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ANALYSIS OF AGE-DEPENDENT RESILIENCE FOR A HIGHWAY NETWORK WITH AGING BRIDGES
Abstract
Bridges are key links connecting different critical facilities in a highway transportation network. Bridge damage in the event of an extreme hazard may cause severe traffic disruption and thus directly affect the functionality of a highway network. The extent of damage that a particular bridge may experience under a certain extreme event condition depends on various factors including severity of the extreme event (e.g., earthquake magnitude), proximity of the bridge with reference to the event location (e.g., the distance from the epicenter of an earthquake), structural health (e.g., chloride induced deterioration, aging), to name a few. Based on the extent of damage that bridges in a highway network may undergo, efforts are made to restore the original functionality of a network in a fast and economically efficient way. The concept of network resilience is thus closely tied to promptness in restoring the original functionality of a network after an extreme event occurs. Although the quantification of resilience for highway network greatly depends on the post-event recovery model, network resilience inherently depends on the pre-event structural condition of constituent bridges.
The present study considers a small highway network (with 35 bridges) in the Memphis region. Structural deterioration of constituent bridges due to chlorine diffusion over the bridge life span is studied. The highway network is studied primarily at two different time scenarios, year 2010 and year 2050 for an earthquake of magnitude 6. For each corresponding year, ages of the bridges are identified based on their year of construction and accordingly bridge fragility curves are developed at various stages of bridge life based on past research. Thus developed fragility curves are used in conjunction with recovery patterns to explore time-dependent change of network resilience considering total travel time in the network as the functionality measure. Also, the percentage number of links having different velocity to capacity ratios for each time scenarios is calculated to understand the congestion in different links. It is observed that aging due to chloride deterioration has an adverse impact on seismic resilience of bridge network.
Table of Contents
List of Figures ……………………………………………………………………………………………………………………………. vi List of Tables ……………………………………………………………………………………………………………………………. vii
Acknowledgment ……………………………………………………………………………………………………………………… viii
Chapter 1 ……………………………………………………………………………………………………………………………………. 1
INTRODUCTION ………………………………………………………………………………………………………………………. 1
1.1 Background and Motivation: ………………………………………………………………………………………….. 1
1.2 Research Objective and Scope: ……………………………………………………………………………………….. 2
1.3 Thesis Structure: …………………………………………………………………………………………………………… 4
Chapter 2 ……………………………………………………………………………………………………………………………………. 6
LITERATURE REVIEW …………………………………………………………………………………………………………….. 6
2.1 Fragility Curve Analysis: ……………………………………………………………………………………………….. 6
2.2 Recovery function: ………………………………………………………………………………………………………… 8
2.3 Network Resilience: ………………………………………………………………………………………………………. 9
Chapter 3 ………………………………………………………………………………………………………………………………….. 11
BRIDGE NETWORK ………………………………………………………………………………………………………………… 11
3.1 Study Area: ………………………………………………………………………………………………………………… 11
3.2 Developing and Validation of Network Model:……………………………………………………………….. 14
3.2.1 Node-Link Data: ………………………………………………………………………………………………….. 15
3.2.2 Origin-Destination Data: ……………………………………………………………………………………….. 16
3.3 Validation of Model: ……………………………………………………………………………………………………. 18
3.4 Attenuation Equations: …………………………………………………………………………………………………. 19
Chapter 4 ………………………………………………………………………………………………………………………………….. 22
MODELING OF FRAGILITY DEGRADATION …………………………………………………………………………. 22
4.1 Time Variant Quadratic Model: …………………………………………………………………………………….. 22
4.2 Bridge Damage States: …………………………………………………………………………………………………. 25
4.3 Recovery Patterns: ………………………………………………………………………………………………………. 28
Chapter 5 ………………………………………………………………………………………………………………………………….. 32
NETWORK RESILIENCE …………………………………………………………………………………………………………. 32
5.1 Methodology: ……………………………………………………………………………………………………………… 32
5.2 Results: ………………………………………………………………………………………………………………………. 33
5.3 Observations: ……………………………………………………………………………………………………………… 35 Chapter 6 ………………………………………………………………………………………………………………………………….. 37
Conclusions and Future Scope of work ………………………………………………………………………………………… 37
References ………………………………………………………………………………………………………………………………… 38
Appendix A: Node-Link table ………………………………………………………………………………………………………. 40
Appendix B: Origin-Destination matrix ………………………………………………………………………………………… 59
Chapter 1
INTRODUCTION
1.1 Background and Motivation:
Aging is a natural phenomenon which we see and experience in our day to day lives. Every living being has a definite life span in this universe and to that extent, even the machinery and equipment which we develop through our technology has a defined life span. This is true with infrastructure too. Nothing can perform at its best permanently. Hence, it is general norm to define the average life span of a machinery or infrastructure such as buildings and bridges. During the lifespan of any infrastructure say bridges, performance degrades as aging occurs due to various internal and external factors. This performance degradation might be due to usual wear and tear in case of machinery, amount of traffic on the structure in case of bridges and roads, or some environmental stressor such as corrosion etc. apart from performance degradation due to natural hazards.
