Seismic Resilience of Highway Bridges
Open Access
- Author:
- Venkittaraman, Ashok
- Graduate Program:
- Civil Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 27, 2013
- Committee Members:
- Dr Swagata Banerjee Basu, Thesis Advisor/Co-Advisor
Gordon Patrick Warn, Thesis Advisor/Co-Advisor
Andrew Scanlon, Thesis Advisor/Co-Advisor - Keywords:
- Concrete bridges
fragility analysis
resilience
sensitivity study
cost analysis - Abstract:
- Highway transportation network is one of the important civil infrastructure systems. Various components of this system, especially bridges, are highly vulnerable to extreme natural hazards such as earthquakes. Extreme events can cause severe damage to highway bridges and thus can result in disrupted functionality of highway transportation systems. Bridge damage not only causes direct economic losses due to post-event bridge repair and restoration, but also produces indirect losses arising from network downtime and traffic delay. Therefore, it is always desirable to minimize these negative consequences from extreme events and to maximize disaster resilience of highway transportation systems. Seismic retrofitting of highway bridges is one of the most common approaches undertaken by state Departments of Transportation (state DOTs) and by bridge owners to enhance system performance during seismic events. In this relation, this study evaluates the effectiveness of different retrofit techniques to enhance seismic resilience of highway bridges. The study considers a reinforced concrete bridge in La Cienega-Venice Boulevard sector of the I-10 freeway in Los Angeles, California. The bridge was severely damaged during the 1994 Northridge earthquake due to shear failure of one of the bridge piers. Post-event reconnaissance indicated that the failure was initiated from inadequate lateral confinement of bridge piers due to which vertical load carrying capacity of the bridge reduced significantly resulting in crushing of core concrete and buckling of longitudinal re-bars of bridge piers during the seismic event. Seismic vulnerability of the as-built bridge is estimated through finite element (FE) analysis of the bridge under a suite of time histories that represent seismic hazard at the bridge site. Appropriate loss and recovery models are used to calculate seismic resilience of the as-built bridge. Three retrofit strategies are applied to the bridge to observe the effectiveness of these strategies in enhancing bridge seismic resilience in case the bridge was retrofitted prior to the earthquake event. Seismic vulnerability of retrofitted bridge models are estimated through time history analyses of these models under the same set of ground motions used for the as-built bridge. Seismic resilience of a highway bridge can be represented as a combined measure of bridge seismic performance and its recovery after the occurrence of seismic events. For each method of seismic retrofit, seismic resilience of the bridge is calculated. Difference in resilience obtained before and after bridge retrofits and the respective costs incurred are evaluated. Comparison of these values indicates the relative effectiveness of different retrofit techniques in enhancing the seismic resilience of the bridge. Results show that one of the retrofit strategies is most effective in enhancing the seismic resilience of the bridge, whereas other two strategies are not effective at all. Cost benefit analysis is performed to calculate the benefit obtained from the most effective retrofit strategy over a period of 30-80 years after bridge retrofit. Hence, results obtained from this study help in educated decision-making for selecting efficient and cost-effective seismic design and/or retrofit strategies for highway bridges.