Vibrations In Civil Engineering Structures Research Articles

Influence of inter-panel connections on vibration response of CLT floors due to pedestrian-induced loading

Long-span cross-laminated timber (CLT) floors are typically an assembly of prefabricated CLT panels connected together on the site. The actual connections are commonly neglected in design calculations. Hence, a CLT floor is modelled either as a monolith slab or more frequently as a set of CLT panels with no connections at all. This paper presents a numerical study designed to examine the influence of two most common inter-panel connections, i.e. single surface spline and half-lapped joint, on vibration modes and vibration responses of a range of different CLT floors due to pedestrian-induced loading. Although the inter-panel connections are relatively complex in reality, they are modelled here as an equivalent 2D elastic strip between the CLT panels. This relatively simple yet robust model can be used with ease in design practice, regardless finite element (FE) software used to extract vibration modes of a CLT floor. The corresponding monolith floors and floors without inter-panel connections are studied for the comparison of the results. Vertical vibration responses are simulated for low-frequency and high-frequency floors using the corresponding walking force models given in a popular design guideline for footfall induced vibrations of civil engineering structures. Vibration responses were calculated for single pedestrian occupants and their walking paths parallel and perpendicular to the line of connection. The results showed that including the inter-panel connections in a FE model resulted in up to 2.5 higher RMS acceleration levels. Hence, the common practice of modelling CLT floors as monolith slabs or as a set of panels without connections should be left behind.

Experimental Study of High Axial Damping Rubber (HADR) in New Viscoelastic Dampers

Abstract In the last few years, dampers with viscoelastic material as passive energy dissipation devices have been considered, with their dual behavior, in the modern methods of seismic performance-based design. In these new dampers, energy dissipation of viscoelastic material, unlike ordinary viscoelastic dampers obtained by shear strain, is provided by amplified axial strain. Hence, the production of a High Axial Damping Rubber (HADR) is required in these dampers. This article presents the results of experimental work carried out to characterize the mechanical response of a HADR to be used in the design and construction of new viscoelastic dampers for controlling strong vibrations in civil engineering structures. The experimental results showed that the HADR behavior is better than that of styrene butadiene rubber, leading to improved mechanical properties in the range of standard rubber. The hardness, tensile strength, elongation at break, compressive strength, and rate of resilience of this rubber are obtained as, respectively, 60 durometer (shore A), 16.56 MPa, 519 %, 1,730 kPa, and 50 %. Finally, the uniaxial tension and compression data of HADR for its modeling in the finite element program are discussed.

Equivalent model and parameter analysis of non-packed particle damper

A non-packed particle damper (NPPD) is an advantageous passive damping device with a wide frequency band and good robustness. However, its damping mechanism remains unclear, and its application for controlling vibrations in civil engineering structures is being explored. By analysing the particle motion state, this paper proposes a double inertia mass equivalent model (DIMEM) to reflect the interaction between particles. The effect of inertia was introduced in the DIMEM to consider the rolling effect of particles on the damping performance of the NPPD. An electromagnetic vibration table test of a single-storey frame structure with an NPPD was designed and performed. The parameter determination method and applicability of the DIMEM were also evaluated based on experimental and theoretical analyses. Furthermore, the effects of the parameters on the damping performance of the NPPD were systematically analysed. The results confirm that the equivalent model can reflect the damping performance and mechanism of the NPPD. The particle group inertia is an inherent property of the NPPD. With an increase in the ratio of inertance to particle mass, the optimal vibration damping performance deteriorates under harmonic excitation, and the corresponding equivalent connection stiffness gradually increases. The equivalent connection stiffness, additional mass ratio, recovery coefficient, and acceleration normalised collision distance significantly affect the damping performance and mechanism. However, the effects of the equivalent connection damping coefficient and rolling friction coefficient are negligible. The proposed DIMEM and the corresponding parameter analysis can provide an important reference for the application of NPPDs in civil engineering.

