Transportation Test Bed Project: Assessing Lifelines in Charleston, South Carolina

Reginald DesRoches and Jamie E. Padgett (Rice University)

Student: Emily Nilsson

Recent earthquakes and hurricanes in the US have shown the potential for large losses due to damage to bridges and roads ($1.8 billion in Loma Prieta, $150 in million in Northridge, $1.4? billion in Katrina). Furthermore, it has been shown that a resilient transportation system and effective evacuation planning are two of the most critical factors to ensure a fast recovery from a natural disaster.

In 2001 South Carolina EMD performed a “Comprehensive Seismic Risk and Vulnerability” study for the state of South Carolina, with part of the effort developed to the transportation system.  One of the recommendations which came out of this study was a need for a more comprehensive study which would assess potential losses, evaluate evacuation routes, and over traffic conditions following an earthquake event.  Furthermore, it is noted that the software package used at the time did not have bridge data that is representative of the characteristics of bridges in South Carolina. 

It is with this in mind that this project was initiated

Goals and Objectives

The goal of the Transportation Test Bed project is to use recently developed tools to perform a comprehensive seismic risk assessment of the transportation network in Charleston, South Carolina.  The project involves assessing the expected severity and location of bridge damage, expected bridge functionality and potential losses from different earthquake events in Charleston, South Carolina.   In addition, specific potential lifeline routes were evaluated (US17 and I26), to understand the level of damage expected on these lifelines.  Several deterministic (Mw=4.0, Mw=5.5, and Mw=7.0) and probabilistic (2% PE in 50 years, 5% PE in 50 years, and 10% PE in 50 years) earthquakes are used in the assessment.

Results

• The most vulnerable bridges were the multi-span continuous steel, multi-span simply supported steel, multi-span continuous concrete, and multi-span continuous slab types.
• A level Mw=4.0 earthquake results in enough damage to warrant deployment of inspection teams.
• At all hazard levels the Multi-Span Continuous Steel girder bridge contributes the most to the losses
• For a moderate earthquake (Mw=5.5)
• Over 180 bridges may be expected to sustain at least Moderate damage within the Charleston region
• The average level of functionality of the bridges across the region is expected to be approximately 75% within a day. 
• Total direct and indirect losses are expected to be on the order of $300-$900 Million
• US 17 has less damage and higher level of functionality compared to I-26

The results of Phase I provide the foundation for lifeline evaluation assessment as well as a retrofit prioritization program for bridges on the lifeline routes.   This is critical for making lifeline selection a reality.

Figure 2: Bridge Damage in Charleston Region for 3 Scenario Earthquakes

Figure 3: Bridge Functionality Following Earthquake Event