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Rocking as a means of seismic isolation relies on utilizing the rotational inertia of the structure through (purposely) activated dynamic motion (i.e. rigid body rotation). This is a radically different concept than conventional seismic... more
Rocking as a means of seismic isolation relies on utilizing the rotational inertia of the structure through (purposely) activated dynamic motion (i.e. rigid body rotation). This is a radically different concept than conventional seismic design that regards dynamic motion as an “unpleasant” by-product of structural deformation. Rigid body rotations around predefined pivot points isolate the structure during strong ground motions. Therefore, stresses on the structure are significantly reduced, relieving it from deformation and damage. The mechanical configuration of the rocking frame has been proposed as a “damage avoidance design” for bridges. The rocking frame can be either freestanding or hybrid when supplemented with (unbonded) central tendons and energy dissipaters exhibiting flag-shaped hysteretic behavior. From the standpoint of practical bridge engineering applications, a question that persists is that of the seismic reliability of the (hybrid) rocking behavior. Motivated by t...
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Research Interests: Geology and Seismology
ABSTRACT: The present work investigates the seismic performance of a rocking bridge bent, which is either freestanding or hybrid (supplemented with energy dissipation and recentering devices), exhibiting flag-shaped hysteretic behaviour.... more
ABSTRACT: The present work investigates the seismic performance of a rocking bridge bent, which is either freestanding or hybrid (supplemented with energy dissipation and recentering devices), exhibiting flag-shaped hysteretic behaviour. Such hybrid systems have been proposed by several researchers as high-performance systems that can survive major earthquakes without substantial damage. This study considers three different structural rocking systems with either negative, zero, or positive lateral stiffness and compares their seismic performance with the pertinent freestanding structure. Both pulse-type and nonpulse-type ground motions are considered. The analysis demonstrates performance enhancement as the stiffness of the system increases and as the size of the columns decreases. However, this improvement is marginal among the examined stiffness systems. Further, it is shown that depending on the characteristics of the examined earthquake record, a different rocking design solutio...
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In light of the resurgence of rocking as a means of seismic isolation for modern structures/bridges, there is an increasing need to predict the response of complex rocking structures. To date, most analytical investigations into the... more
In light of the resurgence of rocking as a means of seismic isolation for modern structures/bridges, there is an increasing need to predict the response of complex rocking structures. To date, most analytical investigations into the rocking behavior assume a simple model involving a single rigid rocking block on a rigid half-space. This paper proposes the prediction of the rocking response of a complex (multiple block) rocking structure by considering the response of a single rigid rocking block. In particular, it describes a methodology to derive a dynamical equivalence between a planar rocking bridge bent and the archetypal rocking block. Through the proposed concept of the (dynamically) equivalent rocking block, this approach makes the vast existing research on the rocking block useful for the treatment of more realistic rocking structures. To investigate the efficient of the proposed approach, the study assesses the seismic response of a bridge bent designed to rock during earth...
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Research Interests: Engineering, Civil Engineering, Geophysics, Structural Engineering, Earthquake Engineering, and 15 moreStructural Dynamics, Applied Mechanics, Structural Earthquake Engineering, Dimensional Analysis, Frequency, Selection Criteria, Oscillations, Acceleration, Seismic Analysis, Length scale, Seismic response, Ground Motion, Response Analysis, Response Spectra, and Excitation
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Research Interests: Engineering, Mechanical Engineering, Civil Engineering, Physics, Engineering Mechanics, and 11 moreStructural Engineering, Earthquake Engineering, Applied Mechanics, Vibration, Structural Earthquake Engineering, Dimensional Analysis, Stress analysis, Oscillations, Stress Analysis, Stop, and Unilateral
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In this paper, the dynamic response of the rocking block subjected to base excitation is revisited. The goal is to offer new closed-form solutions and original similarity laws that shed light on the fundamental aspects of the rocking... more
In this paper, the dynamic response of the rocking block subjected to base excitation is revisited. The goal is to offer new closed-form solutions and original similarity laws that shed light on the fundamental aspects of the rocking block. The focus is on the transient dynamics of the rocking block under finite-duration excitations. An alternative way to describe the response of the rocking block, informative of the behaviour of rocking structures under excitations of different intensity, is offered. In the process, limitations of standard dimensional analysis, related to the orientations of the involved physical quantities, are revealed. The proposed dimensionless and orientationless groups condense the response and offer a lucid depiction of the rocking phenomenon. When expressed in the appropriate dimensionless–orientationless groups, the rocking response becomes perfectly self-similar for slender blocks (within the small rotations range) and practically self-similar for non-sle...
