Since 2009, there has been a dramatic increase in the number of earthquakes in the central United States. States such as Oklahoma, Kansas, Arkansas, and Texas have not historically experienced earthquakes at the rate currently observed, nor of this magnitude. Studies have linked the increased rate of seismic activity since 2009 to wastewater injection in disposal wells. These induced earthquakes are not limited to the U.S., but are also experienced in other countries including Canada, China, and the United Kingdom. The seismicity of places such as California and the New Madrid seismic zone is well documented and generally thought of when discussing seismic hazards in the contiguous U.S., yet the cumulative moment in Oklahoma over the last two years (1 January 2015 to 31 December 2016) exceeds that of southern California and the New Madrid seismic zones.
While collapse is unlikely for the induced earthquakes currently observed, the cumulative effects of a large number of small earthquakes on bridges are not fully understood. These cumulative effects compounded with the occasional moderate earthquake (M5.0 and larger) may lead to damage requiring rapid repairs to avoid acute traffic control issues at the affected bridge sites. To reduce impacts to the driving public, accelerated bridge construction (ABC) techniques have been developed over recent years, but have primarily focused on rapidly constructing new or replacement structures. Another benefit derived from these ABC methods is rapid post-earthquake repair of damaged structures. Post-earthquake accelerated column repair/replacements has focused solely on moderate-to-high seismic zones. The need for additional analysis, new techniques, and associated specifications is also critical for low-to-moderate seismic zones affected by induced earthquakes. This project addresses the current knowledge gap on the effects of low-level frequent seismic events on bridges, as well as ABC methods to repair/retrofit damaged bridges.
The recent surge in seismic activity in the central U.S. has motivated the need for rapid repair techniques that leverage ABC methods. The overarching objective of this project is to develop analysis techniques to study the effect of large number of small earthquakes on bridges and identify appropriate ABC methods for repair of bridges damaged by induced earthquakes. The project will use Oklahoma as a case study and develop techniques and tools that can be applied to other regions experiencing low-level frequent seismic events.
This project follows an integrated program of seismic hazard analysis, numerical modeling, response prediction, and guideline development. The following tasks will be performed to achieve the project objective in Year 1 of this 2-year project:
- Task 1 – Compile Ground-Motion Data: The first task of this project is to compile ground-motion data for earthquakes impacting Oklahoma’s bridges. Metadata, such as station longitude/latitude, soil conditions, channels, etc., will be curated as well. In addition to the processed ground-motion time histories, key ground-motion intensity measures, such as peak ground acceleration (PGA), peak ground velocity (PGV), and the 5%-damped spectral acceleration (PSA), will be compiled.
- Task 2 – Characterize Cumulative Seismic Demand: This task will use ground-motion data acquired in Task 1 to quantify the cumulative (or cyclic) seismic demand due to induced earthquakes. OpenSees models of typical Oklahoma bridges will be used to run simulations and to determine the number of cycles, and the amplitude of these cycles, that Oklahoma bridges were subjected to over the period of highest seismic activity (2015).
- Task 3 – Develop and Evaluate a Fatigue Damage Index: This task will use the cumulative seismic demand found in Task 2 to develop a fatigue damage index (FDI). The FDI will be used to capture structural deterioration due to accumulated seismic damage by quantifying how close a bridge is to its fatigue limit for a given earthquake sequence, from which the remaining service life can be determined.
- Task 4 – Final Report: The project findings from the previously identified tasks will be prepared by means of a final report. The report will include guidelines for the appropriate use of the FDI developed in Task 3.
Principal Investigator: Dr. P. Scott Harvey Jr.
Co-Principal Investigator: Dr. K.K. “Muralee” Muraleetharan
Research Assistant: Sumangali Sivakumaran
Previous Progress Reports: