Abdollah Shafieezadeh

Fractional Order Filter Enhanced LQR for Seismic Protection of Civil Structures

This study presents fractional order filters to enhance the performance of the conventional linear quadratic regulator (LQR) method for optimal robust control of a simple civil structure. The introduced filters modify the state variables fed back to the constant gain controller. Four combinations of fractional order filter and LQR are considered and optimized based on a new performance criterion defined in the paper. Introducing fractional order filters is shown to considerably improve the results for both the artificially generated ground motions and previously recorded earthquake data.

Scenario-based resilience assessment framework for critical infrastructure systems: Case study for seismic resilience of seaports

A number of metrics in the past have been proposed and numerically implemented to assess the overall performance of large systems during natural disasters and their recovery in the aftermath of the events. Among such performance measures, resilience is a reliable metric. This paper proposes a probabilistic framework for scenario-based resilience assessment of infrastructure systems. The method accounts for uncertainties in the process including the correlation of the earthquake intensity measures, fragility assessment of structural components, estimation of repair requirements, the repair process, and finally the service demands. The proposed method is applied to a hypothetical seaport terminal and the system level performance of the seaport is assessed using various performance metrics. Results of this analysis have shown that medium to large seismic events may significantly disrupt the operation of seaports right after the event and the recovery process may take months. The proposed framework will enable port stakeholders to systematically assess the most-likely performance of the system during expected future earthquake events.

Age-Dependent Fragility Models of Utility Wood Poles in Power Distribution Networks Against Extreme Wind Hazards

Wood poles comprise a portion of the power utilitys aging infrastructure that make a significant impact on customers reliability. A large number may fail under the influence of severe wind storms and hurricanes, sometimes resulting in millions of dollars in replacement costs per year to the utilities. A holistic approach to risk assessment of wood poles in power distribution networks would therefore consider the simultaneous effects of decay and natural hazards on the failure probability of the poles. Toward this goal, this paper presents a framework for the development of age-dependent fragility curves of utility wood poles that relies on age-dependent probabilistic capacity models of wood poles and wind induced demand models. The framework considers uncertainties in the initial fiber strength of the wood poles, the age-dependent capacity loss model, the geometric features of wood poles of different classes, and the applied wind loads. The results of this study show that the decay process in wood poles may increase the fragility of the poles significantly as the age of the poles increase. The fragility curves provided in this research may constitute a major component of risk assessment approaches of power distribution networks against hurricanes and strong winds.

Seismic Performance of Pile-Supported Wharf Structures Considering Soil-Structure Interaction in Liquefied Soil

Many existing pile-supported marginal wharves within ports along the West Coast of the United States were designed in the late 1960s and early 1970s using the seismic design criteria available then, which were much less robust than the current criteria. As a result, structures designed using these criteria have often been severely damaged during the past earthquakes. This paper investigates the modal properties and vulnerability of such structures by using advanced structural and soil modeling procedures to perform two-dimensional nonlinear plane-strain seismic analyses using time histories of ground displacement and excess pore water pressures within the underlying soil embankment. Results show that the wharf structure experiences large permanent deformations and undergoes failure of the piles and pile-deck connections and pullout of batter piles in tension under large seismic events. Such failures were observed at the Port of Oakland during the 1989 Loma Prieta earthquake and also during other earthquakes throughout the world.

Experimental study of the semi-active control of a nonlinear two-span bridge using stochastic optimal polynomial control

This study performs a series of numerical simulations and shake-table experiments to design and assess the performance of a nonlinear clipped feedback control algorithm based on optimal polynomial control (OPC) to mitigate the response of a two-span bridge equipped with a magnetorheological (MR) damper. As an extended conventional linear quadratic regulator, OPC provides more flexibility in the control design and further enhances system performance. The challenges encountered in this case are (1) the linearization of the nonlinear behavior of various components and (2) the selection of the weighting matrices in the objective function of OPC. The first challenge is addressed by using stochastic linearization which replaces the nonlinear portion of the system behavior with an equivalent linear time-invariant model considering the stochasticity in the excitation. Furthermore, a genetic algorithm is employed to find optimal weighting matrices for the control design. The input current to the MR damper installed between adjacent spans is determined using a clipped stochastic optimal polynomial control algorithm. The performance of the controlled system is assessed through a set of shake-table experiments for far-field and near-field ground motions. The proposed method showed considerable improvements over passive cases especially for the far-field ground motion.

A decision framework for managing risk to airports from terrorist attack

This article presents an asset-level security risk management framework to assist stakeholders of critical assets with allocating limited budgets for enhancing their safety and security against terrorist attack. The proposed framework models the security system of an asset, considers various threat scenarios, and models the sequential decision framework of attackers during the attack. Its novel contributions are the introduction of the notion of partial neutralization of attackers by defenders, estimation of total loss from successful, partially successful, and unsuccessful actions of attackers at various stages of an attack, and inclusion of the effects of these losses on the choices made by terrorists at various stages of the attack. The application of the proposed method is demonstrated in an example dealing with security risk management of a U.S. commercial airport, in which a set of plausible threat scenarios and risk mitigation options are considered. It is found that a combination of providing blast-resistant cargo containers and a video surveillance system on the airport perimeter fence is the best option based on minimum expected life-cycle cost considering a 10-year service period.

