Si Published by the S ) ‘American Association of State Highway and Transportation Officials AASHTO LRFD Bridge Design Specifications SI Units Third Edition 2005 Interim Revisions (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav.SECTION 3 (SI): LOADS AND LOAD FACTORS TABLE OF CONTENTS 3.1 SCOPE 3.2 DEFINITIONS. 33 NOTATION 33.1 General 3.3.2 Load and Load Designation 3.4 LOAD FACTORS AND COMBINATIONS. 34.1 Load Factors and Load Combinations 3.4.2 Load Factors for Construction Loads, 3.4.2.1 Evaluation atthe Strength Limit State 3.4.2.2 Evaluation of Deflection at the Service Limit State 3.4.3 Load Factors for Jacking and Post-Tensioning Forces. 3.4.3.1 Jacking Forces 3.4.3.2 Force for Post-Tensioning Anchorage Zones 3.5 PERMANENT LOADS. 3.5.1 Dead Loads: DC, DIV, and BV 3.5.2 Earth Loads: EH. BS, and DD. 3.6 LIVE LOADS, 3.6.1 Gruvity Loads: 1 and PL 3.6.1.1 Vehicular Live Load 36.1.1.1 Number of Design Lanes 3.6.1.12 Multiple Presence of Live Load 3.6.1.2 Design Vehicular Live Load. 3.6.1.2.1 General 36.122 Design Truck 36.123 Design Tandem, 36.124 Design Lane Low 3.6.1.2.5 Tire Contact Area 3.6.1.2. Distribution of Wheel Loads Through Earth Fills, 3.6.1.3 Application of Design Vehicular Live Loads 3.6.13. General 3.6.3.2 Loading for Optional Live Load Deflection Evaluation 3.6.1.3. Design Loads for Decks, Deck Systems, and the Top Slabs of Box Culverts, 36.134 Deck Overhang Load. 3.6.14 Fatigue Load. 3.6.1.4.1 Magnitude and Configuration 3.6.14.2 Frequency 36.143 Load Distribution for Fatigue 36.14.34 Refined Methods, 3.6.1.4.30 Approximate Methods. 3.6.1.5 Rail Transit Loud. 3.6.1.6 Pedestrian Loads 3.6.1.7 Loads on Railings 3.6.2 Dynamic Load Allowance: 1M 3.6.2.1 General 3.6.2.2 Buried Components 3.6.2.3 Wood Components 3.6.3 Centrifugal Forces: Cl 3.64 Braking Force: BR. 365 Vehicular Collision Force: CT 3.6.5.1 Protection of Structures 3.68.2 Vehicle and Railway Collision with Structures 3.6.53 Vehicle Collision with Barriers 3 (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav.34 AASHTO LRED Brine! 3.7 WATER LOADS: 111 3.7.1 Static Pressure 3.7.2 Buoyancy 3.73 Stream Pressure 3.7.3.1 Longitudinal 3.7.3.2 Lateral 3.74 Wave Load, 3.7.5 Change in Foundations Due to Limit State for Scour 3.8 WIND LOAD: JIL AND 1/5. 3.8.1 Horizontal Wind Pressure 3.8.1.1 General 3.8.1.2 Wind Pressure on Structures: 17S 3.8.1.2. General 3.8.1.2.2 Loads from Superstructures 3.8.1.2.3 Forces Applied Directly to the Substructure 3.8.1.3 Wind Pressure on Vehicles: 1/7. 3.82 Vertical Wind Pressure 3.83 Aeroelastic Instability 1 General 2 Acroelastic Phenomena, 3 Control of Dynamic Responses. 4 Wind Tunnel Tests 3.9 ICELOADS: IC 3.9.1 General 3.9.2 Dynamic Ice Forces on Piers 3.9.2.1 Effective Ice Strength, 3.9.2.2 Crushing and Flexing, 3.9.2.3 Small Streams 3.9.2.4 Combination of Longitudinal and Transverse Forces 3.9.2.4.1 Piers Parallel to Flow 3.9.2.4.2 Piers Skewed to Flow 3.9.2.5 Slender and Flexible Piers. 3.9.3 Static Ice Loads on Piers. 3.9.4 Hanging Dams and Iee Jams 3.9.5 Venical Forces due to Ice Adhesion 3.9.6 Ice Accretion and Snow Loads on Superstructures. 3.10 EARTHQUAKE EFFECTS: £0, 3.10.1. General 3.10.2. Acceleration Coefficient 3.10.3 Importance Categories. 3.10.4 Seismic Performance Zones. 3.10.5 Site Effects 3,105.1 General 3.10.52 Soil Profile Type 1 83. 383. 383. 10.33 Soil Profile Type IL 10.54 Soil Profile Type Ill 3.10.5.5 Soil Profile Type IV 3.10.6 Elastic Seismic Response Coefficient 3.10.6. General 3.10.62 Exceptions 3.10.7 Response Modification Factors 3.10.7.1, General 3.10.72 Application. 3.10.8 Combination of Seismic Force Erfects 3.10.9 Calculation of Design Forces. Estes SrecinicaTioNs (SD) 331 3531 331 3431 3331 3533 3.33 333 34TanLeor Contexts (SD, 3.10.9.1 General 3.10.92 Seismic Zone 1 3.10.93 Seismic Zone 2 3.10.94 Seismic Zones 3 and 4 3.10.9.4.1 General 3.10.9.42 Modified Design Forces 3.10.9.4.3 Inelastic Hinging Forces 3.10.9.43a General 3.10,9.4.3b Single Columns an Piers, 3.10,9.4.3¢ Piers with Two or More Columns. 3.10,9.4.34 Column and Pile Bent Design Forces 3.10.9.4.3e Pier Design Forces. 3.10,9.4.3f Foundation Design Forces, 3.10.95 Longitudinal Restrainers. 3.10,9.6 Hold-Down Devices 3.10.10 Requirements for Temporary Bridges and Stage Construction 3.11 EARTH PRESSURE: FH, ES, LS, AND DD 3.11.1 General, 3.11.2 Compaction 3.113 Presence of Water 3.114 Effect of Earthquake 3.11.5 Earth Pressure: EH 3.11,5.1 Lateral Earth Pressure 3.11.52 AtRest Lateral Earth Pressure Coefficient, f, 311.53 Active Lateral Earth Pressure Coefficient, ki, 3.11.54 Passive Lateral Earth Pressure Coefficient, 3.11.55 Equivalent-Fluid Method Of Estimating Rankine Lateral Earth Pressures 3.11.56 Lateral Earth Pressures For Nongravity Cantilevered Walls 3.11.5.7 Apparent Earth Pressures For Anchored Walls, 3.11.5.7.1 Cohesionless Soils. 3.11,5.7.2. Cohesive Soils 3.11.5.7.2a Stiff to Hard 3.11.5.7.2b Soft to Medium Sut 3.11.58 Lateral Earth Pressures for Mechanically Stabilized Earth Walls 3.11.5.8.1 General 3.11.58.2 Internal Stability 3.11.59 Lateral Earth Pressures For Prefabricated Modular Walls. 3.11.6 Surcharge Loads: £8 and LS 3.11.6.1 Uniform Surcharge Loads (8) 3.11.62 Point, Line And Strip Loads (8) —Walls Restrained From Movement 3.11.63 Strip Loads (£S)—Flexible Walls, 3.11.64 Live Load Surcharge (5) 3.11.65 Reduction of Surcharge 3.11.7 Reduction due to Earth Pressure 3.11.8 Downdrag 3.12 FORCE EFFECTS DUE TO SUPERIMPOSED DEFORMATIONS: TU, 76, Sif, CR, SE 3.12.1 General 3.12.2 Uniform Temperature 3.12.2.1 Temperature Range for Procedure A 3.12.22 Temperature Range for Procedure B. 3.12.23 Design Thermal Movements, 3.12.3 Temperature Gradient 3.12.4 Differential Shrinkage. 3.12.5 Creep, 3.12.6 SettlementBav AASHTO LRED Bainer Drsies Sprcinicatioxs (SI) 3.13 FRICTION FORCES: FR 3.97 3.14 VESSEL COLLISION: CI 3.98 3.14.1 General 3-98. 3.14.2 Owner's Responsibility 3-99 3.14.3 Importance Categories. 3.99 3.144 Design Vessel 3-99) 3.14.5 Annual Frequency of Collapse. 3-100 3.14.5.1 Vessel Frequency Distribution. 3-101 3.14.52. Probability of Aberrancy 3-102 3.14.5.2.1 General 3-102 3.14.5.2.2 Statistical Method 3-102 3.14.5.2.3 Approximate Method 3-102 3.14.53 Geometric Probability 3-105 3.14.54 Probability of Collapse. 3-106 3.146 Design Collision Velocity 3-106 3.14.7 Vessel Collision Energy 3-107 3.148 Ship Collision Force on Pier 3 3.14.9 Ship Bow Damage Length 3-109 3.14.10 Ship Collision Force on Superstructure. 3 3.14.10.1 Collision with Bow 3 3.14.10.2 Collision With Deck House 3-110 14.103 Collision with Mast 11 3.14.11 Barge Collision Force on Pier 3-111 3.14.12 Barge Bow Damage Length 3-112 3.14.13 Damage at the Extreme Limit State 313 3.14.14 Application of Impact Force. 3-113 3.14141 Substructure Design 3-113 3.14.14.2 Superstructure Design 3-14 3.14.15 Protection of Substructures 3-115SecrI0N3 (SD LOADS AND LOAD FACTORS 3.1 SCOPE ‘This section specifies minimum requirements for loads and forces, the limits of their application, load factors, and load combinations used forthe design of new bridges. The load provisions may also be applied to the structural evaluation of existing bridges. ‘Where multiple performance levels are provided, the selection of the design performance level is the responsibility ofthe Owner. ‘A minimum load factor is specified for force effects that-may develop during construction. Additional requirements for construction of segmental concrete bridges are specified in Article 5.14.2 32 DEFINITIONS ca ‘This section includes, in addition to traditional loads, the force effects due to collisions, earthquakes, and settlement and distortion of the structure. Vehicle and vessel collisions, earthquakes, and acroelastic instability develop force effects that are ‘dependent upon structural response. Therefore, such Force effects cannot be determined without analysis and/or testing With the exception of segmental concrete bridges, construction loads are not provided, but the Designer should obiain pertinent information from prospective contractors Active Earth Pressure—Lateral pressure resulting from the retention of the earth by a structure or component that is tending to move away from the soil mass, Active Earth Wedge—Wedge of earth with a tendency to become mobile if not retained by a structure or component. Aeroelastic Vibration ‘Axle Unit—Single axle or tandem axle Berm—An earthwork used to redirector slaw down: ground and cut slopes Periodic, elastic response of a structure to wind. ging vehicles or vessels alto stabilize fll, embankment, or soft Centrifugal Force—A lateral force resulting from a change in the direction of a vehicle's movement. Danper—A device that transfers and reduces forces between superstructure elements and/or superstructure and substructure elements, while permitting thermal movements. The device provides damping by dissipating energy under seisic, braking or other dynamic loads, Deep Draft Waterways—A navigable waterway used by merchant ships with loaded drafts of 4200-18 000+ mn Design Lane—A notional traffic lane positioned transversely on the roadway. Design Thermal Movement Range—The structure movement range resulting from the difference between the maxim as defined in Article 3.12, Design Water Depth—Depth of water at mean high water, Distortion—Change in structural geometry Dolphin—Protective object that may have its own fender system and that is usually circular in plan andl structurally independent from the bridge. Dynamic Load Allowance—An increase in the applied static force effects to account for he dynamic interaction between the bridge and moving vehicles Equivalent Fluid—A notional substance whose density is such that it would exert the same pressure as the soil itis seen to replace for computational purposes.32 AASHTO LRED Brince Desicy SPeciricaTions (SI) Expased—A condition in which a portion ofa bridge's substructure or superstructure is subject to physical contact by any portion of a colliding vessel's bow, deck house, or mast Exireme—A maximum ora Fonder—Protection hardware attached to the structural component to be protected or used to delineate channels or 10 redirect aberrant vessels, FrarilIce—Ice resulting from turbulent water flow. GlobalPentinent to the entire superstructure orto the whole bridge. Influence Surface—A continuous or discretized function over a bridge deck whose value ata point, m acting normal to the deck at that point, yields the force effect being sought. iplied by a load Lano—The area of deck receiving one 3 one uniform load line Lever Rule—The statical summatior f moments about one point to calculate the reaction at a second pois Liquefaction —The loss of shear strength in a saturated soil due to excess hydrostatic pressure. In saturated, cohesionless soils, such a strength loss can result from loads that are applied instantancousty or cyclicly, particulary in loose fine to medium sands that are uniformity graded Load—The effect of acceleration, including that due to gravity, imposed deformation, or volumetric change. Local—Pertinent to a component or subassembly of components, ‘Megagram (Mg)—1000 kg (a unit of mass). “Mode of Vibration—A shape of dynamic deformation associated with a frequency of vibration. Navigable Waterway—A waterway, determined by the U.S. Coast Guard as being suitable for interstate or foreign commerce, as described in 33CFR205-25. Nominal Load—An arbitrarily selected design load level Normally Consolidated Soit—A soil for which the current effective overburden pressure is the same as the maximum, pressure that has been experienced. Overconsolidated Sol!—A soll that has been under greater overburden pressure than currently exists, Overall Stability Stability of the entire retaining wal or abutment structure and is determined by evaluating potential slip surfaces located outside ofthe whole structure. Overconsolidation Ratio—Ratio of the maximum preconsolidation pressure to the overburden pressure. Passive Earth Pressure—Lateral pressure resulting from the earth’s resistance to the lateral movement of a structure or component into the soil mass. Permanent Loads—Loads and forces that are, or are assumed to be, constant upon completion of construction, Permit Vehicle—Any vehicle whose right to travel is administratively restricted in any way due to its weight or size. Reliability ndex—A quantitative assessment of safety expressed asthe ratio ofthe difference between the mean resistance ‘and mean force effect to the combined standard deviation of resistance and force effectSECTION3 (SI): LOADS AND LoaD FACTORS 33 Restrainers—A system of high-strength cables or rods that transfers forces between superstructure elements and/or superstructure and substructure elements under seismic or other dynamic loads after an initial slack is taken up, while permitting thermal movernents, Roadway Width—Clear space between barriers and/or curbs. Setting Temperaturo—A structure's average temperature, which is used to determine the dimensions ofa structure when a component is added or set in place. Shallow Draft Waterways—A navigable waterway used primarily by barge vessels with loaded drafts of less than 2700 to 3000 mm, Shock Transmission Unit (STU)—A device that provides a temporary rigid link between superstructure elements and/or superstructure and substructure elements under seismic, braking or olher dynamic loads, while permitting thermal movements. Structurally Continuous Barrier—A barvier, or any part thereof, that is interrupted only at deck joints Substruciure—Structural parts of the bridge that support the horizontal span. ‘Superstructure—Siructural parts of the bridge that provide the horizontal span, Surcharge—A load used to model the weight of earth fill or other loads applied to the top of the retained material Tandem—Two closely spaced axles, usually connected to the same under-carriage, by which the equalization of load between the axles is enhanced. Wall Friction Angle—An angle whose arctangent represents the apparent friction between a wall and a soil mass. Wheet—Single or dual tire at one end of an axle Whee! Line—A transverse or longitudinal grouping of wheels. 