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Minutes of Subcommittee Meeting
Subcommittee AFF50(1) – Geoseismic Concerns
(Parent Committee AFF50 – Seismic Design of Bridges)
2005 Annual Meeting of TRB
Tuesday, January 24, 2006 1:00 – 3:15 pm
Congressional, Marriott Hotel
Washington, D.C.
I.
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VI.
Attendance: List attached
Agenda
a. Opening remarks
b. Self introductions
c. AFF50 Sessions
d. TRB Announcements
e. FHWA Initiatives on geotechnical issues
f. Update on NCHRP 12-70
g. Discussion of Committee scope, research needs, and future sessions
General Items of Record
a. Next year’s (2007) TRB meeting is scheduled for January 21 – 25
b. 2008 TRB meeting is scheduled for January 13 – 17
Opening Remarks (Ed Kavazanjian, Chair)
a. This is the first meeting of the “Geoseismic Concerns” subcommittee.
b. The subcommittee’s parents are AFF50 (Seismic design of bridges) and AFS30
(Foundations of Bridges and Other Structures). This subcommittee will provide
geotechnical input to these two parent committees.
Sessions
a. Sessions this year at TRB sponsored or co-sponsored by AFF50
i. Session 583 – Effective stress site response analysis for liquefiable ground
ii. Session 658 – Seismic retrofitting and current seismic research
b. AFF50 Committee meeting – Wednesday at 2 30 pm, Shoreham Exhibit Hall B
FHWA Initiatives (Jerry DiMaggio & Peter Osborne, FHWA)
a. Background for two major activities.
i. MCEER retrofit manuals have been completed
ii. A new FHWA Reference Manual and NHI Training Course will be
develop that combines structural and geotechnical issues with modules on
Retrofit and on Design. The start of this activity is pending the outcome
of AASHTO adoption of the new LRFD guidelines that are currently
under revision. The activity will be a 2-step process:
1. Step 1: Develop new manuals incorporating AASHTO LRFD
guidelines. This effort includes updating Geotechnical
Engineering Circular (GEC) Number 3 and incorporating
information from the MCEER retrofit manual.
2. Step 2: Developing the new training course.
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24 January 2006
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DRAFT
b. The subcommittee engaged in an extended discussion about the pending
AASHTO LRFD guidelines regarding: (1) adopted/proposed probable levels of
ground motion exceedance (i.e., earthquake return periods) [the next draft will
apparently call for a single level of design earthquake with a 1000 year return
period]; (2) the potential conflicts between the proposed design earthquake in the
new draft guidelines and work done on NCHRP Projects 12-49 [which was based
upon two design earthquake levels, with a 2500 year return period for the upper
level] and 12-70 [work in progress] for geotechnical / geo seismic LRFD issues;
and (3) the section of the new draft guidelines concerning liquefaction analyses.
Concern was expressed over the suggestion that no liquefaction analyses would
be required if the design earthquake magnitude was less than 6.5.
VII. Update on NCHRP 12-70: Seismic Design and Analysis of Retaining Walls, Buried
Structures, Slopes and Embankments (Don Anderson – CH2M Hill)
a. NCHRP 12-70 is a three-year program to evaluate and improve DOT procedures
for the seismic design of free-standing retaining walls, slopes and embankments,
and buried structures. The project includes proposing specifications to be used in
the AASHTO LRFD Bridge Design Specifications and developing design
examples for these topics. Work is being performed by a Project Team consisting
of CH2M Hill, Earth Mechanics, and Parsons Brinkerhoff. Dr. Anderson’s
presentation will be posted to the committee web site.
b. The NCHRP 12-70 Project Team is making the proposed
specifications compatible with those being developed under NCHRP Project 2007. This second NCHRP Project is being conducted by Imbsen & Associates and
involves updating the seismic provisions for bridge design in the current AAHTO
LRFD Bridge Design Specifications. The final report for the NCHRP 20-07
Project is being completed. in the near future and will tentatively be voted upon
by AASHTO in July of 2007 after a series of trial applications are conducted.
