Highway Bridge Networks Research Articles

Seismic Reliability Assessment of Aging Highway Bridge Networks with Field Instrumentation Data and Correlated Failures, II: Application

The bridge reliability in networks (BRAN) methodology introduced in the companion paper is applied to evaluate the reliability of part of the highway bridge network in South Carolina under a selected seismic scenario. The case study demonstrates Bayesian updating of deterioration parameters across bridges after spatial interpolation of data acquired from limited instrumented bridges. The updated deterioration parameters inform aging bridge seismic fragility curves through multi-dimensional integration of parameterized fragility models, which are utilized to derive bridge failure probabilities. The paper establishes the correlation structure among bridge failures from three information sources to generate realizations of bridge failures for network-level reliability assessments by Monte Carlo analysis. Positive correlations improve the reliability of the case study network, as predicted from network topology. The benefits of the BRAN methodology are highlighted in its applicability to large networks, while addressing some of the existing gaps in bridge network reliability and prioritization studies.

Seismic Reliability Assessment of Aging Highway Bridge Networks with Field Instrumentation Data and Correlated Failures, I: Methodology

The state-of-the-practice in seismic network reliability assessment of highway bridges often ignores bridge failure correlations imposed by factors such as the network topology, construction methods, and present-day condition of bridges, among others. Additionally, aging bridge seismic fragilities are typically determined simply using historical estimates of deterioration parameters. This research presents a methodology to estimate bridge fragilities using spatially interpolated and updated deterioration parameters from a limited set of instrumented bridges in the network, while incorporating the impacts of overlooked correlation factors in bridge fragility estimates. Simulated samples of correlated bridge failures are used in an enhanced Monte Carlo method to assess bridge network reliability, and the impact of different correlation structures on the network reliability is discussed. The presented methodology aims to provide more realistic estimates of seismic reliability of aging transportation networks and to potentially help network stakeholders to more accurately identify critical bridges for maintenance and retrofit prioritization.

Cost Assessment of Highway Bridge Network Subjected to Extreme Seismic Events

A transportation network is the economic backbone of a developed country. For that reason, it is important that the network maintain functionality after catastrophic natural events and minimize downtime to reduce adverse effects on society and the economy. A holistic framework that integrates seismic risk, vulnerability of system components, and a traffic model is developed. This framework is used to evaluate the direct and indirect costs associated with extreme seismic events. The combined effect of ground motion and liquefaction is considered to estimate the seismic risk of the system. Bridges are considered the most vulnerable network components. The concept of fragility curves is used to combine the probability of bridge failure with the postevent functionality of the network. An integrated traffic model is used to predict route choices after an earthquake. Finally, the developed framework is used to estimate the earthquake risk of the test bed transportation network in the San Francisco Bay Area of California. The direct and indirect costs associated with several earthquake scenarios in the region are estimated, and annual risk curves are developed.

Bridge retrofit prioritisation for ageing transportation networks subject to seismic hazards

The deteriorating state of highway bridges is traditionally ignored in estimating the seismic reliability of transportation networks. In this study, the present day seismic reliability of ageing bridges in highway networks is evaluated through a time-dependent seismic fragility analysis of typical bridge classes. An efficient algorithm based on finite-state Markov Chain Monte Carlo simulations is also presented to assess the reliability of large ageing highway bridge networks without the need to simplify the network topology. The criticality of ageing bridges is then assessed through different proposed ranking strategies to arrive at an optimised seismic retrofit prioritisation. A case study on an existing bridge network with 515 bridges in the state of South Carolina, USA reveals striking differences between results of the proposed ranking strategies and those from state-of-the-practice methods. Such differences emphasise the significance of accounting for network-level importance in seismic retrofit programs of ageing transportation networks.