Development of stiffness-adjustable tuned mass dampers for frequency retuning

Tuned mass damper is an attractive strategy to mitigate the vibration of civil engineering structures. However, the performance of a tuned mass damper may show a significant loss due to the frequency detuning effect. Hence, an inerter-induced negative stiffness (apparent mass effect) and magnetic-force-induced positive/negative stiffness are proposed to integrate a stiffness-adjustable vertical tuned mass damper and pendulum tuned mass damper for frequency retuning, respectively. Based on the established differential equations of motion for a vertical tuned mass damper coupled with an inerter and a pendulum tuned mass damper integrated with a magnetic-force-induced positive-/negative-stiffness device, the frequency retuning principles of a vertical tuned mass damper and a pendulum tuned mass damper are, respectively, demonstrated. The frequency retuning strategies for both the vertical tuned mass damper and the pendulum tuned mass damper are confirmed and clarified by model tests. Furthermore, the performance of a retuned vertical tuned mass damper for mitigating vibration of a linear undamped single-degree-of-freedom primary structure is discussed, and the effects of the amplitudes of the pendulum tuned mass damper on magnetic-force-induced stiffness as well as the frequency of the pendulum tuned mass damper are also investigated. Both theoretical analysis and experimental investigations show that the proposed frequency tuning methodologies of tuned mass dampers are efficient and cost-effective with relatively simple configurations.

Modeling, design, and testing of a proof-of-concept prototype damper with friction and eddy current damping effects

Friction is considered as one of the most reliable mechanisms of energy dissipation that has been utilized extensively in passive damping devices to mitigate vibration of civil engineering structures subjected to extreme natural hazards such as earthquakes and windstorms. However, passive friction dampers are well-known for having a highly nonlinear hysteretic behavior caused by stick-slip motion at low velocities, a phenomenon that is inherent in friction and increases the acceleration response of the structure under control unfavorably. The authors have recently proposed the theoretical concept of a new type of damping device termed as “Passive Electromagnetic Eddy Current Friction Damper” (PEMECFD) in which an eddy current damping mechanism was utilized not only to decrease the undesirable effects of stick-slip motion, but also to increase the energy dissipation capacity of the damping device as a whole. That study was focused on demonstration of the theoretical performance of the proposed damping device through numerical simulations. This paper further investigates the influence of eddy current damping on energy dissipation due to friction through modeling, design, and testing of a proof-of-concept prototype damper. The design of this damper has been improved over the design in the previous study. The normal force in this damper is produced by the repulsive magnetic force between two cuboidal permanent magnets (PMs) magnetized in the direction normal to the direction of the motion. The eddy current damping force is generated because of the motion of the two PMs and two additional PMs relative to a copper plate in their vicinity. The dynamic models for the force-displacement relationship of the prototype damper are based on LuGre friction model, electromagnetic theory, and inertial effects of the prototype damper. The parameters of the dynamic models have been identified through a series of characterization tests on the prototype damper under harmonic excitations of different frequencies in the laboratory. Finally, the identified dynamic models have been validated by subjecting the prototype damper to two different random excitations. The results indicate that the proposed dynamic models are capable of representing force-displacement behavior of the new type of passive damping device for a wide range of operating conditions.

Toward an adaptive vibration absorber using shape-memory alloys, for civil engineering applications

This article explores the capabilities of a novel adaptive vibration absorber for civil engineering structures, with regard to frequency self-tuning, based on the temperature modulation of shape-memory alloy restitution elements. This real-time temperature modulation of shape-memory alloys, through Joule effect, enables to control the elastic modulus of these elements, by inducing thermal martensitic transformations, and allows for the adaptation of the stiffness of the absorber, in order to be continuously tunable for a wide frequency range. A series of simulations are performed, using numerical models of a lively footbridge, to give an additional insight into the high potentialities of this adaptive control approach in the mitigation of vibrations in civil engineering structures.

Numerical analysis using state space method for vibration control of car seat by employing passive and semi active dampers

In passenger cars the vibrations developed at the ground are transmitted to the passengers through seats. Due to vibrations discomfort is experienced by the passengers. Dampers are being successfully utilized to reduce the vibrations in civil engineering structures. Few dampers are used in passenger cars as well. In the present study viscous dampers and semi-active variable friction dampers are used in passenger cars. The car and car seat are modeled together as two degrees of freedom system. The study is carried out for two cases namely car moving on sagged bridges and car moving on road humps. The paper also presents the comparison of performance of both the dampers for the two cases. State space method has been employed for the numerical analysis of the study. It is found that the amplitude of displacements is reduced considerably by the employment of dampers and resonance is avoided. Performance wise viscous damper is found to be slightly better than semi-active variable friction damper.Keywords: Car seat, viscous damper, semi-active variable friction damper, two degrees of freedom, state space method

Measuring human-induced vibrations of civil engineering structures via vision-based motion tracking

We present a novel framework for measuring the body motion of multiple individuals in a group or crowd via a vision-based tracking algorithm, thus to enable studies of human-induced vibrations of civil engineering structures, such as floors and grandstands. To overcome the difficulties typically observed in this scenario, such as illumination change and object deformation, an online ensemble learning algorithm, which is adaptive to the non-stationary environment, is adopted. Incorporated with an easily carried and installed hardware, the system can capture the characteristics of displacements or accelerations for multiple individuals in a group of various sizes and in a real-world setting. To demonstrate the efficacy of the proposed system, measured displacements and calculated accelerations are compared to the simultaneous measurements obtained by two widely used motion tracking systems. Extensive experiments illustrate that the proposed system achieves equivalent performance as popular wireless inertial sensors and a marker-based optical system, but without limitations commonly associated with such traditional systems. The comparable experiments can also be used to guide the application of our proposed system.

