LRFD Bridge Design - Pages
LRFD Bridge DesignAASHTO LRFD Bridge DesignSpecificationsLoading and General InformationCreated July 2007
This material is copyrighted byThe University of Cincinnati,Dr. James A Swanson, andDr. Richard A MillerIt may not be reproduced, distributed, sold,or stored by any means, electrical ormechanical, without the expressed writtenconsent of The University of Cincinnati, Dr.James A Swanson, and Dr. Richard A Miller.July 31, 2007
LRFD Bridge DesignAASHTO LRFD Bridge Design SpecificationLoads and General InformationBackground and Theoretical Basis of LRFD .1AASHTO Chapter 1 .13AASHTO Chapter 2 .17AASHTO Chapter 3 .23AASHTO Chapter 4 .59Loads Case Study.71
James A SwansonAssociate ProfessorUniversity of CincinnatiDept of Civil & Env. Engineering765 Baldwin HallCincinnati, OH 45221-0071Ph: (513) 556-3774Fx: (513) 556-2599James.Swanson@uc.edu
AASHTO LRFD Bridge DesignSpecificationsJames A SwansonRichard A Miller AASHTO-LRFD Specification, 4th Ed., 2007References “Bridge Engineering Handbook,” Wai-Faf Chen and Lian Duan, 1999, CRC Press (08493-7434-0)“Four LRFD Design Examples of Steel Highway Bridges,” Vol. II, Chapter 1AHighway Structures Design Handbook, Published by American Iron and SteelInstitute in cooperation with HDR Engineering, Inc. Available at http://www.aisc.org/“Design of Highway Bridges,” Richard Barker and Jay Puckett, 1977, Wiley & Sons(0-471-30434-4)AASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 1 --Loads & Analysis: Slide #2
References AASHTO Web Site: http://bridges.transportation.org/ “Load and Resistance Factor Design for Highway Bridges,” Participant Notebook,Available from the AASHTO web site.AASHTO-LRFD 2007ODOT Short CourseCreated July 2007Loads & Analysis: Slide #3References AISC / National Steel Bridge Alliance Web Site: http://www.steelbridges. org/ “Steel Bridge Design Handbook”AASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 2 --Loads & Analysis: Slide #4
References “AASHTO Standard Specification for Highway Bridges,” 17th Edition, 1997, 2003“AASHTO LRFD Bridge Design Specifications,” 4th Edition, 2007“AASHTO Guide Specification for Distribution of Loads for Highway Bridges”AASHTO-LRFD 2007ODOT Short CourseCreated July 2007Loads & Analysis: Slide #5Philosophies of Design ASD - Allowable Stress DesignLFD - Load Factor DesignLRFD - Load and Resistance Factor DesignAASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 3 --Loads & Analysis: Slide #6
Philosophies of DesignASD: Allowable Stress Design For Safety:Fyf FA F .S .f - computed stressFA - Allowable StressIn terms of bending moment MS Fy1.82ASD does not recognize different variabilities of different load types.Chen & DuanAASHTO-LRFD 2007ODOT Short CourseCreated July 2007Loads & Analysis: Slide #7Philosophies of DesignLFD: Load Factor Design For Safety: γ Q Rn Q - Load EffectR - Component Resistanceγ - Load FactorIn terms of bending moment 1.30 M D 2.17 M ( L I ) φ M n φ - Strength Reduction FactorIn LFD, load and resistance are not considered simultaneously.Chen & DuanODOT Short CourseAASHTO-LRFD 2007Created July 2007-- 4 --Loads & Analysis: Slide #8
Philosophies of DesignLRFD: Load & Resistance Factor Design For Safety: γ Q φ Rn Q - Load EffectR - Component Resistanceγ - Load Factorφ - Resistance FactorThe LRFD philosophy provides a more uniform,systematic, and rational approach to the selectionof load factors and resistance factors than LFD.Chen & DuanAASHTO-LRFD 2007ODOT Short CourseLoads & Analysis: Slide #9Created July 2007Philosophies of Design - LRFD FundamentalsVariability of Loads and Resistances: Suppose that we measure the weight of 100 students WeightNumber ofSamplesWeightNumber age 180lbsSt Deviation 38lbsAASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 5 --Loads & Analysis: Slide #10