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The deck-abutment contact (e.g. pounding) during earthquake shaking often triggers the rotation of the deck. Contact at the deck level might alter dramatically the effective mechanical system activating unforeseen, in the design stage,... more
The deck-abutment contact (e.g. pounding) during earthquake shaking often triggers the rotation of the deck. Contact at the deck level might alter dramatically the effective mechanical system activating unforeseen, in the design stage, behavior. This discrepancy between the assumed during design seismic behavior, and the actual seismic behavior governed by the nonsmooth planar deck dynamics, can be detrimental leading even to deck unseating/collapse. The impact-induced rotation mechanism is usually encountered in skew bridges, but it is observed also in straight bridges. As a reference, the 2013 experimental shake-table study of a four-span straight bridge by Saiidi et al. [1] showed unexpected large in-plane rotations. This resulted in significant residual displacement of the bents. The present paper simulates the response of that benchmark straight bridge in an attempt to capture the deck-abutment impact and the subsequent in-plane rotation. The study brings forward the (friction-...
Abstract. This paper studies the effect of vehicle-bridge interaction (VBI) on the vibration of the supporting bridge, and subsequently proposes a decoupled analysis scheme for the VBI problem with reference to high-speed railway systems.... more
Abstract. This paper studies the effect of vehicle-bridge interaction (VBI) on the vibration of the supporting bridge, and subsequently proposes a decoupled analysis scheme for the VBI problem with reference to high-speed railway systems. The study examines the VBI problem analytically and reveals the main coupling parameters between vehicles and bridges. It proves that, except for the stiffness ratio, the impedance ratio, defined as the ratio of the vehicle’s damping and bridge’s mechanical impedance, is also a dominant coupling parameter between vehicles and bridges. Following, the study shows that VBI alters the mechanical system of the bridge via an additional damping, an additional stiffness and a modified loading term. The coupling terms (i.e., the vehicle response) appear solely in the modified loading term. Assuming small stiffness ratio, which is realistic for practical train-bridge systems, the proposed decoupling scheme eliminates the vehicle response from the bridge’s eq...
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Early analytical investigations into the rocking behavior of structures assumed a simple model involving a single rigid rocking block on a rigid half-space. This paper investigates the use of rocking response spectra, analogous to linear... more
Early analytical investigations into the rocking behavior of structures assumed a simple model involving a single rigid rocking block on a rigid half-space. This paper investigates the use of rocking response spectra, analogous to linear elastic response spectra but instead derived from this simple rocking model, to predict the rocking response of more complicated structures. Fundamental rocking parameters are clarified, and examples of rocking spectra for trigonometric ground acceleration impulses are reviewed. Two specific rocking structures are addressed: the stone masonry arch and the stone masonry spire. Effective rocking parameters are derived for each of these structures, and the equivalence of the rocking response is investigated. Results indicate the utility of the fundamental rocking parameters for conducting a first order prediction of rocking response, although limitations are also discussed. While the focus is on masonry structures, the methodology applies to a wider cl...
