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Publications (174)
Exceeding serviceability limits due to wind-induced motions in tall buildings can cause discomfort for residents and adversely affect auxiliary building services, such as elevator operations. A tuned liquid damper (TLD) is an attractive type of dynamic absorber because of its simplicity and affordability. However, its dimensions and geometry can be...
A flat bottom tank geometry has traditionally been used for tuned liquid dampers (TLDs) to control the resonant response of tall buildings. However, the bottom geometry may be dictated by building space availability. Different bottom geometries have been proposed to conform to strict floor plans. Previous studies focused on modelling TLDs with irre...
Liquid sloshing inside a Tuned Liquid Damper (TLD) equipped with screens introduces significant numerical modelling challenges. A 2D Incompressible Smoothed Particle Hydrodynamics (ISPH) model employing a novel macroscopic screen model is presented to capture the complex flow associated with screens and significantly minimize the high computation c...
Seismic fragility analysis is deemed to be a functional tool for evaluating the performance of bridges subjected to natural hazards such as earthquakes. Although there have been many studies on developing fragility curves for generic bridges, few have focused on the existing bridges (particularly long-span bridges). Moreover, the majority of studie...
Power infrastructure networks are susceptible to performance disruptions induced by natural or anthropogenic hazard events. Forexample, extreme weather events or cyberattacks can disrupt the functionality of multiple network components concurrently or sequentially,resulting in a chain of cascading failures throughout the network. Mitigating the imp...
A third-order nonlinear multimodal model is developed for tanks with non-flat bottoms. A 6-node finite element model is used to determine the mode shapes of the velocity potential and the associated natural sloshing frequencies. Using this modal information, equations of motion are developed that accommodate the nonlinear coupling among the first t...
The nonlinear response of a series-type pendulum tuned mass damper-tuned liquid damper (TMD-TLD) system is investigated in this study. The TLD is mounted on the pendulum TMD in series to remove the need for costly viscous damping elements. Since the response of the TMD is greater than that of the primary structure, the TLD experiences a significant...
Annular tuned sloshing dampers equipped with damping screens are studied experimentally and analytically. A nonlinear multimodal model is presented to simulate the coupled response among the lowest order sloshing modes in a tank equipped with damping screens, which leads to velocity-squared damping. Shake table tests are conducted on annular tanks...
The tuned liquid damper (TLD) uses liquid sloshing in a tank to suppress unwanted wind-induced vibration of a flexible structure. The tank interior height is traditionally selected such that sloshing waves do not impact the tank ceiling by providing sufficient freeboard between the free surface and the tank ceiling. To optimize a TLD for a space wi...
The design provisions of current blast protection standards are primarily focused on the response of single components and do not provide adequate tools to quantify the overall performance of critical infrastructure systems (CIS), let alone the interdependence of such systems. Methodologies that can translate blast-induced damage into information a...
This study investigates the seismic performance of a seismically isolated soil-pile-structure system incorporating the effects of isolation system, soil layers of low stiffness and strength, pile inclination, pile-soil-pile interactions, and bridge-embankment interaction. A coupled three-dimensional nonlinear finite element model of an existing bri...
Power infrastructure networks continue to be at risk under natural and anthropogenic hazard events. Cyberattacks targeting power grids aim at magnifying the impacts through damage propagation to other dependent infrastructure network. In this respect, the current study focuses on the “draw-down” phase of power infrastructure network resilience cons...
Highway bridges are considered to be one of the most susceptible constituents of transportation networks when they are subjected to severe natural hazards such as earthquakes. The serviceability and functionality of these structures are a prerequisite to ensure continuous transport and emergency routes. To facilitate and enhance pre-hazard event mi...
Seismic isolation systems are typically used in bridge structures to mitigate the damage risk of bridge components against natural hazards including earthquakes. The objective of base isolation is to provide an intermediate layer with high vertical stiffness to accommodate the gravitational forces and low horizontal stiffness to decouple the supers...
A seismically resilient transportation network entails preprioritized retrofit plans for conventionally designed highway bridges. This is particularly important for the province of Ontario in Canada, where more than 44% of the multispan bridges have been constructed prior to 1970. To support future seismic risk mitigation efforts, this study evalua...
The current blast response limits for reinforced masonry (RM) walls in North American blast standards are based on parameters that neither account for the wall ductility capacities nor the influence of different design configurations on the wall damage tolerance levels. Specifically, ASCE (2011) and CSA (2012) currently assign a support chord rotat...
