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Real-time hybrid substructuring (RTHS) has previously been shown to be an effective tool to quantify the effect of parametric uncertainties on the response of a structural system. Proposed and implemented in this paper is a method that combines RTHS, Principal Component Analysis, and Kriging to metamodel the frequency response functions of a structure. The proposed method can be used to account for parametric variation in both the numerical and physical substructures. This approach is demonstrated using a series of bench-scale RTHS tests of a magnetorheological (MR) fluid damper used to control a 2 degree-of-freedom mass-spring system. The numerical system spring stiffnesses and the physical current supplied to the MR damper are each treated as uniformly distributed random variables. The RTHS test data is used to train computationally fast metamodels, which can then be used to conduct Monte Carlo simulations to determine distributions of the system response. The proposed methodology is shown to be both efficient and accurate.

Structural health monitoring (SHM) has been conducted by placing sensors on structures, so-called contact sensors, to measure displacements, strains, and accelerations of engineering structures. Contact sensing is accurate and effective, but suffers from some critical shortcomings, such as high cost, intensive labor, and traffic interruption. With the advancement and wide availability of digital video cameras, compounded with the development and enhancement of computer vision algorithms, vision-based sensing using a video camera as a sensor for SHM has become a viable alternative and a complementary method to remotely capture structural responses. Several computer vision algorithms are proposed, together with specific type of video camera, for capturing and processing the SHM video for the dynamic structural responses, e.g. displacements of selected targets. Up to date, there is a limited number of successful applications using video camera as a sensor in SHM practice. To facilitate the real-world applications of vision-based SHM, this paper presents the integrated methods, and a software tool for analyzing SHM videos using template matching algorithms along with a subpixel method that enhances the accuracy of the vision-based structural responses. The integrated approach is flexible and versatile for not only extracting displacements, strains, velocities, and accelerations, but also detecting damage of the desired multiple points or areas (templates) from videos. The methods and the software tool have been applied to a comprehensive analysis of the lab structural test, which was video-recorded by a third party without any involvement of the authors or any intension in using video camera as sensor. Good agreement for the lab test has been achieved for the structural responses (e.g. displacement and strain) and the damage detection recorded by the conventional sensors and extracted from the video by applying the integrated tool. The approach has been further validated on a highway bridge in the field, where a contact-based SHM system is permanently installed on the bridge and serves a good baseline reference for validating the proposed approach. The vision-based SHM results obtained for the highway bridge application show good correlation with the structural responses captured by conventional sensors and indicate that the developed analysis methods and software tool perform well for highway bridge test and structural health monitoring.

Hybrid simulation is a tool for investigating the dynamic response of a structural prototype subjected to realistic loading. Hybrid simulation is conducted using a hybrid model that combines physical and numerical substructures interacting with each other in a feedback loop. As a result, the tested substructure interacts with a realistic assembly subjected to a credible loading scenario. In the current practice, experimental results obtained via hybrid simulation support conceptualization and calibration of computational models for structural analysis. Instead, this paper extends the scope of hybrid simulation in constructing a safe/failure state classifier for the tested substructure by adaptively designing a sequence of parametrized hybrid simulations. Such a classifier is intended to compute the state of any physical-substructure-like component within system-level numerical simulations. It follows that the main contribution of this paper lies in the way experimental results are aggregated and integrated with structural analysis. The proposed procedure is experimentally validated for a three-degrees-of-freedom hybrid model subjected to Euler buckling.

Actuator tracking and compensation are important in the general field of experimental structural dynamics to effectively conduct vibration testing. Real-time hybrid substructuring (RTHS) is...

Bridge Weigh-In-Motion (BWIM) has been demonstrated to be reliable for obtaining critical information about the characteristics of trucks that travel over the highways. Continued improvements provides greater opportunity for increased use of BWIM. Traditional BWIM systems based on measuring the bending strain of the bridge have various challenges which has led to a class of BWIM methodologies that employ the use of shear strain in determining the gross vehicle weight (GVW) of crossing trucks. However, the known techniques of these shear-strain BWIM methods assume or measure the shear influence line for the calculation of the GVW. In this paper, an alternative shear-strain based BWIM technique is proposed. The method presented here is independent of the influence line, does not require a measurement of the speed of the truck, and is based on the difference in magnitude observed at the discontinuity of the shear strain record as a truck crosses over the sensor location on the bridge. A series of field tests is presented that demonstrate this shear-strain based BWIM method has error levels consistent with other more complex BWIM methods and as such has great potential to be used for determining the GVWs of trucks that travel on simple or multispan bridges in a consistent and reliable manner. Existe literatura que demuestra que el pesaje en movimiento con puentes, conocido por sus siglas en inglés como BWIM (Bridge Weigh-In-Motion) es confiable para obtener información acerca de las característicasde los camiones que transitan por las carreteras. El mejoramiento continuo de estos sistemas presenta oportunidades para incrementar su uso. Los métodos BWIM tradicionales basados en la flexión en vigasenfrentan distintos retos, los cuales han propiciado la aparición de otras metodologías que emplean deformaciones unitarias cortantes. Sin embargo, las técnicas conocidas que utilizan deformaciones unitariascortantes, asumen o miden líneas de influencia para el cálculo de los pesos brutos vehiculares. En este artículo, se propone una metodología BWIM alternativa, que es independiente de las líneas de influencia, norequiere mediciones de la velocidad de los camiones y se basa en la discontinuidad que se observa en el registro de deformaciones unitarias cortantes, la cual ocurre cuando un camión cruza sobre el lugar en donde se coloca el sensor. A partir de una serie de experimentos realizados en campo, se demuestra que los niveles de error obtenidos con el método propuesto son similares a los obtenidos con otros métodos BWIM más complejos, por lo que se considera que existe potencial para poder ser utilizado para obtener los pesos brutos vehiculares de camiones que transitan por puentes continuos o simplemente apoyados, en una forma consitente y confiable.

