Seismic Design of Highway Bridges

Instructors

Dr. Roy A. Imbsen, P.E., D. Eng.
Dr. Imbsen is  the President of Imbsen and Associates, Inc., (IAI), Sacramento, California, has over 45 years of bridge engineering experience, the first 15 of which were spent with Caltrans, Division of Structures. A world-recognized expert in the field of seismic bridge engineering and bridge design,

Dr. Imbsen helped develop and conduct the one-week FHWA course on seismic design of bridges. Dr. Imbsen is a member of the Task Force for Highway Structure Seismic Design Damage Investigations of the Earthquake Engineering Research Institute, Committee on Natural Disasters Investigations of the National Research Council, Committee on Concrete Bridges of the Transportation Research Board, and of ASCE.

Dr.Fadel Alameddine, Ph.D., P.E.
Dr. Alameddine is the Senior Bridge Engineer with the Office of Earthquake Engineering in the California Department of Transportation. Dr.Alameddine has more than 20 years of experience in the field of Earthquake Engineering, bridge design, seismic analysis and retrofitting. Following the 1989 Loma Prieta earthquake, Dr.Alameddine became involved in updating the seismic design criteria and practice for Caltrans. He is a member of the Implementation Advisory

Course Description

“Seismic design and retrofitting of bridges is progressing from a force-based approach to a new performance-based approach. This change is reflected in the recently published NCHRP 20-7(193) report “Recommended LRFD Guidelines for Seismic Design of Highway Bridges”being considered for adoption by AASHTO to replace the current Division 1-A.
The seismic hazard has been changed from 10% to 5% probability of exceedence in 50 years increasing the return period from 500 to 1000 years. This increased hazard together with the new Two Point Method for describing the design spectra are improvements in the definition of the seismic hazard through-out the United States. These improvements are particularly important for the eastern portion of the conterminous United States in establishing a more realistic representation of the larger earthquakes that could occur in this region. Additionally, site effects on the ground motions have also been expanded from four to six in the new guidelines to include the current technology in soil response. Site coefficients are now given for the short-period range and the long-period range.

Seismic Design Categories (SDC) is partitioned into four groups to define the design and detailing requirements for the range of seismic hazards throughout the United States.
 The new guidelines include a catalog of earthquake resisting systems and components from which to choose from to obtain an optimum overall seismic design for the type of bridge the design has selected for design. Three types of overall seismic design strategy are defined which include:

1) Ductile substructure with an essentially superstructure,
2) Essentially elastic substructure with a ductile superstructure, and
3) Elastic substructure and superstructure with a fusing mechanism at 
     the interface between the substructure and superstructure.

A new FHWA manual entitled “Seismic Retrofitting Manual for Highway Structures:
Part 1-Bridges”2006 will be referenced in the lectures. This manual is a synthesis of the previous manuals and the recent results from research and lesions learned from postearthquake investigations.
Seismology, structural dynamics, and some computer applications are reviewed, but the main thrust of the seminar is AASHTO’s seismic specification plus the upcoming changes to be made in the LRFD (Load and Resistance Factor Design) Specifications. Recently funded efforts by FHWA and NCHRP to assist in the implementation of the LRFD seismic design technology has now been completed and will be presented in this seminar. The objectives of these efforts were to recommend a national seismic hazard,expand the limited and no analysis zones,and streamline the Guidelines into a consensus user friendly document. This seminar is tailored to bridge configurations applicable to the entire country including cast-in-place, steel and precast bridges. Additional topics include seismic loading, seismic response analysis, plus design and retrofit concepts.

Seminar Benefits

Seminar attendees receive comprehensive course notes and reference material. After attending, participants will be able to:

• Apply AASHTO’s seismic specification to design or retrofit a highway bridge
• Understand basic structural dynamics and effect on bridge design
• Identify types of bridge failures
• Understand practical retrofitting concepts
• Tackle all seismic bridge issues
• Find out about the latest research and information from post-earthquake field investigations
• Learn from the developers of the current seismic design criteria
• Get the latest information on seismic isolation for bridges
• Become familiar with AASHTO seismic design criteria
• Learn precise and simplified seismic modeling
• Review the basics of dynamic analysis
• Conduct a pushover analysis or rocking analysis
• Develop understanding of Seismic Performance Based Criteria

Who Should Attend

Structural design engineers who are responsible for designing highway bridges. While this seminar should be of interest to bridge engineers at all levels, it is primarily for experienced designers seeking to learn more, or desiring a refresher on AASHTO's seismic design specification and upcoming changes to be made in the LRFD specifications.

Summary Outline

Day One

• Introduction to Seismic Design and Retrofitting of Bridges
  • Past earthquake damage to bridges
  • Seismic design and philosophy
  • Seismic design and retrofitting strategies
• Fundamental Concepts in Structural Dynamics
  • Dynamic loading and D’Alembert’s Principle
  • Single degree-of-freedom systems
• Introduction to Seismic Design
  • AASHTO Specifications
  • Example problems and solutions
  • Seismic Base Isolation
• Seismic Loading
  • Seismic design loading
• Design Concepts
  • Abutments, columns, and footings
  • Reinforced concrete columns and piers
  • Bearings, restrainers, shear keys
  • Example problems and solutions

Day Two

• Seismic Response Analysis
  • Practical modeling guidelines
  • Equivalent static force methods
  • Single mode spectral
  • Multi-degree-of-freedom systems
  • Example problems and solutions
  • Pushover and rocking analysis
• LRFD Guidelines for Seismic Design
  • Interactive USGS maps
  • Seismic design categories SDC A B C D
  • Earthquake resistant systems
  • Implicit and explicit displacement capacity
  • Superstructure and substructure modeling
  • Concrete and steel component design
• Retrofitting
  • Retrofitting concepts
  • Example problems and solutions