VIII. Committee Scope (Ed Kavazanjian, Chair)
a. Geoseismic issues that are considered within the scope of the sub-committee
include:
i. Seismic hazard analysis & seismic risk
ii. Site response (including nonlinear & effective stress based analyses)
iii. Dynamic soil properties
iv. Liquefaction (including triggering and consequences)
v. Seismic design of deep and shallow foundations
1. capacity and stiffness
2. soil-structure interaction
vi. Seismic design of retaining walls & abutments
vii. Seismic design of bridge approaches
1. embankments
2. cuts and fills
b. Additional issues discussed by committee members and guests as appropriate for
the subcommittee included:
i. Liquefaction mitigation
ii. Seismic design of buried structures
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DRAFT
iii. Post-earthquake evaluation of bridges (geoseismic aspects/foundations)
iv. Response spectrum and return period issues (w.r.t. seismic hazard)
v. Performance-based design
Committee Research Needs
a. Prior to the meeting, sub-committee members were asked to identified issues that
could be the basis of a Research Needs statement developed by the subcommittee. The following suggestions were received:
i. Teh Sung (NYDOT)
1. guidelines for soil-pile-structure interaction analysis
a. criteria for determining level of analysis
b. appropriate analysis methods & software
c. evaluation of geotechnical parameters
2. lateral response of piles in liquefiable soils
ii. Bill Kramer (IDOT)
1. return period for ULE
2. dynamic stiffness of layered soil profiles
a. impact of thin ( < 2.5 ft) liquefiable layers
3. evolution of dynamic forces and pore pressures during shaking
a. if peak dynamic force is early and liquefaction is later, do
we need to analyze for both?
iii. Tom Cooling (URS)
1. lateral spreading forces on large (100 ft+) caissons (with and
without liquefiable crust)
2. tolerable lateral movements for foundations subject to dynamic
loads
a. is AASHTO 1.5-inch limit appropriate and does it apply to
static plus seismic movement?
3. seismic design of auger-cast piles
a. ductility and survivability
b. detailing of pile head and pile cap connection
iv. Lee Marsh (ABAM)
1. improved and simplified techniques to integrate structural and
geotechnical phenomena
2. rational methods to combine vibrational (shaking) response and
ground deformation (e.g., lateral spreading)
v. Ed Kavazanjian (ASU)
1. evaluating residual shear strength of sandy soils
2. predicting the impacts of liquefaction
a. lateral spreading
b. forces on piles
c. settlement
d. site response & dynamic forces
e. performance of mitigation measures (e.g., stone columns,
vertical drains, reinforced soil mats)
b. Additional research needs discussed by committee members and guests
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i. Active fault displacements
ii. Near-field effects
1. ground motions & fling effect
2. liquefaction
iii. Shallow foundation design
1. soil-foundation-structure interaction
2. stiffness design (i.e., spring constants) in layered soils
iv. Response spectrum of soft soils (2-point method is unconservative for
soft, coastal South Carolina soils)
v. LRFD methods calibrated to average soil properties
vi. Site response of improved ground
vii. Residual shear strength & dynamic soil properties of silty sands
viii. Performance based geotechnical design criteria
1. performance requirements
2. allowable displacements & settlements
3. performance during extreme events, e.g., vessel collision, wave
forces, scour
Priorities for Future Sessions, Recommended NCHRP Project Statements, and
Recommended NCHRP Syntheses (Ed Kavazanjian, Chair)
a. Performance of Foundations subject to Seismic and Other Extreme Loads
i. Research statement with AFS30:
ii. Topics to include
1. large diameter caissons subject to liquefaction
2. performance based design criteria
b. Evaluation of Residual Shear Strength
i. Joint session with AFS30 and maybe AFP30
c. Performance of Piles in Liquefiable Soil
i. Proposed Synthesis report
d. Soil Properties for Seismic Analysis
i. Future effort
ii. Topics to include
1. recommendations for laboratory and field testing
2. LRFD calibration
e. Seismic design of shallow foundations
i. Future effort
ii. Topics to include
1. methods of analysis
2. soil properties
3. LRFD calibration
Meeting adjourned at 3:15 pm.
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