Los sistemas de pesaje en movimiento para puentes, en inglés Bridge-Weigh-In-Motion (BWIM), han sido utilizados con éxito para identificar algunas de las propiedades de los vehículos pesados que transitan sobre una vía. No obstante, las fuentes de incertidumbre no son siempre fáciles de controlar y por lo tanto podrían afectar la confiabilidad de los resultados. En esta investigación, se estudió la influencia de algunas de las dificultades experimentales que se presentan al utilizar el método BWIM basado en deformaciones unitarias. En particular, se analizaron tres efectos: el nivel de ruido presente en la señal, la ubicación de los sensores en el puente y la tasa de muestreo utilizada para la recolección de datos. Estos efectos se simularon numéricamente al añadir ruido generado sintéticamente a una onda de respuesta idealizada. En este trabajo se discuten los resultados con énfasis en posibles consecuencias sobre las estimaciones de velocidad y peso de vehículos pesados en pruebas de campo.

Spacecraft are subjected to a variety of extreme loads during the course of a mission. One period during which these demanding loads are observed occurs during the parachute deployment stage of reentry. The deployment process utilizes a mortar in order to deploy the parachute and the corresponding reaction forces from deployment generate large impulsive loads on the spacecraft and cause vibrations throughout the spacecraft. Accurate prediction of the forces exerted on the spacecraft during deployment is paramount to the design and safety of the spacecraft. Typically the time history of the reaction forces exerted during parachute deployment are measured experimentally using a tripod-mounted mortar assembly. This approach introduces coupling between the force generated by the mortar and the dynamics of the tripod legs, and does not account for the structural compliance of the actual spacecraft system. This will lead to erroneous results if compared to the true reaction forces observed during the in-service deployment of the parachute during reentry.

In hybrid substructuring, a structural system is partitioned into a numerical substructure and a physical substructure. Typically, the physical substructure consists of a system component whose behavior is difficult to model while the numerical substructure consists of a computational model of the remainder of the system. Hybrid substructuring has previously been shown to be an effective method to quantify the effect of parametric uncertainties in the numerical substructure on the response of the system. This paper proposes and implements a methodology where the effect of parametric uncertainty can also be incorporated into the physical substructure. This idea is implemented in a series of small-scale Real-Time Hybrid Substructuring (RTHS) tests on a magneto-rheological fluid damper used to control a two degree-of-freedom mass-spring system. The physical current supplied to the damper is treated as a random variable. Using the RTHS test results, a metamodel of the system’s frequency domain behavior is developed using Principal Component Analysis and Kriging. This metamodel is then used to evaluate probabilistic system performance.

This paper presents approximate and exact stability analysis to determine the critical time delays of one and two degree of freedom (DOF) single-actuator real-time hybrid substructuring (RTHS). The approximate stability analysis is based on applying the Routh-Hurwitz stability criterion using a first-order Taylor expansion of the actuator dynamics represented by a constant gain and pure time delay. The exact stability analysis involves solving the critical frequencies first by canceling the exponential delay term of the closed-loop characteristic equation through multiplication by its complex conjugate. The exact critical time delays are then found using the phase of the closed-loop characteristic equation evaluated at the critical frequencies. These stability analysis techniques are applied to several 1-DOF and 2-DOF mass-spring configurations of single-actuator RTHS. Results show that the critical time delays are highly dependent on the mass, stiffness, and damping partitioning of the physical and numerical substructures as well as the actuator gain. This information provides useful insight into the stability behavior of a particular substructure partitioning configuration to evaluate the feasibility of conducting RTHS tests of these systems.

