Shear Building Research Articles

A Computationally Efficient Method for Optimum Tuning of Single-Sided Pounding Tuned Mass Dampers for Structural Vibration Control

Pounding tuned mass dampers (PTMD), which relies on impact to dissipate vibration energy, have shown remarkable performance in suppressing structural vibrations with its modest design. However, the optimum design of PTMDs is computationally expensive due to non-smooth contact-impact behavior. This study provides a computationally efficient approach to determine the optimal parameters of single-sided PTMDs used in vibration control of structural systems. An optimization strategy is used to minimize the maximum response of the controlled structure. As is well-known, the calculation of the dynamic response of a structure could be cumbersome when conventional time-stepping techniques are used in each iteration of the optimization routine. Hence, an exact analytical solution of the steady-state vibration is used to calculate the response for different excitation frequencies, which substantially decreases the computational burden. The adopted method is computationally very inexpensive with respect to the conventional time-stepping techniques used to solve the nonlinear equations of motion to obtain response quantities. The exact solution only requires the solution of the system of five nonlinear equations in order to evaluate the steady-state response per each excitation frequency of harmonic force. A four-storey shear building is used to evaluate the optimally-tuned PTMD by the proposed procedure. In addition, simplified design equations for the coefficient of restitution and frequency ratio are provided using curve and surface fitting for preliminary design. It was shown that the effect of damping ratio of the primary structure on the optimal coefficient of restitution value is not considerable, while it has significant influence on the optimal frequency ratio. It was also realized that the objective function used in optimum parameter design has only one local optimum, which is suitable for the application of gradient-based optimization methods.

A Common Framework for Tuned and Active Mass Dampers: Application to a Two-Storey Building Model

This paper presents a common framework for designing tune mass dampers (TMD) and active mass dampers (AMD) to control the vibrations of shear buildings. This common framework is used for tuning the parameters of TMD and AMD devices in order to achieve a particular control objective. Thus, TMD and AMD can be better compared in practical applications. As an application example, two scaled TMD and AMD prototypes are tuned and installed in a two-storey building model. The parameters of the TMD and AMD are obtained by using this common framework and the same control objective. Finally, the performance assessment of these scaled prototypes is presented, highlighting the theoretical limitations and implementation problems, which can be used as practical guidelines for future real implementations.

Soil erosion and the influenced factors: A review article

Unacceptable rates of soil erosion are one of the main important factors that the hydrologists and the water engineers should keep in their mind to prevent soil detachment and increasing of the sediment yields from occurring. Unnoticed soil erosion due to slow process may lead to serious problems with the time due to wash of soil surface that leads to decrease the shear strength and building failure may occur. This review paper focuses on the forms of soil erosion, the affecting factors and prediction of the soil erosion. Forms of soil erosion are presented clearly and the formations of the rills, inter-rills, gullies due to steam flow are explained. Historical sequence of main important equations of the soil erosion determinations from art-of-literature is presented. Hydraulic, topographical and soil critical condition for the erosion with empirical equations are explained in details. Finally, the sedimentation which is the results of the soil erosion, sediment transport and the sediment yields process has been considered in this paper.

Optimal design of nonlinear energy sinks for mitigation of seismic response on structural systems

This paper proposes an approach for the optimal design of nonlinear energy sinks (NES) installed in structures subjected to stochastic excitation. The response of these nonlinear systems subjected to stationary or non-stationary stochastic excitations has been characterized by the time-history of its covariance matrix. However, time-invariant equivalent linearization methods of NES equipped structures will not always converge due to its essential nonlinearity. A solution strategy is proposed using equivalent linearization at each time step of the governing matrix differential equation, obtained through a sequence of Lyapunov equations. The adequacy of this method for optimization problems is evaluated by comparison with Monte Carlo simulations of two representative NES examples. Moreover, the influence of the Gaussian assumption of the equivalent system response is studied in these examples. An optimization formulation to design systems equipped with NES devices is proposed, in which the performance function is defined in terms of the maximum variance over the time-history. This result is obtained by using the proposed method with a Gaussian assumption of the equivalent linear system. To illustrate the proposed methodology, parametric optimization of an NES installed at the top of a shear building structure is performed.

