Jamie E. Padgett

Bridge Functionality Relationships for Improved Seismic Risk Assessment of Transportation Networks

Relationships between bridge damage and the resulting loss of functionality of the bridge are critical to assessing the impact of an earthquake event on the performance of the transportation network. This study addresses this data need by use of a Web-based survey of central and southeastern U.S. Department of Transportation bridge inspectors and officials. Results of the 28 responses are analyzed and offer a link between various types of bridge component damage and the expected level of allowable traffic carrying capacity due to closure decisions and repair procedures. This data is utilized to assess the probability of meeting various damage states, expressed in terms of restoration of functionality, and subsequently facilitate the refinement of component limit-state capacities for analytical fragility curve development. The bridge functionality relationships and methodology outlined serve as the basis for refinement of critical tools in the seismic risk assessment framework and improved assessment of transportation network performance.

Large scale testing of nitinol shape memory alloy devices for retrofitting of bridges

A large scale testing program was conducted to determine the effects of shape memory alloy (SMA) restrainer cables on the seismic performance of in-span hinges of a representative multiple-frame concrete box girder bridge subjected to earthquake excitations. Another objective of the study was to compare the performance of SMA restrainers to that of traditional steel restrainers as restraining devices for reducing hinge displacement and the likelihood of collapse during earthquakes. The results of the tests show that SMA restrainers performed very well as restraining devices. The forces in the SMA and steel restrainers were comparable. However, the SMA restrainer cables had minimal residual strain after repeated loading and exhibited the ability to undergo many cycles with little strength and stiffness degradation. In addition, the hysteretic damping that was observed in the larger ground accelerations demonstrated the ability of the materials to dissipate energy. An analytical study was conducted to assess the anticipated seismic response of the test setup and evaluate the accuracy of the analytical model. The results of the analytical simulation illustrate that the analytical model was able to match the responses from the experimental tests, including peak stresses, strains, forces, and hinge openings.

Retrofitted Bridge Fragility Analysis for Typical Classes of Multispan Bridges

Retrofitted bridge fragility curves provide a powerful tool for assessing the effect of retrofit measures on the seismic performance of different bridge types under a range of loading levels. Traditional methods for retrofit assessment typically evaluate the effectiveness of retrofit based on the performance of individual components. However, the use of fragility curves for retrofitted bridges has the ability to capture the impact of retrofit on the bridge system vulnerability. Using three-dimensional nonlinear analysis, fragility curves are developed for four common classes of multispan bridges and five retrofit methods. The results show that the effectiveness of retrofit is a function of bridge type and damage state. General conclusions of the influence of the different retrofit measures on the fragility of each class of typical bridges in the Central and Southeastern United States, as well as the fragility parameters, are presented. The results from this work can be used to enhance regional seismic risk assessment and can form the basis for retrofit cost-benefit studies.

Analytical Fragility Curves for Multispan Continuous Steel Girder Bridges in Moderate Seismic Zones

Multispan continuous steel girder bridges are one of the most common bridge types in the central and southeastern United States. Seismic fragility curves for these highway bridges are essential for risk assessment of highway transportation networks exposed to seismic hazards. This study focuses on developing and comparing fragility curves for seismically and nonseismically designed bridges that are common in this region. The primary differences between seismically and nonseismically designed bridges are the column details and bridge bearings. Detailed three-dimensional (3-D) nonlinear analytical models, which account for the nonlinear behavior of the column, girders, and abutments, are developed with the use of the OpenSees platform. The fragility curves are developed with a suite of ground motions representative of the seismic hazard in the region. Unlike most previous studies, the fragility curves are developed with geometric variations such as column height, deck width, and length considered to study the effect of these variations on the fragility curves within the same class of bridges. The results provide insight into the level of uncertainty introduced in the analysis of fragility curves for portfolios of bridges with the use of 3-D analytical models and nonlinear time–history analyses. Component and system fragility curves are obtained and are compared for the case of nonseismically and seismically designed bridges.

Fragility Analysis of Skewed Single-Frame Concrete Box-Girder Bridges

Damage to skewed bridges in recent earthquakes has reinforced the potential vulnerability of these structures. The effect of skew angleonabridges fragility couldvary for different bridge types, ages, or geometric configurations. This paperconducts a probabilistic seismic assessment of skewed bridge performance, focusing on single-frame concrete box-girder bridge subclasses. The effect of skew angle on bridge seismicfragilityisinvestigatedforbridgeswithsingle-ortwo-columnbents,integralorseat-typeabutments,andminimalorsignificantlevelsof seismic design. Component and system-level damage states consistent with HAZUS-MHdefinitions are also explored in this study. The results reveal that older bridges, which are more likely to experience higher damage states, are particularly susceptible to column damage and are not sensitivetoskew.Similarly,thepresenceofintegralabutmentsinnewerbridgessignificantlyreducesthevulnerabilityandminimizestheimpact oftheskewangleonbridgefragility.Fornewbridgeswithseat-typeabutments,thebridgeskewanglehasasignificanteffectoncomponentand system fragility for both single- and two-column bent bridges. Forthese subclasses,HAZUS-MHskew factors are foundto reasonably estimate theshiftinmedianvaluefragilityfromtheirstraightcounterparts.DOI:10.1061/(ASCE)CF.1943-5509.0000435.©2014AmericanSocietyof

Sustainability of Natural Hazard Risk Mitigation: Life Cycle Analysis of Environmental Indicators for Bridge Infrastructure

AbstractThe performance of structures and infrastructure under natural hazards can have a significant impact on the sustainability of the system, often characterized in terms of environmental, economic, or social indicators of performance. This paper commences with a brief review of the relation of natural hazard performance to sustainability and an assessment of bridge infrastructure sustainability with an emphasis on environmental indicators. A framework for life cycle sustainability analysis (LCS-A) is then posed that elucidates the role of natural hazard risks when evaluating sustainable bridge performance using risk-based indicators of environmental sustainability, including embodied energy and carbon dioxide (CO2) emissions. Its application provides insight on the sustainability of mitigating damage from natural hazards through retrofitting deficient structures, considering uncertainty in the hazard occurrence, structural performance, and repair or reconstruction actions that affect energy expenditu...