Detecting structural damage in civil engineering structures has become an increasingly viable option for efficient maintenance and management of infrastructures. Vibration-based damage detection methods have been widely used for structural health monitoring. However, those methods may not be effective when modal properties have significant variance under environmental effects, especially severe temperature changes. In this paper, an extended Kalman filter-based artificial neural network (EKFNN) method is developed to eliminate the temperature effects and detect damage for structures equipped with long-term monitoring systems. Based on the vibration acceleration and temperature data obtained from an in-service highway bridge located in Connecticut, United States, the correlations between natural frequencies and temperature are analyzed to select proper input variables for the neural network model. Weights of the neural network are estimated by extended Kalman filter, which is also used to derive the confidence intervals of the natural frequencies to detect the damage. A year-long monitoring data are fed into the developed neural network for the training purpose. To assess the changes of natural frequencies in real structural damages, structural damage scenarios are simulated in the finite element model. Numerical testing results show that the temperature-induced changes in natural frequencies have been considered prior to the establishment of the threshold in the damage warning system, and the simulated damages have been successfully captured. The advantages of EKFNN method are presented through comparing with benchmark multiple linear regressions method, showing the potential of this method for structural health monitoring of highway bridge structures.

While numerical simulations can be used to predict the dynamic performance of structural systems, there are some instances where the dynamical behaviour and uncertainties of specific system components may be difficult to accurately model. In these instances, structural reliability assessments may be conducted by employing the cyber-physical real-time hybrid sub-structuring (RTHS) test method. In this approach, a numerical model of a larger structural system, incorporating uncertainty in specific parameters, is coupled with a physical test specimen of a system component to fully capture system-level dynamic interactions and facilitate uncertainty propagation. This paper specifically details a study performed to experimentally validate the previously proposed adaptive Kriging-Hybrid simulation (AK-HS) structural reliability method. The AK-HS method combines Kriging metamodeling, an adaptive learning algorithm, Monte Carlo simulation, and RTHS testing to iteratively estimate a structural system's probability of failure given random parameters in the numerical model. The method is validated with a series of bench-scale RTHS tests on a viscous damper connecting two adjacent 6-degree-of-freedom rigid body structures. The AK-HS method is shown to accurately predict probabilities of failure for systems with up to 24 random variables using a reasonable number of RTHS tests.

In the field of structural dynamics, real-time hybrid simulation (RTHS) continues to receive increased interest from researchers conducting component testing incorporating system-level behaviour. Increased digital computing power has allowed advances in RTHS. However, limitations in RTHS will persist due to the effects of discrete errors caused by quantisation and corresponding numerical integration time step limitations, which can limit the bandwidth and nonlinearities of the system studied. In this paper, an analogue electronic computer is constructed to conduct RTHS of a modelled base-isolated structure with a physically tested viscous damping device. The analogue computer models a two-degree-of-freedom (2DOF) structure and solves the equations of motion required in RTHS testing. Results of the RTHS tests using the analogue computer are compared to RTHS tests implemented with a digital computer in order to validate the proposed analogue RTHS method. Further applications of RTHS testing with analogue computing including high-frequency dynamic testing are discussed.

The following paper presents a frequency domain method to perform time varying linear identification of deterministic non-linear systems and provides an empirical example to illustrate the application of the method for a nonlinear structural dynamic system. The proposed method employs the Kronecker product form of convolution matrices to enable the least mean squares solution of arbitrarily structured cross frequency coupled responses. The mathematical framework allows for solution of different parts of the time varying frequency response depending upon information known about the system. Definitions of time varying coherence, cross and autospectra are derived, and are shown to be equivalent to conventional definitions when simplified to the linear time invariant form. These methods are applied to a physical beam damper system with observed nonlinear behavior tested at the University of Connecticut in order to identify an accurate time varying frequency domain model of the nonlinear system. The new model shows improved coherence relative to a standard linear time invariant model.

Spacecraft are subjected to a variety of extreme loads during the course of a mission. One such demanding period during reentry is parachute deployment when a mortar on the spacecraft is used to deploy the parachute. Firing the mortar to expel the parachute imparts an impulsive force on the spacecraft and results in vibration throughout the spacecraft. Successful deployment of the parachute is critical to the success of the mission, and accurate prediction of the impulsive forces exerted on the spacecraft during deployment is paramount to the design and safety of the spacecraft. Typically the time history of the reaction force of the mortar is measured experimentally using a rigid mounting system. This approach neglects the structural compliance of the spacecraft and thus neglects the dynamic interaction between the mortar and spacecraft. This may lead to differences between the force profile observed during laboratory testing and those observed during the mission of the spacecraft.

A feasibility study was conducted to develop a novel method to determine the temporal changes of tensile forces in bridge suspender cables using time-frequency analysis of ambient vibration measurements. An analytical model of the suspender cables was developed to evaluate the power spectral density (PSD) function of a cable with consideration of cable flexural stiffness. Discrete-time, short-time Fourier transform (STFT) was utilized to analyze the recorded acceleration histories in both time and frequency domains. A mathematical convolution of the analytical PSD function and time-frequency data was completed to evaluate changes in cable tension force over time. The method was implemented using acceleration measurements collected from an in-service steel arch bridge with a suspended deck to calculate the temporal variation in cable forces from the vibration measurements. The observations served as proof of concept that the proposed method may be used for cable fatigue life calculations and bridge weigh-in-motion studies.