Vibration analysis based on surface acoustic wave sensors

It is important to know, whether a civil engineering structure is safe or unsafe. One way to determine this is to measure vibrations at critical locations and feeding this data into an appropriate algorithm. Albido Corporation has developed wireless strain sensors based on surface acoustic wave (SAW) principles that are mainly employed on rotating structures and in harsh environments. Albido's sensors could also be used to measure vibrations in civil engineering structures. They are small (~1 × 3 mm), passive and inexpensive (< 1$ in volume). They are powered by the electromagnetic field emanating from the antenna of a Reader System, similar to an RFID. The Reader System is essentially a computer with special software and has signal processing capability. One Reader System can service a multitude of sensors. The Reader antenna has to be within the reading range of the sensor. If large distances are required, a small electronic component acting as a Reader System can be placed within the reading range of the sensor that receives the sensor signal, generates a radio signal and encodes the sensor information on the radio signal. Then, the final data processing center can be placed anywhere.

Modeling and analysis of magnetorheological inner mass single unit impact dampers

In this article, ongoing studies to apply semi-active control devices to reduce undesired vibrations of civil engineering structures are investigated. In doing so, the barrier of the nonlinear inner mass single unit impact dampers is equipped by the magnetorheological fluid dampers. For convenience, this kind of impact dampers is briefly named smart impact dampers. Dynamic behavior of a vibratory system equipped with the smart impact damper is modeled based on the modified Bouc–Wen model for the magnetorheological damper. Performance of the smart impact damper to suppress free vibration of an Euler–Bernoulli beam is investigated. Furthermore, effects of varying applied current to the magnetorheological fluid damper on vibratory behavior of the beam are illustrated in user-oriented charts. The analysis results show that the smart impact dampers with optimal parameters can suppress undesired vibrations much better than conventional impact damper systems.

Identification of parameters of Maxwell and Kelvin–Voigt generalized models for fluid viscous dampers

Fluid viscous dampers have been widely applied to reduce the effects of vibrations in civil engineering structures. A good understanding of the dynamical behavior of these devices is required to analyze structures equipped with fluid viscous dampers. The simple Kelvin–Voigt and Maxwell rheological models do not have enough parameters to suitably capture the frequency dependence of device parameters, so other models representing some generalizations of the basic Kelvin–Voigt and Maxwell models have been developed. This paper deals with parameter identification for basic and generalized Kelvin–Voigt and Maxwell models for fluid viscous dampers. The identification procedure gives the best mechanical parameters by minimizing a suitable objective function that represents a measure of difference between analytical and experimental applied forces. For this purpose, the particle swarm optimization is adopted. Results are obtained under various test conditions, comparing the agreement of various models with experimental data. Finally, a numerical investigation is performed on a simple one degree of freedom structure, equipped with fluid viscous dampers and subject to a real seismic motion.

Enhancing active vibration control of pedestrian structures using inertial actuators with local feedback control

Active vibration control (AVC) via inertial actuators is considered a viable technique for the mitigation of excessive vibrations in civil engineering structures. In particular, several recent field trials have shown that this technique has the potential to be effective for the cancellation of human-induced vibrations in pedestrian structures. However, prior to the implementation of AVC using inertial actuators, several drawbacks have to be dealt with. The main disadvantages come from the dynamic behaviour of the inertial actuators employed for this application, which are: (i) their low frequency dynamics (that might interact with the structure dynamics), and (ii) their nonlinearities (stroke and force saturation). Thus, any control technique to be implemented has to tackle stability problems (caused by the low frequency response of the actuators) and stroke and force saturation, which might lead to poor vibration cancellation performance. To alleviate such drawbacks, this work proposes to use an AVC strategy based on two control loops: (i) a loop, closed within the actuator, designed to artificially modify the actuator frequency response according to its maximum stroke and force and the structure dynamics, and (ii) a loop designed to impart damping to the structure. This work focuses on the design process such that stability and actuator saturations are taken into account to improve the efficiency of a given inertial actuator when the AVC system is based upon velocity feedback. Experimental results on a full-scale concrete laboratory structure using a commercial actuator are presented to illustrate the performance of the AVC strategy proposed, which ensures adaptability to a given structure without requiring hardware modifications.