Philosophies of Design - LRFD FundamentalsVariability of Loads and Resistances:AASHTO-LRFD 2007ODOT Short CourseLoads & Analysis: Slide #11Created July 2007Philosophies of Design - LRFD FundamentalsVariability of Loads and Resistances: Now suppose that we measure the strength of 100 ropes WeightNumber ofSamplesWeightNumber 00Average 320lbsSt Deviation 28lbsAASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 6 --Loads & Analysis: Slide #12
Philosophies of Design - LRFD FundamentalsVariability of Loads and Resistances:15141312Number of Occurrences1110987654321220 230 240 250 260 270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420StrengthAASHTO-LRFD 2007ODOT Short CourseCreated July 2007Loads & Analysis: Slide #13Philosophies of Design - LRFD FundamentalsNumber of OccurrencesVariability of Loads and Resistances:AASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 7 --Loads & Analysis: Slide #14
Philosophies of Design - LRFD FundamentalsVariability of Loads and Resistances:σ ( R Q ) σ R 2 σ Q 2β Mean ( R Q )σ ( R Q )AASHTO-LRFD 2007ODOT Short CourseLoads & Analysis: Slide #15Created July 2007Philosophies of Design - LRFD FundamentalsReliability 33%AASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 8 --Loads & Analysis: Slide #16
Philosophies of Design - LRFD FundamentalsReliability Index:AISC: βD (L or S)D L WD L EMembers3.02.51.75Connections4.54.54.5AASHTO: β 3.5 Super/Sub Structuresβ 2.5 FoundationsAASHTO-LRFD 2007ODOT Short CourseLoads & Analysis: Slide #17Created July 2007Philosophies of Design - LRFD FundamentalsReliability Index:LRFD Bridge Designs (Expected)544Reliability IndexReliability IndexASD / LFD Bridge Designs532103210275481Span Length (ft)108180Chen & DuanODOT Short Course00275481Span Length (ft)108180AASHTO-LRFD 2007Created July 2007-- 9 --Loads & Analysis: Slide #18
Philosophies of Design - LRFD Fundamentals Resistance Factor:φ Rm [ 0.55 β COV( Rm )]eRnRm - Mean Value of R (from experiments)Rn - Nominal Value of Rβ - Reliability IndexCOV(Rm) - Coeff. of Variation of RAASHTO-LRFD 2007ODOT Short CourseCreated July 2007Loads & Analysis: Slide #19Created July 2007Loads & Analysis: Slide #20AASHTO-LRFD SpecificationAASHTO-LRFD 2007ODOT Short Course-- 10 --
AASHTO-LRFD eral Design and LocationFeaturesLoads and Load FactorsStructural Analysis andEvaluationConcrete StructuresSteel StructuresAluminum Structures8.9.10.11.12.13.14.15.Wood StructuresDecks and Deck SystemsFoundationsAbutments, Piers, and WallsBuried Structures and TunnelLinersRailingsJoints and BearingsIndexAASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 11 --Loads & Analysis: Slide #21
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AASHTO-LRFDChapter 1: Introduction AASHTO-LRFD Specification, 4th, 2007Chapter 1 – Introduction§1.3.2: Limit States Service: Strength: Intended to ensure that strength and stability are provided to resist statisticallysignificant load combinations that a bridge will experience during its design life.Extensive distress and structural damage may occur at strength limit stateconditions, but overall structural integrity is expected to be maintained.Extreme Event: Deals with restrictions on stress, deformation, and crack width under regularservice conditions.Intended to ensure that the bridge performs acceptably during its design life.Intended to ensure structural survival of a bridge during an earthquake, vehiclecollision, ice flow, or foundation scour.Fatigue: Deals with restrictions on stress range under regular service conditions reflectingthe number of expected cycles.Pg 1.4-5; Chen & DuanODOT Short CourseAASHTO-LRFD 2007Created July 2007-- 13 --Loads & Analysis: Slide #23