This paper present a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing where the building superstructure is tested while the isolation layer is numerically modeled can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test with a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.

Hybrid simulation combines numerical simulation and physical testing, and is thus considered to be an efficient alternative to traditional testing methodologies in the evaluation of global ...

The following paper illustrates a mathematical framework for identifying discrete convolution filters and applies that framework to a time varying dynamic problem. Convolution matrices, formulated using Kronecker products, allow for least means squares solution of arbitrarily structured discrete convolution models. The framework exposes the convolution structure and the filter coefficients independently in order to solve for the time varying weights of a known model, or an unknown time varying filter. Transforms are shown to apply standard discrete spectral processing methods to this architecture. The identification methods were successfully applied to identify the stiffness-like and damping-like operating regimes of a typical viscous damper in a dynamic system subjected to periodic motion. The results show that discrete time varying system identification successfully predicts measured test data and provides intuitive results showing stiffness-like behavior at low force inputs and damping-like behavior for higher force inputs.

Some engineering structures, such as bridges in transportation network, may be subject to unexpected hazardous events, which calls for the rapid identification of their structural properties using portable hardware and data analysis system to evaluate their remaining load-carrying capacity. A significant challenge in such mission is the lack of baseline information of the structure to be evaluated. In this research, we formulate a vibration-based methodology using modal testing to identify properties of column-supported bridge-type structure. An assumed-mode based discretization is adopted to establish an equivalent nominal model that is a function of the unknown structural properties. The system identification algorithm is built upon the mass response method, i.e., introducing a known added mass to the structure and measuring respectively the modal information before and after this mass is added. This approach enables the structural identification without a priori information of the mass. Systematic case studies are then carried out to evaluate the effectiveness of this methodology. It is found that the new algorithm formulated can yield very accurate and robust identification results.

This paper addresses the reduction of earthquake effects on nonlinear buildings. Three large-scale 200 kN magneto-rheological (MR) fluid dampers were implemented in a three-story nonlinear building to provide protection against severe earthquakes. Clipped-optimal and Lyapunov control algorithms were adapted to control the MR dampers. Numerical and experimental investigations were executed to examine the efficacy of the proposed controllers. The George E. Brown, Jr. Network for Earthquake Engineering Simulation fast hybrid testing (FHT) facility at the University of Colorado Boulder was used. Results show that the proposed controllers were successfully applied in real-time FHT simulations and can enhance the response reduction. In addition, a dissipativity analysis is carried out to further understand the performance characteristics of the semi-active control strategy.

Bridges play a significant role in postevent recovery and disaster resiliency of communities. Recent megadisasters, such as the 2011 Great East Japan Earthquake, have prompted the technical community to understand the robustness of infrastructure when subjected to extreme events and the shortcomings of conventional structural systems under multiple hazards. Columns are the most critical load-carrying elements of bridge structures. Enhancing the robustness of bridge columns can improve the resiliency of the bridge itself and the surrounding community by reducing repair costs and downtime after an extreme event. In recent years, the concrete-filled fiber reinforced polymer (FRP) tube (CFFT) system has been widely investigated as a durable and cost-effective alternative design for more robust bridge columns. However, the current AASHTO guide specifications are limited to nonductile, unreinforced CFFT elements. This study summarizes the findings of blast, fire, and seismic experiments performed on CFF...

Main tension elements are critical to the overall stability of cable-supported bridges. A dependable and rapid determination of cable tension is desired to assess the state of a cable-supported bridge and evaluate its operability. A portable smart sensor setup is presented to reduce post-processing time and deployment complexity while reliably determining cable tension using dynamic characteristics extracted from spectral analysis. A self-recording accelerometer is coupled with a single-board microcomputer that communicates wirelessly with a remote host computer. The portable smart sensing device is designed such that additional algorithms, sensors and controlling devices for various monitoring applications can be installed and operated for additional structural assessment. The tension-estimating algorithms are based on taut string theory and expand to consider bending stiffness. The successful combination of cable properties allows the use of a cable’s dynamic behavior to determine tension force. The tension-estimating algorithms are experimentally validated on a through-arch steel bridge subject to ambient vibration induced by passing traffic. The tension estimation is determined in well agreement with previously determined tension values for the structure.