Simultaneous Online Damage Detection and Vibration Control of Structures Using Synchronization and Semi-Active Control

In this paper, a smart structure is developed by integrating a semi-active control strategy with an online synchronization-based damage detection method. In this algorithm, the structural damages are identified in real-time with the synchronization-based method using displacement and velocity measurements of the structure. Then, a fuzzy logic controller is applied for determination of the control forces according to the occurrence of damages. A five-story linear shear building equipped with magneto-rheological (MR) dampers is studied numerically to verify the performance and efficiency of the proposed integrated method for both damage detection and vibration suppression. One damage scenario and four earthquake records are used for such purpose. Results demonstrate that the proposed algorithm has the capability of identifying structural damages satisfactorily while exerting suitable control forces to compensate for the damages occurrence and mitigating the dynamic responses of the structure. Furthermore, it is shown that in comparison with the long-established method of only vibration control, the total energy consumption is significantly reduced, an issue of concern in optimal control of structures.

Implementation of dynamic hybrid simulation for response evaluation of shear building

Dynamic hybrid simulation is a testing method, which is developed in the past few decades, to find the dynamic response of a structure. It involves splitting of the structure into two parts: physical substructure that contains the key region of interest, which is tested in a laboratory, and virtual substructure that contains the remaining part of the structure in the form of a numerical model. This paper presents the implementation of DHS for response evaluation of a shear building. The bottom storey alone was tested physically in the laboratory. Electromagnetic shaker was used to emulate the effect of the remaining structure. DHS is found to be an effective tool for dynamic response evaluation of structures.

Response surface-based structural damage identification using dynamic responses

Response surface methodology (RSM) is efficient in updating a model as compared to a finite element model (FEM) based on updating techniques. This feature of RSM can be used to replace the time-consuming FEM-based updating step with a response surface-based surrogate model. In addition, RSM also solves the problem of slow convergence and time consumption. The present study deals with the applicability of RSM for damage identification in a six-storey shear building. At first, the theoretical overview of RSM has been provided, followed by a detailed description of the proposed algorithm for damage identification. For this purpose, different types of design of experiments (DoEs) have been used for generating the response surface (RS) model. A simulation study has been carried out on a six-storey numerical building model, along with an experimental investigation on a three dimensional six-storey miniature model of a shear building in a laboratory environment. For executing the methodology, dynamic responses of the structures are analyzed to get the translational modal parameters (frequencies and mode shapes) using frequency domain decomposition (FDD). The RS equations have been generated using these modal parameters through various DoEs (namely, central composite design, Box-Behnken design, and D-optimal), and they have been found to be equally efficient in identifying the damage. A comparative study over RSM based damage detection using different modal parameters have been presented. It has been observed that the RS model generated using the first three translational modal frequency and the corresponding first two mode shapes are quite efficient in detecting as well as localizing the damage in the shear building with proper quantification.

Relative Performance of Linear Quadratic Regulator and Pole Placement Technique for Active Seismic Control of Structures

This paper presents the study conducted on the comparison of the performance of the two popular active control algorithms viz. Linear Quadratic Regulator (LQR) and Pole Placement technique in terms of their capability to alleviate the response of a structure to an earthquake. To compare the performance of the two control algorithms, a ten story regular shear building frame with three active tendons located in 1st, 4th and 5th Storys and subjected to an El Centro earthquake has been considered. A comparison of the numerical results shows that the reductions of maximum top floor displacement, maximum story drift and base shear obtained using LQR control algorithm are 71.48%, 59.70% and 62.7% while the reductions obtained using Pole Placement technique are 73.77%, 73.14% and 77% respectively. The percentage reduction of the three performance parameters per unit control force obtained using the two methods have also been estimated and compared. Pole placement technique gives higher reduction while the LQR algorithm gives more reduction per unit control force.

Interval Type-2 Fuzzy Hybrid Control of a High-Rise Building Including Soil–Structure Interaction Under Near-Field and Far-Field Ground Motions

