Browsing by Author "Saad, Timothy"

Now showing 1 - 4 of 4
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    Determining Strength Capacity of Deteriorated Reinforced Concrete Bridge Substructures
    (2010) Saad, Timothy; Fu, Chung C; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Corrosion of steel reinforcement is a major factor in the deterioration of highway and bridge infrastructure. Knowing the initiation time of corrosion on a reinforced concrete structure provides a much needed source of information in evaluating the service life of the structure. To find the corrosion initiation time the effects of carbonation and chloride are examined. Furthermore, the different variables that affect the ingress of carbonation and chloride are also examined and analyzed together. Probabilistic modeling and stochastic design of these variables will determine the initiation of corrosion, the amount of corrosion, and the strength loss of the concrete pier. This process will help classify deteriorating structure into the National Bridge Inventory (NBI) condition ratings from the Federal Highway Administration.
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    Development of a Fatigue Life Assessment Model for Pairing Fatigue Damage Prognoses with Bridge Management Systems
    (IntechOpen, 2018-12-18) Saad, Timothy; Fu, Chung C.; Zhao, Gengwen; Xu, Chaoran
    Fatigue damage is one of the primary safety concerns for steel bridges reaching the end of their design life. Currently, US federal requirements mandate regular inspection of steel bridges for fatigue cracks; however, these inspections rely on visual inspection, which is subjective to the inspector’s physically inherent limitations. Structural health monitoring (SHM) can be implemented on bridges to collect data between inspection intervals and gather supplementary information on the bridges’ response to loads. Combining SHM with finite element analyses, this paper integrates two analysis methods to assess fatigue damage in the crack initiation and crack propagation periods of fatigue life. The crack initiation period is evaluated using S-N curves, a process that is currently used by the FHWA and AASHTO to assess fatigue damage. The crack propagation period is evaluated with linear elastic fracture mechanic-based finite element models, which have been widely used to predict steady-state crack growth behavior. Ultimately, the presented approach will determine the fatigue damage prognoses of steel bridge elements and damage prognoses are integrated with current condition state classifications used in bridge management systems. A case study is presented to demonstrate how this approach can be used to assess fatigue damage on an existing steel bridge.
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    Development of a Fatigue Life Assessment Model for Pairing Fatigue-Damage Prognoses with Bridge Management Systems
    (2015) Saad, Timothy; Fu, Chung C; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Fatigue damage is one of the primary safety concerns for steel bridges reaching the end of their design life. Currently, federal requirements mandate regular inspection of steel bridges for fatigue cracks with evaluative reporting to bridge management systems. The quality of the inspection is subjective and time delayed due to inspection cycles, which are scheduled for every two years. However, structural health monitoring (SHM) data collected between inspection-intervals can provide supplementary information on structural condition that ameliorates some drawbacks of current inspection methods. Through the use of SHM and finite element models, fatigue performance assessments can be utilized throughout the service life of fatigue sensitive bridge elements for mitigating fatigue damage and preventing sudden fatigue failure. These assessments will additionally be useful to inspectors when reporting bridge condition evaluations to bridge management systems. The main goal of this study is to develop a fatigue life assessment method used for determining the remaining useful life of steel bridges and to map these results to existing bridge management systems. In order to achieve this goal, the current practices and methodologies associated with fatigue life of bridge elements and the use of bridge management systems are investigated. For analyses of fatigue damage, the fatigue life is split into two different periods of analyses: a crack initiation period and crack growth period. In order to quantify the effects of fatigue damage, each period of the fatigue life is associated with a unique assessment method, an empirical correlation assessment and a fracture mechanics assessment. Structural health monitoring techniques are employed to monitor the behavior of the bridge components and bridge elements. These two assessment methods are combined to form a damage accumulation model to estimate the fatigue life. The proposed damage accumulation model uses the acquired data from structural health monitoring alongside finite element modeling to derive a damage prognosis of bridge elements. The damage prognosis attempts to forecast the structure's performance by measuring the cumulative fatigue damage, estimating future loads, and ultimately determining the remaining useful life of the bridge element. A technique for mapping the results of the damage prognosis into condition state classifications is proposed. The suitability and applicability of the proposed damage accumulation model is illustrated on an existing highway bridge. This bridge was selected as a good candidate for fatigue monitoring due to the average daily truck traffic and the identification of existing and active fatigue cracks. The application of the damage accumulation model is demonstrated and a damage prognosis is derived. Finally, the damage accumulation results are integrated with current condition state classifications used in bridge management systems.
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    Fatigue Assessment of Highway Bridges under Traffic Loading Using Microscopic Traffic Simulation
    (IntechOpen, 2018-11-13) Zhao, Gengwen; Fu, Chung C.; Lu, Yang; Saad, Timothy
    Fatigue is a common failure mode of steel bridges induced by truck traffic. Despite the deterioration caused by environmental factors, the increasing truck traffic volume and weight pose a premier threat to steel highway bridges. Given the uncertainties of the complicated traffic loading and the complexity of the bridge structure, fatigue evaluation based on field measurements under actual traffic flow is recommended. As the quality and the quantity of the available long-term traffic monitoring data and information have been improved, methodologies have been developed to obtain more realistic vehicular live load traffic. A case study of a steel interstate highway bridge using microscopic traffic simulation is presented herein. The knowledge of actual traffic loading may reduce the uncertainty involved in the evaluation of the load-carrying capacity, estimation of the rate of deterioration, and prediction of remaining fatigue life. This chapter demonstrates a systematic approach using traffic simulation and bridge health monitoring-based fatigue assessment.