Chapter 1 – Introduction§1.3.2: Limit StatesQ ηi γ i Qi(1.3.2.1-1)γi - Load FactorQi - Load Effectηi - Load ModifierWhen the maximum value of γi is appropriateηi ηD ηR ηI 0.95(1.3.2.1-2)When the minimum value of γi is appropriateηi 1 1.00ηD ηR η I(1.3.2.1-3)AASHTO-LRFD 2007Pg 1.3ODOT Short CourseCreated July 2007Loads & Analysis: Slide #24Chapter 1 – Introduction§1.3.2: Limit States - Load ModifiersApplicable only to the Strength Limit State ηD – Ductility Factor: for nonductile membersfor conventional designs and details complying with specificationsfor components for which additional ductility measures have beentakenηR – Redundancy Factor: ηD 1.05ηD 1.00ηD 0.95ηR 1.05ηR 1.00ηR 0.95for nonredundant membersfor conventional levels of redundancyfor exceptional levels of redundancyηI – Operational Importance: ηI 1.05ηI 1.00ηI 0.95for important bridgesfor typical bridgesfor relatively less important bridgesThese modifiers are applied at the element level, not the entire structure.Pgs. 1.5-7; Chen & DuanODOT Short CourseAASHTO-LRFD 2007Created July 2007-- 14 --Loads & Analysis: Slide #25
§ 3.4 - Load Factors and Combinations§1.3.2: ODOT Recommended Load ModifiersFor the Strength Limit States ηD – Ductility Factor: Use a ductility load modifier of ηD 1.00 for all strength limit statesηR – Redundancy Factor: Use ηR 1.05 for “non-redundant” membersUse ηR 1.00 for “redundant” members Bridges with 3 or fewer girders should be considered “non-redundant.” Bridges with 4 girders with a spacing of 12’ or more should be considered “nonredundant.”Bridges with 4 girders with a spacing of less than 12’ should be considered“redundant.”Bridge with 5 or more girders should be considered “redundant.”AASHTO-LRFD 2007ODOT Short CourseCreated July 2007Loads & Analysis: Slide #26§ 3.4 - Load Factors and Combinations§1.3.2: ODOT Recommended Load ModifiersFor the Strength Limit States ηR – Redundancy Factor: Use ηR 1.05 for “non-redundant” membersUse ηR 1.00 for “redundant” members Single and two column piers should be considered non-redundant. Cap and column piers with three or more columns should be consideredredundant.T-type piers with a stem height to width ratio of 3-1 or greater should beconsidered non-redundant.For information on other substructure types, refer to NCHRP Report 458Redundancy in Highway Bridge Substructures.ηR does NOT apply to foundations. Foundation redundancy is included in theresistance factor.AASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 15 --Loads & Analysis: Slide #27
§ 3.4 - Load Factors and Combinations§1.3.2: ODOT Recommended Load ModifiersFor the Strength Limit States ηI – Operational Importance: In General, use ηI 1.00 unless one of the following appliesUse ηI 1.05 if any of the following apply Design ADT 60,000 Detour length 50 miles Any span length 500’Use ηI 0.95 if both of the following apply Design ADT 400 Detour length 10 milesDetour length applies to the shortest, emergency detour route.AASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 16 --Loads & Analysis: Slide #28
AASHTO-LRFDChapter 2: General Design andLocation Features AASHTO-LRFD Specification, 4th Ed., 2007Chapter 2 – General Design and Location FeaturesContents 2.1 – Scope 2.2 – Definitions 2.3 – Location Features 2.3.1 – Route Location2.3.2 – Bridge Site Arrangement2.3.3 – Clearances2.3.4 – Environment2.4 – Foundation Investigation 2.4.1 – General2.4.2 – Topographic StudiesAASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 17 --Loads & Analysis: Slide #30
Chapter 2 – General Design and Location FeaturesContents 2.5 – Design Objectives 2.5.1 – Safety2.5.2 – Serviceability2.5.3 – Constructability2.5.4 – Economy2.5.5 – Bridge Aesthetics2.6 – Hydrology and Hydraulics 2.6.1 – General2.6.2 – Site Data2.6.3 – Hydrologic Analysis2.6.4 – Hydraulic Analysis2.6.5 – Culvert Location and Waterway Area2.6.6 – Roadway DrainageAASHTO-LRFD 2007ODOT Short CourseCreated July 2007Loads & Analysis: Slide #31§ 2.5.2 - Serviceability§2.5.2.6.2 Criteria for DeflectionODOT requires the use of Article 2.5.2.6.2 and 2.5.2.6.3 for limitingdeflections of structures.ODOT prohibits the use of “the stiffness contribution of railings,sidewalks and median barriers in the design of the compositesection.”AASHTO-LRFD 2007ODOT Short CourseCreated July 2007-- 18 --Loads & Analysis: Slide #32
§ 2.5.2 - Serviceability§2.5.2.6.2 Criteria for Deflection Principles which apply When investigating absolute deflection, load all lanes and assume allcomponents deflect equally.When investigating relative deflection, choose the number and positionof loaded lanes to maximize the effect.The live load portion of Load Combination Service I (plus impact) shouldbe used.The live load is taken from Article 3.6.1.1.2 (covered later).For skewed bridges, a right cross-section may be used, for curvedbridges, a radial cross section may be used.ODOT prohibits the use of “the stiffness contribution of railings,sidewalks and median barriers in the design of the composite section.”Pg 2.10-14ODOT Short CourseAASHTO-LRFD 2007Created July 2007Loads & Analysis: Slide #33§ 2.5.2 - Serviceability§2.5.2.6.2 Criteria for DeflectionIn the absence of other criteria, these limits may be applied tosteel, aluminum and/or concrete bridges:LoadLimitGeneral vehicular loadSpan/800Vehicular and/or pedestrian loadSpan/1000Vehicular load on cantilever armsSpan/300Vehicular and/or pedestrian load oncantilever armsSpan/375For steel I girders/beams, the provisions of Arts. 6.10.4.2 and 6.11.4 regardingcontrol of deflection through flange stress controls shall apply.Pg 2.10-14ODOT Short CourseAASHTO-LRFD 2007Created July 2007-- 19 --Loads & Analysis: Slide #34
§ 2.5.2 - Serviceability§2.5.2.6.2 Criteria for DeflectionFor wood construction:LoadLimitVehicular and pedestrian loadsSpan/425Vehicular loads on wood planks and panels: extremerelative deflection between adjacent edges0.10 inPg 2.10-14ODOT Short CourseAASHTO-LRFD 2007Created July 2007Loads & Analysis: Slide #35§ 2.5.2 - Serviceability§2.5.2.6.2 Criteria for DeflectionFor orthotropic plate decks:LoadLimitVehicular loads on deck platesSpan/300Vehicular loads on ribs of orthotropic metal decksSpan/1000Vehicular loads on ribs of orthotropic metal decks:extreme relative deflection between adjacent ribs0.10 inPg 2.10-14ODOT Short CourseAASHTO-LRFD 2007Created July 2007-- 20 --Loads & Analysis: Slide #36