33 NOTATION 3.3.1 General A = plan area of ice floe (mn); seismic acceleration coefficient; depth of temperature gradient (mm) (C3.9.2.3) 10.2) 6.12.3) AF = annual frequency of bridge element collapse (numberiyr) (C3.14.4) a length of uniform deceleration at braking (mm); truncated distance (mm); average bow damage length (mim) (C364) (C395) (C3.149) as bow damage length of standard hopper barge (mm) (3.14.11) a bow damage length of ship (an) (3.14.9) B equivalent footing width (mm) (3.11.6.3) B, = width of excavation (mmm) (3.11.5.7.2b) Bu ‘beam (width) for barge, barge tows, and ship vessels (mm) (C3.14.5.1) 5, ‘width of bridge pier (nim) (3.14.5.3) ER = vehicular braking force: base rate of vessel aberrancy (3.3.2) (3.14.5.2.3) b braking force coefficient; width of a discrete vertical wall element (mm) (C3.6.4) (8.11.5.6) by ‘width of applied load or footing mm) (3.11.6.3) C= _coeficient to compute centrifugal forces; constant for terrain conditions in reation to wind approach (3.6.3) (38.1.1) C, = coeficient for force due to crushing of ice (3.9.2.2) G drag coefficient (sec.? Nim’) (3.7.3.1) Cy hydrodynamic mass coefficient (3.14.7) Cr _ateral drag coefficient (C3.7.3.1)a AASHTO LRED Brine! Estes SrecinicaTioNs (SD) G coefficient for nose inclination to compute Fs (3.9.2.2) Coy = clastic seismic response coefficient forthe m' mode of vibration (3.10.1) ©” = soil cohesion (MPa) @.11.5.4) % distance from back ofa wall face tothe front of an applied load oF footing (mm) 3.11.63) D depth of embedment fora permanent nongravity cantilever wal with discrete vertical wal elements (mm) G15) Dy bow depth (mm) (C3.14.5.1) Ds ‘minimum depth of earth cover (mm) 3.62.2) D, calculated embedment depth to provide equilibrium for nongravity cantilevered with continous vertical clements by the simplified method (mm) (3.11.5.6) DIT = size of vessel based on deadweight tonnage (Mg) (C3.14.1) D, effective width of applied load at any depth (mmm) (3.11.6.3) d= depthof potential base failure surface below base of excavation mi); horizontal distance from the back ofa ‘wall face to the centerline of an applied load (mam) (3.11.5.7.2b) (3.11.63) E ‘Youns’s modulus (MPa) (C3.9.5) By deformation energy (J) (C3.14.11) e eccentricity of load on footing (mm) (.11.6.3) F longitudinal force on pier due to ice floc (N); force required to fal an ice sheet (Nim); force at base of nongravity cantilevered wall required to provide force equilibrium (N/mm) (3.9.2.2) (C3.9.5) 3.11.5.6) fy horizontal force due to failure of ice flow duc to bending (N) 3.9.2.2) F. = horizontal force duc o crushing of ice (N) (3.9.2.2) FSny = factor of safety against basal heave (C3.11.5.6) F,-= transverse force on pier due to ice flow (N) G.9.2.4.1) FE, —-=_vertical ie force due to adhesion (N) 3.9.5) By lateral force duc o earth pressure (N/mm) @3.11.6.3) I lateral force due to traffic surcharge (N/mm) 3.11.6.3) £ constant applied in tho coefficient used to compute centrifugal forces. taken equal to 4/3 for Jad combinations other than fatigue and 1.0 for fatigue G.6.3) f specified compressive strngth of concrete for usc in design (MPa) (3.5.1) = gravitational acceleration (m/sec) 3.63) u ultimate bridge clement strength (N); final height of retaining wall (mm); total excavation depth (mmm resistance of bridge component to a horizontal force (N) (C3.11.1) G.11.5.7.1) G.14.5.4) HM, = depth of barge head-block on its bow (mm) (3.14.14.1) H, = ulate bridge pier resistance (N) (3.14.54) H ultimate bridge superstructure resistance (N) G.14.5.4) i, distance from ground surface to uppermost ground anchor (mm) (3.11.5.7.1) Hoot distance from base of excavation to lowermost ground anchor (mum) (3.11 5.7.1) ‘y= notional height of earth pressure diagram (mmm) G.11.57) hig equivalent height of soil for vehicular load (mum) (3.11.6:4) ar dynamic load allowance (C3.6.12.5) KE design impact enerey of vessel collision 0) 3.14.7) ky {ce force reduction factor for small streams (C3.9.2.3) k coefficient of lateral earth pressure (3.11.6.2) k coefficient of active lateral earth pressure 3.11.5.1) ke coefficient of at rest lateral earth pressure (3.11.5.1) 4K, = coefficient of passive lateral carth pressure (3.11.3.1) k coefficient of earth pressure due to surcharge (3.11.6.1) 1 = perimeter of pier (mm); length of sol reinforcing elements in an MSE wall (mm); length of footing (mum) espansion length (mm) 3.9.5) G.11..8) G.11.63) G.12.2.3) ‘ characteristic length (mm); centerto-center spacing of vertical wall elements (mm) (C3.9.5) 3.11.56) LOA Jength overll of ship or barge tow including th tug or tow boat (mm) G.14.8 MM = mass of vessel (Mg) 3.14.7) m multiple presence factor G.6.1.1.2) v number of one-way passages of vessels navigating through the bridge (number/1.) (3.14.5) X, = stability number B.11.5.6) OCR = overconsolidation ratio (3.115.2)SECTION3 (SI): LOADS AND LoaD FACTORS 35 Pos ho = Tn Trax Thuserio Truoega= maximum vertical force for single ice wedge (N); load resulting from vessel impact (N); concentrated wheel load (\); live load intensity: point load (N) (C3.9.5) (3.14.5.4) (C36.1.2.5) (C3.11.6.2) B.11.6.1) probability of vessel aberrancy (3.14.5) force resultant per unit width of wall (Nimm) (3.11.5.8.1) barge collision impact force for head-on collision between barge bow and a rigid object (N); base wind pressure corresponding to a wind speed of 160 kn. (MPa) (3.14.11) (3.8.1.2) average equivalent static barge impact force resulting from Meit-Domberg Study (N) (C3.14.11) ship collision impact force between ship bow and a rigid superstructure (N} (3.14.10.1) probability of bridge collapse (3.14.5) design wind pressure (MPa) (3.8.1.2.1) ship collision impact force between ship deck house and a rigid superstructure (N) (3.14.5.4) geometric probability of vessel collision with bridge pier/span (3.14.5) Tateral force due to superstructure or other concentrated lateral loads (N/mm) (3.11.6.3) horizontal component of resultant earth pressure on wall (N/mm) (3.11.5.5) ship collision impact force between ship mast and a rigid superstructure (N) (3.14.5.4) passive earth pressure (N/mm) (3.1.5.4) ship collision impact force for head-on collision between ship bow anc a rigid object (N) (3.14.5.4) vertical component of resultant earth pressure on wall (N/mm); load per linear mm of strip footing (N/mm) (3.11.5.5) (3.11.6.3) Toad on isolated rectangular footing or point load (N) (3.11.6.3) effective ice crushing strength (MPa); stream pressure (MPa); basic earth pressure (MPa); fraction of truck traffic in a single lane; load intensity (MPa) (3.9.2.2) (3.7.3.1) (G.11.5.1) (3.6.1.4.2) @.11.6.1) apparent earth pressure (MPa); maximum ordinate of pressure diagram (MPa) (3.11.5.3) (.11.5.7.1) passive earth pressure (MPa) (3.11.5.4) total factored load: load intensity for infinitely long line loading (N/mm) (3.4.1) (8.11.6.2) force effects (3.4.1) surcharge pressure (MPa) (3.11.6.3) uniform surcharge pressure (MPa) (3.11.6.1) radius of curvature (mn); radius of circular pier (mm): seismic response modification factor; reduction factor of lateral passive earth pressure: radial distance from point of load application to point on the wall (mm): reaction force to be resisted by subgrade below base of excavation (N/mm) (3.6:3) (3.9.5) (3.10.7.1) G115.4) B116.1) 8.1157.) PA correction factor for bridge location (3.14.5.2.3) ratio of exposed superstructure depth tothe total ship bow depth (3.14.10.1) PA correction factor for currents parallel to vessel transit path (3.14.5.2.3) PA correction factor for vessel traffic density (3.14.5.2.3) reduction factor for ship deck house collision force (3.14.10.2) PA correction factor for cross-currents acting perpendicular to vessel transit path (3.14.5.2.3) radius of pier nose (mm) (C3.9.2.3) coefficient related to site conditions for use in determining seismic loads (3.10.5.1) freezing index (C3.9.2.2) shear strength of rock mass (MPa) (3.11.5.6) undrained shear strength of cohesive soil (MPa) (3.11.5.6) undrained strength of soil below excavation base (MPa) (3.11.5.7.2b) vertical spacing of reinforcements (mit) (3.11.5.8.1) mean daily air temperature (°C) (C39.2.2) horizontal load in anchor j (N/mm) (3.11.5.7.1) period of vibration for m* mode (sec,) (3.10.6.1) applied load to reinforcement in a mechanically stabilized earth wall (Nimm) (3.11.5.8.2) maximum design temperature used for thermal mavement effects (°C) minimum design temperature use for thermal movement effects (*C)(3.12.2.1) (3.12.2.2) (3.12.2.3 thickness of ice (mm): thickness of deck (mm) (3.9.2.2) (3.12.3) design velocity of water (misec:); design impact speed of vessel (misec,) (37.3.1) (3.14.6) base wind velocity taken as 160 knw’. (3.8.1.1) ‘waterway current component acting parallel to the vessel transit path (knw) (3.14.5.2.3) design wind velocity at design Elevation Z (knw/hr) (3.8.1.1)36 AASHTO LRED Brine! Estes SrecinicaTioNs (SD) Va ‘minimum design impact velocity taken not les than the yearly mean current velocity for the bridge location (ahr) (3.14.6) Vy, = vessel transit speed in the navigable channel (kin/r.) (3.14.6) Feo ‘waterway current component acting perpendicular to the vessel transit path (knvbr.) (3.14.5.2.3) rs friction velocity, a meteorological wind characteristic for various upwind surface characteristics (knw/hr,) G81) Vp ‘wind speed at 10 000 mm above low ground or water level (km/h) (3.8.1.1) v highway design speed (1wsec-) (3.6.3) w ‘width of clear roadway (mm), width of pier at level of ice action (mm); density of water (kg/m) (3.6.1.1.1) 6.9.2.2) (C3.73.1) x orizontal distance from back of wall to point of load application (mm); distance to bridge element from the centerline of vessel transit path (mm) (3.11.6.2) 3.14.6) X. = distance to edge of channel from centerline of vessel transit path (mm) @.14.6) Xi distance from centerline of vessel transit path equal t0 3 x LO (mmm) G.14.6) X= distance from the back ofthe wall to the start ofthe line load (mim) (3.11.6.2) > length of the line load (mim) (3.11.6.2) Zz structure height above low ground or water level > 10 000 mm (mm); depth below surface of soil (mm) depth from the ground surface toa point on the wall under consideration (mn): vertical distance from point of load application to the elevation of a point on the wall under consideration (mm) (3.8.1.1) (3.11.6.3) 6.1162) Zy = fection length of upstream fetch, a meteorological wind characteristic (mm) (3.8.1.1) Zz depth where effective width intersects back of wall face (mm) (3.1.6.3) = = depth below surface of backfill (nim) G.11.5.1) @ = constant for terrain conditions in elation to wind approach: coefficient for local ice condition: inclination of pier nose with respect to a vertical axis (°); inclination of back of wall with respect to a vertical axis (°) angle between foundation wall and a line connecting the point on the wall under consideration anda point on the bottom comer of the footing nearest to the wall (rad); coefficient of thermal expansion (mm/mnv"C) (C3811) (3.9.2.2) G.9.2.2) (C3.11.53) B.116.2) 3.12.23) B notional slope of backfill (°) 3.11.58.1) B safety index: nose angle in a horizontal plane used to calculate transverse ice forces (°); slope of backfill surface behind retaining wall; {+ for slope up from wall, ~forslope down from wall} (°)(C3.4.1)(3.9.24.1) G.115.3) 8’ = slope of ground surface in front of wall {+for slope up from wall: —forslope down from wall} °)(3.11.5.6) y= Toad factors: density of materials (kg/m’); density of water (kg/m); density of soil (kgim’) (C34.1) G.3.1) (C393) G.115.1) % density of soil (kg/m?) (3.11.5.1) Ye effective soil density (ke/m’) (3.1.5.6) wo load factor for live load applied simultaneously with seismic loads (3.4.1) Yo) = equivalent-fluid unit weight of soil (kg/m) (3.11 5.5) y= Toad factor 3.4.1) % load factor for permanent loading (3.4.1) Yor load factor for settlement (3.4.1) no Toad factor for temperature gradient (3.4.1) A= movement of top of wall required to reach minimum active ormasinum passive pressure by tilting orfateral translation (mm) (C3.11.1) G.115.5) ’, constant horizontal earth pressure due to uniform surcharge (MPa) (3.1.6.1) dn constant horizontal pressure distribution on wall resulting from various types of surcharge loading (MPa) 6.1162) ‘A; = design thermal movement range (num) 3.12.2.3) Aon horizontal tress due to surcharge load (MPa) (3.11.6.3) 6, vertical stress due to surcharge load (MPa) (3.11.63) 3 = angle of truncated ice wedge (°) friction angle between fill nd wall (°), angle between foundation wall and ine connecting the point on the wall under consideration and a point on the bottom comer of the footing furthest from the wall (rad.) (C3.9.5) (3.11.5.3) 3.1.6.2) ny = load modifier specified in Article 1.3.2; wall face batter (3.4.1) (3.1.5.9) 0 angle of back of wall to the horizontal (°); angle of channel turn or bend (°); angle between direction of stream flow and the longitudinal axis of pier (?) 