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LRFD Bridge Design AASHTO LRFD Bridge Design Specifications Loading and General Information Created Jul y 2007 This material is copyrighted by The University of Cincinnati, Dr. James A Swanson, and Dr. Richard A Miller 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, Dr. James A Swanson, and Dr. Richard A Miller. July 31, 2007 LRFD Bridge Design AASHTO LRFD Bridge Design Specification Loads and General Information Background and Theoretical Basis of LRFD 1 AASHTO Chapter 1 13 AASHTO Chapter 2 17 AASHTO Chapter 3 23 AASHTO Chapter 4 59 Loads Case Study 71 James A Swanson Associate Professor University of Cincinnati Dept of Civil & Env. Engineering 765 Baldwin Hall Cincinnati, OH 45221-0071 Ph: (513) 556-3774 Fx: (513) 556-2599 James.Swanson@uc.edu AASHTO LRFD Bridge Design Specifications James A Swanson Richard A Miller  AASHTO-LRFD Specification, 4 th Ed., 2007 Created July 2007 Loads & Analysis: Slide #2 AASHTO-LRFD 2007 ODOT Short Course References  “Bridge Engineering Handbook,” Wai-Faf Chen and Lian Duan, 1999, CRC Press (0- 8493-7434-0)  “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 http://www.aisc.org/  “Design of Highway Bridges,” Richard Barker and Jay Puckett, 1977, Wiley & Sons (0-471-30434-4) 1 Created July 2007 Loads & Analysis: Slide #3 AASHTO-LRFD 2007 ODOT Short Course References  AASHTO Web Site: http://bridges.transportation.org/  “Load and Resistance Factor Design for Highway Bridges,” Participant Notebook, Available from the AASHTO web site. Created July 2007 Loads & Analysis: Slide #4 AASHTO-LRFD 2007 ODOT Short Course References  AISC / National Steel Bridge Alliance Web Site: http://www.steelbridges. org/  “Steel Bridge Design Handbook” 2 Created July 2007 Loads & Analysis: Slide #5 AASHTO-LRFD 2007 ODOT Short Course 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” Created July 2007 Loads & Analysis: Slide #6 AASHTO-LRFD 2007 ODOT Short Course Philosophies of Design  ASD - Allowable Stress Design  LFD - Load Factor Design  LRFD - Load and Resistance Factor Design 3 Created July 2007 Loads & Analysis: Slide #7 AASHTO-LRFD 2007 ODOT Short Course  For Safety:  f - computed stress  F A - Allowable Stress  In terms of bending moment… y A F fF F S ≤= 1.82 y F M S ≤ ∑ Philosophies of Design ASD: Allowable Stress Design ASD does not recognize different variabilities of different load types. Chen & Duan Created July 2007 Loads & Analysis: Slide #8 AASHTO-LRFD 2007 ODOT Short Course Philosophies of Design LFD: Load Factor Design  For Safety:  Q - Load Effect  R - Component Resistance  γ - Load Factor  In terms of bending moment…  φ - Strength Reduction Factor n QR γ ≤ ∑ () 1.30 2.17 DLIn M MM φ + +≤ In LFD, load and resistance are not considered simultaneously. Chen & Duan 4 [...]... 2007 Philosophies of Design - LRFD Fundamentals Reliability Index: ASD / LFD Bridge Designs LRFD Bridge Designs (Expected) 4 Reliability Index 5 4 Reliability Index 5 3 2 1 0 3 2 1 0 27 54 81 Span Length (ft) 108 180 Chen & Duan ODOT Short Course 0 0 27 54 81 Span Length (ft) 108 180 AASHTO -LRFD 2007 Created July 2007 9 Loads & Analysis: Slide #18 Philosophies of Design - LRFD Fundamentals Resistance... Philosophies of Design - LRFD Fundamentals Reliability Index: β P(Failure) 1.0 2.0 3.0 3.5 15.9% 2.28% 0.135% 0.0233% AASHTO -LRFD 2007 ODOT Short Course Created July 2007 8 Loads & Analysis: Slide #16 Philosophies of Design - LRFD Fundamentals Reliability Index: AISC: β D+(L or S) D+L+W D+L+E Members 3.0 2.5 1.75 Connections 4.5 4.5 4.5 AASHTO: β= 3.5 Super/Sub Structures β= 2.5 Foundations AASHTO -LRFD 2007... Loads & Analysis: Slide #13 Philosophies of Design - LRFD Fundamentals Number of Occurrences Variability of Loads and Resistances: AASHTO -LRFD 2007 ODOT Short Course Created July 2007 7 Loads & Analysis: Slide #14 Philosophies of Design - LRFD Fundamentals Variability of Loads and Resistances: σ ( R −Q ) = σ R 2 + σ Q 2 β= Mean ( R −Q ) σ ( R −Q ) AASHTO -LRFD 2007 ODOT Short Course Loads & Analysis:... following apply Design ADT ≥ 60,000 Detour length ≥ 50 miles Any span length ≥ 500’ Use ηI = 0.95 if both of the following apply Design ADT ≤ 400 Detour length ≤ 10 miles Detour length applies to the shortest, emergency detour route AASHTO -LRFD 2007 ODOT Short Course Created July 2007 16 Loads & Analysis: Slide #28 AASHTO -LRFD Chapter 2: General Design and Location Features AASHTO -LRFD Specification,... traffic Reinforced concrete Slabs Prestressed Concrete Steel ODOT states that “designers shall apply the span-to-depth ratios shown.” Pg 2.10-14 ODOT Short Course AASHTO -LRFD 2007 Created July 2007 21 Loads & Analysis: Slide #37 22 AASHTO -LRFD Bridge Design Specification Section 3: Loads and Load Factors AASHTO -LRFD Specification, 4th Ed., 2007 § 3.4 - Loads and Load Factors §3.4.1: Load Factors... Value of R β - Reliability Index COV(Rm) - Coeff of Variation of R AASHTO -LRFD 2007 ODOT Short Course Created July 2007 Loads & Analysis: Slide #19 Created July 2007 Loads & Analysis: Slide #20 AASHTO -LRFD Specification AASHTO -LRFD 2007 ODOT Short Course 10 AASHTO -LRFD Specification Contents 1 2 3 4 5 6 7 Introduction General Design and Location Features Loads and Load Factors Structural Analysis... Index AASHTO -LRFD 2007 ODOT Short Course Created July 2007 11 Loads & Analysis: Slide #21 12 AASHTO -LRFD Chapter 1: Introduction AASHTO -LRFD Specification, 4th, 2007 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... members Use ηR = 1.00 for “redundant” members Bridges with 3 or fewer girders should be considered “non-redundant.” Bridges with 4 girders with a spacing of 12’ or more should be considered “nonredundant.” Bridges with 4 girders with a spacing of less than 12’ should be considered “redundant.” Bridge with 5 or more girders should be considered “redundant.” AASHTO -LRFD 2007 ODOT Short Course Created July... Deviation = 38lbs AASHTO -LRFD 2007 ODOT Short Course Created July 2007 5 Loads & Analysis: Slide #10 Philosophies of Design - LRFD Fundamentals Variability of Loads and Resistances: AASHTO -LRFD 2007 ODOT Short Course Loads & Analysis: Slide #11 Created July 2007 Philosophies of Design - LRFD Fundamentals Variability of Loads and Resistances: Now suppose that we measure the strength of 100 ropes… Weight...Philosophies of Design LRFD: Load & Resistance Factor Design For Safety: ∑γ Q ≤ φ R 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 AASHTO -LRFD 2007 ODOT Short Course Loads & Analysis: . Miller. July 31, 2007 LRFD Bridge Design AASHTO LRFD Bridge Design Specification Loads and General Information Background and Theoretical Basis of LRFD 1 AASHTO Chapter 1. LRFD Bridge Design AASHTO LRFD Bridge Design Specifications Loading and General Information Created Jul y . Highway Bridges” Created July 2007 Loads & Analysis: Slide #6 AASHTO -LRFD 2007 ODOT Short Course Philosophies of Design  ASD - Allowable Stress Design  LFD - Load Factor Design  LRFD -