LRFD Steel Design. AASHTO LRFD Bridge Design Specifications. Slide Shows

Transcription

1 LRFD Steel Design AASHTO LRFD Bridge Design Specifications Slide Shows Created July 2007

2

3 This material is copyrighted by The University of Cincinnati and Dr. James A Swanson. It may not be reproduced, distributed, sold, or stored by any means, electrical or mechanical, without the expressed written consent of The University of Cincinnati and Dr. James A Swanson. July 31, 2007

4

5 LRFD Steel Design AASHTO LRFD Bridge Design Specification Slide Shows Review of Loads and Analysis...1 Scope, Materials, and Limit States...33 Fatigue and Fracture...45 Tension Members...59 Compression Members...67 Bending Members - Flexural Theory...81 Bending Members - Flexural Provisions Bending Members - Shear Strength Web Strength and Stiffeners Connections and Splices Cost Effective Design of Steel Bridges...261

6 James A Swanson Associate Professor University of Cincinnati Dept of Civil & Env. Engineering 765 Baldwin Hall Cincinnati, OH Ph: (513) Fx: (513) James.Swanson@uc.edu

7 Review of Loads and Analysis AASHTO LRFD Review of Loads and Analysis James A Swanson AASHTO-LRFD Specification, 4 th Ed., 2007 References Bridge Engineering Handbook, Wai-Faf Chen and Lian Duan, 1999, CRC Press (ISBN: ) Four LRFD Design Examples of Steel Highway Bridges, Vol. II, Chapter 1A Highway Structures Design Handbook, Published by American Iron and Steel Institute in cooperation with HDR Engineering, Inc. Available at Design of Highway Bridges, 2 nd Ed. Richard Barker and Jay Puckett, 2007, Wiley & Sons (ISBN: ) ODOT Short Course Created July 2007 Review of Loads: Slide #

8 Review of Loads and Analysis References AASHTO Web Site: Load and Resistance Factor Design for Highway Bridges, Participant Notebook, Available from the AASHTO web site. ODOT Short Course Created July 2007 Review of Loads: Slide #3 References AISC / National Steel Bridge Alliance Web Site: org/ Steel Bridge Design Handbook ODOT Short Course Created July 2007 Review of Loads: Slide #

9 Review of Loads and Analysis References Steel Structures Design and Behavior, 4 th Ed. Charles G. Salmon and John E. Johnson, 1996, Harper Collins Guide to Stability Design Criteria for Metal Structures, 5 th Ed. Edited by Theodore V. Galambos, 1998, John Wiley & Sons, Available at Design of Steel Structures, 3 rd Ed., Edwin H. Gaylord, Charles N. Gaylord, and James E. Stallmeyer, 1992, McGraw-Hill ODOT Short Course Created July 2007 Review of Loads: Slide #5 References AASHTO Standard Specification for Highway Bridges, 17th Edition, 1997, 2003 AASHTO LRFD Bridge Design Specifications, 4 th Edition, 2007 AASHTO Guide Specification for Distribution of Loads for Highway Bridges ODOT Short Course Created July 2007 Review of Loads: Slide #

10 Review of Loads and Analysis Philosophies of Design LRFD: Load & Resistance Factor Design For Safety: γ Q φr n Q - Load Effect R - Component Resistance γ - Load Factor φ - Resistance Factor The LRFD philosophy provides a more uniform, systematic, and rational approach to the selection of load factors and resistance factors than LFD. Chen & Duan ODOT Short Course Created July 2007 Review of Loads: Slide #7 Philosophies of Design - LRFD Fundamentals Reliability Index: ASD / LFD Bridge Designs LRFD Bridge Designs (Expected) Reliability Index 3 2 Reliability Index Span Length (ft) Span Length (ft) Chen & Duan ODOT Short Course Created July 2007 Review of Loads: Slide #

11 Review of Loads and Analysis AASHTO-LRFD Specification Contents 1. Introduction 2. General Design and Location Features 3. Loads and Load Factors 4. Structural Analysis and Evaluation 5. Concrete Structures 6. Steel Structures 7. Aluminum Structures 8. Wood Structures 9. Decks and Deck Systems 10. Foundations 11. Abutments, Piers, and Walls 12. Buried Structures and Tunnel Liners 13. Railings 14. Joints and Bearings 15. Index ODOT Short Course Created July 2007 Review of Loads: Slide #9 Chapter 1 Introduction 1.3.2: Limit States Service: Deals with restrictions on stress, deformation, and crack width under regular service conditions. Intended to ensure that the bridge performs acceptably during its design life. Strength: Intended to ensure that strength and stability are provided to resist statistically significant load combinations that a bridge will experience during its design life. Extensive distress and structural damage may occur at strength limit state conditions, but overall structural integrity is expected to be maintained. Extreme Event: Intended to ensure structural survival of a bridge during an earthquake, vehicle collision, ice flow, or foundation scour. Fatigue: Deals with restrictions on stress range under regular service conditions reflecting the number of expected cycles. Pgs 1.4-5; Chen & Duan ODOT Short Course Created July 2007 Review of Loads: Slide #