Technologies for Mitigation of Human-induced Vibrations Iin Civil Engineering Structures

-Previous civil engineering vibration mitigation research has focused primarily on the mitigation of earthquake and wind-induced vibrations in civil engineering structures. This paper provides a review of various technologies appropriate for mitigation of much lower level human-induced vibrations in civil engineering structures. It highlights technologies or combinations thereof that have been implemented in real-life civil engineering structures as well as some reduction levels in structural responses (velocity, acceleration) that have been achieved. A review of vibration mitigation techniques with this particular focus has not been presented before. A brief background to human-induced vibration serviceability primarily in floors, foot-bridges, grandstands and staircases is provided and various technologies available for mitigation of human-induced vibrations in civil engineering structures are introduced. A detailed review of these technologies is described as well as their real-life implementations in civil engineering structures prone to human-induced vibrations. Some improvements in vibration performances of some of the civil engineering structures are also presented. The technologies that show most promise for future application in vibration serviceability of civil engineering structures are outlined.

Wind-excited vibrations—Solution by passive dynamic vibration absorbers of different types

Passive dynamic vibration absorbers have been used up to now as an effective tool to face wind-excited vibrations of civil engineering structures like high masts, slender bridges and esp. footbridges, etc. Their idea is simple, but the way of application can be different according to the type of structure and to the space where the absorber can be placed—that is why different types of absorbers were developed since the half of last Century. The paper compares the effect of pendulum, ball and sloshing liquid absorbers and assesses the effectiveness of each of them, summing up the experience of the author and of some of his colleagues in the Czech Republic.

High Damping Rubber Model for Energy Dissipating Devices

This work presents the results of a study carried out to characterize the mechanical response of a high damping rubber to be used in designing and constructing energy dissipating devices and base isolators for controling strong vibrations in civil engineering structures. A new parametric model of the elastomer is proposed to be employed in the design procedure and structural analysis of passive controlled structures. The parameters of the model are calibrated using experimental data obtained from tests on rubber specimens under different loading paths. The main dissipating energy mechanisms of the rubber are identified. The proposed model is able to reproduce those main mechanisms as well as geometric second order effects such as tension stiffening due to the effect of axial strains in the response. The response predicted by the proposed model is compared with that obtained from experimental tests and from the Kelvin and plasticity models.

インパクトダンパーおよび振子式インパクトダンパーの建設系構造物への応用

The classical impact damper (CID) and the pendulum impact damper (PID) are studied for the suppression of horizontal vibrations of civil engineering structures. Experiments on the PID to verify the validity of the mathematical model are done and comparisons with simulation results are provided. Parametric study under harmonic excitation shows that the effectiveness of the CID is sensitive to changes in the amplitude of the excitation. On the other hand, the PID is insensitive to changes in the amplitude of the excitation when its frequency is close to the structural frequency, and it is less sensitive to deviations in tuning than the tuned mass damper (TMD). Comparison of the CID, PID and TMD shows optimum efficiency in terms of mass ratio, under steadystate motion and ideal conditions, to be highest for the TMD and lowest for the PID. Included is a discussion of the practical constraints that may govern the actual choice of damper.

Control of wind-induced vibrations in civil engineering structures

Various passive-type control means for wind-induced vibrations of civil engineering structures (mainly bridges) are reviewed. Control means discussed primarily are, Aerodynamic means·Tuned mass dampers (TMD) including Tuned liquid dampers (TLD) and·Non-tuning type dampersApplication of such means to actual structures are also presented. Effectiveness and design of TMD to wind-induced self-excited vibration are discussed in some detail.

Application of Optimal Control Theory to Civil Engineering Structures

Modern control theory has been successfully applied to control the motions of aerospace vehicles. An exploratory study is made herein to investigate the feasibility of applying such a theory to control the vibration of civil engineering structures under random loadings. It is assumed that random excitations to structures, such as wind loads and earthquakes, can be modeled by passing either a stationary Gaussian white noise or a nonstationary Gaussian shot noise through a filter. The performance index to be minimized consists of the covariances of both the structural responses and the control forces. Under these conditions, the optimal control law is a linear feedback control. The optimal control forces are obtained by solving a matrix Riccati equation. Applications of the optimal control to a multi-degree-of-freedom structure, under stationary wind loads and nonstationary earthquakes, are demonstrated. It is shown that significant reduction in covariances of the structural responses can be achieved by the use of an active control system.