Rocking motion is a dynamic behavior particularly sensitive to the characteristics of the ground excitation. This study focuses on the identification of strong ground motion parameters critical to the (pure) rocking behavior. The paper... more
Rocking motion is a dynamic behavior particularly sensitive to the characteristics of the ground excitation. This study focuses on the identification of strong ground motion parameters critical to the (pure) rocking behavior. The paper formulates intensity measures (IMs) based on well-established (or slightly modified) strong ground motion parameters that can be grouped into three categories: (i) intensity-based, (ii) frequency-based and (iii) duration-based. The proposed IMs hinge on a dimensionless (orientationless) description of the rocking behavior following principles of dimensional and orientantional analysis. This study employs a suite of (natural) earthquake records and evaluates the ability of the candidate IMs to estimate the peak response rotation of different in size and slenderness freestanding rocking structures. The present analysis investigates also the need for vector-valued IMs. To assess the effectiveness of the examined IMs, this paper proposes selection criteri...
AbstractThis study presents a first attempt toward the rational design of bamboo multiculm axial members with dowel-type connections. Specifically, it implements an original combination of grading,...
Mitigating excessive vibration of civil engineering structures using various types of devices has been a conspicuous research topic in the past few decades. Some devices, such as electromagnetic transducers, which have a capability of... more
Mitigating excessive vibration of civil engineering structures using various types of devices has been a conspicuous research topic in the past few decades. Some devices, such as electromagnetic transducers, which have a capability of exerting control forces while simultaneously harvesting energy, have been proposed recently. These devices make possible a self-regenerative system that can semi-actively mitigate structural vibration without the need of external energy. Integrating mechanical, electrical components, and control algorithms, these devices open up a new research domain that needs to be addressed. In this study, the feasibility of using an actor-critic based reinforcement learning control algorithm for simultaneous vibration control and energy harvesting for a civil engineering structure is investigated. The actor-critic based reinforcement learning control algorithm is a real-time, model-free adaptive technique that can adjust the controller parameters based on observati...
The present research examines the performance of newly developed multi-full-culm bamboo to steel connections under monotonic axial loading. The culms are of Kao Jue (Bambusa pervariabilis) bamboo species. Findings reveal that the plain... more
The present research examines the performance of newly developed multi-full-culm bamboo to steel connections under monotonic axial loading. The culms are of Kao Jue (Bambusa pervariabilis) bamboo species. Findings reveal that the plain (unreinforced) connections fail early by undesirable brittle longitudinal splitting of bamboo culms. The confinement provided by hose-clamps inhibits this brittle failure mode, and with sufficient end-lengths, drastically increases the strength and ductility of the connection. Compared to the hollow-section connections with hose clamps, adding mortar infill further increases the strength. However, it also restricts bolt-deformation and thus diminishes the ductility. More importantly, the European Yield Model (which refers to dowelled timber connections) can analytically estimate the obtained experimental yield loads with satisfying accuracy. This is a promising direction towards a more rational and safer structural design of bamboo structures.
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The present study proposes an original approach for easily constructible footbridges to tackle the overwhelming lack of bridges in underprivileged rural areas. In many poor rural areas worldwide, the scarcity of funding and resources... more
The present study proposes an original approach for easily constructible footbridges to tackle the overwhelming lack of bridges in underprivileged rural areas. In many poor rural areas worldwide, the scarcity of funding and resources results in a devastating lack of even primitive footbridges that hinders socio-economic development. This research aims to empower local communities offering a design solution that it is easily constructible, inexpensive and scalable. In a nutshell, the present study proposes a simple design for truss bamboo footbridges that can be rapidly assembled on site by non-experienced personnel from prefabricated full culm structural members and low-cost steel gusset plate connections following simple instructions. The main objectives of this study are to address the challenges of the structural design and the construction process of bamboo footbridges, and to identify points that merit further research. It firstly evaluates experimentally the physical and mecha...
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Abstract This paper investigates the additional damping effect that vehicle-bridge interaction (VBI) has on the vibration of bridges. It also establishes a generic analytical expression that accurately predicts the additional damping... more
Abstract This paper investigates the additional damping effect that vehicle-bridge interaction (VBI) has on the vibration of bridges. It also establishes a generic analytical expression that accurately predicts the additional damping effect for a broad class of (conventional and high-speed) train-bridge systems. The analysis adopts the classic assumption of continuous contact between the rails and the wheels. The proposed approach allows a multi-mode description of the additional damping, as well as, the deduction of the time-varying additional damping matrix of bridges. The study also offers simplified formulas for common bridge types, such as simply supported and continuous bridges. More importantly, it shows that additional damping can obtain negative values, which implies influx instead of dissipation of energy. Numerical analyses on various vehicle-bridge configurations validate the accuracy of the proposed approach. The results further demonstrate that the suggested formulas outperform currently available methods to estimate the additional damping on bridges, such as the Additional Damping Method (ADM) of Eurocode 1.