12 Review of Loads and Analysis Chapter 1 Introduction 1.3.2: Limit States Q = ηγ Q i i i ( ) γ i - Load Factor Q i - Load Effect η i - Load Modifier When the maximum value of γ i is appropriate η=ηηη 0.95 i D R I ( ) When the minimum value of γi is appropriate 1 η= i 1.00 ηηη D R I ( ) Pg 1.3 ODOT Short Course Created July 2007 Review of Loads: Slide #11 Chapter 1 Introduction 1.3.2: Limit States - Load Modifiers Applicable only to the Strength Limit State η D Ductility Factor: η D = 1.05 for nonductile members η D = 1.00 for conventional designs and details complying with specifications η D = 0.95 for components for which additional ductility measures have been taken η R Redundancy Factor: η R = 1.05 for nonredundant members η R = 1.00 for conventional levels of redundancy η R = 0.95 for exceptional levels of redundancy η I Operational Importance: η I = 1.05 for important bridges η I = 1.00 for typical bridges η I = 0.95 for relatively less important bridges These modifiers are applied at the element level, not the entire structure. Pgs ; Chen & Duan ODOT Short Course Created July 2007 Review of Loads: Slide #

13 Review of Loads and Analysis Load Factors and Combinations 1.3.2: ODOT Recommended Load Modifiers For the Strength Limit States η D Ductility Factor: Use a ductility load modifier of η D = 1.00 for all strength limit states η R Redundancy Factor: Use η R = 1.05 for non-redundant members Use η R = 1.00 for redundant members Bridges with 3 or fewer girders should be considered non-redundant. Bridges with 4 girders with a spacing of 12 or more should be considered nonredundant. Bridges with 4 girders with a spacing of less than 12 should be considered redundant. Bridge with 5 or more girders should be considered redundant. ODOT Short Course Created July 2007 Review of Loads: Slide # Load Factors and Combinations 1.3.2: ODOT Recommended Load Modifiers For the Strength Limit States η R Redundancy Factor: Use η R = 1.05 for non-redundant members Use η R = 1.00 for redundant members Single and two column piers should be considered non-redundant. Cap and column piers with three or more columns should be considered redundant. T-type piers with a stem height to width ratio of 3-1 or greater should be considered non-redundant. For information on other substructure types, refer to NCHRP Report 458 Redundancy in Highway Bridge Substructures. η R does NOT apply to foundations. Foundation redundancy is included in the resistance factor. ODOT Short Course Created July 2007 Review of Loads: Slide #

14 Review of Loads and Analysis Load Factors and Combinations 1.3.2: ODOT Recommended Load Modifiers For the Strength Limit States η I Operational Importance: In General, use η I = 1.00 unless one of the following applies Use η I = 1.05 if any of the following apply Design ADT 60,000 Detour length 50 miles Any span length 500 Use η I = 0.95 if both of the following apply Design ADT 400 Detour length 10 miles Detour length applies to the shortest, emergency detour route. ODOT Short Course Created July 2007 Review of Loads: Slide #15 AASHTO-LRFD Chapter 3: Loads and Load Factors James A Swanson AASHTO-LRFD Specification, 4 th Ed.,

15 Review of Loads and Analysis Loads and Load Factors 3.4.1: Load Factors and Load Combinations Permanent Loads DD - Downdrag DC - Structural Components and Attachments DW - Wearing Surfaces and Utilities EH - Horizontal Earth Pressure EL - Locked-In Force Effects Including Pretension ES - Earth Surcharge Load EV - Vertical Pressure of Earth Fill Pg 3.7 ODOT Short Course Created July 2007 Review of Loads: Slide # Loads and Load Factors 3.4.1: Load Factors and Load Combinations Transient Loads BR Veh. Braking Force CE Veh. Centrifugal Force CR - Creep CT - Veh. Collision Force CV - Vessel Collision Force EQ - Earthquake FR - Friction IC - Ice Load LL - Veh. Live Load IM - Dynamic Load Allowance LS - Live Load Surcharge PL - Pedestrian Live Load SE - Settlement SH - Shrinkage TG - Temperature Gradient TU - Uniform Temperature WA - Water Load WL - Wind on Live Load WS - Wind Load on Structure Pg 3.7 ODOT Short Course Created July 2007 Review of Loads: Slide #

16 Review of Loads and Analysis Loads and Load Factors 3.4.1: Load Factors and Load Combinations Table Load Combinations and Load Factors Load Combination DC DD DW EH EV ES EL LL IM CE BR PL LS WA WS WL FR TU CR SH TG SE Use One of These at a Time EQ IC CT CV STRENGTH I (unless noted) γ p /1.20 γ TG γ SE STRENGTH II γ p /1.20 γ TG γ SE STRENGTH III γ p /1.20 γ TG γ SE STRENGTH IV γ p / STRENGTH V γ p /1.20 γ TG γ SE Pg 3.13 ODOT Short Course Created July 2007 Review of Loads: Slide # Loads and Load Factors 3.4.1: Load Factors and Load Combinations Load Combination EXTREME EVENT I EXTREME EVENT II FATIGUE LL, IM, & CE ONLY Table Load Combinations and Load Factors (cont.) DC DD DW EH EV ES EL γ p γ p -- LL IM CE BR PL LS γ EQ WA WS WL FR TU CR SH TG SE EQ Use One of These at a Time IC CT CV Pg 3.13 ODOT Short Course Created July 2007 Review of Loads: Slide #

17 Review of Loads and Analysis Loads and Load Factors 3.4.1: Load Factors and Load Combinations Load Combination SERVICE I SERVICE II SERVICE III SERVICE IV Table Load Combinations and Load Factors (cont.) DC DD LL DW IM EH CE EV BR TU ES PL CR EL LS WA WS WL FR SH TG SE EQ /1.20 γ TG γ SE / /1.20 γ TG γ SE / Use One of These at a Time IC CT CV Pg 3.13 ODOT Short Course Created July 2007 Review of Loads: Slide # Loads and Load Factors 3.4.1: Load Factors and Load Combinations Strength I: Basic load combination relating to the normal vehicular use of the bridge without wind. Strength II: Load combination relating to the use of the bridge by Owner-specified special design vehicles, evaluation permit vehicles, or both, without wind. Strength III: Load combination relating to the bridge exposed to wind in excess of 55 mph. Strength IV: Load combination relating to very high dead load to live load force effect ratios. (Note: In commentary it indicates that this will govern where the DL/LL >7, spans over 600, and during construction checks.) Strength V: Load combination relating to normal vehicular use with a wind of 55 mph. Pg ODOT Short Course Created July 2007 Review of Loads: Slide #