3.11.53) G.14.52.3) 3.7.3.2)SECTIONS (SI): LOADS AND LOAD FACTORS, 31 0, = friction angle between ice floe and pier (°} (3.9.2:4.1) ° standard deviation of normal distribution (3.14.5.3) or tensile sirength of ice (MPa) (C3.9.5) y Poisson's Ratio (dim) (3.11.6.2) 6 resistance factors (C3.4.1) o angle of internal friction (°) (8.11.5:4) Or = effective angle of internal friction (°) (3.11.5.2) 6 internal friction angle of reinforced fill (2) (3.11.6:3) 41, = angle of internal friction of retained soil (*) (8.11.5.6) 3.32 Load and Load Designation The following permanent and transient loads and forces shall be considered: ‘© Permanent Loads DD = downdrag DC = dead load of structural components and nonstructural attachments DWW’= dead load of wearing surfaces and utilities EH = horizontal earth pressure load EL = accumulated locked-in force effects resulting from the consiruction process, including the secondary forces from post-tensioning ES = earth surcharge load vertical pressure from dead load of earth fill g © Transient Loads vehicular braking force ‘vehicular centrifugal force creep vehicular collision force vessel collision force earthquake FR = friction IC = iceload IM = vehicular dynamic load allowance LL = vehicular live load LS = live load surcharge PL = pedestrian live load SE = settlement SH = shrinkage TG = temperature gradient TU = uniform temperature WA = water load and stream pressure WL = wind on live load WS = wind load on structure 3.4 LOAD FACTORS AND COMBINATIONS 3.4.1 Load Factors and Load Combinations C344 The total factored force effect shall be taken as The background for the load factors specified herein, and the resistance factors specified in other sections of Q= E0710 (3.4.1-1) these Specifications is developed in Nowak (1992)wher: vy = load modifier specified in Adicle 1.3.2 Q, = force effects from loads specified herein ‘ty = load factors specified in Tables 1 and 2 Components and connections of a bridge shall satisfy Eq, 1.3.2.1-1 for the applicable combinations of factored ‘extreme force effects as specified at each ofthe following limit sates ‘¢ STRENGTH I—Basic load combination relating to the normal vehicular use ofthe bridge without wind. © STRENGTH 1—Load combination relating to the use ofthe bridge by Owner-specified special dlesign vehicles, evaluation permit vehicles, or both without wind © STRENGTH IIl—Load combination relating to the bridge exposed to wind velocity exceeding 90 koh. © STRENGTH IV—Load combination relating to very high dead load to live load force effect ratios, AASHTO LRED Brince Destcw Sprcirrcations (SD, A reduced value of 0.50, applicable to al strength load combinations, specified for TU, CR, and SH, used ‘when calculating force effets other than displacements at the strength limit slate, represents an expected reduction ofthese force effects in conjunction with the inelastic response of the structure. The calculation of displacements for these loads utilizes a factor greater than 1.0 to avoid undersized joints and bearings. The cffect and significance of the temperature gradient remains unclear at this writing, Consult Article (€3.123 for further information. The permit vehicle should not be assumed to be the nly vehicle on the bridge unless so assured by traffic control See Article 4.6.2.2 regarding other trafficon the bridge simultaneously Vehicles become unstable at higher wind velocities Therefore, high winds. prevent the presence of significant live load on the bridge. ‘The standard calibration process for the strength limit sate consists of trying out various combinations of load and resistance factors on a numberof bridges and their components. Combinations that yield a safety index close tothe target value of f= 3.5 are retained for potential application, From these are selected constant load factors y and corresponding resistance factors for each type of structural component reflecting its use. (© 2005 by the American Association of State Highway and Transportation Oficial ‘All ight reserved, Duplication @ Violation of applicable lave.SECTION3 (SI): LOADS AND LoaD FACTORS + STRENGTH V—Load combination relating to normal vehicular use of the bridge with wind of 90 kmh. velocity © EXTREME EVENT I—Load combination including earthquake. © EXTREME EVENT T—Load combination relating to ice load, collision by vessels and vehicles, and certain hydraulic events with a reduced live load other than that which is part of the vehicular collision load, C7. (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav. 39 This calibration process had been carried out for a large number of bridges with spans not exceeding 60 000 mm, ‘These calculations were for_completed bridges. For the primary components of large bridges. the ratio of dead and live load force effects is rather high, and could result in a set of resistance factors different from those found acceptable for small- and rmedium-span bridges. It is believed 0 be more practical to investigate one additional load case than to require the use of two sets of resistance factors with the load factors provided in Strength Load Combination I, depending on other permanent loads present. Spot checks had been madle on a few bridges with up fo 183.000 mm spans, and it appears that Strength Load Combination IV will govern where the dead! load to live load force effect ratio exceeds about 7.0. This load combination _can_control_during investigation of construction stages. Although this iit state includes water loads, WA, the effects due to Ware considerably less significant than the effects on the structure stability due to degradation Therefore, unless specific site conditions dictate otherwise, local pier scour and contraction scour depths should not be included inthe design. However, the effects due to degradation ofthe channel should be considered. Live load coincident with an earthquake is discussed elsewhere inthis article. The recurrence interval of extreme events is thought 10 exceed the design life. The joint probability ofthese events is extremely low, and, therefore, the events are specified to be applied separately. Under these extreme conditions, the structure is expected to undergo considerable inelastic deformation by which locked-in force effects due to TU, TG, CR, SH, and SE are expected to be relieved The 0.50 live load factor signifies a low probability of the concurrence of the maximum vehicular live load (other than C7) and the extreme events.310 AASHTO LRED Brince Destcw Sprcirrcations (SD, ‘+ SERVICE I—Load combination relating to the normal operational use of the bridge with a 90 Jawhr. wind and all Ioads taken at their nominal values. Also related to. deflection control in buried metal structures, tunnel liner plate, ane thermoplastic pipe, to control crack width in reinforced concrete structures, and for transverse al analysis relating to tension in concrete segmental gitders. This load combination should also be used forthe investigation of slope stability. ‘© SERVICE II—Load combination intended to control yielding of steel structures and slip of slip-crtical connections due to vehicular live load + SERVICE Load combination for longitudinal_analysis relating to tension in presiressed_ concrete. supersiructures with the abjective of crack control and o peincipal tension inthe webs of segmental concrete girders. + SERVICE IV—Load combination relating only to tension in prestressed concrete substructures with the objective of crack control ‘+ FATIGUE—Fatigue and — fracture load combination relating to repetitive gravitational vehicular live load and dynamic responses under a single design truck having the axle spacing specified in Article 3.6.1.4.1 Interim Bed Compression in prestressed concrete components is investigated using this load combination, Service I is used 10 investigate tensile stresses in prestressed ‘concrete components. ‘This Load combination corresponds to the overload provision for steel structures in past editions of the AASIITO Specifications, and itis applicable only to steel structures. From the point of view of load level, this combination is approximately halfway between that used for Service I and Strength I Limit States. ‘The live load specified in these Specifications reflects, among other things, current exclusion weight limits ‘mandated by various jurisdictions. Vehicles permitted under these limits have been in service for many years prior to 1993, For longitudinal loading, there is no nationwide physical evidence that these vehicles have caused detrimental cracking in existing prestressed Conerete components, The statistical significance of the 0.80 factor on live lad i that the event is expected to ‘occur about once a year for bridges with two traffic Janes, less often for bridges with more than tw traffic lanes, and about once a day for bridges with a single traffic lane. Service T should be used for_checking tension related_to_transverse_analysis_ of concrete segmental ginders, “The principal tensile stress checkis introduced in ore to verify the adequacy of webs of segmental concrete sinder bridges for longiuudinal shear and torsion, ‘The 0.70 factor on wind represents a 135 kn. wind. ‘This should result in. zero tension in prestressed conerete substructures for ten-year mean reoccurrence ‘winds, The prestressed concrete substructures must slill meet strength requirements as set forth in Load Combination Sirengti HT in Article 3.4.1 It fs not recommended that thermal gradient be combined with high wind forces. Superstructure ‘expansion forces are included. The load factor, applied to a single design truck, reflects a load level found to be representative of the truck population with respect to a large number of retum cycles of stresses and to their cumulative effects insteel elements, components, and connections (© 2005 by the American Association of State Highway and Transportation Oficial ‘All nights reserved, Duplication i a Wolation of appicable law.SECTION3 (SI): LOADS AND LoaD FACTORS The load factors for various loads comprising a design load combination shall be taken as specified in Table 1. All relevant subsets of the load combinations. shall be investigated. For each load combination, every load that is indicated to be taken into account and that is germane to the component being designed, including all significant cffects due 10 distortion, shall be multiplied by the appropriate load factor and multiple presence factor specified in Article 36.1.1.2, if applicable, The products shall be summed as specified in Eq. 1.3.2.1-1 and mnultiplied by the load modifiers specified in Article 1.3.2 The factors shall be selected to produce the total ‘extreme factored force effect. For each load combination, both positive and negative extremes shall be investigated. Inload combinations where one force effect decreases another effect, the minimum value shall be applied tothe Toad reducing the force effect. For permanent force effects, the load factor that produces the more critical combination shall be selected from Table 2. Where the permanent load increases the stability or load-canying capacity of a component or bridge, the minimum value ofthe load factor for that permanent Icad shall also be investigated The larger of the two values provided for load factors of TU, CR. and SH shall be used for deformations and the smaller values forall other effects The evaluation of overall stability of retained fills, as, ‘well as earth slopes with or without a shallow or deep founslation unit should be investigated at the service limit state based on the Service I Load Combination and an appropriate resistance Factor as specified in Article 10.5.2 and Article 11.5.6. For structural plate box structures complying with the provisions of Article 12.9, the live load factor for the Vehicular live loads LL and IM shal be taken as 2.0. (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav. 3.10. This Article reinforces the traditional method of selecting load combinations to obtain realistic extreme ‘effects and is intended to clarify the issue ofthe variability of permanent loads and their effects. As has always been the case, the Owner or Designer may determine that not all of the loads in given load combination apply to the situation under investigation Iris recognized herein that the actual magnitude of permanent loads may also be less than the nominal value ‘This becomes important where the permanent load reduces the effects of transient loads. Tt has been observed that permanent loads are more likely to be greater than the nominal value than to be less than this value. Inthe application of permanent loads, force effects for ‘each of the specified six load types should be computed separately. Itis unnecessary to assume that one type of load varies by span, length, or component within a bridge. For example, when investigating uplift at a bearing in a continuous beam, it would not be appropriate to use the ‘maximum load factor for permanent Toads in spans that produce a negative reaction and the minimum load factor spans that produce a positive reaction. Consider the investigation of uplift. Uplift, which was treated as a separate load case in past editions of the AASHTO Standard Specifications, now becomes a strength load combination. Where a permanent load produces uplift that load would be multiplied by the maximum load factor, regardless of the span in which it is located. If another permanent load reduces the uplift, it would be multiplied by the minimum load factor, regardless of the span in \hich iti located. For example, at Strength I Limit State ‘where the permanent load reaction is positive and live load can cause a negative reaction, the load combination would be O.9DC + 0.65DW'+ 1.75(LL + IM) If both reactions were negative, he load combination would be 1.25DC + 15ODW + L.15(LL + IM). For each force effect, both extreme combinations may need to be investigated by applying cither the high or the low load factor as appropriate, The algebraic sums of these products are the {otal force effects for which the bridge and its components should be designed Applying these criteria forthe evaluation ofthe sliding,3.102 AASHTO LRED Braver Desion Sercinieaions (ST) This page is intentionally left blank. Allright reserves, Duplication is @volation of applicable lav,‘SrcTION3 (SI): Loaps AND Loap Factors Sal The load factor for temperature gradient, yrq. and settlement, ys, should be considered on a project-specific basis. In lieu of project-specific information to the contrary, Yq may be taken as: © 0.0 at the strength and extreme event limit states, © 1Oat the service limit state when live load is not considered, and © 0.50 at the service limit state when live load is considered. For scementally constructed bridges, the following ‘combination shall be investigated atthe service limit state: DC+DW+EH + EV +ES +WA4OR4SH +TG+ EL 4.12) resistance of walls ‘+ The vertical carth load on the rear of a cantilevered retaining wall would be multiplied Dy pun (1.00) and the weight of the structare would be multiplied by Ypmi(0:90) because these forces result in an inerease in the contact stress (and shear strength) at the base of the wall and foundation. ‘+ The horizontal earth load on a cantilevered retaining wall would be multiplied by pa (1-50) for an active earth pressure distribution because the force results in a more critical siding force at the base of the wal Simitasy, the values of Ypma for structure weight (1.25), vertical earth load (1.38) and horizontal active earth pressure (1.50) would represent the critical Toad combination for an evaluation of foundation bearing resistance. ‘Water load and friction are included in all strength load combinations at ther respective nominal values, For creep and shrinkage, the specified nominal values should be used. For friction, setlement, and water loads, ‘both minimum and maximum values need to be nvestigated 0 produce extreme load combinations. ‘he load factor for temperature gradient should be determined on the basis ofthe: © Type of structure, and ‘© Limit state being investigated. Open girder construction and multiple steel box girders have traditionally, but pethaps not necessarily correctly, been designed without consideration of temperature gradient, ie. Yo = 00. (© 2004 by the American Assocation of Sate Highway and Transporation Ofc. "A ats reseved. Dupleation sa vilaton of eppcabe a.saz AASHTO LRED Beupck Desicn SreciticaTions (SI) ‘Table 3.4.1-1Load Combinations and Load Factors. ond Combination | DC Tse One of These ata Time DD | LL pw | mM EH | CE rv | BR w ES | PL CR Limit State EL | Ls WA Ws | WL | FR SH TG | SE| £0 | Ic cr | cv STRENGTAT | y | h| 90 | — [— | 100 | OsOT THe [we | — | —|—]|— (unless noted) ‘STRENGTH IL y | 135 | 100 | — — | 100 | 0.50/1.20 | yc | yse | — _ = _ ‘STRENGTH IL » |= 1.00 | 1.40 [ — | 1.00 | 0.50/1.20 | yr | yse | — _ = _ STRENGTH IV EHEV.ESDW | | — | 100 | — | — | 100] oson2o} —}—| —) — |] —] = DCONLY 15 ‘STRENGTH vw | 135 | 100 [040 | 10 [100 | 0500.20 | rm [we | — | — | —)— EXTREME | to | to | — [— 10); — |—|—|im@>—|—][— EVENT EXTREME % | 050 | L007 | — | — | 100 = =f =P — 7 100 | 1.00 | 1.00 EVENT IL ‘SERVICE T 1.00 | 1.00 | 1.00 | 0.30 | 1.0 | 1.00 | 1.00/1.20 | yre | yse | — = = = SERVICE TT 100 [1.30 [100 — | — | r00 | to0n20 | —f—p—)—]|—f— SERVICE | 100] 080] 100 | — | — 100] 1.00120 ye fa | — = |= P= SERVICE [Tao] — [Tao [Or] — | 100} TOR | — Prep — 7 — ff FATIGUE [| — om] —|—}f— }—] — |-l-l=1-l-1lo IM& CEONLY ‘Table 34.1-2 Load Factors for Permanent Loads, Toad Factor ‘Type of Load Maximum — | Minimum ‘DC: Component and Atachments 125 0.90 DD: Downdrag 180 0.45 ‘DIF. Wearing Surfaces and Uiilities 130 0.65 FFE Hloriontal Earth Pressure + Active 150 0.90 * AtRest 1.35 0.90 TEE: Locked-in Erection Sireses 1.00. 