Three-Dimensional Wharf Response to Far-Field and Impulsive Near-Field Ground Motions in Liquefiable Soils

AbstractSeismic performance evaluation of wharf structures constitutes the core of the vulnerability assessment of seaport infrastructure exposed to seismic events. Because this performance will depend on complex interactions between the surrounding potentially liquefiable soils and wharf foundation and structure, detailed and careful implementation of advanced modeling techniques is needed. These models are required to capture such highly nonlinear phenomena as permanent seaward deformation of embankment soils, soil-structure interaction in liquefiable soils, spread of plasticity in prestressed piles, and force-deformation of pile-deck connections. This study utilizes such modeling approaches to investigate the three-dimensional (3D) nonlinear response of a typical pile-supported container wharf structure in liquefiable embankment soils. Input excitations for this analysis consist of embankment soil deformations for a far-field and an impulsive near-field ground motion. These excitations are derived usin...

Fragility Assessment of Wood Poles in Power Distribution Networks Against Extreme Wind Hazards

Distribution networks in wind-prone areas along the Gulf Coast of the United States suffer extensive damage during hurricane seasons. This often results in loss of power in both small and large geographical areas depending on the configuration of the network and the spatial distribution of damage to the network components. Wood poles support overhead lines, which are primary components of power distribution networks, and are highly vulnerable to failure during strong winds. This paper presents the failure fragility function of typical classes of wood poles against strong winds. Using the provisions of the ASCE7 standard, an analytical model for wind load profiles along distribution wood poles is considered. Also assessed are categories of dimensions and material properties of dominant classes of wood poles. Uncertainties in applied wind loads and the structural response of the wood poles are accounted for in this framework to improve the accuracy of the derived fragility curves. This is achieved by making reasonable assumptions on the dispersion of the pole dimensions and material properties. The Latin hypercube sampling technique is used to generate and randomly pair 5,000 samples of the parameters of wind load and pole response. A Monte Carlo simulation is then used to compare realizations of the wind demand and pole capacities across a wide range of wind speeds, which serve as the intensity measure of the demand. The failure fragility curve is developed from the comparisons. The results of this research constitute a portion of risk analysis of power distribution networks against strong winds.

Mitigation of the seismic response of multi-span bridges using MR dampers: Experimental study of a new SMC-based controller

Pounding between adjacent structures has been a concern in multi-span bridges in recent earthquakes. In this paper, a pounding mitigation strategy using magnetorheological dampers is proposed, and its performance is tested for a three-span bridge using a series of shake-table experiments. A new semi-active control algorithm called SMC-OPC is developed that is based on a clipped sliding mode control (SMC) with sliding surfaces designed using an optimal polynomial control (OPC) approach. The control design uses a stochastically linearized model of the nonlinear bridge with passive components of the magnetorheological dampers embedded to achieve a more representative system characterization. Optimal weighting matrices for the optimal polynomial control are found through a genetic algorithm. The proposed method along with uncontrolled, passive-off, and passive-on cases are tested on shake-tables for several scaled near-field Kobe ground motion records. Although no pounding is observed in all control cases for small earthquakes, significant pounding occurs in the uncontrolled and passive-off systems under large earthquakes. For these ground motions, the performance of the semi-active controller converges to that of the passive-on case but with noticeably reduced power consumption. The study shows that the use of magnetorheological dampers between adjacent spans is very effective in mitigating critical bridge responses especially under large earthquakes. In addition, the proposed SMC-OPC semi-active control strategy enables achieving balance among multiple performance objectives with significantly reduced power consumption as compared to passive-on case.

Ohio Bridge Condition Index

Ohio has one of the largest portfolios of transportation assets with the second largest number of bridges in the United States. These bridges, of varying ages, comprise diverse configurations and structural features and are exposed to various environmental conditions and service loads. These factors, among others, pose a significant challenge in evaluating the performance of these assets and managing their safety and serviceability. This paper presents a practical and efficient measure called the bridge condition index (BCI) for the reliable condition assessment of Ohio bridges through the effective use of the Ohio Department of Transportation’s bridge databases. The Ohio BCI (OBCI) is intended to evaluate bridges at the element, component, bridge, and network levels and reflect the impact on the condition of the system of existing defects as well as maintenance, repair, and replacement actions for the condition enhancement of individual elements. To compare the direct and indirect consequences to users and agencies of various condition states of bridges, a unified metric based on cost is proposed for the OBCI formulation. This index is demonstrated for a real bridge in Ohio. To examine the efficiency of the OBCI, the results are compared with the bridge health index, which is a common bridge performance metric. The proposed metric can assist in the proper maintenance of transportation systems and effectively enhance their efficiency, safety, and capacity.