18 Review of Loads and Analysis Loads and Load Factors 3.4.1: Load Factors and Load Combinations Extreme Event I: Load combination including earthquakes. Extreme Event II: Load combination relating to ice load, collision by vessels and vehicles, and certain hydraulic events with a reduced live load. Fatigue: Fatigue and fracture load combination relating to repetitive gravitational vehicular live load and dynamic responses under a single design truck. Pg ODOT Short Course Created July 2007 Review of Loads: Slide # Loads and Load Factors 3.4.1: Load Factors and Load Combinations Service I: Load combination relating to normal operational use of the bridge with a 55 mph wind and all loads at nominal values. Compression in precast concrete components. Service II: Load combination intended to control yielding of steel structures and slip of slip-critical connections due to vehicular load. Service III: Load combination relating only to tension in prestressed concrete superstructures with the objective of crack control. Service IV: Load combination relating only to tension in prestressed concrete columns with the objective of crack control. Pg ODOT Short Course Created July 2007 Review of Loads: Slide #

19 Review of Loads and Analysis Loads and Load Factors 3.4.1: Load Factors and Load Combinations Table Load Factors for Permanent Loads, γ p Type of Load, Foundation Type, and Method Used to Calculate Downdrag DC: Component and Attachments DC: Strength IV only DD: Downdrag Piles, αtomlinson Method Plies, λ Method Drilled Shafts, O Neill and Reese (1999) Method DW: Wearing Surfaces and Utilities EH: Horizontal Earth Pressure Active At-Rest EL: Locked in Erections Stresses Load Factor Maximum Minimum Pg 3.13 ODOT Short Course Created July 2007 Review of Loads: Slide # Loads and Load Factors Common load combinations for Steel Design Strength I: 1.25DC DW (LL+IM) Service II: 1.00DC DW (LL+IM) Fatigue: 0.75(LL+IM) ODOT Short Course Created July 2007 Review of Loads: Slide #

20 Review of Loads and Analysis 3.5 Permanent Loads Dead Loads: DC and DW DC is the dead load of the structure and components present at construction. These have a lower load factor because they are known with more certainty. DW are future dead loads, such as future wearing surfaces. These have a higher load factor because they are known with less certainty. ODOT Short Course Created July 2007 Review of Loads: Slide # Live Loads : Lane Definitions # Design Lanes = INT(w/12.0 ft) w is the clear roadway width between barriers. Bridges 20 to 24 ft wide shall be designed for two traffic lanes, each ½ the roadway width. Examples: A 20 ft. wide bridge would be required to be designed as a two lane bridge with 10 ft. lanes. A 38 ft. wide bridge has 3 design lanes, each 12 ft. wide. A 16 ft. wide bridge has one design lane of 12 ft. Pg 3.16 ODOT Short Course Created July 2007 Review of Loads: Slide #

21 Review of Loads and Analysis Live Loads : Application of Design Vehicular Loads The governing force effect shall be taken as the larger of the following: The effect of the design tandem combined with the design lane load The effect of one design truck (HL-93) combined with the effect of the design lane load For negative moment between inflection points, 90% of the effect of two design trucks (HL-93 with 14 ft. axle spacing) spaced at a minimum of 50 ft. combined with 90% of the design lane load. Pg ODOT Short Course Created July 2007 Review of Loads: Slide # Live Loads : Design Truck 8 kip 32 kip 32 kip 14' - 0" 14' - 0" to 30' - 0" 6' - 0" Pg ODOT Short Course Created July 2007 Review of Loads: Slide #

22 Review of Loads and Analysis Live Loads : Design Tandem Pg 3.23 ODOT Short Course Created July 2007 Review of Loads: Slide # Live Loads : Design Lane Load kip / ft is applied SIMULTANEOUSLY with the design truck or design tandem over a width of 10 ft. within the design lane. NOTE: the impact factor, IM, is NOT applied to the lane load. It is only applied to the truck or tandem load. This is a big change from the Standard Specifications Pg 3.18 ODOT Short Course Created July 2007 Review of Loads: Slide #

23 Review of Loads and Analysis Live Loads AASHTO Standard Spec vs LRFD Spec: 8 kip 32 kip 32 kip 25 kip 25 kip Truck Tandem 640 plf Lane Load Old Std Spec Loading: HS20 Truck, or Alternate Military, or Lane Load New LRFD Loading: HL-93 Truck and Lane Load, or Tandem and Lane Load, or 90% of 2 Trucks and Lane Load ODOT Short Course Created July 2007 Review of Loads: Slide # Live Loads Live Loads for Maximum Positive Moment in Span 1 The impact factor is applied only to the truck, not the lane load Although a truck in the third span would contribute to maximum response, by specification only one truck is used. ODOT Short Course Created July 2007 Review of Loads: Slide #

24 Review of Loads and Analysis Live Loads Live Loads for Shear at Middle of Span 1 Ignore this axle for this case Impact is applied only to the truck. In this case, the front axle is ignored as it does not contribute to the maximum response. ODOT Short Course Created July 2007 Review of Loads: Slide # Live Loads Live Loads for Maximum Moment Over Pier 1 Use only 90% of the effects of the trucks and lane load Impact is applied to the trucks only. The distance between rear axles is fixed at 14 ft. The distance between trucks is a minimum of 50 ft. This applies for negative moment between points of contraflexure and reactions at interior piers ODOT Short Course Created July 2007 Review of Loads: Slide #