The interval type-2 fuzzy logic controller (IT2FLC) has emerged as one of the most effective high-tech control strategies to improve the performance of structures under near-field and far-field ground motions. The present study discusses the application of this strategy in the hybrid control of the behaviour of a real high-rise shear building by considering soil–structure interaction. In this regard, a hybrid control technique, consisting of a tuned mass damper (TMD) and a magneto-rheological (MR) damper is proposed. Using an MR damper on a TMD (MR + TMD) helps to reduce the seismic responses of a high-rise building in soil–structure interaction. The utilization of this hybrid device is very useful because it does not require huge power sources. By applying the observer–teacher–learner–based optimization (OTLBO) method, the fuzzy rules of IT2FLC, the TMD parameters, and the voltage of the MR damper have been optimized for a fifteen-storey shear building under four seismic near-field and far-field excitations. Minimization of the peak displacement of the top floor by using the square root of sum of squares (SRSS) of each response to each earthquake was utilized as the optimization criterion. Then, the optimized type-2 fuzzy rules and optimized TMD parameters were examined under seven new earthquake records in the fifteen-storey building. The results obtained by comparing the proposed control and uncontrolled systems in terms of the structure interaction with soft and dense soils show that the IT2FLC- using OTLBO is an efficient control method. It is also shown that the responses of this building to the hybrid controller have been effectively improved.

Identification of joint structural state and earthquake input based on a generalized Kalman filter with unknown input

Accurate and real-time information of structural states and earthquake input is the prerequisite for structural seismic safety assessment and vibration control. When the earthquake input to a structure is not measured, it has been tried to identify structural state and the unknown earthquake input using the measured structural responses as an inverse problem. However, only structural absolute acceleration responses instead of the relative ones can be measured in this case, which limits the real-time performance of the existing Kalman filter with unknown input (KF-UI). In this paper, a generalized Kalman filter with unknown input (GKF-UI) is proposed to identify structural states and unknown earthquake inputs in real-time. Structural motion equations are established in the relative coordinate system and the observation equations are structural absolute acceleration-only measurements. The analytical derivation of the proposed GKF-UI is a direct extension of the classical Kalman filter (KF). It is also proven that the identification by the proposed GKF-UI using the absolute acceleration-only measurements under unknown earthquake excitation does not lead to the so-called drifted results in the previous identifications under unknown external excitations. Moreover, structural modeling errors can be considered in the identification by the proposed method. Then, it is extended to investigate the identification of the structural state of high-rise shear buildings and unknown earthquake inputs by combining the proposed GKF-UI with the modal expansion. Hybrid dynamic motion equations in modal space and observation equations in physical space are established to both reduce the state dimension and keep the one-dimension of unknown earthquake input instead of the increased number of unknown modal inputs. In addition, absolute accelerations are used in the observation equations, which avoids the dilemma that absolute accelerations cannot be converted into relative modal accelerations in the relative coordinate system under unknown earthquake input. Some numerical examples are used to verify the proposed method. Moreover, a shaking table test is adopted to further validate the performances of the proposed method.

Bayesian model updating of a twin-tower masonry structure through subset simulation optimization using ambient vibration data

A Bayesian model updating method using subset simulation optimization given ambient vibration data is proposed to improve the efficiency in sampling and avoid local optimums, which is applied to a full-scale high-rise structure. In the proposed method, the Bayesian fast Fourier transform method is used to extract the most probable values (MPVs) and coefficients of variation (COVs) of modal parameters of the structure, which are considered as the weighting factors in the likelihood function. The posterior probability density function (PDF) of the updating parameters is then derived considering the prior PDF as the regularization term. The subset simulation optimization algorithm is extended to find the global optimal solution of the posterior PDF. The MPVs and COVs of the updating parameters are finally presented. The proposed method is first verified by updating the 15 story stiffness scaling factors of a shear building model. Then, the proposed method is investigated through a numerical application of a four-story frame structure, in which accurate parameter estimations are observed independent of the prior PDF. Finally, the proposed method is applied to a real-world 13-story twin-tower masonry structure which is a modern heritage building. Ambient vibrations were measured through a series of accelerometers instrumented in the structure. The updating parameters are the moduli of elasticity of selected substructures with two model classes studied: three parameters and six parameters. The model-predicted modal parameters from the updated model are in good agreement with their identified counterparts. It is also shown that the case using three parameters provides larger evidence based on the Bayesian model class selection method. The updated refined finite element model provides a basis for the long-term structural health monitoring.