The Magneto-rheological (MR) dampers have been widely used in many building and bridge structures against earthquake and wind loadings due to its advantages including mechanical simplicity, high dynamic range, low power requirements, large force capacity, and robustness. However, research about structural damage detection methods for MR damper controlled structures is limited. This paper aims to develop a real-time structural damage detection method for MR damper controlled structures. A novel state space model of MR damper controlled structure is first built by combining the structure’s equation of motion and MR damper’s hyperbolic tangent model. In this way, the state parameters of both the structure and MR damper are added in the state vector of the state space model. Extended Kalman filter is then used to provide prediction for state variables from measurement data. The two techniques are synergistically combined to identify parameters and track the changes of both structure and MR damper in real time. The proposed method is tested using response data of a three-floor MR damper controlled linear building structure under earthquake excitation. The testing results show that the adaptive extended Kalman filter based approach is capable to estimate not only structural parameters such as stiffness and damping of each floor, but also the parameters of MR damper, so that more insights and understanding of the damage can be obtained. The developed method also demonstrates high damage detection accuracy and light computation, as well as the potential to implement in a structural health monitoring system.

In the design of mechanical systems, there are constraints imposed on the vibration of mechanical equipment to limit the vibration transmission into its support structure. To accurately predict the coupled system response, it is important to capture the coupled interaction of the two portions, i.e., the mechanical equipment and the support structure, of the mechanical system. Typically during a design, the analysis of the full mechanical system is not possible because a large part of the system may be non-existent. Existing methods known as Transfer Path Analysis and Frequency Based Substructuring are techniques for predicting the coupled response of vibrating mechanical systems. In this paper, a control based hybrid substructuring approach to Transfer Path Analysis is proposed. By recognizing the similarities between feedback control and dynamic substructuring, this paper demonstrates that this approach can accurately predict the coupled dynamic system response of multiple substructured systems including operating mechanical equipment with a complex vibration source. The main advantage of this method is that it uses blocked force measurements in the form of a power spectral density matrix measured uncoupled from the rest of the system. This substructuring method is demonstrated using a simplified case study comprised of a two-stage vibration isolation system and excited by operating mechanical equipment.

The blast performance of concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) bridge columns was studied through a two-phase study comprised of blast and residual axial capacity experiments. Two one-fifth-scale CFFT columns and two one-fifth-scale conventional RC columns having comparable flexural capacities were subjected to distinct levels of explosive loading, causing damage but not complete failure. The blast resilience of the damaged columns was quantified by measuring the residual axial capacity of each column. The damaged CFFT columns exhibited superior strength and ductility retention compared with the damaged RC columns. Additionally, the damaged CFFT columns demonstrated a more predictable axial compressive mode of failure because the exterior FRP tube resisted the shear crack initiation observed in the damaged RC columns.

Damage detection for civil structures is limited by several factors including poor signal-to-noise ratios, a large number of unknown parameters, and a limited set of measured responses. Global vibration techniques that track modal parameters often remain insensitive to common forms of structural damage. Moreover, large sets of identified parameters make inverse problems ill-conditioned. To overcome some of these limitations, researchers have advanced substructure identification as a methodology to directly detect local stiffness changes using measured responses to improve damage detection and scalability in civil structures. This paper develops a substructure identification estimator that identifies the story stiffness of a shear building. Concurrent with the estimator derivation, identified parameter confidence intervals are developed and identification performance is predicted. Using the developed estimator, experimental testing is performed on a 3.66-m (12-ft) four-story steel structure subject...

SUMMARY Magnetorheological (MR) dampers are promising control devices in civil engineering structures as they combine reliability and stability of passive systems while maintaining versatility of active devices without large power requirements. These dampers are intrinsically nonlinear, so one of the challenging aspects of applying this technology is the development of accurate models to describe their behaviour for control design and evaluation purposes. This paper deals with the parametric identification of three large-scale MR dampers which are modelled using the viscous + Dahl model. Experimental results show reasonably good agreement with the forces predicted by the identified models. Copyright © 2011 John Wiley & Sons, Ltd.

Real-time hybrid testing (RTHTing) is a relatively new form of experimental testing where only the critical components of the system are physically tested while the rest of the structure is simulated. A RTHT can provide a cost-effective means for testing semiactive controlled civil structures. This paper describes the experimental validation of the RTHT facility at the University of Connecticut through comparison of RTHT results with corresponding shake table responses of a Magneto-Rheological (MR) fluid damper controlled test structure. The two-story structure has an MR damper connected between the ground and first story and is excited by ground accelerations. For the shake table tests the fully physical building model and MR damper are tested on a medium-scale shake table. In the RTHT the MR damper alone will be tested physically while the rest of the test structure and ground excitation is simulated in the RTHT control computer. The performance of the RTHT is validated by comparing the building responses and measured damper force with those from the shake table test in both the time and frequency domains.

