| Principal Investigator and Institution
Stuart D. Werner, Seismic Systems & Engineering Consultants
Objective
The objective for Research Year 3 of Task B1-2 is to begin the
development of REDARS as a public-domain software package for seismic risk
analysis (SRA) of highway systems. This will include: (a) software
development planning and initial programming, (b) technical improvements
to the various REDARS modules, (c) development of guidelines for assessing
whether the number of simulations assumed for a user's probabilistic SRA
is sufficient, and (d) development of plans and procedures for adapting
REDARS for use as a decision guidance tool that will facilitate evaluation
of alternative seismic risk reduction strategies for a highway system.
These efforts will provide the framework for work during future years of
MCEER Highway Project 094, which will focus on programming, documentation,
and example application of REDARS.
Approach
Research on this task will be conducted via the following subtasks:
Subtask 1 - REDARS Software Development During Research
Year 2, Task B1-2 evaluated various technical and software development
options to be considered for the development of the REDARS software
package during future years of the project. For each option, evaluations
considered scope, costs, assessments of the importance of the option for
meeting anticipated user needs, and whether the overall cost of the option
could be accommodated within estimated project budget constraints for the
remainder of this project. From this, a general plan for developing REDARS
during the remaining years of the project was developed.
Under this subtask, work will be initiated to develop the REDARS
software in accordance with these plans. This will include more detailed
planning of the program structure and specific features to be included in
the software package, as well as initial programming efforts. The detailed
planning will focus on the basic REDARS platform into which the hazards,
component, and system modules will interface, the specifics of these
interfaces, input database redesign specifics, and graphic/GIS features
and editing options.
Subtask 2 - REDARS Module Development Enhancements will be
made to the systems, component, and hazards modules, as summarized below.
For the systems module, enhancements will include post-earthquake traffic
demand modeling, improvement of the minimum search path algorithm, and
investigation of the MAM matrix training scheme in concert with the effort
under Task B1-4. Work on the component module will address two main
issues: modeling of the performance of bridges subjected to liquefaction
induced ground displacements, and the performance of roadway pavements
during earthquakes. Work on the hazards module will address two main
issues: liquefaction hazard modeling, and incorporation of earthquake and
ground motion models for additional regions of the United States.
It is well known that bridges can be damaged by liquefaction of the
backfills or subsurface soils during an earthquake. Although REDARS will
include a credible model for estimating site-specific liquefaction
hazards, it does not yet include a sufficiently credible model for
estimating how bridges and their foundations perform when subjected to
these hazards. Procedures for developing fragility curves for bridges
subjected to liquefaction-induced permanent ground deformation will be
investigated, along with similar procedures for roadway pavements. This
will include review of: (a) empirical data and damage reports from past
earthquakes, (b) results from experimental and analytical programs, and
(c) data on repair procedures, costs, and downtimes for bridges damaged by
liquefaction-induced ground deformation. In addition, engineers and
highway-roadway maintenance personnel from Caltrans who have observed and
repaired bridges subjected to liquefaction damage during recent
earthquakes will be interviewed. From this, a strategy will be developed
for modeling the performance of bridges subjected to liquefaction.
In recent discussions, several DOT agency representatives also
underscored the importance of including the performance of roadway
pavements when evaluating seismic risks to highway systems. A first order
model of the performance of pavements during earthquakes was prepared
under Project 106 (see Section 5.5 of MCEER Technical Report 00-0014).
This will be further investigated to determine how this model can be
updated, through review of empirical data from past earthquakes, and
interviews will be conducted with engineers and highway maintenance
personnel from Caltrans who have observed and repaired roads that were
damaged during recent earthquakes.
REDARS currently includes a liquefaction hazard analysis procedure
developed as part of the earlier Project 106. Although well suited for
application at individual bridge sites (where soil exploration and testing
to obtain the required detailed soils input data is practical), this
procedure is less practical for application to multiple bridge sites
throughout a spatially distributed highway system where these detailed
soils data are often not readily available nor easily obtained. The
applicability of alternative liquefaction hazard models for use in REDARS
will therefore be assessed. These models should build on prior databases
yet require less extensive site soils data that are more likely to be
available at the large numbers of bridge or component sites within a
spatially dispersed highway system. One promising candidate procedure that
will be considered in this context is the recent liquefaction modeling
work of Professor Bardet at USC.
Finally, for REDARS to be applicable to highway systems throughout the
United States, it must include a range of earthquake and ground motion
models that encompass the range of seismologic and geologic conditions
that may be encountered in various regions of moderate to high earthquake
activity nationwide. REDARS currently includes such models for the Central
U.S., and the inclusion of models for California is being planned for a
possible future project by Caltrans. During Year 3, earthquake and ground
motion models for one additional region of the country will be
incorporated into REDARS (e.g., Charleston, SC). This will serve as a
template for including models for other regions of the nation into REDARS
during future years of this project.
Subtask 3 - Confidence Levels MCEER Technical Report
00-0014 describes an approach for estimating nominal confidence levels for
the average annualized loss, as a function of the number of simulations
used in the risk analysis. Under this subtask, work will be done to
clarify how to also determine confidence levels for point estimates of
loss (e.g., 100-year loss estimates), and how confidence levels can be
used to assess whether the number of simulations used in a REDARS
application to a given highway system is sufficient. The subtask will also
assess if methods are available for reducing the number of simulations
needed for a given REDARS analysis, while still achieving a desired
confidence level for the results. If successful, this would simplify
future REDARS applications by reducing run-time requirements.
Subtask 4 - Decision Guidance Framework An important
aspect of REDARS is its suitability for use as a decision guidance tool.
This will require adapting REDARS to provide cost and risk results for
alternative seismic risk reduction strategies, in forms that could be used
to guide decision making. This subtask will establish a framework for
using REDARS as a decision guidance tool, by showing how it can be adapted
to several of the more common decision procedures available. This use of
REDARS as a decision guidance tool will be demonstrated in a future
example application of REDARS; i.e., one that is planned for Research
Years 5 and 6, after REDARS software development has been completed.
Products
- REDARS Software Development Progress Report 1 - Description of the
software development steps carried out during Research Year 3,
problems encountered and resolved, and an updated plan for continuing
software development during Research Year 4 and beyond.
- Technical Report - Documentation of results of subtasks 2 through 4,
problems encountered and resolved, and discussion of how these results
and models will be incorporated into REDARS during Research Year 4.
Technical Challenges
The challenges for Research Year 3 will be: (a) laying the groundwork
for eventual development of REDARS as a technically sound, practical,
efficient, and useful software package; and (b) coordination of the
modeling and analysis results from subtasks 2 through 4, and from Tasks
B1-3 and B1-4 into the software planning in subtask 1, so that software
planning and subsequent programming proceeds efficiently.
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