Since the first edition of the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications in 1994, highway bridge design in the United States has shifted to load and resistance factor design (LRFD). Prior to that, for more than half a century, highway bridge design practice had used load factor design (LRFD) and service load design (SLD) in accordance with AASHTO’s Standard Specifications for Highway Bridges.
Additionally, in 2003, the first edition of the AASHTO Manual for Condition Evaluation and Load and Resistance Factor Rating (LRFR) of Highway Bridges was published.
In 2007, AASHTO mandated the LRFD specification in the United States after more than a decade of preparation, including pilot use and software development. Due to Federal Highway Administration (FHWA) requirements and consistency, many states have begun implementing LRFR practices for bridges designed according to the LRFD.
About the Book
This book is an introduction to the LRFD and LRFR method for highway bridges and can be used as a textbook for the first undergraduate or graduate course on highway bridge design and evaluation.
At the time this book was prepared, the 6th edition of the AASHTO LRFD Bridge Design Specifications, published in 2012, was the most recent design standard.
Therefore, this document refers to this edition of the specifications as the AASHTO Specifications, AASHTO Design Specifications, or AASHTO LRFD Specifications, depending on context. For bridge evaluation and load rating, the 2011 edition of the AASHTO Bridge Evaluation Manual, Second Edition, was the most current at the time this document was prepared and is referred to as the AASHTO Manual or AASHTO Evaluation Specifications, depending on context. This set of specifications is sometimes collectively referred to as the AASHTO Specifications, along with the LRFD Specifications.
There are seven chapters in this book:
Chapter 1 is an introduction to bridge engineering, including design and evaluation. Chapter 2 covers both the general and specific requirements of the AASHTO specifications for highway bridge design. It also presents the concept of structural reliability, which was used to calibrate both AASHTO specifications discussed here.
Chapter 3 presents more detailed specific requirements of the specifications for highway bridge component loads, load effects, and combinations thereof.
Chapter 4 of the book deals with the superstructure portion of bridge design, Chapter 5withbearings, and Chapter 6withsubstructure. Chapter 7 shifts the focus from design to evaluation (load evaluation).
Chapter7 shifts the focus from design to evaluation (load evaluation).
This book is designed as a textbook for the first undergraduate and/or graduate course on the design and evaluation of highway bridges according to current AASHTO specifications; it is recommended that a 3credit hour undergraduate course cover Chapters 1, 3, and 4 (or with Chapter 5). Chapter 5 (or Chapter 6) may be added to a 4-credit hour undergraduate course.
For graduate courses, Chapters 1 through 6 may be covered for 3 credit hours, and Chapter 7may be added for 4 credit hours.
Structural analysis is a prerequisite for use of this textbook, and steel frame design and concrete design should be prerequisites but may be core requirements. Up on completion of this course, the student will be able to perform the duties of an entry-level engineer in the design and evaluation of bridges according to current AASHTO specifications.
Upon completion of this course, the learner will be able to perform the duties of an entry-level engineer in bridge design and evaluation according to current AASHTO specifications.