1.0 EV: Vertical Earth Pressure + Overall Stability 1.00 NIA © Retaining Walls and Abutments 1.35 1.00 + Rigid Buried Structure 130 9.90 + Rigid Frames 1.35 0.90 Flexible Buried Structures other 1.95 920 than Metal Box Culverts, ¢ Flexible Metal Box Culverts 150 9.90 ES Barth Surcharge 130 075 {© 2005 by the American Assocation of State Highway and Transportation Officials. Al nights reservee. Duplication is @ violation of applicable law.SECTION3 (SI): LOADS AND LoaD FACTORS 33 Where prestressed components _are used _in conjunction with steel girders, the force effects from the following. sources shall_be considered as construction loads, EL: ‘© Inconjunetion with longitudinal prestessing of a ‘precast deck prior ta making the deck sections ‘composite with the girders, the friction between the precast deck sections and the steel girders, ‘© When longitudinal post-tensioning is performed afler_the deck becomes composite with the ‘girders, the additional forces incluced in the steel ‘girders and shoar connectors, ‘© Thecffects of differential creep and shrinkage of, ithe concrete, ‘+ The Poisson effect ‘The load factor for live load in Extreme Event Load Combination 1, yao. shall be determined on a project specific bass, 3.4.2 Load Factors for Construction Loads 3.4.2.1 Evaluation at the Strength Limit State ‘All_appropriate_strengih toad _ combinations in ‘Table 34-1, modified _as_specified_herein, shall_be investigated ‘When investigating Strength Load Combinations II and V during construction, Joad factors for the weight of the structure and appurtenances, DC and DW, stall not be taken tobe less than 1.25. Unless otherwise specified by the Owner, the load factor for construction loads and for any_associated dynamic effects shall not be less than 1.5 in Strength Load bination L. The load factor for wind in Strength Load Combination IT shall not be less than 1.25, {© 2005 by the American Assocation of State Highway and Transportation Officials. Al nights reservee. Duplication is @ violation of applicable law. ‘The_most_common_applications_of prestressed concretein_steel_girder bridges are_transverse_post- tensioning of the deck and integral pier caps in_which the {endons penetrate the girder webs. When a composite deck is prestressed longitudinally, the shear connectors transfer force to the steel. The effect of shrinkage and long-term creep around the shear connectors should be evaluated 10 censure thal the composite girder is able to recognize the prestressing over the life ofthe bridge. The contribution of Jong-term deformations in closure pours between precast creep may need evaluation, “The Poisson effect recognizes the bulging of concrete when subjected to prestressing. When used in pier caps, resulting in a longitudinal siess in the steel girders, Past editions ofthe Standard Specifications used 720: 0.0. This issue is not resolved. The possiblity of partial live load, i.e.. veo < 1.0, with earthquakes should be considered. Application of Turkstra’s rule for combining uncorrelated loads indicates that yzq = 0.50 is reasonable for a wide range of values of average daily truck traffic (ADT? ‘load factor for passive lateral earth pressure is not given in Table 2 because, strictly speaking, passive lateral carth pressure isa resistance and nota load. For discussion of the selection of a passive lateral earth pressure resistance factor see Article C10.54 C3421 ‘The load factors presented here should not relieve the contractor of responsibility for safety and damage control during construction. Construction toads are permanent loads and other loads that act on the structure-only during construction, Construction Joads include the mass of equipment such as deck finishing machines of loads applied to the structure through falsework or other temporary supports. Often the construction loads are_not accurately known at design ‘ime: however, the magnitude and location of these loads ‘considered in the design should be noted on the contract documents. Interim EaEvaluation of Deflection at the Service State In.the absence of special provisions to the contrary, \where evaluation of construction deflections are required by the contract documents, Load Combination Service I shall apply, Construction dead loads shall be considered as part of the permanent load and construction transient loads considered part of the live load. The associated ppermilted deflections shall be included in the contract documents 3.43 Load Factors for Jacking and Post-Tensioning Forces 34.3.1 Jacking Forces Unless otherwise specified by the Owner, the design forces fr jacking in service shall not be less than 1.3 times the permanent Ioad reaction at the bearing, adjacent to the point of jacking ‘Where the bridge will not be closed to traffic during, the jacking operation, the jacking load shall also contain a live load reaction consistent with the maintenance of traffic plan, multiplied by the load factor for live load. 3.4.3.2 Foree for Post-Tensioning Anchorage Zones ‘The design force for post-tensioning anchorage zones shall be taken as 1.2 times the maximum jacking force 3.5 PERMANENT LOADS 3.5.1 Dead Loads: DC, DW, and EV Dead load shall include the weight of all components of the structure, appurtenances and utilities attached thereto, earth cover, wearing surface, future overlays, and planned widenings. Tn the absence of more precise information, the densities, specified in Table 1, may be used for dead loads, AASHTO LRED Brince Desicy SPeciricaTions (SI) C35. Table 1 provides traditional densities. The density of ‘granular materials depends upon the degree of compaction and water content. The density of concrete is primarily affected by the density of the aggregate, which varies by ‘geological location and increases with conerete compressive strength. The density of reinforced concrete is ‘generally taken as 72 kg/m greater than the density of Plain concrete. The values provided for wood include the mass of mandatory preservatives. The mass of transit rail, t., isto be used only for preliminary design. Densities shown with the units kg/m’ and kg/mm are in mass units, not force units. To convert to force units of ‘Nim multiply by the gravitation at constant g = 9.8066 misec.” and collect the units kg mvsee.? as a Newton (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav.SECTION3 (SI): LOADS AND LoaD FACTORS ‘Table 3.5.1-1 Densities. Sad ‘Aluminum Alloys Bituminous Wearing Surfaces 2250. Cast iron 7200 Cinder Filling 360 ‘Compacted Sand, Sik, or Clay 1925 Concrete Low-lensi W775 Sand-low-dlensi 1925 ‘Normal Density with 7, =35 MPa 2320 Normal Density with 35 < f= 105 MPa | 2040 + 2.29 Loose Sand, Silt, or Gravel 1600 Soft Clay 1600 Rolled Gravel, Macadam, or Ballast 2250 Steel 7850. ‘Stone Masonry 2125 Wood Hard 960 Soft 800 Water Fresh 1000 ‘Salt 1025 ‘Mass per Unit Item Length (kg/mm) “Transit Rails, Ties, and Fastening per Track. 030, 3.5.2 Earth Loads: EH, ES, and DD Earth pressure, earth surcharge, and downdrag loads, shall be as specified in Article 3.11. 3.6 LIVE LOADS 3.6.1 Gravity Loads: LL and PL 3.6.1.1 Vehicular Live Load 36.1.1.1 Number of Design Lanes C26.111 Generally, the number of design lanes should be determined by taking the integer part of the ratio w/3600, here wis the clear roadway width in mm between curbs ‘anxor barriers, Possible future changes in the physical or tional clear roadway width of the bridge should be considered. Tn cases where the traffic lanes ae less than 3600 mm. wide, the number of design lanes shall be equal to the number of traffic lanes, and the width of the design lane {© 2005 by the American Assocation of State Highway and Transportation Officials. Al nights reservee. Duplication is @ violation of applicable law. isnot the intention of this Article to promote bridges with narrow traffic lanes. Wherever possible, bridges should be built to accommodate the standard design lane Interim Ea3442 AASHTO LRED Bravo Desicx Srectrrcarions ($2) ‘This page intentionally left blank, ‘ll ghts reserved. Ouplication i @violabon of appicatte lay‘SrcTION3 (SI): Loaps AND Loap Factors a5 shall be taken as the width of the traffic lane. Roadway widths from 6000 to 7200 mm shall have two design lanes, each equal to one-half the roadway width, 36.1.1.2 Multiple Presence of Live Load ‘The provisions of this article shall not be applied to the fatigue limit state for which one design truck is used, regardless of the number of design lanes. Where the single- lane approximate distribution factors in Articles 4.6.2.2 ‘and 4.6.2.3 are used, other than the lever rule and staical ‘method, the force effects shall be divided by 1.20. Unless specified otherwise herein, the extreme live load force effect shall be determined by considering each possible combination of number of loaded lanes multiplied by a corresponding multiple presence factor to account for the probability of simultaneous lane occupation by the full HLS3 design live load. In Tiew of site specific data, the values in Table 1: ‘© Shall be used when investigating the effectof one Ine loaded, © May be used when investigating the effect of three or more lanes loaded or the purpose of determining the umber of lanes when the loading condition includes the pedestrian loads specified in Article 3.6.1.6 combined with one or more Ines of the vehicular live load, the pedestrian loads may bee taken to be one loaded lane ‘The factors specified in Table | shall not be applied in conjunction with approximate load distribution factors specified in Articles 4.6.2.2 and 4.6.2.3, except where the lever rule is used or where special requirements for ‘exterior beams in beam-slab bridges, specified in Article 4.6.2.2.2d, are used. ‘Table 3..1.1.2-1 Multiple Presence Factors m. Numiberof | _ Multiple Loaded | Presence Lanes | Factors m 1 1.20. 2 1.00) 3 0.85, 33 0.65, and appropriate shoulders. C3.6.1.1.2 ‘The multiple presence factors have been included in the approximate equations for distibution factors in Articles 4.6.2.2 and 4.6.2.3, both for single and multiple Janes Toaded, The equations are based on evaluation of several combinations of loaded lanes with heir appropriate multiple presence factors and are intended to account for the worst case scenario, Where use of the lever rile is specified in Article 4.6.2.2 and 4.6.2.3 the Engineer must determine the number and location of vehicles an lanes, and, therefore, mus include the multiple presence. Stated smother way, if a sketch is required to determine load distribution, the Engineer is responsible for including multiple presence factors and selecting the worst design cease. ‘The factor 1.20 from ‘Table 1 has already been included in the approximate equations and should be removed forthe purpose of fatigue investigations. ‘The entry greater than 1.0 in Table 1 results from statistical calibration ofthese Specifications on the basis of pairs of vehicles instead of « single vehicle. Therefore, ‘when a single vehicle is on the bridge, it can be heavier than each one of a pair of vehicles and stil have the same probability of occurrence ‘The consideration of pedestrian loads counting as a “loaded lane" for the purpose of determining a multiple presence factor (m) is based on the assumption that simultaneous occupancy by a dense loading of people combined with a 75-year design live Toad is remote. For the purpose of this provision, its been assumed that ia bridge is used as a viewing stand for eight hours each year for a total time of about one month, the appropriate five load to combine with it would have 2 one-month recurrence interval. Tis is reasonably approximated by use of the multiple presence factors, even though they are ‘originally developed for vehicular live load, Thus, if component supported a sidewalk and one lane, it would be investigated for the vehicula live load alone with m = 1.20, and for the pedestrian loads combined With the Vehicular live load with m = 1.0. Ifa component supported sidewalk and two lanes of vehicular live load, it would be investigated for: © One lane of vehicular live load, m= 1.20; ‘©The greater of the more significant lanes of vehicular ive load and the pedestrian loads or two lanes of vehicular live load, m= 1.0, applied to the governing case; and ‘+ Two lanes of vehicular ive load and the pedestrian loads, m = 0.85, (© 2004 bythe American Associaton of State Highviay and Transportation Offi ‘Al rights reseved. Duplication isa vlan af appicable iw.316 3.6.1.2 Design Vehicular Live Load 3.6.1.2.1 General Vehicular live loading on the roadways of bridges or incidental structures, designated HL-93, shall consist of ‘combination of the: ‘© Design truck or design tandem, and + Design lane load. Except as modified in Anicle 3.6.1.3.1, each desiga lane under consideration shall be occupied by either the design truck or tandem, coincident with