25 Review of Loads and Analysis Live Loads : Application of Design Vehicular Live Loads In cases where the transverse position of the load must be considered: The design lanes are positioned to produce the extreme force effect. The design lane load is considered to be 10 ft. wide. The load is positioned to maximize the extreme force effect. The truck/tandem is positioned such that the center of any wheel load is not closer than: 1.0 ft. from the face of the curb/railing for design of the deck overhang. 2.0 ft. from the edge of the design lane for design of all other components. Pg 3.25 ODOT Short Course Created July 2007 Review of Loads: Slide # Live Loads Both the Design Lanes and 10 Loaded Width in each lane shall be positioned to produce extreme force effects. 42' - 0" Out to Out of Deck 39' - 0" Roadway Width Traffic Lane #1 Traffic Lane #2 Traffic Lane #3 Center of truck wheels must be at least 2 from the edge of a design lane The lane load may be at the edge of a design lane. 3'-0" 3 12' - 0" 3'-0" Pg 3.25 ODOT Short Course Created July 2007 Review of Loads: Slide #

26 Review of Loads and Analysis Live Loads Multiple Presence Factor # of Loaded Lanes MP Factor > These factors are based on an assumed ADTT of 5,000 trucks If the ADTT is less than 100, 90% of the specified force may be used If the ADTT is less than 1,000, 95% of the specified force may be used Multiple Presence Factors are NOT used with the Distribution Factors Pg ODOT Short Course Created July 2007 Review of Loads: Slide # Live Loads 3.6.2: Dynamic Load Allowance Impact Factors, IM Deck Joints 75% ODOT EXCEPTION 125% of static design truck or 100% of static design tandem Fatigue 15% All other cases 33% The Dynamic Load Allowance is applied only to the truck load (including fatigue trucks), not to lane loads or pedestrian loads. Pg 3.29 ODOT Short Course Created July 2007 Review of Loads: Slide #

27 Review of Loads and Analysis Fatigue and Fracture Considerations : Fatigue Truck 8 kip 32 kip 32 kip 14' -0" 30' -0" (Fixed) 6' - 0" The fatigue truck is applied alone lane load is NOT used. The dynamic allowance for fatigue is IM = 15%. The load factor for fatigue loads is 0.75 for LL, IM and CE ONLY. No multiple presence factors are used in the Fatigue Loading, the distribution factors are based on one lane loaded, and load modifiers (η) are taken as Pg 3.27 ODOT Short Course Created July 2007 Review of Loads: Slide #41 AASHTO-LRFD Chapter 4: Structural Analysis and Evaluation James A Swanson AASHTO-LRFD Specification, 4 th Ed.,

28 Review of Loads and Analysis 4.4 Acceptable Methods of Structural Analysis Simplified Analysis Distribution Factor Refined Analysis Finite Element Modeling Pg ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis Dist Factors Lateral Load Distribution Beam and Slab Bridges Design live load bending moment or shear force is the product of a lane load on a beam model and the appropriate distribution factor. M U,LL = (DF)(M Beam Line ) The following Distribution Factors are applicable to Reinforced Concrete Decks on Steel Girders, CIP Concrete Girders, and Precast Concrete I or Bulb-Tee sections. Also applies to Precast Concrete Tee and Double Tee Sections when sufficient connectivity is present. ODOT Short Course Created July 2007 Review of Loads: Slide #

29 Review of Loads and Analysis Approximate Methods of Analysis Lateral Load Distribution Beam and Slab Bridges The simplified distribution factors may be used if: Width of the slab is constant Number of beams, N b > 4 Beams are parallel and of similar stiffness Roadway overhang d e < 3 ft* Central angle < 4 0 Cross section conforms to AASHTO Table * ODOT Exception: The roadway overhang d e < 3 ft. does not apply to interior DFs for sections (a) and (k). ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis Distribution Factors This is part of Table showing common bridge types. The letter below the diagram correlates to a set of distribution factors. Slab-on-Steel-Girder bridges qualify as type (a) cross sections. Pg ODOT Short Course Created July 2007 Review of Loads: Slide #

30 Review of Loads and Analysis Approximate Methods of Analysis Distribution Factors This is a part of Table b-1 showing distribution factors for moment. A similar table exists for shear distribution factors. The table give the DF formulae and the limits on the specific terms. If a bridge does NOT meet these requirements or the requirements on the previous slide, refined analysis must be used. Pg ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis Distribution Factors Pg 4.35 ODOT Short Course Created July 2007 Review of Loads: Slide #

31 Review of Loads and Analysis Approximate Methods of Analysis Moment Distribution - Interior Girders Interior Girders: One Lane Loaded: DF M,Int S = S K g 3 12 L Lts Two or More Lanes Loaded: DF M,Int S = S K g 3 12 L Lts This term may be taken as 1.00 for prelim design Pg Table b-1 ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis Beam-Slab Bridges Parameter Definitions & Limits of Applicability: S - Beam or girder spacing (ft.) L - Span length of beam or girder (ft.) K g - Longitudinal stiffness parameter (in 4 ) t s - Thickness of concrete slab (in) d e - Distance from exterior beam to interior edge of curb (ft.) (Positive if the beam is inside of the curb.) 3.5 S L k K g 7M 4.5 t s d e 5.5 Pgs 4.29 and 4.35 ODOT Short Course Created July 2007 Review of Loads: Slide #