Review of Methods to Assess, Design for, and Mitigate Multiple Hazards

Large parts of the world are subjected to one or more natural hazards, such as earthquakes, tsunamis, landslides, tropical storms (hurricanes, cyclones, and typhoons), coastal inundation, and flooding; although, many regions are also susceptible to artificial hazards. In recent decades, rapid population growth and economic development in hazard-prone areas have greatly increased the potential of multiple hazards to cause damage and destruction of buildings, bridges, power plants, and other infrastructure; thus, grave danger is posed to the community and economic and societal activities are disrupted. Although an individual hazard is significant in many parts of the United States, in certain areas more than one hazard may pose a threat to the constructed environment. In such areas, structural design and construction practices should address multiple hazards in an integrated manner to achieve structural performance that is consistent with owner expectations and general societal objectives. The growing interest and importance of multiple-hazard engineering has been recognized recently. This has spurred the evolution of multiple-hazard risk-assessment frameworks and development of design approaches, which have paved way for future research towards sustainable construction of new and improved structures and retrofitting of the existing structures. This paper provides a review of literature and the current state of practice for assessment, design and mitigation of the impact of multiple hazards on structural infrastructure. It also presents an overview of future research needs related to multiple-hazard performance of constructed facilities.

Bridge Seismic Retrofitting Practices in the Central and Southeastern United States

This paper conducts a detailed review of the seismic hazard, inventory, bridge vulnerability, and bridge retrofit practices in the Central and Southeastern United States (CSUS). Based on the analysis of the bridge inventory in the CSUS, it was found that over 12,927 bridges (12.6%) are exposed to 7% probability of exceedance (PE) in 75-year peak ground acceleration (PGA) of greater than 0.20 g, and nearly 3.5% of bridges in the CSUS have a 7% PE in 75-year PGA of greater than 0.50 g. Since many of the bridges in this region were not designed with explicit consideration of the seismic hazard, many of them are in need of seismic retrofitting to reduce their seismic vulnerability. While several of the states in the CSUS have retrofitted some of their bridges, systematic retrofit programs do not currently exist. The review of retrofit practices in the region indicates that the most common retrofit approaches in the CSUS include the use of restrainer cables, isolation bearings, column jacketing, shear keys, and seat extenders. The paper presents an overview of the common approaches and details used for the aforementioned retrofit measures. This paper serves as a useful tool for bridge engineers in the CSUS as they begin to perform systematic retrofit of vulnerable bridges in the region.

Regional Seismic Risk Assessment of Bridge Network in Charleston, South Carolina

This article presents the results of a seismic risk assessment of the bridge network in Charleston, South Carolina and the surrounding counties to support emergency planning efforts, and for prioritization of bridge retrofit. This study includes an inventory analysis of the approximately 375 bridges in the Charleston area, and convolution of the seismic hazard with fragility curves analytically derived for classes of bridges common to this part of the country. State-of-the-art bridge fragility curves and replacement cost estimates based on region-specific data are used to obtain economic loss estimates. The distribution of potential bridge damage and economic losses are evaluated for several scenario events in order to aid in the identification of emergency routes and assess areas for investment in retrofit. This article also evaluates the effect of uncertainty on the resulting predicted economic losses. The findings reveal that while the risk assessment is very sensitive to both the assumed fragility curves and damage ratios, the estimate of total expected economic losses is more sensitive to the vast differences in damage ratio models considered.

Efficient Longitudinal Seismic Fragility Assessment of a Multispan Continuous Steel Bridge on Liquefiable Soils

The increased failure potential of aging U.S. highway bridges and their susceptibility to damage during extreme events necessitates the development of efficient reliability assessment tools to prioritize maintenance and rehabilitation interventions. Reliability communication tools become even more important when considering complex phenomena such as soil liquefaction under seismic hazards. Currently, two approaches are widely used for bridge reliability estimation under soil failure conditions via fragility curves: liquefaction multipliers and full-scale two- or three-dimensional bridge-soil-foundation models. This paper offers a computationally economical yet adequate approach that links nonlinear finite-element models of a three-dimensional bridge system with a two-dimensional soil domain and a one-dimensional set of p-y springs into a coupled bridge-soil-foundation CBSF system. A multispan continuous steel girder bridge typical of the central and eastern United States along with heterogeneous liquefiable soil profiles is used within a statistical sampling scheme to illustrate the effects of soil failure and uncertainty propagation on the fragility of CBSF system components. In general, the fragility of rocker bearings, piles, embankment soil, and the probability of unseating increases with liquefaction, while that of commonly monitored components, such as columns, depends on the type of soil overlying the liquefiable sands. This component response depen- dence on soil failure supports the use of reliability assessment frameworks that are efficient for regional applications by relying on simplified but accepted geotechnical methods to capture complex soil liquefaction effects.