Support structures of traffic signals are flexible, lightly damped structures that are highly susceptible to wind-induced vibration. The sustained large-amplitude deflections caused by these dynamic vibrations can result in fatigue cracking and failure. The proposed innovative vibration absorber reduces fatigue in support structures of traffic signals with the use of the mass of the signal head as a damped-vibration absorber. This novel concept, referred to as a signal head vibration absorber (SHVA), provides energy absorption in the form of increased damping to the lightly damped signal support structure. A prototype smart vibration absorber, envisioned as an inexpensive retrofit to signal support structures that were experiencing excessive wind-induced vibration, was tested in a full-scale laboratory experiment at the University of Connecticut. The SHVA was experimentally shown to have increased the damping in the signal support structure from 0.2% of the critical damping ratio to 10.1%. For steady state vibration, this difference is equivalent to a 98.3% reduction in the response and virtually eliminates any deflections. A single SHVA can be applied to a wide range of signal support structures while still achieving reasonable performance. The SHVA can change the way vibration in traffic signal support structures is mitigated.

In this paper, in-field ambient vibration testing of a highway bridge in South Korea under traffic loadings has been conducted to update its finite element model for future predictive analysis and diagnosis purpose. The research results presented in this paper are outcomes from an international REU (Research Experience for Undergraduates) program in smart structures funded by US-NSF (National Science Foundation) and hosted abroad by the Korean Advanced Institute of Science and Technology (KAIST). The monitoring, modeling, and model updating of civil infrastructures are vital in maintaining new design and maintenance standards. Using the frequency domain decomposition (FDD), experimental modal properties of the structure were found and, after a finite element model was created and updated based on the modal properties. From the results, it has been concluded that (a) the FDD method successfully identified the modal characteristics of the structure from ambient vibration, (b) that model updating improved the accuracy of the finite element model, (c) Representing the structural supports as springs in the FEM improved the results from the ideally supported model.

A probabilistic structural health monitoring (SHM) method was identified to detect global damage in a highway bridge while accounting for the variability associated in calculating the desired damage measure. The proposed vibration-based monitoring method is applied to the bridge health monitoring benchmark problem. The benchmark structure is a scaled laboratory model of a typical highway bridge. The associated finite element model of this structure is excited with a simulated traffic excitation. The proposed SHM method is intended to meet the practical requirements of using a small number of sensors and detection of damage in a global sense. As such, accelerations are measured at a single location on the bridge. The bridge natural frequencies for a healthy state and a variety of damaged states are considered to help quantify and detect the potential damage. The natural frequencies are determined from the peaks in the power spectral density functions of the measured acceleration response. These natural frequencies are observed to be random variables with a normal distribution. The probability that the current natural frequency is greater than the previously measured healthy natural frequency can then be calculated from the assumed probability density functions and is used to predict, in a global sense, whether damage has occurred on the bridge structure. The results of this simulation-based study were used to extend and apply this method to actual highway bridges in Connecticut.

Magneto-rheological (MR) fluid dampers have been identified as a particularly promising type of semiactive control device for hazard mitigation in civil engineering structures. Large-scale experimental testing is important to verify the performance of MR fluid dampers for seismic protection of civil structures. Real-time hybrid testing, where only the critical components of the system are physically tested while the rest of the structure is simulated, can provide a cost-effective means for large-scale testing of semiactive controlled structures. This paper describes the real-time hybrid simulation experimental setup for multiple large-scale MR fluid dampers and demonstrates the capability at the University of Colorado at Boulder shared-use Fast Hybrid Test facility to conduct real-time hybrid testing within the Network for Earthquake Engineering Simulation.

Structural control of adjacent flexible structures has been shown to be effectively accomplished using the connected control method (CCM), which uses an auxiliary structure to provide a reaction force. A perceived constraint of the CCM is the ineffective control of structures with similar dynamics. However, the writers have presented a modified CCM mechanism in which dampers are connected between dynamically similar structures with a difference in connection height using cantilever structures. The research described in this paper extends the CCM to couple two dynamically similar structures and determines optimal stiffness and damping in the connector link. A two-degree-of-freedom building model is developed for the optimal design of the connected control devices. The optimal solutions of the connector stiffness and damping take into account the presence of fixed points in the systems transfer functions. Analytical results confirm the effectiveness of the proposed method and design. Experimental tests then verify the response reduction capabilities of the proposed optimal design.

Editor's Note : This is the second of a two-part Eduquakes series on educational shake tables. In Seismological Research Letters 78(3), Eduquakes provided a brief survey of low-end shake tables and activities; here Shirley Dyke and co-authors describe an ongoing effort to allow wide access (via the Internet) to more sophisticated shake tables. These bench-top tables are capable of matching realistic earthquake ground motion and would enhance any seismology class. For example, students could first calculate the expected waveforms from an earthquake and then test the effects on a model building, thereby providing a system-level “rupture-to-rafters” understanding of earthquakes and their effects. Although developed primarily for earthquake engineering, these tools are potentially useful to a much wider audience. Bench-scale shake tables are an engaging tool for educating students at all levels about the importance of earthquake engineering. Shake tables allow for classroom demonstrations and hands-on experimentation regarding structural response to earthquake ground motions. Demonstrations for K-12 students allow students to gain an understanding of earthquake motions and how structures can be designed or retrofitted to better withstand seismic motions. At more advanced levels, undergraduate and graduate students can conduct experiments to test their knowledge of fundamental concepts. Students may also build or modify scaled structural models to experiment with their own innovations and may also gain experience with modern sensors. While theoretical and analytical discussions are necessary, hands-on experiments are quite effective for demonstrating basic concepts in structural dynamics and earthquake engineering and nicely supplement more traditional educational methods. The University Consortium on Instructional Shake Tables (UCIST) was developed by Shirley Dyke in 1998 to enhance undergraduate and graduate education in earthquake engineering (see http://ucist.cive.wustl.edu/). This consortium, head-quartered at Washington University in St. Louis, was initially a cooperative educational effort among 23 universities associated with the three U.S. national earthquake …