The focus of this research is on spatially distributed aging bridges due to induced chloride corrosion in a highway transportation network. Highway bridges have a very important role in transportation networks and act as major links to various critical routes such as hospitals, schools etc. Frangopol and Bocchini (2012) defined bridge network as a transportation network in which bridges are the only elements which can experience structural damage during an extreme event. Damage of bridges in the event of an extreme natural hazard causes severe disruption to the traffic and can affect the functionality of a part or entire portion of the highway network. The extent of damage a particular bridge experiences depends on various factors such as intensity of the extreme event, location of the bridge with reference to the epicenter of the extreme event, chloride induced deterioration, aging etc. Based on the damage extent the bridges undergo, efforts are made to restore the complete network to its original functionality or close to its normal functionality in a fast and economically efficient way.
To quantify this promptness of restoration, the concept of ‘Resilience’ is used.
Many definitions of resilience have been defined in literature and also resilience has been calculated for various lifeline systems, networks and infrastructure groups. The most widely accepted definition of resilience in the literature is of Bruneau et al. (2003) who conceptualized resilience of a social system to be having 4 R’s – Robustness, Redundancy, Resourcefulness and Rapidity. A system is considered to be robust based on the resistance offered by the system for an external demand or extreme event and is able to withstand the adverse conditions. A redundant system is one which has alternative paths and options during an extreme event without affecting the total system equilibrium. System resourcefulness is measured by the ability to devise ways and means to address the emergency situations during the extreme event. System rapidity, as the word suggests, can be measured based on the speed at which the system recovers and overcome the losses due to the extreme event. This study tries to addresses the robustness, redundancy and rapidity questions for the bridge network chosen for an earthquake scenario.
1.2Research Objective and Scope:
The main objective of this research is to obtain the seismic resilience of a highway bridge network due to aging using suitable recovery patterns for each damage state.
To achieve this objective, the following major tasks are carried out.
- Task 1: Develop a user-equilibrium model for the chosen network and validate the model with real-time data
- Task 2: Develop the time dependent polynomial fit for the median values considering a bridge life span of 100 years.
- Task 3: Calculate adjusted Peak Ground Acceleration (PGA) values at bridge sites using suitable ground motion attenuation model.
- Task 4: Define bridge damage states as well as the associated links damage states by using attenuated PGA values at bridge sites and fragility curves of bridges
- Task 5: Develop post-event recovery patterns for network capacities and corresponding gain in speed limits at each damage level
- Task 6: Calculate the network functionality in terms of total travel time at different scenarios and calculate network resilience
Within the scope of this research, time-variant seismic vulnerability model of bridges, and seismic recovery models are studied. The combined effect of aging of bridges in a network and seismic event on bridge network resilience over a period of 40 years is studied. The resilience of the bridge network is compared between the initial year of observation and 40th year of observation.
As can be seen from Figure 1-1 and 1-2, Memphis region in Tennessee State is moderate to high seismically active and may experience 12-24 inches of annual snowfall. Deicing salt used during the winter season may deteriorate health of bridges in this region, and hence make bridges more vulnerable under seismic ground motion. Hence, it is important to study the change in seismic resilience of the bridge network in Memphis region due to aging.
Fig 1-1: Earthquake Hazard Map of United States
Fig 1-2: Annual Average Snowfall in inches for United States
1.3Thesis Structure:
This thesis is organized into six chapters. The initial chapter introduces the concepts involved in this study and gives a background and importance of this study. Also, the research objective is discussed and the important tasks undertaken to achieve this objective has been detailed.
Chapter 2 discusses on the past work done by researchers in the major areas of this study which are on Fragility curves for Memphis region and fragility degradation for different types of bridges, recovery patterns used and developed in different studies and also studies on network resilience.
Chapter 3 introduces the bridge network considered for analysis and resilience calculations. It defines the basic details of the bridge network and also validating the model developed. Ground motion attenuation equations details used for getting the peak ground acceleration (PGA) at each bridge site locations are also discussed.
Chapter 4 details the fragility degradation modelling for the type of bridge chosen and also defines the damage states of bridges for a given earthquake during the observed year. Recovery patterns developed for capacity and speed reductions at different time scenarios for each damage state are also discussed in detail.
Chapter 5 defines the methodology developed for calculating network functionality and further obtaining the network resilience. Primary results along with the observations are documented in this chapter.
Chapter 6 presents the overall conclusion for this work and the effect of aging due to chloride deterioration in resilience of a bridge network. Major assumptions are also discussed and also the probable sources of error involved while achieving the objective of this study are detailed. The impact and future scope of work based on this thesis work is also identified and discussed in this chapter.