the lane load, AASHTO LRED Brapce Destcy Srectrtcati0Ns ($1) ‘The multiple presence factor of 1.20 for single lane ‘does not apply to the pedestrian loads. Therefore, the case ‘of the pedestrian loads without the vehicular live load is a ‘subset of the second bulleted item, ‘The multiple presence factors in Table 1 were developed on the basis of an ADTT of 5000 trucks in one direction. ‘The force effect resulting from the appropriate number of lanes may be reduced for sites with lower ADTT as follows: + If 100 < ADIT < 1000, 95 percent of the specified force effect may be used: and ‘+ IEADTT< 100, 90 percent ofthe specitied force cffect may be used. ‘This adjustment is based on the reduced probability of attaining the design event during a 75-year desiga life with reduced truck volume. C36.121 Consideration should be given to. site-specific modifications to the design truck, design tandem, and/or the design lane load under the following conditions: © The egal load of a given jurisdiction is significantly greater than typical: ‘©The roadway is expected to carry unusually high percentages oF truck traffic; ‘+ Flow control, such as. stop sign, traffie signal, or toll booth, causes trucks to collect on certain areas of a bridge or to not be interrupted by light tuatfic; or ‘© Special industrial loads are common due to the location of the bridge. See also discussion in Article C3.6.1.3.1 ‘The live load model, consisting of either a truck or tandem coincident with a uniformly distributed load, was developed as @ notional representation of shear and moment produced by a group of vehicles routinely permitted on highways of various states under “grandfather” exclusions to weight laws. The vehicles considered to be representative of these exclusions were based on a study conducted by the ‘Transportation Research Board (Cohen 1990). ‘The load mode! is called “notional” because it is not intended © represent any particular truck, In the initial development of the notional live load model, no attempt was made to relate to escorted permit loads, illegal overloads, or short duration special permits. (© 2004 by the American Associaton of State Highway and Transportation Ofc. ‘All ratis reseved. Dupleation sa vlaton &appicable am‘SrcTION3 (SI): Loaps AND Loap Factors a7 where applicable, The loads shall be assumed to occupy 3000 mm transversely within a design lane. ‘The moment and shear effects were subsequently compared f0 the results of truck weight studies (Csagoly ‘and Knobel 1981; Nowak 1992), selected WIM data, and the 1991 OHBDC live load model, These subsequent ‘comparisons showed that the notional load could be scaled by appropriate load factors to be representative of these ‘other load spectra ‘The following nomenclature applies to Figures CL through C6, which show results of live load studies involving two equal continuous spans or simple spans: MPOSO4L — = positive moment at 4/10 point either span MNEGOSL = negative moment at 4/10 point neither span MSUPPORT = moment at interior support Vab = shear adjacentto etherexterior support Voa shear adjacent to interior support Mss ‘midspan moment in a simply supported span ‘The “span” is the length of the simple-span or of one ‘of each of the two continuous spans. The comparison is in the form of ratios of the load effects produced in either simple-span or two-span continuous girders. A ratio _ereater than 1.0 indicates that one or more ofthe exelusion vehicles produces a larger load effect than the HS20 loading. The figures indicate the degree by which the exclusion loads deviate from the HS loading of designation, ¢-g., HS25 Figures Cl and C2 show moment and shear ‘comparisons between the envelope of effects caused by 22 truck configurations chosen to be representative of the exclusion vehicles and the HS20 loading, either the HS20_ truck or the lane load, or the interstate load consisting of ‘wo 110 000-N axles 1200 mm apart, as used in previous editions of the AASHTO Standard Specifications. The largest and smallest of the 22 configurations can be found in Kulicki and Merz (1991). In the case of negative ‘moment at an interior support, the results presented are ‘based on two identical exclusion vehicles in tandem and separated by at least 15 000 mm. (© 2004 by the American Assocation of Sate Highway and Transporation Ofc. "A ats reseved. Dupleation sa vilaton of eppcabe a.38 AASHTO LRED Brapce Destcy Srectrtcati0Ns ($1) 19 9] a sal f wee 214 ate B 14| gor ast \ 1 344 sd os} ee a oy] of 10 20 « 40 SPAN IN METERS “= M POS OAL -+M NEG.O4L +N SUPPORT. —=Ws Figure C3.61.2.1-1 Moment Ratios: Exclusion Vehicles to 1HS20 (ruck or ine) or Two 110 000-N Axes at 1200 mum, 19 es ua a sabe os 8 © a a ‘SPAN IN METERS -Van-POS kvaD NEG + von +N 1HS20 (truck oF lane) or Two 110 O00-N Ales at 1200 mn, Figures C3 and C4 show comparisons between the force effects produced by single exclusion ruck per ine and the notional load model, except for negative moment, \where the tandem exclusion vehicles were used. Inthe case ‘of negative moment ata suppor, the provisions of Article 3.6.1.3.1 requiring investigation of 90 percent ofthe effect of two design trucks, plus 90 percent of the design lane load, has been included in Figures C3 and CS. Compared with Figures CI and C2, the range of ratios can be seen as more closely grouped: # Over the span range, ‘+ Both for shear and moment, and + Both fr simple-span and continous spans ‘The implication of close grouping is thatthe notional load model with a single-load factor has general applicability. (© 2004 by the American Associaton of State Highway and Transportation Ofc. ‘All ratis reseved. Dupleation sa vlaton &appicable am‘SrcTION3 (SI): Loaps AND Loap Factors a9 “= POG OAL FM NEG.O4L m4 GUPRORT = Abe Figure C3.6.1.2.1.3 Moment Ratios: Exclusion Vehicles to Notional Model. 11g Figure €3.6.1.2.1-4 Shear Ratios: Exelusion Vehicles to Notional Model Figures C5 and C6 show the ratios of force effects produced by the notional load model and the greatest of the HS20 truck or lane loading, or Alternate Military Loading. (© 2004 by the American Assocation of Sate Highway and Transporation Ofc. "A ats reseved. Dupleation sa vilaton of eppcabe a.3.20 3.6.1.2.2 Design Truck ind wheels forthe ‘gure 1. A dynamic ified in Article ‘The weights and spacings of axle design truck shall be as specified in load allowance shall be considered as spe 3.6.2 Except as specified in Articles 3.6.1.3.1 and3.6.1.4.1, the spacing berween the two 145 000-N axles shall be varied berween 4300 and 9000 mm ta produce extreme force effects {© 2004 by the Amercan Association of State Highway AASHTO LRED Brapce Destcy Srectrtcati0Ns ($1) SPAN METERS Figure €3.6.1.2.15 Moment Ratios: Notional Model to S20 (truck or lane) oF Two 110 000-N Axles at 1200 m Figure €3.6.1.21 (Urwek and lane) or Two 110 000-N Axles at 1200 mu In reviewing Figures C5 and C6, it should be noted that the total desi factor, loud modifi allowance. Force effect is also a funetion of load load distribution, and dynamic load Transportation Ofte. ‘All ratis reseved. Dupleation sa vlaton &appicable amSuct10N 3 (SI): Loaps Ax Loa. 35000N 145 000N 145 000N 4300mm ,| 4300 to 9000 mm, 600mm General 300mm Deck Overhang Design Lane 3600 mm '1800mm ‘Truck. 3.6.1.2.3 Design Tandem ‘The design tandem shall consist ofa pair of 110 000- N axles spaced 1200 mm apart, The transverse spacing of Wheels shall be taken as 1800 mm. A dynamic load allowance shall be considered as specified in Article 3.6.2 3.6,1.24 Design Lane Load ‘The design lane load shall consist of « load of 9.3 ‘N/mm uniformly distributed in the longitudinal direction. Transversely, the design lane load shall be assumed to be uniformly distributed over a 3000-mm width. The force effects from the design lane load shall not be subject to a dynamic load allowance, 3.6.1.2.5 Tire Contact Area The tire contact area of a wh consisting of one or ‘wo tires shall be assumed to bea single rectangle, whose width is 510 mm and whose length is 250 mm, ‘The tire pressure shall be assumed t© be uniformly distributed over the contact area, The tire pressure shall be assumed to be distributed as follows: © On continuous surfaces, uniformly over the specified contact area, and © On interrupted surfaces, uniformly over the actual contact arca within the footprint with the pressure inereased in the ratio of the specified to actual contact areas. Bat C3.6.1.2.5 The area load applies only to the design truck and tandem. For other design vehicles, the tire contact area should be determined by the enginecr. As a guideline for other truck loads, the tre area in mm? may be calculated from the following dimensions: Tire wid Png ‘Tire length = 165y(1 + 16/100) where: load factor IM = dynamic load allowance percent (© 2004 bythe American Aesoclaton of State Highy and Transportation Ofc, "A ats reseved. Dupleation sa vilaton of eppcabe a.32 3.6.1.26 Distribution of Whee! Loads Through Earth Fills ‘Where the depth of fil i les than 600 mm, live loads shall he distributed to the top slabs of culverts as specified Article 4.6.2.10, Tn licu of a more precise analysis, or the use of other acceptable approximate methods of load_distribution permitted in Section 12, where the depth of fill is 600 nm ‘greater, wheel loads may be considered to be uniformly distributed over a rectangular area with sides equal fo the dimension of the tire contact area, as specified in Article 3.6.1.2.5, and increased by either 1.15 times the depth of the fll in select granular backfill or the depth of the fll in all other cases. The provisions of Articles 3.6.1.12 andl 3.6.1.3 shall apply, ‘Where such areas from several wheels overlap, the total load shall be uniformly distributed over the area, For single-span culverts, the effects of live load may be neglected where the depth of fill is more than 2400 mm an exceeds the span length; for multiple span culverts, the cffects may be neglected where the depth of fill exceeds the distance between faces of end walls ‘Where the live load and impact moment in concrete slabs, based on the distribution ofthe wheel load through carth fills, exceeds the live load and impact moment calculated according to Article 4.62.10, the latter moment shall be used. 3.6.1.3 Application of Design Vehicular Live Loads 36.1.3.1 General Unless otherwise specified, the extreme force effect shall be taken asthe larger of the following ‘+The effect of the design tandem combined with the effect ofthe design lane load, or ‘©The effect of one design truck with the variable axle spacing specified in Article 36.1.2.2, combined with the effect of the design lane load, and ‘© For both negative moment between points of contraflexure under a uniform load on all spans, and reaction at interior piers only, 90 percent of the effect of two design trucks spaced a minimum AASHTO LRED Brince Desicy SPeciricaTions (SI) P= design whee! load (N) C3.6.1.26 Elastic solutions for pressures produced within an infinite half-space by loads on the ground surface can be found in Poulos and Davis (1974), NAVEAC DM-7.1 (1982), and soil mechanics textbooks. This approximation is similar to the 60° rule found in many texts on soil mechanics. The dimensions of the tire contact area are determined at the surface based on the dynamic Ioad allowance of 33 percent at depth = 0. They are projected through the soil as specified. The pressure intensity on the surface is based on the wheel load without dynamic load allowance. A dynamic load allowance is aided to the pressure on the projected area, The dynamic load allowance also varies with depth as specified in Article 3.6.2.2. The design lane load is applied where appropriate and multiple presence factors apply. This provision applies to relieving slabs below grade and to top slabs of box culverts, Traditionally, the effect of fills less than 600 mm deep con live load has been ignored, Research (McGrath, eta 22004 has shown that in design of hox sections allowing distribution_of live load_through fill in_the direction parallel othe span provides a more accurate design model {0 predict moment, thrust, and shear forces. Provisions in Article 4.6.2.10 provide a means to address the effect of shallow fills, C3.6.1.3.1 The effects of an axle sequence and the lane load are superposed int order (0 obtain extreme values. This is a deviation from the traditional AASHTO approach, in ‘which either the truck or the lane load, with an additional concentrated load, provided for extreme effects. The lane load is not interrupted to provide space for the axle sequences of the design tandem or the design truck: interruption is needed only for patch loading patterns to produce extreme force effects. The notional design loads were based on the information described in Article C36.1.2.1, which contained data on “low boy” type vehicles weighing up to about 490 000 N. Where multiple lanes of heavier versions of this type of vehicle are considered probable, consideration should be given to investigating negative (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav.SECTION3 (SI): LOADS AND LoaD FACTORS ‘of 15 000 mm between the lead axle of one truck and the rear axle of the other truck, combined with 90 percent of the effect of the design lane load. The distance between the 145 000-N axles of each truck shall be taken as 4300 mm, Axles that do not contribute tothe extreme force effect under consideration shall be neglected. Both the design lanes and the 3000-mm loaded width in each lane shall be positioned to produce extreme force effects. The design truck or tandem shall be positioned transversely such thatthe center of any wheel load is not closer than: ‘© For the design of the deck overhang—300 mm from the face ofthe curb or railing, and ‘© Forthe design ofall other components—600 mm. from the edge of the design lane. Unless otherwise specified, the lengths of design lanes, or pars thereof, that contribute tothe extreme force effect under consideration, shall be loaded with the design lane load 3.6.1.3.2 Loading for Optional Live Load Deflection Evaluation IF the Owner invokes the optional live load deflection criteria specified in Article 2.5.2.6.2, the deflection should be taken as the larger of ‘© That resulting from the design truck alone, or ‘+ That resulting from 25 percent ofthe design truck taken together with the design lane loa. 3.6.1.3.3 Design Loads for Decks, Deck Systems, and the Top Slabs of Box