The connected control method (CCM) has been shown previously to be a viable means to protect adjacent flexible structures. The CCM works by using an auxiliary structure to provide a reaction force for control. The CCM can be applied to a variety of structural systems including civil, mechanical, or aerospace structures, and can incorporate various types of control strategies including passive, active, or semiactive control. This paper focuses on the application of the CCM to seismically excited adjacent buildings employing semiactive control and extends the previous research in semiactive coupled building control to examine the effects of relative building height and coupling link location on the semiactive performance. The optimal semiactive coupled building configuration is shown to follow two guidelines: (1) The dominant frequencies of the two coupled buildings do not coincide and (2) the coupling link is not placed at the node of a dominant vibratory mode. Additionally, it is shown that semiactive con...

Real-time hybrid substructuring (RTHS) is a relatively new method of vibration testing for characterizing the system-level performance of physical hardware components. With RTHS, a dynamic system is partitioned into physical and numerical substructures and interfaced together in real-time similar to hardware-in-the-loop testing. This paper presents an overview of RTHS including the challenges posed by its real-time constraints and the application to system-level testing of physical vibration control devices and mechanical equipment. Two laboratory RTHS experiments performed at the University of Connecticut Structures Research Laboratory are used to demonstrate the benefit of RTHS. The first test examines the connected control method using viscous damper hardware as the physical substructure coupled to adjacent base isolation systems as the numerical substructure. The second test involves a multi-stage isolation system comprised of an operating mechanical component on isolators as the physical substructure coupled to an intermediate mass on similar isolators as the numerical substructure. In these RTHS tests, feedforward inverse compensation combined with feedback is used to compensate the frequency-dependent dynamics of the multi-actuator system. Experimental results demonstrate that RTHS accurately captures the system-level behavior of the coupled system and allows for repeatable tests of various conditions and potential system improvements to be efficiently examined.Copyright © 2015 by ASME

As magnetorheological (MR) control devices increase in scale for use in real-world civil engineering applications, sophisticated modeling and control techniques may be needed to exploit their unique characteristics. Here, a control algorithm that utilizes overdriving and backdriving current control to increase the efficacy of the control device is experimentally verified and evaluated at large scale. Real-time hybrid simulation (RTHS) is conducted to perform the verification experiments using the nees@Lehigh facility. The physical substructure of the RTHS is a 10-m tall planar steel frame equipped with a large-scale MR damper. Through RTHS, the test configuration is used to represent two code-compliant structures, and is evaluated under seismic excitation. The results from numerical simulation and RTHS are compared to verify the RTHS methodology. The global responses of the full system are used to assess the performance of each control algorithm. In each case, the reduction in peak and root mean s...

The fire performance of protected concrete-filled fiber reinforced polymer (FRP) tube (CFFT) and conventional reinforced concrete (RC) bridge columns is studied through two phases of experimental research comprised of fire exposure and residual axial capacity tests. Two one-fifth scale CFFT columns and two one-fifth scale conventional RC columns having similar axial and flexural capacities were subjected to two durations of extreme temperature exposure. The CFFT columns were protected by the Tyfo® CFP fire protection system during the experiments. Subsequently, the post-fire robustness of the columns was quantified by measuring the residual axial capacity characteristics of each column. The protected CFFT columns exhibited superior axial strength and stiffness retention compared to the RC columns after fire exposure.

Structural health monitoring has drawn significant attention in the past decades with numerous methodologies and applications for civil structural systems. Although many researchers have developed analytical and experimental damage detection algorithms through vibration-based methods, these methods are not widely accepted for practical structural systems because of their sensitivity to uncertain environmental and operational conditions. The primary environmental factor that influences the structural modal properties is temperature. The goal of this article is to analyze the natural frequency-temperature relationships and detect structural damage in the presence of operational and environmental variations using modal-based method. For this purpose, correlations between natural frequency and temperature are analyzed to select proper independent variables and inputs for the multiple linear regression model and neural network model. In order to capture the changes of natural frequency, confidence intervals to detect the damages for both models are generated. A long-term structural health monitoring system was installed on an in-service highway bridge located in Meriden, Connecticut to obtain vibration and environmental data. Experimental testing results show that the variability of measured natural frequencies due to temperature is captured, and the temperature-induced changes in natural frequencies have been considered prior to the establishment of the threshold in the damage warning system. This novel approach is applicable for structural health monitoring system and helpful to assess the performance of the structure for bridge management and maintenance.