32 Review of Loads and Analysis Approximate Methods of Analysis Beam-Slab Bridges Parameter Definitions & Limits of Applicability: K + 2 ( I ) g = n Ae g ( ) n - Modular ratio, E Beam / E Deck (See Section b, Pg 6.70) I - Moment of inertia of beam (in 4 ) A - Area of beam (in 2 ) e g - Distance between CG steel and CG deck (in) ODOT Exception: For interior beam DF, include monolithic wearing surface and haunch in e g and K g when this increases the DF. Pg 4.30 ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis d Moment Distribution - Exterior Beams Exterior Girders: One Lane Loaded: Lever Rule Two or More Lanes Loaded: DF ext = e DF int de e = Pg Table d-1 ODOT Short Course Created July 2007 Review of Loads: Slide #

33 Review of Loads and Analysis Approximate Methods of Analysis d Moment Distribution - Exterior Beams Lever Rule: Assume a hinge develops over each interior girder and solve for the reaction in the exterior girder as a fraction of the truck load. This example is for one lane loaded. Multiple Presence Factors apply 1.2 is the MPF MH 1.2Pe RS = 0 1.2Pe 1.2e R= DF = S S In the diagram, P is the axle load. Pg Table d-1 ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis e Moment Distribution - Skewed Bridges Correction for Skewed Bridges: The bending moment may be reduced in bridges with a skew of 30 θ 60 DF ' M = 1.5 ( 1 C ( Tanθ ) ) DFM K g S C1 = Lts L 0.5 When the skew angle is greater than 60, take θ = 60 Pg Table e-1 ODOT Short Course Created July 2007 Review of Loads: Slide #

34 Review of Loads and Analysis Approximate Methods of Analysis a Shear Distribution - Interior Beams Interior Girders: One Lane Loaded: S DF V,Int = Two or More Lanes Loaded: DF V,Int S S = Pg Table a-1 ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis b Shear Distribution - Exterior Beams Exterior Girders: One Lane Loaded: Lever Rule Two or More Lanes Loaded: DF Ext = e DF Int de e = Pg Table b-1 ODOT Short Course Created July 2007 Review of Loads: Slide #

35 Review of Loads and Analysis Approximate Methods of Analysis c Shear Distribution - Skewed Bridges Correction for Skewed Bridges: The shear forces in beams of skewed bridges shall be adjusted with a skew of 0 θ ' 12Lt s DFV = Tanθ DFV K g Pg Table c-1 ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis d Exterior Beams Minimum Exterior DF: (Rigid Body Rotation of Bridge Section) DF Ext, Min N = N L b + X Ext N b N L x 2 e (C d-1) N L - Number of loaded lanes under consideration N b - Number of beams or girders e - Eccentricity of design truck or load from CG of pattern of girders (ft.) x - Distance from CG of pattern of girders to each girder (ft.) X Ext - Distance from CG of pattern of girders to exterior girder (ft.) Pg 4.37 ODOT Short Course Created July 2007 Review of Loads: Slide #

36 Review of Loads and Analysis Approximate Methods of Analysis d Exterior Beams Minimum Exterior DF: (Rigid Body Rotation of Bridge Section) DF Ext, Min N = N L b + X Ext N b N L x 2 e (C d-1) N L - Number of loaded lanes under consideration N b - Number of beams or girders e - Eccentricity of design truck or load from CG of pattern of girders (ft.) x - Distance from CG of pattern of girders to each girder (ft.) X Ext - Distance from CG of pattern of girders to exterior girder (ft.) Pg 4.37 ODOT Short Course Created July 2007 Review of Loads: Slide # Approximate Methods of Analysis Dead Load Distribution Where bridges meet the conditions specified herein, permanent loads of and on the deck may be distributed uniformly among the beams and/or stringers. For this type of bridge, the conditions are: Width of deck is constant Unless otherwise specified, the number of beams is not less than four Beams are parallel and have approximately the same stiffness Unless otherwise specified, the roadway part of the overhang, d e, does not exceed 3.0 ft Curvature in plan is less then the limit specified in Article Cross-section is consistent with one of the cross-sections shown Table Pg 4.29 ODOT Short Course Created July 2007 Review of Loads: Slide #

37 Review of Loads and Analysis Case Study: 2-Span Steel-Girder Bridge ODOT Short Course Created July 2007 Review of Loads: Slide #61 Case Study: Single-Span Steel-Girder Bridge Cross Frames 22' - 0" cc G 1 G 2 G 3 G 4 G 5 G 6 166' - 4" cc Bearings 172' - 4" Total Girder Length ODOT Short Course Created July 2007 Review of Loads: Slide #

38 Review of Loads and Analysis Case Study: Single-Span Steel-Girder Bridge ODOT Short Course Created July 2007 Review of Loads: Slide #63 Example: Single-Span Pony Truss ODOT Short Course Created July 2007 Review of Loads: Slide #

39 Materials and Limit States AASHTO-LRFD Chapter 6: Material and General Information James A Swanson AASHTO-LRFD Specification, 4 th Ed., 2007 Chapter 6 Organization 6.1 Scope 6.2 Definitions 6.3 Notation 6.4 Materials 6.5 Limit States 6.6 Fatigue and Fracture Considerations 6.7 General Dimension and Detail Requirements 6.8 Tension Members 6.9 Compression Members 6.10 I-Section Flexural Members 6.11 Box-Section Flexural Members 6.12 Miscellaneous Flexural Members 6.13 Connections and Splices 6.14 Provisions for Structure Type 6.15 Piles App A Plastic Moment of Composite Sections in Negative Moment and Noncomposite Sections App B Moment Redistribution in Continuous Bridges App C Basic Steps for Steel Bridge Superstructures App D Fundamental Calculations for Flexural Members ODOT Short Course Created July 2007 Materials and Limit States: Slide #

