This paper studies the use of a new Tuned Mass Multi-Sliding Friction Damper (TMMSFD) to increase the damping capacity of seismic isolators installed on a two-story base-isolated building to limit their lateral deformations. The proposed TMMSFD consists of a set of several masses that are laterally attached to the superstructure floor through linear springs. These masses are placed on top of each other one by one and are allowed to slide with respect to each other during the earthquake. The bottom mass that carries the weight of upper masses is in contact with the superstructure floor. The damping of system is supplied by the friction generated along the sliding friction surfaces. The TMMSFD has a low cost of installation, operation, and maintenance compared to common TMDs that use viscous fluid dampers for energy dissipation. The mechanical model of TMMSFD is installed on the numerical model of a two-story base-isolated building equipped with elastomeric rubber bearings in order to evaluate its performance in limiting the displacement of base floor. These models are created by the OpenSEESPy package which is a Python 3 interpreter of OpenSEES. A parametric study is performed to obtain the optimum design parameters of the TMMSFD including its total mass, frequency, and static friction coefficients of the siding surfaces for energy dissipation. The results of time-history analysis of numerical model show that the TMMSFD is capable of limiting the displacement of base floor with a little amount of friction implying its potential as a cost-effective tool for seismic protection.
Rail is one of the key elements of the railway system, and its role is to transmit the wheel load to the track bed and guide the train cars along the track. Rail is susceptible to rolling contact fatigue and wear due to being repeatedly subjected to the moving load of the train. This can eventually result in broken-rail damage and train derailment, which if happens on a railroad bridge, it can severely damage the bridge, such as the structural failure of the Tempe Town Lake steel railroad bridge in July 2020 that costed $11 million to repair. Therefore, early detection of defects in rail-bridge system may prevent a critical accident with irreversible damage. The objective of this paper is to use classification-based machine learning techniques to detect broken-rail damage in an open-deck railroad bridge by measuring its acceleration response under the moving load of the train for different speeds. For this purpose, the two-dimensional Finite Element (2D FE) model of a given railroad bridge is created using OpenSEESPy package, which is a Python-3 interpreter of OpenSEES. The changes in the acceleration response due to the damaged rail compared to the undamaged (healthy) rail are characterized by using the Hilbert-Huang Transform in both the time and frequency domains and quantified by defining energy and phase damage indices. The data collected from the 2D FE model are used to train and test several machine learning (ML) classifiers including the Support Vector Machine (SVM), K-Nearest Neighbor (KNN), and Decision Tree (DT) algorithms. The results from the data-analytic study show an acceptable level of precision of these classifiers in identifying the damage to the rail-bridge system.
This paper studies the use of an energy-regenerative tuned mass damper (ER-TMD) to (a) passively control the displacement of superstructure of a two-degree-of-freedom base-isolated building model equipped with elastomeric rubber bearings and (b) simultaneously generate electric energy that can be used to power conventional sensors installed on the building to monitor its response during an earthquake. The proposed passive ER-TMD is composed of two parts: mechanical and electrical. The mechanical part consists of a moving mass (i.e., TMD mass) attached to the base floor through a linear spring-damper system, and the electrical part consists of two large permanent magnets, a rectangular aircore copper coil, and a harvesting circuit designed to maximize the electric power outputted from the proposed ER-TMD. The total damping coefficient of ER-TMD, obtained by adding up the damping effects of the mechanical and electrical parts, is variable and depends on the amplitude of vibration during the earthquake. A parametric study is carried out to find the optimum damping coefficient of proposed ER-TMD. The numerical results show that the proposed ER-TMD can limit the displacement of superstructure to a safe level while it is capable of generating an average electric power about 0.5W which is large enough to power a conventional accelerometer when the building is subjected to an earthquake with the intensity similar to that of maximum considered earthquake (MCE) as defined by ASCE 7–10.
This paper investigates the feasibility of an electromagnetism energy harvester (EMEH) for scavenging electric energy from transportation infrastructures and powering of conventional sensors used for their structural health monitoring. The proposed EMEH consists of two stationary layers of three cuboidal permanent magnets (PMs), a rectangular thick aircore copper coil (COIL) attached to the free end of a flexible cantilever beam whose fixed end is firmly attached to the highway bridge oscillating in the vertical motion due to passing traffic. The proposed EMEH utilizes the concept of creating an alternating array of permanent magnets to achieve strong and focused magnetic field in a particular orientation. When the COIL is attached to the cantilever beam and is placed close to the PMs, ambient and traffic induced vibration of the cantilever beam induces eddy current in the COIL. The tip mass and stiffness of the cantilever beam are adjusted such that a low-frequency vibration due to the passing traffic can effectively induce the vibration of the cantilever beam. This vibration is further amplified by tuning the frequency of the cantilever beam and its tip mass to resonance frequency of the highway bridge. The numerical results show that the proposed EMEH is capable of producing an average electrical power more than 1 W at the resonance frequency 4 Hz over a time period of 1 second that alone is more than enough to power conventional wireless sensors.
This paper is focused on the analytical model, design, and simulation of a variable coil-based friction damper (VCBFD)
for vibration control of structures. The proposed VCBFD is composed of a soft ferromagnetic plate, made of a linear
magnetic material, and two identical thick rectangular air-core coils connected in parallel, each one attached to the plate
through a friction pad. The friction force is provided by a normal force produced through an attractive electromagnetic
interaction between the air-core coils (ACs) and the soft ferromagnetic plate when sliding relative to each other. The
magnitude of the normal force in the damper is varied by a semi-active controller that controls the command current
passing through the ACs. To demonstrate the efficiency of the proposed VCBFD and its semi-active controller, it has
been implemented on a two-degree-of-freedom (2DOF) base-isolated model subjected to the acceleration components of
three records of strong earthquakes. The results show that the performance of the proposed VCBFD in its passive-on
mode is overshadowed by the undesirable effects of stick-slip motion. However, the damper in its semi-active mode is
more successful in not only reducing the displacement of the base-floor but also avoiding stick-slip motion, due to acting
completely in its sliding phase.
This paper presents analytical modeling of a novel type of passive friction damper for seismic hazard mitigation of structural systems. This seismic protective device, which is termed as Passive Electromagnetic Eddy Current Friction Damper (PEMECFD), utilizes a solid-friction mechanism in parallel with an eddy current damping system to dissipate a larger amount of input seismic energy than that by a device with based on solid friction only. In this passive damper, friction force is produced through a magnetic repulsive action between two permanent magnets (PMs) magnetized in the direction normal to the friction surface. The eddy current damping force in the damper is generated because of the motion of the PMS in the vicinity of a conductor. Friction and eddy current damping parts of the damper are able to produce ideal rectangular and elliptical hysteresis loops individually. Seismic hazard mitigation effectiveness of the proposed damper has been demonstrated through an implementation on a two-degree-of-freedom frame building structure. Numerical results show that the proposed damper is more efficient in dissipating input seismic energy than a Passive Linear Viscous Damper (PLVD) with same force capacity.
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