Culverts The provisions of this article shall not apply to decks designed under the provisions of Article 9.7.2, “Empirical Design. (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav. 323 moment and reactions at interior suppors for pairs ofthe design tandem spaced from 8000 mm to 12 000 mm apar. combined with the design lane load specified in Article 3.6.1.2.4. One hundred percent ofthe combined effect of the design tandems and the design lane load should be used. This is consistent with Article 3.6.1.2.1 and should not be considered a replacement forthe Strength II Load Combination. Only those areas or parts of areas that contribute to the same extreme being sought should be loaded. The Tadd length should be determined by the points where the influence surface meets the centerline of the design lane. Where a sidewalk is not separated from the roadway by a crashworthy traffic barrier, consideration should be given to the possibility that vehicles can mount the sidewalk €3.6.1.3.2 As indicated in C2.5.2.6.1, live load deflection is a service issue, nota strength issue. Experience with bridges designed under previous editions of the AASHTO Standard Specifications indicated no adverse effects of live Toad deflection per se. Therefore, there appears to be little reason to require that the past criteria be compared to a deflection based upon the heavier live load required by these Specifications. The provisions ofthis article are intended to produce apparent live load deflections similar to those used in the past. The current design truck is identical to the H1S20 {nuck of past Standard Specifications. For the span lengths ‘where the design lane load controls, the design lane load together with 25 percent of the design truck, ie., three concentrated loads totaling 80 000 N, is similar tothe past Tane load with its single concentrated load of 80 000 N C36.1.3.3 This article clarifies the selection of wheel loads to be used in the design of bridge decks, slab bridges, and top slabs of box culverts The design load is always an axle loa single wheet loads should not be considered324 AASHTO LRED Beupck Desicn SreciticaTions (SI) Where the approximate strip method is used to analyze decks and top slabs of culvens, force effects shall be determined on the following basis: ‘© Where the slab spans primarily in the transverse direction, only the axles of the design truck of Amlicle 3.6.1.2.2 or design _tandem of Article 3.6.1.2.3 shall be applied to the deck slab cr the top slab of box culverts. ‘© Where the slab spans direction: marily n the longitudinal © Fortop slabs of hox culverts ofall spansand for_all_other cases, including slab-type bridges where the span does not exceed 4600 mm, only the axle loads of the design ‘muck or design tandem of Articles 3.6.1.2.2 and 3.6.1.2.3, respectively, shall be a © For all other cases, including_slab-type bridges (excluding top slabs of box culver) ‘where the span exceeds 4600 mm, all oF the Toad_specified_in_Anicle 3.6.1.2 shall be appli ‘Where the refined methods are used ta analyze decks, force effects shall be determined on the following basis: ‘* Where the slab spans primarily in the transverse direction, only the axles of the design truck of Article “3.6.1.2.2 or design tandem of Article 3.6.1.2.3 shall be applied tothe deck slab. direction (including slab als specified in Anice. bridges), all of the 1.2shall beapplied, ‘Wheel loads shall be assumed to be equal within an axle unit, and amplification of the wheel loads due to centrifugal and braking forces need not be considered for the design of decks 3.6.1.3.4 Deck Overhang Load For the design of deck overhangs with a cantilever, not exceeding 1800 mm fram the centerline ofthe exterior inter to the face of a structurally continuous concrete railing, the outside row of wheel loads may be replaced with a uniformly distributed line load of 14.6 N/om Intensity, located 300 mm from the face ofthe railing, Horizontal loads on the overhang resulting from vehicle collision with barriers shall be in accordance with the provisions of Section 13. ‘The design truck and tandem without the lane load and with a multiple presence factor of 1,2 results in factored force effects that are similar to the factored force cffects using earlier specifications for typical span ranges cof box culverts Individual owners may choose to develop other axle ‘weights and configurations to capture the load effects of ‘the actual loads in ther jurisdiction based upon local legal- load and permitting policies. Triple axle configurations of single unit vehicles have been observed 1 have load effects in excess of the HL-93 tandem axle load, tis theoretically possible that anexireme force effect could result from 2 145 000-N axle in one lane and a 220 000-N tandem ina second lane, but such sophistication is not warranted in practical design. C36.1.3.4 Structurally continuous barriers have been observed to be effective in distributing wheel loads in the overhang Implicit in this. provision is the assumption that the 110 000-N half weight of a design tandem is distributed over a longitudinal length of 7600 mm, and that there isa ‘ross beam or other appropriate component at the end of the bridge supporting the barrier which is designed for the half tandem weight. This provision does not apply if the barrier isnot structurally continuous. {© 2005 by the American Assocation of State Highway and Transportation Officials. Al nights reservee. Duplication is @ violation of applicable law.SucTION3 (SD; Loans aNp Loa Factors 3.6.14 Fatigue Load 36.141 Magnitude and Configuration ‘The fatigue load shall be one design truck or axles thereof specified in Anicle 3,6.1.2.2, but with a constant spacing of 9000 mm between the 145 000-N axles The dynamic load allowance specified in Anicle 3.6.2 shall be applied to the fatigue load 36.142 Frequency ‘The frequency of the fatigue load shall be taken as the single-lane average daily. truck uaflic (ADIT). This frequency shall be applied to all components ofthe bridge, even to those located under lanes that cary a lesser number of trucks. In the absence of better information, the single-lane average daily truck traffic shall be taken as: ADTT,, = px ADTT 6.614.241) where: ADIT = the numberof tricks per day inone direction averaged over the design life (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav. 3241 36.142 nce the fatigue and fracture limit state is defined in terms of accumulated stress-range cycles, specification of load alone is not adequate. Load should be specified along ‘with the frequency of load occurrence. For the purposes of this atticle, a truck is defined as any vehicle with more than either two axles or four wheels, The single-lane ADTT is that for the traffic lane in which the majority of the truck traffic crosses the bridge On a typical bridge with no nearby entrancevexit ramps, the shoulder lane carries most ofthe truck traffic, Since future traffic patterns on the bridge are uncertain, the frequency of the fatigue load for a single Tne is assumed to apply’to all lanes. Research has shown that the average daily traffic (ADT), including all vehicles, ie., cars and trucks, is322 AASHTO LRED Bravo Desicx Srectrrcarions ($2) ‘This page is intentionally let blank. ‘ll ghts reserved. Ouplication i @violabon of appicatte lay‘SrcTION3 (SI): Loaps AND Loap Factors ADIT, = the number of trucks per day ina single-lane averaged over the design life P taken as specified in Table 1 ‘Table 3.6.1.4.2-1 Fraction of Truck ‘Tralfie ina Single Lane, p- Number of Lanes Available to Trucks |p 1 1.00 2 0.85 3or more ‘0.80 3.6.1.4.3 Load Distribution for Fatigue 3.6.1.4.3a Refined Methods ‘Where the bridge is analyzed by any refined method, as specified in Article 4.6.3, a single design truck shall be positioned transversely and longitudinally to maximize stress range at the detail under consideration, regardless of the position of trafic or design lanes on the deck 3.6.1.4.36 Approximate Methods Where the bridge is analyzed by approximate load distribution, as specified in Article 4.6.2, the distribution factor for one trafic lane shall be used. 3.6.1.5 Rail Transit Load Where a bridge also carries rail-transit vehicles, the (Owner shal specify the transit load characteristics and the ‘expected interaction between transit and highway traffic 3.25 physically limited to about 20 000 vehicles per lane per day under normal conditions. This limiting value of traffic should be considered when estimating the ADTT. The ADT can be determined by multiplying the ADT by the fraction of trucks in the traffic, In liew of site-specific fraction of truck traffic data, the values of Table C1 may bbe applied for routine bridges. ‘Table C3.61.4.2-1 Fraction of Trucks in Traffic, Fraction of Class of Highway | ‘Trucks in Traffic Rural Interstate 0.20. Urban Interstate Os (Other Rural (Other Urban 0.5 C3.6.1.4.30 fc were assured thatthe trafic lanes would remain fas they are indicated at the opening of the bridge throughout its entire service life, it would be more appropriate to place the truck at the center of the traffic Jane that produces maximum stress range in the detail ‘under consideration, But because future traffic patteras on the bridge are uncertain and in the interest of minimizing the number of calculations required of the Designer, the position ofthe truck is made independentof the location of both the traffic lanes and the design lanes 036.15 ‘frail transit is designed to occupy an exclusive lane, transit loads should be included in the design, but the bridge should not have less strength than if it had been designed as a highway bridge of the same width. If the rail transit is supposed to mix with regular highway traffic, the Owner should specify or approve an ‘appropriate combination of transit and highvvay loads for the design, ‘Transit load characteristics may include: = Loads, © Load distribution, © Load frequency, (© 2004 by the American Aesoiton of State Highviay and Transportation Of "A rights reserved. Dupleation sa vation of appicabe lw.3.26 3.6.1.6 Pedestrian Loads A pedestrian load of 3.610 MPa shall be applied to all sidewalks wider than 600 mm and considered simultaneously with the vehicular design live load Bridges for only pedestrian and/orbicycle traffic s bbe designed for a live load of 4.110 MPa, i Where sidewalks, pedestrian, and/or bieycle bridges are intended to be used by maintenance and/or other incidental vehicles, these loads shall be considered in the design, The dynamic load allowance need not be considered for these vehicles, Where vehicles can mount the sidewalk, sidewalk ‘pedestrian load shall not be considered concurrently 3.6.1.7 Loads on Railings Loads on railings shall_be taken as specified in Section 13. 3.6.2 Dynamic Load Allowance: IM 3.6.2.1 General Unless otherwise permitted in Articles 3.6.2.2 and 3.6.2.3, the static effects of the design truck or tandem, other than centrifugal and braking forces, shall be increased by the percentage specified in Table 1 for ‘dynamic load allowance. ‘The factor to be applied to the static load shall be taken as: (1+ JM100), ‘The dynamic load allowance shall not be applied (0 pedestrian loads or tothe design lane lond, Table 36.2.1-1 Dynamic Load Allowance, IM. ‘Component T Deck Joinis—All Limit States 75% Al Other Components © Fatigue and Fracture | 15% Limit State ©All Other Limit States 33% ‘The application of dy namic load allowance for buried ‘components, covered in Section 12, shall be as specified in Article 3.6.2.2, Dynamic load allowance need not be applied to: ‘© Retaining walls not subject to vertical reactions from the superstructure, and AASHTO LRED Brine! Estes SrecinicaTioNs (SD) © Dynamic allowance, and ‘© Dimensional requirements, 3.6.1.6 See the provisions of Attcle 3.6.1.1.2 forapplying the pedestrian loads in combination with the vehicular live Toad. The conservatism in this article reflects the unpredictable nature of pedestrian load, which gains significance where it becomes a primary load. jow removal and other maintenance vehicles sometimes have access to pedestrian bridges. The slow speed of such vehicles justifies the omission of dynamic cffects 3.6.2.1 Page (1976) contains the basis for some of these provisions The dynamic load allowance (1M) in Table 1 is an increment io be applied to the static whee! Toad to account for whe load impact from moving vehicles. Dynamic effects due t moving vehicles may be attributed to two sources: © Hammering effect isthe dynamic response ofthe wheel assembly to riding surface discontinuities, such as deck joints, cracks, potholes, and delaminations, and ‘© Dynamic response of the bridge as a whole to passing vehicles, which may be due to long undulations in the roadway pavement, such as those caused by settlement of fill, oF to resonant excitation as a result of similar frequencies of vibration between bridge and vehicle Field tests indicate that in the majority of highway bridges, the dynamic component of the response does not exceed 25 percent ofthe static response to vehicles. This is the basis for dynamic lond allowance with the exception of dock joints. However, the specified ive load combination of the design trick and lane load, represents a group of exclusion vehicles that are atleast 4/3 of those caused by the design truck alone on short-and medium-span bridges, (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav.SECTION3 (SI): LOADS AND LoaD FACTORS ‘+ Foundation components that are entirely below ground level ‘The dynamic load allowance may be reduced for componenis, other than joints, if justified by sufficient evidence, in accordance with” the provisions of Article 4.7.2.1 3.6.22 Buried Components ‘The dynamic load allowance for culverts and other buried structures covered by Section 12, in percent, shall be taken as IM = 33(1.0-4.1%10" D,) 20% (3622.1) where: De = the minimum depth of earth caver above the structure (mm) 3.6.2.3 Wood Components Dynamic load allowance need nat be applied to wood components (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav. 321 ‘The specified value of 33 percent in Table 1 is the product of 43 and the basic 25 percent Generally speaking, the dynamic amplification of trucks follows the following general trends: + AS the weight of the vehicle goes up, the apparent amplification goes down. © Multiple vehicles produce a lower dynamic amplification than a single vehicle © More axles result amplification. ina lower dynamic For heavy permit vehicles which have many axles compared to the design truck, a reduction in the dynamic Toad allowance may be warranted. A study of dynamic cffects presented in a report by the Calibration Task Group (Nowak 1992) contains details regarding the relationship between dynamic load allowance and vehicle configuration. This article recognizes the damping effect of soil ‘when in contact with some buried structural components, suich as footings. To qualify for relief from impact, the entire component must be buried. For the purpose of this atcle, a retaining type component 1s considered ta be buried to the top ofthe 3.6.23 Wood sinuctures are known to experience reduced dynamic wheel load effects due to internal friction between the components and the damping characteristics ‘of wood, Additionally, wood is stronger for short duration Toads, as compared to longer duration loads. Ths increase in strength is greater than the increase in force effects resulting from the dynamic load allowance.3.28 2 CE 3.6.3 Centrifugal Fore For the purpose of computing the radial force or the overturning effect on whee! loads. the centrifugal effecton live load shall be taken as the product of the axle weights of the design truck or tandem and the factor C. taken as: where v= highway design speed (msec.) {= 405 for toad combinations ther than fatigue and 1.0 for fatigue g gravitational acceleration; 9.807 (m/sec.) R= radius of curvature of trafic Lane (mm) Highway design speed shall not be taken {0 be less tian the value specified in the current edition of the AASHTO publication, A Policy of Geometric Design o1 Highways and Streets The multiple presence factors specified in Article 3.6.1.1. shall apply Centrifugal forces shall be applied horizontally at a distance 1800 mmabove the roadway surface, A toad path fo carry the radial force to the subsiru be provided The effect_of superelevation_in_reducing_the overtuming effect of centrifugal force on vertical wheel Toads may be considered. 