40 Materials and Limit States Scope This chapter covers the design of steel components, splices and connections for straight or horizontally curved beam and girder structures, frames, trusses and arches, cable-stayed and suspension systems, and metal deck systems, as applicable. Although horizontally curved girder structures are now included in the AASHTO-LRFD Specification, they will not be specifically addressed in this course. Pg 6.1 ODOT Short Course Created July 2007 Materials and Limit States: Slide # Materials Structural Steels Pins, Roller, and Rockers Bolts, Nuts, and Washers Stud Shear Connectors Weld Metal Cast Metal Stainless Steel Cables ODOT Short Course Created July 2007 Materials and Limit States: Slide #

41 Materials and Limit States Materials 6.4.1: Structural Steels Table Minimum Mechanical Properties of Structural Steel AASHTO M270 M270 M270 M270 Designation Grade 36 Grade 50 Grade 50S Grade 50W Equivalent ASTM A709 A709 A709 A709 Designation Grade 36 Grade 50 Grade 50S Grade 50W Thickness of Up to 4.0 Up to 4.0 Not Up to 4.0 Plate (in) incl. incl. Applicable incl. Minimum Tensile Strength, F u (ksi) Minimum Yield Strength, F y (ksi) AASHTO M270 M270 M270 Designation Gr HPS 50W Gr HPS 70W Grades 100/100W Equivalent ASTM A709 A709 A709 Designation Gr HPS 50W Gr HPS 70W Grades 100/100W Thickness of Up to 4.0 Up to 4.0 Up to to 4.0 Plate (in) incl. incl. incl. incl. Minimum Tensile Strength, F u (ksi) Minimum Yield Strength, F y (ksi) Pgs ODOT Short Course Created July 2007 Materials and Limit States: Slide # Materials BDM : Material Requirements Types of steel to be selected in the design of bridges is as follows: ASTM A709 grade 50W shall be specified for an un-coated weathering steel bridge. ASTM A709 grade 50 shall be specified for a coated steel bridge. ASTM A709 grade 36 is not recommended and is being discontinued by the steel mills. High Performance Steel (HPS), A709 grade 70W, un-coated weathering steel is most economical when used in the flanges of hybrid girders. Consult the Office of Structural Engineering for recommendations prior to specifying its use. A plan note is provided in the appendix. BDM Pg 3-19 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

42 Materials and Limit States Materials 6.4.3: Bolts, Nuts, and Washers Bolts shall conform to one of the following: ASTM A307 F u = 60 ksi AASHTO M164 (ASTM A325) F u = 120 ksi / 105 ksi AASHTO M253 (ASTM A490) F u = 150 ksi Prohibited by ODOT Nuts shall conform to: AASHTO M291 (ASTM A563) for use with M164 and M253 bolts Washers shall conform to: AASHTO M293 (ASTM F436) Pgs ODOT Short Course Created July 2007 Materials and Limit States: Slide # Materials 6.4.4: Stud Shear Connectors Stud connectors shall conform to one of the following: AASHTO M169 (ASTM A108) F u = 50 ksi or 60 ksi AISC Now Lists F u = 65 ksi for ASTM A108 Shear Studs Pg 6.25 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

43 Materials and Limit States Materials 6.4.5: Weld Metal Refers to AWS D1.5 - Bridge Welding Code Pg 6.25 ODOT Short Course Created July 2007 Materials and Limit States: Slide # Limit States General Service Limit State Fatigue and Fracture Limit State Strength Limit State Extreme Event Limit State 6.5.1: General Structural behavior of steel components shall be investigated for each stage that may be critical during Construction, Handling, Transportation, and Erection as well as during the Service life of the structure. Structural components shall be proportioned to satisfy requirements at Service, Strength, Extreme Event, and Fatigue and Fracture Limit States. Pg 6.27 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

44 Materials and Limit States Limit States 6.5.2: Service Limit State Covers Elastic Deformations For flexural members ( 6.10 and 6.11), provides limits to prevent permanent deformations due to localized yielding. Pg 6.27 ODOT Short Course Created July 2007 Materials and Limit States: Slide # Limit States 6.5.3: Fatigue and Fracture Limit State Components and details shall be investigated for Fatigue as specified in 6.6 for the combinations and loads specified in and , respectively. Flexural members shall be investigated as specified in 6.10 and Special fatigue requirements for thin webs and shear connectors. Bolts subject to tensile fatigue shall be investigates as specified in Fracture toughness requirements shall be in conformance with Pg 6.27 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

45 Materials and Limit States Limit States 6.5.4: Strength Limit State Strength and Stability shall be considered using the applicable load combinations in Table The Design Resistance, R r, shall be taken as φr n. Resistance Factors Gross-Section Yielding φ y = 0.95 Net-Section Fracture φ u = 0.80 Axial Compression φ c = 0.90 Flexure φ f = 1.00 Shear φ v = 1.00 A325 & A490 Bolt Tension, Shear, and Bearing φ t = φ s = φ bb = 0.80 Pgs ODOT Short Course Created July 2007 Materials and Limit States: Slide # Limit States 6.5.5: Extreme Event Limit State All applicable extreme event load combinations in Table shall be investigated. All resistance factors for the extreme event limit state, except for bolts, shall be taken as 1.00 Bolted joints not protected by capacity design or structural fuses may be assumed to behave as bearing-type connections at the extreme event limit states. Pg 6.29 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