§ 2.5.2 - Serviceability§2.5.2.6.3 Optional Criteria for Span-to-Depth ratiosTable 2.5.2.6.3-1 Traditional Minimum Depths for Constant Depth SuperstructuresMinimum Depth (Including Deck)When variable depth members are used, values may be adjusted to account forchanges in relative stiffness of positive and negative moment sectionsSuperstructureMaterialTypeSimple SpansContinuous Spans1.2( S 10)30S 10 0.54 ft .30T-Beams0.070L0.065LBox Beams0.060L0.055LPedestrian Structure Beams0.035L0.033L0.030L 6.5 in.0.027L 6.5 in.CIP Box Beams0.045L0.040LPrecast I-Beams0.045L0.040LPedestrian Structure Beams0.033L0.030LAdjacent Box Beams0.030L0.025LOverall Depth of Composite I-Beam0.040L0.032LDepth of I-Beam Portion of Composite I-Beam0.033L0.027Trusses0.100L0.100LSlabs with main reinforcement parallel to teelODOT states that “designers shall apply the span-to-depth ratios shown.”Pg 2.10-14ODOT Short CourseAASHTO-LRFD 2007Created July 2007-- 21 --Loads & Analysis: Slide #37
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AASHTO-LRFDBridge Design SpecificationSection 3: Loads and Load Factors AASHTO-LRFD Specification, 4th Ed., 2007§ 3.4 - Loads and Load Factors§3.4.1: Load Factors and Load CombinationsPermanent Loads DD - DowndragDC - StructuralComponents andAttachmentsDW - Wearing Surfacesand Utilities EH EL - ES - EV - Pg 3.7ODOT Short CourseHorizontal Earth PressureLocked-In ForceEffects IncludingPretensionEarth SurchargeLoadVertical Pressure ofEarth FillAASHTO-LRFD 2007Created July 2007-- 23 --Loads & Analysis: Slide #39
§ 3.4 - Loads and Load Factors§3.4.1: Load Factors and Load CombinationsTransient Loads BR –CE –CR CT CV EQ FR IC LL IM -Veh. Braking ForceVeh. Centrifugal ForceCreepVeh. Collision ForceVessel Collision ForceEarthquakeFrictionIce LoadVeh. Live LoadDynamic Load Allowance LS PL SE SH TG TU WA WL WS -Live Load SurchargePedestrian Live LoadSettlementShrinkageTemperature GradientUniform TemperatureWater LoadWind on Live LoadWind Load on StructurePg 3.7AASHTO-LRFD 2007ODOT Short CourseLoads & Analysis: Slide #40Created July 2007§ 3.4 - Loads and Load Factors§3.4.1: Load Factors and Load CombinationsTable 3.4.1-1 Load Combinations and Load FactorsUse One of These ata TimeDCDDDWEHEVESELLLIMCEBRPLLSWAWSWLSTRENGTH I(unless noted)γp1.751.00--STRENGTH IIγp1.351.00--STRENGTH IIIγp1.00STRENGTH IVγpSTRENGTH GγSE--------Pg 3.13ODOT Short CourseAASHTO-LRFD 2007Created July 2007-- 24 --Loads & Analysis: Slide #41
§ 3.4 - Loads and Load Factors§3.4.1: Load Factors and Load CombinationsTable 3.4.1-1 Load Combinations and Load Factors (cont.)Use One of These at aTimeDCDDDWEHEVESELLLIMCEBRPLLSWAWSWLEXTREMEEVENT IγpγEQ1.00--EXTREMEEVENT IIγp0.501.00FATIGUE – LL,IM, & CE -----------------Pg 3.13AASHTO-LRFD 2007ODOT Short CourseLoads & Analysis: Slide #42Created July 2007§ 3.4 - Loads and Load Factors§3.4.1: Load Factors and Load CombinationsTable 3.4.1-1 Load Combinations and Load Factors WSWLSERVICE I1.001.001.000.301.0SERVICE II1.001.301.00--SERVICE III1.000.801.00SERVICE IV1.00--1.00Use One of These ata �SE--------0.70--1.001.00/1.20--1.0--------Pg 3.13ODOT Short CourseCVAASHTO-LRFD 2007Created July 2007-- 25 --Loads & Analysis: Slide #43