3.64 Braking Force: BR ‘The braking force shall be taken as the greater of ‘* 2Spercent of the axle weights of the design truck or design tandem or, ‘+ 5 petcent of the design truck plus lane load or 5 percent of the design tandem plus lane load AASHTO LRED Brine! Estes SrecinicaTioNs (SD) 3.63 Centrifugal force is not required to be applied to the design lane load, as the spacing of vehicles at high speed is assumed (0 be large, resulting in a low density of Vehicles following and/or preceding the design truck. For all other consideration of live load other than for fatigue, the design lane load is still considered even though the centrifugal effect isnot applied to it The specified live load combination of the design tnuck and lane load, however, represents @ group of exclusion vehicles that produce force effects of at east 4/3 of those caused by the design truck alone on short and :mediumspan bridges. This ratio is indicated in Eq. 1 for the service and strength limit states, For the fatigue and fracture limit stale. the factor L0 is consistent_with cumulative damageanalvsis. The provision isnot technically perfect, yet it reasonably models the representative exclusion vehicle traveling at design speed ‘ith large headways to other vehicles. The approximation attributed to this convenient representation is acceptable in the framework ofthe uncertainty of centrifugal force from random traffic pattems. 1.0 misec, = 3.60 kin Centrifugal force also causes an overturning effect on the_wheol loads because the radial foree_is_applied 1800 mm above the top of the deck. Thus, centrifuga Tore tends to cause an increase i the vertical whee! loads toward the outside ofthe bridge and an unloading of the ‘whgel_oads toward the inside of the bridge. Superelevation helps to balance the overturning effect due to the centrifugal force and this beneficial effect may be considered, The effects_due_to_vehicle_cases_with centrifugal force effects included should be compared to and the worst case selected. C364 Based on energy principles, and assuming uniform doceleration, the braking force determined as a fraction of vehicle weight is: (364-1) (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav.SECTION3 (SI): LOADS AND LoaD FACTORS This braking force shall be placed in all design lanes which are considered to be loaded in accordance with Article 3.6.1.1.1 and which are carrying traffic headed in the same direction. These forces shall be assumed o act horizontally at a distance of 1800 mm above the roadway surface in either longitudinal direction to cause extreme force effects Al design lanes shall be simultaneously loaded for bridges likely to become one-cdirectional inthe future. ‘The multiple presence factors specified in Article 3.6.1.1.2 shall apply (© 2005 by the American Association of State Highway and Transporation Ofcials ‘Allright reserves, Duplication & voltion of applicable lav. 3.281 ‘where ais the length of uniform deceleration and bis the fraction. Calculations using a braking length of 122 mand a speed of 90 nvr, (25 musec:) yield b= 0.26 for a horizontal force that will act for a period of about 10 seconds. The factor bapplies to all lanes in one direction because all vehicles may have reacted within this time frame. For short- and medlium-span bridges, the specified braking force can be significantly larger than was required inthe Standard Specifications. The braking force specified in the Standard Specifications dates back to at least the carly 1940's without any significant changes to address the improved braking capacity of modern trucks, A review of other bridge design codes in Canada and Europe showed that the braking force required by the Standard Specification is much lower than that specified in other design codes for most typical bridges. One such ‘comparison is shown in Figure C13.282 AASHTO LRED Bravo Desicx Srectrrcarions ($2) ‘This page is intentionally let blank. ‘ll ghts reserved. Ouplication i @violabon of appicatte lay‘SrcTION3 (SI): Loaps AND Loap Factors Brag Fre 4) rxinaFore o8) oBBSESEEE SES ° 329 Force (1 Lane Loaded) ‘OHEOS) cae anna sts, osg2s18 Su Nes “Wr ‘tance tween xp. bs) Eactored Braking Force (2 Lanes Loaded) “aos Lara spats, Dostzeens cs hones wer ‘tance Between xp. Jom) Factored Braking Foree (3 Lanes Loaded) OHBDC: a Factored Braking Force (4 Lanes Loaded) igure €3.641 Comparison of Bra tine eens pes) Force Models. factored braking force as specified in the 3" edition of the Ontario Highway Bridge (© 2004 by the American Assocation of Sate Highway and Transporation Ofc. "A ats reseved. Dupleation sa vilaton of eppcabe a.3.30 AASHTO LRED Brapce Destcy Srectrtcati0Ns ($1) 3.6.5 Vehicular Collision Force: CT 3.6.5.1 Protection of Structures ‘The provisions of Article 36.5.2 need not be ‘considered for structures which are protected by: © Anembankment: ‘+ A structurally independent, crashworthy ground ‘mounted 1370-mm high barrier, located within 3000 mm from the component being protected; or + A 1070-mm high barrier located at more than 3000 mm from the component being protected. In order to qualify for this exemption, such barrier shall be structurally and geometrically capable of surviving the crash test for Test Level 5, as specified in Section 13. Design Code LED factored braking force as specified in the AASHTO Standard Specifications (Load Factor) LRED = factored braking force as specified in previous versions ofthe LRED. Specifications (up to 2001 Interim edition) LRED! = factored braking force as specified in Section 3.6.4 CHBDC= factored braking force as specified in the Canadian Highway Bridge Design Code ‘The sloping portion of the curves represents the braking force that includes a portion of the lane load, This represents the possibility of having multiple lanes of vehicles contributing to the same braking event on a long, bridge. Although the probability of such an events likely to be small, the inclusion of a portion of the lane load gives such an event consideration for bridges with heavy truck traffic and is consistent with other design codes. Because the LRED braking force is significantly hhigher than that required in the Standaed Specifications, this issue becomes important in rehabilitation projects designed under previous versions of the design code. In ceases where substructures are found to be inadequate £0 resist the increased longitudinal forces, consideration should be given to design and detailing strategies which distribute the braking force to additional substructure units during a braking event. 3.65.1 For the purpose of this article, a barrier may be considered seructurally independent if t does not transmit Toads to the bridge. Full-seale crash tests have shown that some vehicles havea greater tendency to Iean over or partially cross over 4 1070-mm high bartier than a 1370-mm high barrier. This bbchavior would allow a significant collision ofthe vehicle ‘with the component being protected if the component is located within a meter or so of the barrier. If the component is more than about 3000 mm behind the Darter, the difference between the 1wo barrier heights is no longer important. (© 2004 by the American Associaton of State Highway and Transportation Ofc. ‘All ratis reseved. Dupleation sa vlaton &appicable am‘SrcTION3 (SI): Loaps AND Loap Factors Bat 36.5.2 Vehicle and Railway Collision with Structures Unless protected as specified in Article 3.6.5.1, abutments and piers located within a distance of 9000 mm to the edge of roadway, or within a distance of 15 000 mm tothe centerline of a railway track, shall be designed for an ‘equivalent statie force of | 800.000 N, which is assumed 10 act in any direction in a horizontal plane, at a distance of 1200 mm above ground, ‘The provisions of Article 2.3.2.2.1 shall apply. 3.6.5.3 Vehicle Collision with Barriers ‘The provi ions of Section 13 shall apply. 3.7 WAI OADS: WA 3.7.1 Static Pressure Static pressure of water shall be assumed 10 act perpendicular 0 the surface that is retaining the water. Pressure shall be calculated as the product of height of water above the point of consideration, the density of water, and g (the acceleration of gravity), Design water levels for various limit states shall be as specified andlor approved by the Owner, 3.7.2 Buoyancy Buoyancy shall be considered to be an uplift force, taken as the sum of the vertical components of static pressures, as specified in Article 3.7.1, acting on all ‘components below design water level. 3.7.3 Stream Pressure 3.7.3.1 Longitudinal ‘The pressure of flowing water acting in the longitudinal direction of substructures shall be taken as: p= 5.14x104C,V? 73.14, where: p= pressure of flowing water (MPa) ©3682 It is not the intent of this provision to encourage Lunproteeted piers and abutments within the setbacks indicated, but rather to supply some guidance for structural design when itis deemed totally impractical to meet the requirements of Article 3.6.5.1 ‘The equivalent state force of 1 $00 000 N is based on the information from full-scale crash tests of barriers for redirecting 360 000-N tractor trailers and from analysis of other truck collisions. The 1 800 000-N train collision load is based on recent, physically unverified, analytical work (Hirsch 1989), For individual column salts, the 1 $0000 -N load should be considered a point load, For wall piers, the load may be considered to be a point load or may be distributed over an area deemed suitable forthe size of the structure and the anticipated impacting vehicle, but not greater than 1500 mm wide by 600 mm high. These dimensions were determined by considering the size of a truck frame, 037.2 For substructures with cavities in which the presence oo absence of water cannot be ascertained, the condition producing the least favorable force effect should be chosen, C3731 For the purpose of this article, the longitudinal direetion refers to the major axis ofa substructure unit. ‘The theoretically correct expression for Eq. | is: o px (3.73.14) (© 2004 by the American Assocation of Sate Highway and Transporation Ofc. "A ats reseved. Dupleation sa vilaton of eppcabe a.aa Co = drag coefficient for piers as specified in Table 1 V_ = design velocity of water for the design flood in strength and service limit states and for the check flood in the extreme event limit state (nusec.) ‘Table 37.3.1-1 Drag Coettci Type Co ‘Semicireular-nosed pier 07, ‘square-ended pier Ls debris lodged against the pier | 14 wedged-nosed pier with nose [0.8 angle 90° or less The longitudinal drag force shall be taken as the product of longitudinal stream pressure and the projected surface exposed thereto. AASHTO LRED Brapce Destcy Srectrtcati0Ns ($1) Y density (unit mass) of water (kg/m) V_ = velocity of water (misec.) ‘The drag coefficient, Cp, and the lateral drag coefficient, C;, given im Tables 1 and 3,7.3.2-1, were adopted from the Ontario Highway Bridge Design Code (7991). The more favorable drag coefficients measured by some researchers for wedge-type pier nose angles of less than 90° are not given here because such pier noses are _more prone to catching debris. Floating logs, roots, and other debris may accumulate at piers and, by blocking parts of the waterway, increase stream pressure load on the pier. Sueh accumulation is a function of the availability of such debris and level of ‘maintenance efforts by which it is removed. It may be accounted for by the judicious increase in both the exposed surface and the velocity of water. ‘The draft New Zealand Highway Bridge Design Specification contains the following provision, which may bbe used as guidance in the absence of site-specific criteria: Where a significant amount of driftwood is carried, water pressure shall also be allowed for on a driftwood raft lodged against the pier. The size of the raft isa matter of judgment, but as a guide, Dimension Ain Figure C1 stiould be half the water depth, but aot greater than 3000 mm. Dimension B should be halt the sum of adjacent span lengths, but no greater than 14.000 mm. Pressure shall be calculated using Eg. 1, with Cp=05, st A Debris Raft Bed Level Figure C3, {cI Debris Raft for Pier Design. (© 2004 by the American Associaton of State Highway and Transportation OF. "Alri reserved. Dupleaion sa vlan appicabe am.