46 Materials and Limit States General Dimension and Detail Requirements Effective Length of Spans Dead Load Camber Minimum Thickness of Steel Diaphragms and Cross Frames Lateral Bracing Pins ODOT Short Course Created July 2007 Materials and Limit States: Slide # General Dimension and Detail Requirements 6.7.1: Effective Length of Spans Span lengths shall be taken as the distance between centers of bearings or other points of support. Effective span lengths may be different for effective width and DF calcs. Pg 6.49 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

47 Materials and Limit States General Dimension and Detail Requirements 6.7.2: Dead Load Camber Steel structures should be cambered during fabrication to compensate for dead load deflection and vertical alignment. Deflection due to steel weight and concrete weight shall be reported separately. Deflections due to future wearing surfaces or other loads not applied at the time of construction shall be reported separately. Vertical camber shall be specified to account for the computed dead load deflection. If staged construction is specified, the sequence of load application should be recognized in determining the camber and stresses. Pg 6.49 ODOT Short Course Created July 2007 Materials and Limit States: Slide # General Dimension and Detail Requirements 6.7.3: Minimum Thickness of Steel Structural steel, including bracing, cross-frames, and all types of gusset plates, except for webs of rolled shapes, closed ribs in orthotropic decks, fillers, and in railings, shall be not less than 5 / 16 in thickness. The web thickness of rolled beams or channels and of closed ribs in orthotropic decks shall not be less than 1 / 4 in thickness. Pg 6.51 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

48 Materials and Limit States General Dimension and Detail Requirements 6.7.4: Diaphragms and Cross-Frames Diaphragms or cross frames may be placed at the ends of the structure, across interior supports, and intermittently along the span to: transfer lateral wind loads from the bottom flange of a girder to the deck and from the deck to the bearings, provide stability to the bottom flange for all loads when it is in compression, provide stability to the top flange in compression prior to curing of the deck, aid in distributing lateral flange bending effects, and aid in transverse distribution of vertical loads applied to the structure. Pg 6.52 ODOT Short Course Created July 2007 Materials and Limit States: Slide # General Dimension and Detail Requirements 6.7.4: Diaphragms and Cross-Frames Diaphragms or cross-frames for rolled beams and plate girders should be as deep as practicable As a minimum, they should be at least: 1/2 of the beam depth for rolled beams 3/4 of the girder depth for plate girders Pg 6.53 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

49 Materials and Limit States General Dimension and Detail Requirements BDM : Intermediate Cross-Frames Skewed crossframes at intermediate support points should be avoided. Crossframes shall be oriented perpendicular to the main steel members regardless of the structure s skew angle. Cross frames shall be perpendicular to stringers and be in line across the total width of the structure. Cross frame spacings between points of dead load contraflexure in the positive moment regions shall not exceed 25 ft. Cross frame spacings between points of dead load contraflexure in the negative moment regions shall not exceed 15 ft. BDM Pg 3-29 ODOT Short Course Created July 2007 Materials and Limit States: Slide #

50

51 Fatigue and Fracture AASHTO-LRFD Chapter 6: Fatigue and Fracture James A Swanson AASHTO-LRFD Specification, 4 th Ed., Fatigue and Fracture Considerations Fatigue Fracture Pg 6.29 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

52 Fatigue and Fracture Fatigue and Fracture Considerations : Load Induced Fatigue Each fatigue detail shall satisfy, γ ( Δf ) ( ΔF) n ( ) where, γ - load factor specified in Table for fatigue (γ fatigue = 0.75) (Δf ) - live load stress range due to the passage of the fatigue load specified in η and φ are taken as 1.00 for the fatigue limit state The live-load stress due to the passage of the fatigue load is approximately one-half that of the heaviest truck expected in 75 years. Pgs ,6.42 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Load Induced Fatigue The force effect considered for the fatigue design of a steel bridge detail shall be the live load stress range. For flexural members with shear connectors provided throughout their entire length, and with concrete deck reinforcement satisfying the provisions of Article (Minimum Negative Flexure Deck Reinforcement), live load stresses and stress ranges for fatigue design may be computed using the short-term composite section assuming the concrete deck to be effective for both positive and negative flexure. Residual stresses shall not be considered in investigating fatigue. Pg ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

53 Fatigue and Fracture Fatigue and Fracture Considerations : Load Induced Fatigue These provisions shall be applied only to details subjected to a net applied tensile stress. In regions where the unfactored permanent loads produce compression, fatigue shall be considered only if the compressive stress is less than twice the maximum tensile live load stress resulting from the fatigue load combination. i.e., where: f 2 f comp, DL fat load, tension Pg 6.30 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Load Induced Fatigue This is based on the typical S-N diagram: Stress Range (ksi) 10.0 A B B' C D E E' ,000 1,000,000 10,000,000 Stress Cycles Pgs 6.42 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

54 Fatigue and Fracture Fatigue and Fracture Considerations : Load Induced Fatigue A ( ) 3 ( ΔF Δ F = ) n N 2 1 TH ( ) A - Fatigue Detail Category Constant - Table N = (365) (75) n (ADTT) SL (75 Year Design Life) ( ) n - # of stress ranges per truck passage - Table (ADTT) SL - Single-Lane ADTT from (ΔF) TH - Constant amplitude fatigue threshold - Table ODOT is planning to simply design for infinite life on Interstate Structures Pg 6.42 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Load Induced Fatigue Tables &3 Fatigue Constant and Threshold Stress Range Detail A x 10 8 (Δ F ) TH Category (ksi 3 ) (ksi) A B B' C C' D E E' M164 Bolts M253 Bolts More about fatigue categories in a minute Pg 6.44 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