Sustainability of Highway Bridge Networks Under Seismic Hazard

In order to evaluate the seismic risk of transportation networks, it is necessary to develop a methodology that integrates the probabilities of occurrence of seismic events in a region, the vulnerability of the civil infrastructure, and the consequences of the seismic hazard to the society, environment, and economy. In this article, a framework for the time-variant seismic sustainability and risk assessment of highway bridge networks is presented. The sustainability of the network is quantified in terms of its social, environmental, and economic metrics. These include the expected downtime, expected energy waste and carbon dioxide emissions, and the expected loss. The methodology considers the probability of occurrence of a set of seismic scenarios that reflect the seismic activity of the region. The performance of network links is quantified based on individual bridge performance evaluated through fragility analyses. The sustainability and risk depend on the damage states of both the links and the bridges within the network following an earthquake scenario. The time-variation of the sustainability metrics and risk due to structural deterioration is identified. The approach is illustrated on a transportation network located in Alameda County, California.

Time-dependent risk associated with deterioration of highway bridge networks

Risk-based performance indicators offer valuable information on the performance of spatially distributed systems, such as highway bridge networks, whose functionality is vital for economic and social purposes. In this paper, the time-dependent expected losses of deteriorated highway bridge networks are investigated. A five-state Markov model is used to predict the time-dependent performance of bridges. The direct consequences are assessed on the basis of scenarios characterized by individual bridge failures and maintenance shutdowns. The indirect consequences are quantified on the basis of scenarios characterized by single and multiple bridges out-of-service, by solving the traffic assignment problem. The variation of direct, indirect and total expected losses in time is computed. The proposed methodology is suitable for the assessment of losses due to the service loads and the effects of deterioration. The proposed approach is illustrated on a highway bridge network. The results indicate that the maximum total expected indirect loss is much higher than the maximum total expected direct loss. The expected loss profiles show a pattern that first increases and then decreases due to the time-variation of the Markov chain state probabilities.

Innovative design approach of precast–prestressed girder bridges using ultra high performance concrete

The construction of new bridges and the maintenance and renewal of aging highway bridge network using ultra high performance concrete can lead to the construction of long life bridges that will require minimum maintenance resulting in low life cycle costs. Ultra high performance concrete (UHPC) is a newly developed concrete material that provides very high strength and very low permeability to aggressive agents such as chlorides from de-icing salts or seawater. Ultra high performance concrete could enable major improvements over conventional high performance concrete (HPC) bridges in terms of structural efficiency, durability, and cost-effectiveness over the long term. A simplified design approach of concrete slab on UHPC girders bridge using the Canadian Highway Bridge Design code and the current recommendations for UHPC design is proposed. An illustrative example demonstrates that the use of UHPC in precast–prestressed concrete girders yields a more efficient design of the superstructure where considerable reduction in the number of girders and girder size when compared to conventional HPC girders bridge with the same span length. Hence, UHPC results in a significant reduction in concrete volume and then weight of the superstructure, which in turn leads to significant reduction in the dead load on the substructure, especially for the case of aging bridges, thus improving their performance.

Effect of Changing Truck Weight Regulations on U.S. Bridge Network

Historically, truck weight regulations have maintained controls on axle and gross weights with legal load formulas based on limiting allowable stresses in certain types of bridges. These stress limitations do not usually lead to consistent or defensible reliability levels and also ignore the impact of the weight regulation on the existing highway bridge network. This paper is the second part of a two-paper series. The companion paper by the first writer illustrated how new truck weight regulations can be developed to provide an acceptable reliability level. The target reliability level was derived from bridge structures designed to satisfy AASHTO standard design specifications that showed safe and adequate performance levels under current truck loading conditions. In this part of the two-paper series, a deterministric load capacity evaluation as well as a reliability assessment are performed to review the consequences of adapting such regulations on the existing U.S. bridge network. A sensitivity analysis shows how changes in the safety criteria used to develop the truck weight regulations would affect the existing bridge network. Detailed load capacity evaluations and reliability analyses are also performed on a representative sample of bridges to provide specific examples of expected changes in rating and safety levels if the proposed truck weight regulation is to be adopted.