§ 3.4 - Loads and Load Factors§3.4.1: Load Factors and Load Combinations Strength I:Basic load combination relating to the normal vehicularuse of the bridge without wind. Strength II:Load combination relating to the use of the ation permit vehicles, or both, without wind. Strength III:Load combination relating to the bridge exposed towind in excess of 55 mph. Strength IV:Load combination relating to very high dead loadto live load force effect ratios. (Note: In commentary itindicates that this will govern where the DL/LL 7,spans over 600’, and during construction checks.) Strength V:Load combination relating to normal vehicular usewith a wind of 55 mph.Pg 3.8-3.10AASHTO-LRFD 2007ODOT Short CourseCreated July 2007Loads & Analysis: Slide #44§ 3.4 - Loads and Load Factors§3.4.1: Load Factors and Load Combinations Extreme Event I:Load combination including earthquakes. Extreme Event II: Load combination relating to ice load, collision byvessels and vehicles, and certain hydraulic events witha reduced live load. Fatigue:Fatigue and fracture load combination relating torepetitive gravitational vehicular live load and dynamicresponses under a single design truck.Pg 3.8-3.10ODOT Short CourseAASHTO-LRFD 2007Created July 2007-- 26 --Loads & Analysis: Slide #45
§ 3.4 - Loads and Load F
2. General Design and Location Features 3. Loads and Load Factors 4. Structural Analysis and Evaluation 5. Concrete Structures 6. Steel Structures 7. Aluminum Structures 8. Wood Structures 9. Decks and Deck Systems 10. Foundations 11. Abutments, Piers, and Walls 12. Buried Structures and Tunnel Liners 13. Railings 14. Joints and Bearings 15 .
Recently, we were made aware of some technical revisions that need to be applied to the AASHTO LRFD Bridge Design Specifications, 6th Edition. Please replace the existing text with the corrected text to ensure that your edition is both accurate and current. AASHTO staff sincerely apologizes for any inconvenience.File Size: 2MBPage Count: 104Explore furtherAASHTO LRFD 2012 Bridge Design Specifications 6th Ed ( US .archive.orgAASHTO Issues Updated LRFD Bridge Design Guideaashtojournal.orgAASHTO Publishes New Manual for Bridge Element Inspection .aashtojournal.orgAASHTO LRFD Bridge Design Specifications. Eighth Edition .trid.trb.orgSteel Bridge Design Handbook American Institute of Steel .www.aisc.orgRecommended to you b
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FHWA/NHI Bridge Design and Analysis Courses (www.nhi.fhwa.dot.gov) NHI Course 130081: LRFD for Bridge Superstructures NHI C 130082NHI Course 130082: LRFD f B id S b t t d ERSLRFD for Bridge Substructures and ERS NHI Course 130092: LRFR for Highway Bridges NHI Course 130093: LRFD Seismic Analysis and Design of Bridges NHI Course 130094: LRFD Seismic Analysis and Design of Tunnels,
MAY 2016 LRFD BRIDGE DESIGN 8-3 AASHTO LRFD shall be obtained from the National Design Specification for Wood Construction (NDS). The AASHTO LRFD tabulated design values assume dry-use conditions. These tabulated values shall be modified if wood will be subject to wet use conditions. Table 8.1.1.1. has an abbreviated list of some typical
foundations will lead to savings or to equivalent foundation costs compared with ASD methods. At the end, a roadmap for development of LRFD design guidance that consists of LRFD design specifications and delivery processes for bridge foundations is discussed. 17. KEY WORDS: LRFD, ASD, limit AASHTO, 18. DISTRIBUTION STATEMENT
AASHTO LRFD Bridge Design Specifications, 7th Edition, 2014 (AASHTO LRFD) v. AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, First Edition, 2015 (AASHTO Signs) vi. Washington State Department of Transportation Bridge Design Manual (LRFD), 2016 (BDM) vii. American Institute of Steel .
designed by the latest edition of AASHTO LRFD Bridge Design Specifications. Designs for the reconstruction or rehabilitation of existing bridge structures should be completed with guidance from the Bridge Design Engineer. This manual documents policy on LRFD bridg
