Limit State (will be discussed later) Structural Resistance Geotechnical Resistance Driven Resistance Service Limit State Resistance Factor = 1.0 (except for global stability) Extreme Event Limit State Seismic, superflood, vessel, vehicle, ice Use nominal resistance (except for uplift) 44 Determining Nominal Axial Geotechnical Resistance of Piles Field methods Static load test Dynamic load test (PDA) Driving Formulae Wave Equation Analysis Static analysis methods 45 15

16 Geotechnical Safety Factors for Piles (ASD) Basis for Design and Type of Construction Control Increasing Design/Construction Control Subsurface exploration X X X X X Static analysis X X X X X Dynamic formula AASHTO STANDARD SPECIFICATIONS X Wave equation X X X X CAPWAP analysis X X Static load test X X Factor of Safety (FS) Pile Testing Methods Analysis Method Resistance Factor ( ) (AASHTO 2012) Capacity Est. Stress Energy Measure Capacity Stress Energy Dynamic formula 0.10 (EOD) or 0.40 (EOD) X Wave equation 0.50 (w field confirmation of hammer) X X X Dynamic testing* 0.65 (2%) or 0.75 (100%) (0.5 uplift) X X X Static load test** 0.75 to 0.80 (wo/w dynamic) (0.6 UPLIFT) X * Dynamic Test requires signal matching **Static Test requires one test pile per site 47 Resistance Factors Static Analysis Methods AASHTO Table Method Resistance Factor, Compression Tension - method b- method method Nordlund- Thurman SPT CPT Group

Driven Pile Time Dependent Effects on Axial Geotechnical Resistance Article 10.7.3.4 Setup Relaxation R S R S R S R S R P R P R P R P 49 Point Bearing on Rock Article 10.7.3.2 Soft rock that can be penetrated by pile driving may be treated similar to soils.

17 Driven Pile Time Dependent Effects on Axial Geotechnical Resistance Article Setup Relaxation R S R S R S R S R P R P R P R P 49 Point Bearing on Rock Article Soft rock that can be penetrated by pile driving may be treated similar to soils. Steel piles driven into soft rock may not require tip reinforcement. On hard rock the nominal resistance is controlled by the structural capacity. See Article and the driving resistances in and 6.15 for severe driving. Dynamic testing should be used when the nominal resistance exceeds 600 kips. C Provides qualitative guidance to minimize pile damage when driving piles on hard rock. 50 Super Coastal Extreme Event 51 17

EXTREME EVENT LIMIT STATES AASHTO 10.5.5.3 Scour Vessel and Vehicle collision Seismic loading and site specific situations. (Uplift Resistance should be 0.80 rather than 1.00 for all extreme checks.

18 EXTREME EVENT LIMIT STATES AASHTO Scour Vessel and Vehicle collision Seismic loading and site specific situations. (Uplift Resistance should be 0.80 rather than 1.00 for all extreme checks.) 52 ASCE LRFD Webinar Series # Topic Fundamentals Part 1 6/30 1/18, 10/13 4/2, 1/7, 8/5 (Mon) 2 of LRFD Part 2 7/15 2/4, 10/21 4/26 1/24; 8/19 (Mon) 3 Subsurface Explorations 4/15 2/17, 8/18 2/3, 11/6 6/27 (Th) 4 Shallow Foundations 1/6, 5/7, 11/8 5/20, 12/12 10/16 5 Driven Piles 1/25, 6/1, 12/14 6/21, 11/7 6/8 2/13 6 Deep Foundations Drilled Shafts 2/8, 6/11 1/7, 7/8 1/23, 7/9 4/15 7 Micropiles 9/10 3/3, 7/29 1/12, 8/9 6/10 (Mon) 8 Fill Walls 8/20 3/11, 9/12 9/10 9 Earth Retaining Cut Walls 10/21 9/30 2/28, 9/28 10 Structures MSE Walls 4/4, 12/2 8/27 5/13 (Mon) 11 Ground Anchors 5/2 3/29, 12/11 4/30 (Tu) 12 Deep Foundations Lateral Analysis 5/7 3/4, 9/16 (Mon) 13 Extreme Events 5/21 3/28, 9/30 (Mon) * Check ASCE website for latest information 53 SINCE THE 1500 s THE NAME and FAMILY DIMAGGIO HAS REPRESENTED THE VERY BEST IN COFFEE, BASEBALL AND GEOENGINEERING AND GEO-CONSTRUCTION EXCELLENCE! 54 18

19 Thank You for Your Attention! Jerry D. Alias Joe D Cousin jdimaggio2@verizon.net Any Questions? 55 19

GEOTECHNICAL LRFD DESIGN

Chapter 8 GEOTECHNICAL LRFD DESIGN Final SCDOT GEOTECHNICAL DESIGN MANUAL August 2008 Table of Contents Section Page 8.1 Introduction... 8-1 8.2 LRFD Design Philosophy... 8-2 8.3 Limit States... 8-3 8.4