The tuned liquid damper (TLD) is a system used to reduce the response of tall structures. Numerical modelling is a very important tool when designing TLDs. Many existing numerical models are capable of accurately capturing the structure-TLD system response at serviceability levels, covering the range where TLDs are primarily intended to perform. Ho...
Although boundary elements have been demonstrated to enhance the in-plane performance of reinforced concrete block shear walls under seismic loading, research evaluating their effect on the walls' out-of-plane performance (e.g., due to earth pressure, wind loading, or blast loading) is very scarce. As such, current blast standards do not assign uni...
Damping screens are often installed within a tuned liquid damper (TLD) to increase the energy dissipation beyond what the sloshing liquid alone can provide. Many numerical models exist to study the response of a TLD; however, there are often associated limitations on fluid depth or excitation amplitude. The smoothed particle hydrodynamics (SPH) met...
The increases in accidental explosion events over the past two decades have demonstrated the urgent need to evaluate the behavior of blast-vulnerable structural components and develop subsequent risk mitigation strategies. In this context, several studies have focused on the out-of-plane behavior of either unreinforced masonry walls or non-load bea...
Reinforced masonry shear wall (RMSW) systems constructed using concrete blocks are widely used within the current North American construction practices. The limited research carried out on the performance of RMSWs under blast loading has reviled their high vulnerability. This study evaluates the blast performance of such loadbearing and non-loadbea...
The performance of nonstructural components in nuclear power plants (NPPs), which is primarily based on experience and historical data, has been attracting increased interest from researchers following the Fukushima Daiichi nuclear disaster in 2011. This disaster demonstrated the importance of using batteries in NPPs as an auxiliary power system, w...
The seismic performance of unanchored slender contents at various floor levels within a building has received little attention in the literature, despite earthquake reconnaissance reports routinely emphasizing the overturning of contents as a pervasive problem. This paper investigates the rocking response of building contents in a four-story concen...
Annular tuned liquid dampers (TLD) may be installed in slender structures with limited floor space, in which people and utilities must pass through the core, such as a wind turbine or observation tower. This study investigates an annular-shaped TLD equipped with damping screens. A linearized equivalent mechanical model capable of capturing the fund...
The increased frequency and magnitude of natural and anthropogenic hazard events that affected infrastructure systems over the past two decades have highlighted the need for more effective risk management strategies. Such strategies are expected to not only manage the immediate disruption to system’s functionality following hazard realization, but...
Space restrictions at the top of tall buildings may necessitate using TSD tanks with large rectangular penetrations to accommodate the structural core of the tower. A finite element model is employed to predict the natural sloshing frequencies and mode shapes of liquid sloshing in a rectangular tank with a rectangular core. Equivalent mechanical pr...
Complex network theory (CNT) has been providing the platform to simulate, analyze, and visualize different complex interdependent networks. Despite the successes of simulating and analyzing infrastructure networks based on their static topological characteristics using CNT, there remain some challenges pertaining to considering the temporal variati...
Although boundary elements have been known to enhance the in-plane performance of reinforced concrete block shear walls under seismic loading, research examining their influence on the walls’ out-of-plane performance (e.g., due to blast loading) is very scarce. Unlike conventional walls with rectangular cross sections, boundary elements allow the u...
A confined explosion inside a critical facility may lead to the total paralysis of pertinent operations. Practical solutions to mitigate such risk include lightweight sacrificial cladding, which can be deployed as a physical barrier to protect high importance (i.e., critical) facilities from potential explosions. More specifically, sandwich panels...
One of the most commonly used types of isolator is the steel-reinforced elastomeric isolator (SREI), but recent research has been completed on the use of fibers as a replacement to the steel reinforcement layers, reducing weight and potentially costs associated with isolation systems. These fiber-reinforced elastomeric isolators (FREI) can be used...
A pendulum-type tuned mass damper (TMD) - tuned sloshing damper (TSD) system is proposed as a cost effective device to reduce wind-induced structural motion. Lagrange's principle is employed to develop an equivalent mechanical model for the system. The sloshing liquid provides additional gravitational restoring force to the pendulum TMD, but does n...
Prediction of peak wave heights early in the TLD design process is critical to ensure proper tank freeboard is allocated. If insufficient freeboard is allocated, the performance of the TLD may be adversely affected by the waves impacting with the tank ceiling. A frequency domain model is developed to predict the spectral response of the first two T...