‘SrcTION3 (SI): Loaps AND Loap Factors 323 37.32 Lateral ‘The lateral, uniformly distributed pressure on a substructure due t0 water flowing at an angle, #, 10 the longitudinal axis of the pier shall be taken as: p = 5.14x10°C,V* GI32-1) whore: p= lateral pressure (MPa) Gi. = lateral drag cooicient specified in Table 1 P Longitudinal ans of plor Figure 37.32-1 Plan View of Pier Showing Stream Flow Pressure. ‘Table 37.3.2 Lateral Drag Coefficient. “Angle, 0, between direction of flow and longitudinal axis ofthe pier G o 00) = OS, 10" o7, 20° 09) 230° 10. ‘The lateral drag force shall be taken as the product of the lateral stream pressure and the surface exposed thereto, 3.74 Wave Load ‘Wave action on bridge structures shall be considered for exposed structures where the development of sant wave forces may occur. 3.7.5 Change in Foundations Due to Limit State for Seour ‘The provisions of Article 2.6.4.4 shall apply. “The consequences of changes in foundation conditions resulting from the design flood for scour shall be considered at strength and service limit states. ‘The ‘consequences of changes in foundation conditions due 10 scour resulting from the check flood for bridge scour and from hurricanes shall be considered at the extreme event 03.732 ‘The discussion of Eq. 3.7.3.1-1 also applies to Eq. 1 a7 ‘Loads due to wave action on bridge structures shal be determined using accepted engineering practice methods, Site-specific conditions should be considered. The latest edition of the Shore Protection Manual, published by the Coastal Engineering Research Center, Department of the Army, is recommended for the computation of wave Statistically speaking, scour is the most common reason for the failure of highway bridges in the United States, Provisions concerning the effects of scour are given in Section 2. Scour per se is not a force effect, but by changing the conditions of the substructure it may significantly alter the consequences of force effects acting (© 2004 bythe American Assokton of State Highway and Traneportation Offi "A ght reseved. Dupleation sa velaton of appicable lw.aa AASHTO LRED Brapce Destcy Srectrtcati0Ns ($1) Hit states. 38 WIND LOAD: WE AND WS 381 Horizontal Wind Pressure 38.1.1 General Pressures specified herein shall be assumed to be caused by a base design wind velocity. Vp, of 160 knv/r. Wind load shall be assumed to be uniformly distributed on the area exposed to the wind, The exposed area shall be the sum of aress of all components, including floor system and railing, as seen in elevation taken perpendicular to the assumed wind direction. ‘This dircetion shall be varied to determine the extreme force cffect in the structure or in its components. Areas that do not contribute t the extreme force effect under ‘consideration may be neglected in the analysis, For bridges or parts of bridges more than 10.000 mm above low ground or water level, the design wind velocity, Voz. should be adjusted according to: 5 v2) o(2) G81) vel a where: Vor design wind velocity at design clevation, Z: (kav) Vig = wind velocity at 10 000 mm above low ground or above design water level (kn) Ve = base wind velocity of 160 knw. at 10 000 mm height. yielding design pressures spocified in Articles 38.1.2 and 38.2 Z = beightofstmcture st which wind loads are being cleulated as meastred from low ground, or from ‘water level, > 10 000 mm Vp = friction velocity, a meteorological wind characteristic taken, as specified in Table 1, for ‘various upwind surface charaeteristis (kav) % = frigtion length of upstream fetch, meteorological wind characteristic token as specified in Table 1 (mm) fon structures. C3841 Base design wind velocity varies significantly due to local conditions. For small and/or low structures, wind usually does not govern, For large and/or tall bridges, however, the local conditions should be investigated. Pressures on windward and leeward sides are to be taken simultaneously in the assumed direction of wind. ‘Typically, a bridge structure should be examined separately under wind pressures from two or more different directions in order to ascertain those windward, eeward, and side pressures producing the most critical Toads on the structure, Eq, 1 is based on boundary layer theory combined ‘with empirical observations and represents the mostrecent approach to defining wind speeds For various conditions as used in meteorology. In the past, an exponential equation ‘was sometimes used to folate wind speed to heights above 10 000 mm. This formulation was based solely on empirical observations and had no theoretical basis, Voe= CV 2) we Vil sae (38.1.1) "The purpose of the term C and exponent a was to adjust the equation for various upstream surface conditions, similar to the use of Table |. Further information ean be found in Liu (/99/) and Simiu (1973, 1976). ‘The following descriptions for the terms “open country,” “suburban,” and “eity” in Table 1 are paraphrased from ASCE-7-93: © Open Country—Open terrain with scattered obstructions having heights generally less than 10 000 mm. This category includes flat open country and grasslands. © Suburban—Urban and suburban areas, wooded areas, oF other terrain with numerous closely spaced obstructions having the size of single amily or larger dwellings. Use of this category shall be limited to those areas for which representative terrain prevails in the upwind direction atleast 500 000 mm, © City—Large city centers with atleast 50 percent of the buildings having a height ia excess of 21,000 mm, Use of this category shall be limited to those areas for which representative terrain prevails in the upwind direction at least 800 000 ‘mm. Possible channeling effects of increased (© 2004 by the American Associaton of Sate Highway and Transportation Offi. ‘args eseved. Duplestion is 3 velation &eppicable‘SrcTION3 (SI): Loaps AND Loap Factors 3.5 ‘velocity pressures duc tothe bridge or structure's location in the wake of adjacent structures shall be taken into account. ‘Table 3.8.1.1-1 Values of Vo and Zp for Various Upstream Surface Conditions. ‘OPEN conprmion | country | SUBURBAN |_crITy Vp (kn) 132) 176 193 Zo (mm) 70 7000 2500 Vip may be established from: ‘+ Basie Wind Speed charts available in ASCE 7-88 for various recurrence intervals, ‘© Site-specific wind surveys, and * Inthe absence of better criterion, the assumption that Vip = Vp = 160 km/hr. 3.8.1.2 Wind Pressure on Structures: WS 3.8.1.2.1 General fjustfied by local conditions, a different base design wind velocity may be selected for load combinations not involving wind on live load. The direction of the design \wind shall be assumed to be horizontal, unless otherwise specified in Article 3.8.3. In the absence of more precise data, design wind pressure, in MPa, may be determined as: ie) ‘Pp = base wind pressure specified in Table | (MPa) Vor" no GB8121-D 25 600 ‘Table 38.1.2-1 Base Pressures, ?y Corresponding (0 Vp = 160 knvhr. SUPERSTRUCTURE | WINDWARD | LEEWARD. COMPONTENT | LOAD. MPa_| LOAD. MPa Trusses, Columns, and | 0.0024 ‘0.0012 Arches Beams 0.0024 NA Large Flat Surfaces 0.0019 NA ‘The total wind loading shall not be taken fess than 4.4 ‘N/mm in the plane of a windward chord and 2.2 N/mm ia the plane of a leeward chord on tuss and arch components, and not less than 4.4 N/mm on beam or girder spans. C38.1.2.1 ‘The stagnation pressure associated with a wind velocity of 160 kuvhr. is 1.23x10" MPa, which is significantly less than the values specified in Table 1. The Jifference reflects the effect of gusting combined with some tradition of long-time usage. ‘The pressures specified in should be chosen to produce the greater net wind load on the structure ‘Wind tunnel tests may be used to provide more precise estimates of wind pressures. Such testing should be ‘considered where wind is a major design load ‘The term “columns” in Table | refers to columns in superstructures such as spandrel columns in arches. (© 2004 bythe American Assokton of State Highway and Traneportation Offi "A ght reseved. Dupleation sa velaton of appicable lw.336 38.1.2.2 Loads from Superstructures ‘Where the wind is not taken as normal tothe structure, the base wind pressures, Ps, for various angles of wind ireetion may be taken as specified in Table | and shall be applied to a single place of exposed area, The skew angle shall be taken as measured from a perpendicular to the longitudinal axis. The wind direction for design shall be that which produces the extreme force effect on the component under investigation, ‘The transverse and longitudinal pressures shall be applied simultaneously. AASHTO LRED Brapce Destcy Srectrtcati0Ns ($1) C3.8.1.2.2 FFor trusses, columns, and arches, the base wind pressures specified in Table I are the sum of the pressures. applied to both the windward and leeward areas. ‘Table 38.1.2.2-1 Base Wind Pressures, Pa, for Various Angles of Attack and Vg = 160 kwh. Trusses, Columns and Arches Girders ‘Skew Angle [Lateral | Longitudinal | Lateral | Longitudinal of Wind | Load Loud Load Load Degrees [MPa MPa MPa ‘MPa oO ‘0.0036 | _0.0000__| 0.0028 | 0.0000 is ‘0.0034 [0.0006 | “0.0021 | 0.0003, 30 ‘0.0031_| 0.0013 | 0.0020 | 0.0006 45 (0.0023 [0.0020 | 0.0016 | 0.0008, 60 0.0011_[ 0.0024 | 0.0008_| 0.0009 3.8.1.2.3 Forces Applied Directly to the Substructure ‘The transverse and longitudinal forces to be applied directly to the substructure shall be calculated from an assumed base wind pressure of 0.0019 MPa. For wind directions taken skewed tothe substructure, this force shall be resolved into components perpendicular to the end and front elevations of the substructure. The component perpendicular 0 the end elevation shall aet on the exposed substructure area as seen in end elevation, and the ‘component perpendicular to the front elevation shall acton the exposed areas and shall be applied simultaneously with ‘the wind loads from the superstructure. 3.8.1.3 Wind Pressure on Vehicles: WL ‘When vehicles are present, the design wind pressure shall be applied to both structure and vehicles. Wind pressure on vehicles shall be represented by an Interruptible, moving force of 1.46 N/mm acting normal to, sand 1800 mm above, the roadway and shall be transmitted to the structure, When wind on vehicles is not taken as normal to the structure, the components of normal and parallel force applied to the live load may be taken as specified in Table | with the skew angle taken as referenced normal to the surface. C3813 Based on practical experience, maximum live loads are not expected to be present on the bridge when the wind velocity exceeds 90 knv/ir. The load factor coresponding, to the treatment of wind on structure only in Load ‘Combination Strength III would be (90/160) (1.4) =0.44, which has been rounded (© 0.40 in the Strength V Load Combination. This load factor corresponds to 03 in Service L. ‘The 1.46 N/mm wind load is based on a long row of randomly sequenced passenger ears, commercial Vans, and trucks exposed to the 90 kuvhr. design wind. This horizontal live load, similar to the design lane load, should be applied only to the tributary areas producing a force effect of the same kind. (© 2004 by the American Associaton of State Highway and Transporation Offi. "Aros reseved. Duplo sa vlaton of epplcabie la.‘SrcTION3 (SI): Loaps AND Loap Factors 3a7 ‘Table 3.8.1.3-1 Wind Components on Live Load. ‘Normal Parallel Skew Angle | Component _| Component Degrees N/mm Ninn 0 146 0.00, 15 1.28 0.18 30 120, 035 45 0.96 oar 60 0.50, 055 3.82 Vertical Wind Pressure Unless otherwise determined in Aricle 3.8.3. 0 vertical upward wind force of 9.610"! MPa simes the width of the deck. including parapets and sidewalks, shall be considered to be «longitudinal line loa, This force shall be applied only for limit states that do not involve ‘wind on live load, and only when te direction of wind is taken to be perpendicelar to the longitidinal axis of the bridge. This lineal force shall be applied atthe windward quarter point ofthe deck width in conjunction with the torizonal wind loads specified in Arie 3.8.1. 383 Aeroelastic Instability 38.3.1 General Aeroelastic force effects shall be taken into aceountin the design of bridges and structural components apt to be \wind-sensitive. For the purpose of this article, all bridges, and structural components thereof with a span length 10 \width or depth ratio exceeding 30.0 shall be deemed to be wind-sensitive, ‘The vibration of cables due to the interaction of wind ‘and rain shall also be considered, 3.8.3.2. Aeroelastic Phenomena ‘The aeroelastic phenomena of vortex excitation, galloping, flutter, and divergence shall be considered Where applicable. 38.2 ‘The intent ofthis article is to account for the effect resulting from interruption of the horizontal flow of air by the superstructure. This load is to be applied even 10 discontinuous bridge decks, such as grid decks. This load ‘may govern where overturning ofthe bridge is investigate 383, Because of the complexity of analyses often necessary for an in-depth evalustion of structural aeroetasticity, this article is intentionally kept to a simple statement, Many bridges, decks, or individual structural components have been shown to be aeroelastically insensitive if their length- to-width or length-to-depth ratios are under about 30.0, a somewhat arbitrary value helpful only in identifying likely wind-sensitive cases, Flexible bridges, such as cable-supported or very long spans of any type, may require special studies based on wind tunnel information. In general, appropriate wind tunnel tests involve simulation of the wind environment local to the bridge site. Details of this are part of the existing wind tunnel state of the art and are beyond the scope of this commentary. 38.3.2 Excitation due to vortex shedding is the escape of wind-induced vortices behind the member, which tend t0 excite the component at its fundamental natural frequency inharmonie motion, Itis important to keep stresses due t0 vortex-induced oscillations below the “infinite life” fatigue stress. Methods exist for estimating such stress amplitudes, but they are outside the scope of this commentary. “Tubular components can be protected against vortex- juced oscillation by adding bracing, strakes, or tuned, ‘mass dampers or by attaching horizontal flat plates parallel to the tube axis above and/or below the central thitd of (© 2004 bythe American Assokton of State Highway and Traneportation Offi "A ght reseved. Dupleation sa velaton of appicable lw.