Real-Time Hybrid Substructuring (RTHS) is a new method of vibration testing that can be used to effectively characterize the system level performance of mechanical equipment. RTHS allows mechanical equipment to be physically tested while coupled through what is called a transfer system to a real-time numerical simulation of the support structure. The challenge in applying RTHS to test mechanical equipment is twofold: the equipment itself can have little inherent damping which, coupled with the inherent dynamics in the transfer system, can result in unstable RTHS tests; and the interface at the attachment points can be complex with multi-directional and rotational motion and reactions which adds significant complexity to the RTHS transfer system. To insure stability and accurately represent the complex interface between the physical and numerical substructures, a high fidelity multiple-input-multiple-output (MIMO) servo-hydraulic actuator system is needed for the RTHS transfer system. This paper presents a methodology to achieve effective control of a six degree-of-freedom (6DOF) shake table and describes the corresponding MIMO system identification and model-based feedforward feedback compensation to facilitate both stable and accurate RTHS testing of lightly damped mechanical systems. Results show that the proposed compensation method can improve the magnitude and phase tracking of a 6DOF shake table located at the University of Connecticut.

Full-scale dynamic earthquake engineering experiments are costly, yet they are vital for the advancement of seismic protection for large structures. The main goal of such large-scale studies is to accurately replicate the response of complex structures. E-Defense, a part of Japan’s National Research Institute for Earth Science and Disaster Prevention (NIED), constructed and tested a four-story reinforced-concrete base-isolated building to study, among other objectives, how different energy dissipation devices in the building isolation layer improve the response subjected to strong impulsive and long period excitations. This structure was subjected in August 2013 to a series of tests. Analyzing the resulting acceleration responses from the random ground motion tests forms the first step in identifying the dynamic characteristics of this test structure. Specifically, enhanced canonical correlation analysis (ECCA) and the advanced numerical algorithm for subspace state-space system identification (N4SID), from the stochastic subspace identification (SSI) family of methods, were used to estimate the modal parameters. Additional identification was then performed using responses recorded during simulated earthquakes. The recovered modal parameters were compared against the nominal parameters to analyze the behavior of the building’s isolation system, as well as the effectiveness of the identification methods. doi: 10.12783/SHM2015/166

Real-time hybrid substructuring (RTHS) is a relatively new method of vibration testing for characterizing the system-level performance of physical components or substructures. With RTHS, the coupled system is partitioned into physical and numerical substructures and interfaced together in real-time as cyber-physical system similar to hardware-in-the-loop testing. Control actuation and sensing is used to enforce the compatibility and equilibrium conditions between the physical and numerical substructures. Since RTHS involves a feedback loop, the frequency-dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. This paper presents a robust stability and performance analysis method for multi-actuator RTHS based on robust stability theory for multiple-input-multiple-output (MIMO) feedback control. This analysis method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics.

This paper presents a reformulation of dynamic substructuring for vibrating structural systems as a feedback control problem. Frequency based substructuring (FBS) using admittance coupling of two substructures is shown to be mathematically equivalent to a feedback control system with the primary substructure acting as the controller and the secondary substructure acting as the plant. This formulation can be used to perform time-domain simulations of dynamic substructuring problems using MATLAB’s Simulink environment, whereby the primary substructure can be modeled by three possible approaches: (1) Laplace domain transfer functions, (2) state-space models, or (3) finite impulse response functions. The secondary substructure can be represented by a variety of Simulink blocks including nonlinear elements. By inserting an actuator transfer system between the two substructures, this formulation also provides the basis for real-time hybrid substructuring (RTHS) for coupling numerical and physical substructures as a cyber-physical system similar to hardware-in-the-loop testing. In typical RTHS the numerical substructure acts as the controller and the actuator with physical substructure acts as the plant. This feedback control formulation will lead to further advancements for both dynamic substructuring and RTHS by adapting methods from classical and modern feedback control theory.

Experimental verification of analytical and numerical studies is very important in the area of structural dynamics and control due to the presence of higher mode participation, control structure interaction, sensor noise and potential nonlinear behavior. This paper describes a bench-scale test structure that extends the typical capabilities of test structures able to incorporate higher mode participation, control structure interaction and sensor noise to include nonlinear material behavior. A portal frame test structure is designed and built to simulate the formation of plastic hinges without actually receiving any damage. To demonstrate the nonlinear test structure’s use, a semiactive control strategy employing a shear mode magnetorheological (MR) fluid damper and acceleration feedback is applied to the test structure for seismic protection. The performance of the semiactive controlled structure is compared to the uncontrolled structure for a broad range of ground motion intensities and varying levels of nonlinear structural behavior to observe the improved reliability of the semiactive controlled structure.