The increase in the number of deliberate and accidental explosion events over the past two decades has necessitated evaluating the performance of blast-vulnerable structural components and developing subsequent risk mitigation strategies. In this context, several studies have focused on the out-of-plane behavior of either unreinforced masonry walls...
Unbonded fiber-reinforced elastomeric isolators (FREIs) were initially proposed as a potential low-cost alternative to conventional steel-reinforced elastomeric isolators (SREIs). FREIs are similar to SREIs but comparatively lightweight as the steel components from SREIs have been replaced with polymer fibers in FREIs. Subsequent experimental inves...
With the increased frequency of accidental and deliberate explosions, evaluating the response of civil infrastructure systems to blast loading has been attracting the interests of the research and regulatory communities. However, with the high cost and complex safety and logistical issues associated with field explosives testing, North American bla...
Auxiliary batteries and battery rack systems are widely used as a risk mitigation strategy in several critical facilities to supply power following loss of external power from the grid. Although these systems might fail during earthquakes, causing cascading catastrophic economic and life losses, they have received little attention in terms of inves...
The world has been becoming deeply dependent on multitudes of physical and cyber critical infrastructure networks. Such networks are not isolated but interdependent in different ways. Although these interdependencies enhance the network-of-network efficiencies, interdependence also increases the network vulnerabilities, where a small damage in one...
Reinforced masonry shear walls with boundary elements have been introduced recently as a seismic force–resisting system as alternative to traditional reinforced masonry shear walls with rectangular cross sections. The introduction of the boundary elements enhances the wall’s in-plane performance because of the confinement action of the horizontal s...
Recent anthropogenic hazards to structures and infrastructure alike defy classical risk assessment schemes, in that the broader consequences of a catastrophic event such as the bombing of a building of strategic or symbolic importance can hardly be estimated by actuary science. The level of uncertainty associated with the aftermath of a terrorist a...
There are two classical types of application for fiber reinforced elastomeric bearings (FREB), namely, “bonded (B)” and “unbonded (UB)” applications. Although the UB-application results in improved seismic isolation efficiency due to rollover deformations, UB-FREB are not capable of transferring tensile forces, and may experience slip under certain...
The recent escalation of terrorism blast events, in terms of their corresponding frequency and magnitude, have fostered the development of risk mitigation measures. This escalation is mainly attributed to the unprecedented vulnerabilities as a result of the explosive device attacks (e.g. suicide and vehicle bombs) that have significantly evolved wi...
The frequent natural and anthropogenic hazards coupled with their negative cascading influences on infrastructure systems have exposed cities to several economic and life losses. Thus, the concept of a resilient city was recently introduced and subsequently utilized to minimize the cascading risk of the city infrastructure interdependencies under s...
Reinforced masonry (RM) walls with boundary elements (BEs) have been recently introduced in different design standards as a new construction technique to replace the conventional RM shear walls with rectangular cross sections. This is because recent research studies demonstrated that BEs enhance both the wall in-plane ductility performance and the...
Stable unbonded fiber-reinforced elastomeric isolators (SU-FREIs) exhibit a characteristic horizontal softening and stiffening response, similar to other adaptive devices such as the triple friction pendulum and sliding systems with variable curvature. The transition between the softening and stiffening occurs at a displacement corresponding to a u...
A tuned liquid damper (TLD) is often used to mitigate the wind-induced vibrations of tall slender structures. A TLD typically consists of a partially filled rigid water tank located near the top of a structure and is often equipped with screens or devices to increase energy dissipation. The required freeboard for the TLD tank is determined by calcu...
The increase in the complexity of city critical infrastructure system’s interdependencies, coupled with the massive amount of these systems’ data, call for a paradigm shift in planning cities to be resilient under cascading (systemic) risks. Furthermore, most of the available resiliency planning frameworks are based on hazard characterization, whic...
The current study forms a part of a larger experimental program investigating the performance of novel, lightweight, cost-effective, cold-formed, steel sandwich panels with different core configurations under blast induced out-of-plane loading. In the body of literature on sandwich panels, no general methodology is provided to assess their post-ela...
Fiber-reinforced elastomeric isolators (FREIs) are relatively lightweight, can be cut to the required size from larger pads, and can be placed unbonded (i.e., unfastened) between the supports. The two major geometric parameters that influence the vertical and lateral response of unbonded fiber-reinforced elastomeric isolators (U-FREIs) are the shap...
Current standards for the blast protection of buildings are primarily focused on the response of single components and do not provide adequate tools to quantify the overall performance of complex structural systems. Methodologies that can translate structural damage into information actionable by policy-makers are greatly needed to support the risk...