55 Fatigue and Fracture Fatigue and Fracture Considerations : Load Induced Fatigue Table C Year (ADTT) SL Equivalent to Infinite Life Detail Category A B B' C C' D E E' 75-Year (ADTT) SL Equivelant to Infinite Life (Trucks / Day) This Table shows the values of (ADTT) SL above which the Infinite Life check governs (Assuming one cycle per truck passage). Pg 6.43 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Load Induced Fatigue Table Cycles per Truck Passage > 40 ft. 40 ft. Simple Span Girders Continuous Girders - Near Interior Supports Elsewhere Cantilever Girders Trusses Span Length Spacing > 20 ft. 20 ft. Transverse Members Pg 6.44 Fatigue details located within L/10 of a support are considered to be near the support. ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

56 Fatigue and Fracture Fatigue and Fracture Considerations : Load Induced Fatigue In the absence of better information, (ADTT) SL = p ADTT ( ) where, p - The fraction of truck traffic in a single lane Table Single Lane Truck Fraction # Lanes Available to Trucks p or more 0.80 Must consider the number of lanes available to trucks in each direction! Pgs ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Load Induced Fatigue In the absence of better information, where, ADTT = (TF) ADT TF - The fraction trucks in the average daily traffic Table C ADT Truck Fraction Class of Highway TF Rural Interstate 0.20 Urban Interstate 0.15 Other Rural 0.15 Other Urban 0.10 ODOT is suggesting that the ADTT be taken as 4 x 20-year-avg ADT Pgs ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

57 Fatigue and Fracture Fatigue and Fracture Considerations : Fatigue Detail Categories Pgs , 6.41 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Fatigue Detail Categories Pgs , 6.41 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

58 Fatigue and Fracture Fatigue and Fracture Considerations : Fatigue Detail Categories Pgs , 6.41 ODOT Short Course Version Created 1 - Do July Not 2007 Duplicate Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Fatigue Detail Categories Pgs , 6.41 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

59 Fatigue and Fracture Fatigue and Fracture Considerations : Fatigue Detail Categories Pgs , 6.41 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Fatigue Detail Categories Pgs , 6.41 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

60 Fatigue and Fracture Fatigue and Fracture Considerations : Fatigue Detail Categories Pgs , 6.41 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations : Fatigue Detail Categories Pgs , 6.41 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

61 Fatigue and Fracture Fatigue and Fracture Considerations : Fatigue Detail Categories Transversely loaded partial-pen groove welds shall not be used except in some metal deck details. Gusset plates attached to girder flanges with only transverse fillet welds shall not be used. Pg 6.42 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations 6.6.2: Fracture The appropriate temperature zone shall be determined from Table Fracture toughness requirements shall be in conformance with Table Table Temperature Zone Designations Min Service Temperature Temperature Zone 0 o F and above 1-1 o F to -30 o F 2-31 o F to -60 o F 3 ODOT Designs Pgs ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

62 Fatigue and Fracture Fatigue and Fracture Considerations 6.6.2: Fracture Except as specified herein, all primary longitudinal superstructure components and connections sustaining tensile force effects due to Strength Load Combination I, and transverse floorbeams subject to such effects, shall require mandatory Charpy V-notch fracture toughness Other primary components and connections sustaining tensile force effects due to the Strength Load Combination I may require mandatory Charpy V-notch fracture toughness at the discretion of the Owner. All components and connections requiring Charpy V-notch fracture toughness shall be so designated on the contract plans. Pgs ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations 6.6.2: Fracture Unless otherwise indicated on the contract plans, Charpy V-notch fracture toughness requirements shall not be considered mandatory for the following items: Splice plates and filler plates in bolted splices Intermediate transverse web stiffeners not serving as connection plates Bearings, sole plates, and masonry plates Expansion dams Drainage material Pgs ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

63 Fatigue and Fracture Fatigue and Fracture Considerations 6.6.2: Fracture Critical Members Fracture Critical Member (FCM) - Component in tension whose failure is expected to result in the collapse of the bridge or the inability of the bridge to perform its function. Unless a rigorous analysis with assumed hypothetical cracked components confirms the strength and stability of the hypothetically damaged structure, the location of all FCMs shall be clearly delineated on the contract plans. FCMs are subject to more stringent toughness requirements than non-fcms Pgs ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations BDM : Fracture Critical Members The designer should make all efforts to not develop a structure design that requires fracture critical members. As specified in Section 301.2, structures with fracture critical details require a concurrent detail design review to be performed by the Office of Structural Engineering. If a girder is non-redundant, include the entire girder in the pay quantity for Item Structural Steel Members, Level 6. The designer shall designate the tension and compression zones in the fracture critical members. This basically means that you have to have a top-of-the-line fabricator BDM Pg 3-32 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #

64 Fatigue and Fracture Fatigue and Fracture Considerations 6.6.2: Fracture Table Fracture Toughness Requirements Welded Members Mech Fastened Fracture Critical Members Min Test Temperature Temperature Temperature Grade Thickness Energy Zone 1 Zone 2 Zone 3 (in) (ft-lbs) o F) o F) o F) 36 t /50S/50W t < t HPS 50W t HPS 70W t /100W t < t Not Permitted 36 t /50S/50W t HPS 50W t HPS 70W t /100W t Pg 6.48 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide # Fatigue and Fracture Considerations 6.6.2: Fracture Table Fracture Toughness Requirements Welded Members Mech Fastened Nonfracture Critical Members Temperature Temperature Temperature Grade Thickness Zone 1 Zone 2 Zone 3 (in) o F) o F) o F) 36 t /50S/50W t < t HPS 50W t HPS 70W t /100W t < t t /50S/50W t HPS 50W t HPS 70W t /100W t Pg 6.48 ODOT Short Course Created July 2007 Fatigue and Fracture: Slide #