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Abstract The present research examines experimentally the performance of a new type of full-culm bamboo to steel bolted connection under monotonic axial loading. The examined culms are of the Kao Jue (Bambusa pervariabilis) bamboo... more
Abstract The present research examines experimentally the performance of a new type of full-culm bamboo to steel bolted connection under monotonic axial loading. The examined culms are of the Kao Jue (Bambusa pervariabilis) bamboo species. The study characterizes the performance of the proposed bamboo to steel connections in terms of failure modes, load-carrying capacity and ductility. It specifically examines the influence on the mechanical behavior of (a) the end-length (i.e. the distance between bamboo culm-end and outer bolt-hole); (b) the transverse confinement provided by hose-clamps, and (c) the grouted cement mortar added within the connection zones. The findings reveal that hose-clamps effectively resist the brittle splitting behavior observed in plain bamboo to steel - bolted connections. Combined with adequate end-lengths the connections achieve remarkable gains in strength and ductility. The results also show that the mortar infill results to connections of higher strength, but often at the cost of reduced ductility, compared to the pertinent hollow-section connections with hose clamps. Importantly, the analytically estimated yield loads of the examined connections using the European Yield Model are in good agreement with the experimentally determined values.
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This paper characterizes the ability of natural ground motions to induce rocking demands on rigid structures. In particular, focusing on rocking blocks of different size and slenderness subjected to a large number of historic earthquake... more
This paper characterizes the ability of natural ground motions to induce rocking demands on rigid structures. In particular, focusing on rocking blocks of different size and slenderness subjected to a large number of historic earthquake records, the study unveils the predominant importance of the strong‐motion duration to rocking amplification (ie, peak rocking response without overturning). It proposes original dimensionless intensity measures (IMs), which capture the total duration (or total impulse accordingly) of the time intervals during which the ground motion is capable of triggering rocking motion. The results show that the proposed duration‐based IMs outperform all other examined (intensity, frequency, duration, and/or energy‐based) scalar IMs in terms of both “efficiency” and “sufficiency.” Further, the pertinent probabilistic seismic demand models offer a prediction of the peak rocking demand, which is adequately “universal” and of satisfactory accuracy. Lastly, the analysis shows that an IM that “efficiently” captures rocking amplification is not necessarily an “efficient” IM for predicting rocking overturning, which is dominated by the velocity characteristics (eg, peak velocity) of the ground motion.
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Abstract Scavenging energy from structural vibration requires an efficient energy harvesting circuit which could introduce nonlinearity into the harvester-structure system. This study examines the performance of a linear structure... more
Abstract Scavenging energy from structural vibration requires an efficient energy harvesting circuit which could introduce nonlinearity into the harvester-structure system. This study examines the performance of a linear structure equipped with an Electromagnetic (EM) energy harvester connected to a nonlinear standard energy harvesting circuit (SEHC) consisting of a full-wave bridge rectifier and a capacitor in parallel with a resistor. To facilitate the understanding of the nonlinear circuit effect on the behavior of the coupled harvester-structure system under sinusoidal excitation, a first-order harmonic balance approximation method is employed. Numerical simulation and experimental study are conducted to validate the accuracy of the proposed approximation method. Results suggest that the blockage effect of diodes in the bridge rectifier in the SEHC should be reduced by using diodes with small voltage drop value or by designing an EM energy harvester with large electromechanical coupling coefficient to improve the vibration mitigation performance and to enhance the optimal energy harvesting capability of the EM energy harvester. Results also show that circuit nonlinearity should be considered in order to estimate the response of the system accurately.