The resilience of the built environment to high explosives poses a significant challenge to the professionals tasked with the design of blast resistant facilities. Current standards––including the ASCE 59-11 and CSA S850-12––fail to address this challenge in design provisions targeting a single parameter of structural performance, while neglecting...
The growing number of terrorist attacks in the past decade has focused the public’s attention on the severity of such a man–made hazard. The rising threat of improvised explosive devices––one of the most successful attack strategies––has significantly increased the number of threats on the ground, in the form of suicide–bombs, vehicle–bombs, etc.,...
The resilience of the built environment to high explosives poses a significant challenge to the professionals tasked with the design of blast resistant facilities. Current standards — including the ASCE 59-11 and CSA S850-12 — fail to address this challenge in design provisions targeting a single parameter of structural performance, while neglectin...
Bidirectional dynamic vibration absorbers (DVAs) can simultaneously reduce the resonant response of two perpendicular modes of lightly damped structures. The performance of the DVA is affected if its directions of motion are not aligned with the structural modes. When the DVA is misaligned, the 2D structure–DVA system is represented as a coupled 4‐...
The protection of the built environment from extreme manmade hazards poses a significant challenge to the professionals engaged in the design and evaluation of exposed assets. Especially insidious are the malicious attacks executed via improvised explosive devices (IEDs), which do not lend themselves to easy modeling owing to the adaptive nature of...
The fallout of natural and anthropogenic disasters on the affected populations and the economy has fostered a protracted effort in the advancement of community resilience and risk mitigation. Amongst the man–made hazards, terrorist attacks generally––and improvised explosive devices (IED) more specifically––are known to be characterized by high unc...
Boundary elements (BEs) have been shown to enhance the in-plane performance of reinforced masonry (RM) walls, in terms of both section capacity and ductility. For this reason, in 2014 these elements were introduced in the Canadian standard S304-14 as a seismic force resisting system. When their out-of-plane performance is considered, BEs can signif...
An unbonded fiber-reinforced elastomeric isolator (U-FREI) is a relatively new type of elastomeric bearing that can be implemented as a seismic isolator for bridges. U-FREIs possess beneficial characteristics, including their potentially low-cost and light-weight construction. Individual U-FREIs can be rapidly produced as they can be easily cut fro...
Sandwich panel systems offer many advantages over other conventional systems, which facilitate their use in several applications, including aerospace, naval, and transportation. The complexity and relatively high cost of sandwich panel system design and fabrication have limited its application in civil engineering applications. In accordance with N...
In this paper, time history analyses are carried out on a structure seismically isolated with fiber-reinforced elastomeric isolators (FREIs). The lateral response of the isolators is simulated using two modeling techniques, the Backbone Curve model, which combines a dashpot with a nonlinear elastic spring, and a new proposed model, named Pivot-Elas...
Analytical solutions for critical design properties of elastomeric bearings, such as the compression modulus, bending modulus, and maximum shear strain due to compression or rotation, including the compressibility of the elastomer, have been developed for most basic laminated elastomeric bearing geometries. Due to the introduction of extensible fib...
Fiber reinforced elastomeric isolators (FREI) can be implemented in a variety of structures, including buildings and bridges. A FREI consists of alternating layers of elastomer and fiber fabric (often carbon fiber). The main role for the fiber reinforcement is to limit the bulging of the elastomer layers, and is the dominant parameter affecting the...
In seismic base isolation applications, fiber reinforcement was initially proposed as a potential cost-saving alternative to conventional steel reinforcement in laminated bearings. Steel reinforcement is often assumed to be rigid, but the extensibility of the reinforcement serves as an additional design parameter that must be considered. Similar to...
Multiple dynamic vibration absorbers (MDVAs) employ multiple auxiliary masses tuned to frequencies near the structural frequency to reduce building motions. Added effective damping is often used to quantify the structural motion reduction attributed to the structural control system. However, the level of added effective damping by a MDVA system is...
The objective of seismic isolation is to decouple the superstructure from earthquake induced ground motions. The introduction of properly designed low horizontal stiffness elements between the superstructure and the foundation, which are capable of carrying the vertical loads to the foundation, results in reduced seismic demand on the structure. Nu...
Computational tools and numerical strategies for the determination of the response of masonry walls under blast overpressure often rely on oversimplifying and conservative assumptions, which, although justifiable for design purposes, are not as warranted when fragility analysis and risk assessment are the objectives. In addition, due to the composi...
Unbonded fiber reinforced elastomeric isolators (U-FREI) have been proposed as a viable alternative to traditional steel reinforced elastomeric isolators (SREI) for use in low-rise building base isolation systems. The viability of U-FREI for this particular application was confirmed through an extensive evaluation of their lateral response under th...
The use of fully grouted reinforced masonry shear walls (RMSWs) has been growing in several areas around the world owing to their relative ease of construction. Although the walls can be detailed to possess a high level of in-plane ductility, they typically have very low out-of-plane ductility due to the standard masonry unit configuration and the...
Increased exposure to the detrimental effects of blast events has led to the release of several guidelines and the recent publication of two North American standards that provide guidance on the hardening and performance quantification of structures subjected to this type of loading. The safety and security logistics and the high cost associated wi...
The response to natural disasters has been increasingly presented under the banner of resilience. However, as stakeholders and policy makers have come to realize, building resilient communities is a wicked problem that defies a simple definition, much less a solution. In this commentary on the role and importance of resilience in a multi–hazard env...
A tuned liquid damper (TLD), which is similar to a tuned mass damper (TMD), is a type of dynamic vibration absorber (DVA) that can be employed to reduce wind induced resonant vibrations of a structure. Improved TLD performance could be realized by equipping TLDs with variable energy dissipating capabilities such as damping screens, which can be adj...
The introduction of alternative reinforcement types for elastomeric bearings has rendered it necessary to consider the extensibility of the reinforcement as an additional design parameter. The extensibility of the reinforcement reduces the lateral restraint on the elastomer and, similar to the compressibility of the elastomer, influences important...
A previous study by the authors provides an overview of existing seismic risk assessment approaches and available seismic fragility information and highlights the lack of relevant information for nonengineered residential buildings. The current paper proposes a procedure for developing empirical seismic fragility curves for nonengineered residentia...
The increased demand for resilient infrastructure under accidental or deliberate explosions has resulted in the urgent need to quantify the performance of both existing and new building components under such extreme loading events. The current study focuses on evaluating the resilience of reinforced masonry (RM) shear wall systems under blast, whic...
Linearized equivalent mechanical models are often used to conduct preliminary tuned liquid damper (TLD) design; however, they cannot capture nonlinear behavior resulting from the coupling among sloshing modes. Therefore, these models underestimate the expected peak wave height, a quantity that is necessary to evaluate the required tank freeboard. I...
Stable unbonded fiber-reinforced elastomeric isolators (SU-FREIs) exhibit a characteristic horizontal softening and stiffening response, similar to other adaptive devices such as the triple friction pendulum and sliding systems with variable curvature. The transition between the softening and stiffening occurs at a displacement corresponding to a u...
Probabilistic risk assessment (PRA) is essential for evaluating different options for blast risk management. However, depending on the risk management approach being considered, a rigorous blast PRA study can be quite demanding. To expedite this process, a simplified PRA framework is proposed for reinforced concrete-block shear wall buildings, in o...
The seismic response of a 2-story reinforced concrete shear wall structure seismically isolated using unbonded rectangular fiber-reinforced elastomeric isolators (FREIs) is investigated. Using rectangular isolators, rather than square or circular, for buildings with masonry or reinforced concrete structural walls allows a more uniform distribution...
In traditional tuned liquid damper (TLD) installations, TLD tank(s) are tuned to a single optimal frequency as determined by well-known dynamic vibration absorber theory. A multiple tuned liquid damper (MTLD) is created when the sloshing frequencies are distributed over a range near the structural frequency. In this paper, an equivalent mechanical...
Stable unbonded fiber-reinforced elastomeric isolators (SU-FREIs) have been presented as a potentially low-cost alternative to conventional steel-reinforced elastomeric isolators. The fiber reinforcement allows for a unique deformed shape to develop during horizontal displacement. This unique deformed shape, known as rollover, is the cause of a des...
Fiber reinforced elastomeric isolators (FREI) possess unique characteristics relative to traditional steel reinforced elastomeric isolators (SREI). FREI can be classified as either bonded or unbonded according to the connection type employed. An understanding of the behavior of FREI under these loading configurations is needed in order to extend th...
http://dx.doi.org/10.1061/AJRUA6.0000823
Implementation of supplemental damping systems (e.g., the dynamic vibration absorbers (DVAs)) to mitigate excessive tall building vibrations induced by external dynamic loads (wind storms or earthquakes) has increased over the last several decades. A tuned liquid damper (TLD) is a specific type of the DVAs that consists of a rigid tank which is par...