Critical Response of Multi-Story Damped Bilinear Hysteretic Shear Building Under Multi Impulse as Representative of Long-Period, Long-Duration Earthquake Ground Motions

The critical response is investigated for a multi-story damped bilinear hysteretic shear building model under a multi impulse as a representative of long-period long-duration earthquake ground motions. The critical response for an elastic-plastic single-degree-of-freedom (SDOF) model under a multi impulse was derived in the previous papers. However, it is difficult to derive the critical response for a multi-degree-of-freedom (MDOF) model under a multi impulse because the phase lag among masses induces a complicated situation. In place of deriving an explicit critical response, a criterion on the criticality of the multi impulse for the elastic-plastic MDOF model is derived and the properties of the critical responses are clarified. In the analysis, a new concept of ‘Multi Impulse Pushover (MIP)’ is introduced and the progressive performance evaluation for the increasing input level is conducted. The analysis of energy response (input energy, dissipated energy, etc.) and the comparison with the response to the corresponding sinusoidal wave are made to enhance the reliability and practicality of the proposed method using the multi impulse as a substitute of sinusoidal waves which are representatives of long-period long-duration earthquake ground motions.

Fully convolutional networks for structural health monitoring through multivariate time series classification

We propose a novel approach to structural health monitoring (SHM), aiming at the automatic identification of damage-sensitive features from data acquired through pervasive sensor systems. Damage detection and localization are formulated as classification problems, and tackled through fully convolutional networks (FCNs). A supervised training of the proposed network architecture is performed on data extracted from numerical simulations of a physics-based model (playing the role of digital twin of the structure to be monitored) accounting for different damage scenarios. By relying on this simplified model of the structure, several load conditions are considered during the training phase of the FCN, whose architecture has been designed to deal with time series of different length. The training of the neural network is done before the monitoring system starts operating, thus enabling a real time damage classification. The numerical performances of the proposed strategy are assessed on a numericalbenchmark case consisting of an eight-story shear building subjected to two load types, one of which modeling random vibrations due to low-energy seismicity. Measurement noise has been added to the responses of the structure to mimic the outputs of a real monitoring system. Extremely good classification capacities are shown: among the nine possible alternatives (represented by the healthy state and by a damage at any floor), damage is correctly classified in up to 95 % of cases, thus showing the strong potential of the proposed approach in view of the application to real-life cases.

High‐resolution time‐frequency representation for instantaneous frequency identification by adaptive Duffing oscillator

Time-frequency analysis of structural vibration responses provides essential information for structural system identification, modal updating, and condition assessment. However, spurious peaks introduced by the strong noise will significantly increase the false positive rate as well as compromise the sparse time-frequency signal representation. This paper proposes a high-resolution time-frequency representation approach for nonstationary signals polluted with strong noise. With a high sensitivity to detect slight frequency shift and an immunity to noise effect, the intermittent chaotic of Duffing oscillator system is introduced to accurately identify the time-varying instantaneous frequencies. Furthermore, an adaptive Duffing oscillator array is adopted to improve the instantaneous frequency identification efficiency. The feasibility and effectiveness of the proposed method are verified with numerical and experimental studies. Numerical studies are conducted on a multicomponent synthetic nonstationary signal as well as on a two-story shear building with time-varying stiffness under seismic loads. In experimental validations, the acceleration response of a laboratory bridge model under moving vehicle load is also analyzed by using the proposed approach to obtain the instantaneous frequency variations induced by the bridge–vehicle interaction. These results are compared with those obtained from a method based on empirical wavelet transform and Hilbert transform (EWT-HT), to highlight the superiority of the proposed approach in obtaining high-resolution time-frequency analysis results for nonstationary signals with strong noise.

Vibration Control of Dynamically Similar Buildings Optimally Connected by Viscoelastic Dampers

Recently, the construction of similar high-rise buildings has increased due to the increasing population. Moreover, due to space constraints, these structures are being built next to each other. When such tall buildings are located in high seismic zones, earthquake protection becomes essential. There have been many studies on vibration control by connecting dampers to adjacent dissimilar buildings. However, reviews with specific recommendations on damper connections to adjacent similar buildings are found to be scarce. This study aims to control the building vibration that is dynamically similar and adjacent to each other through damper connections. In this study, two adjacent ten-storied, dynamically similar RC buildings are considered. The buildings are modeled with shear frame and lumped mass for efficient yet straightforward analysis. The idealized shear buildings were connected with viscoelastic dampers using different damper configurations and then subjected to seven seismic ground motions. A numerical integration technique is used to obtain the seismic response, and a single objective particle swarm optimization technique is employed to optimize the position of dampers. The viscoelastic dampers provided at their optimal locations improved the seismic performance of coupled buildings in an economical way.

New lateral load distribution pattern for seismic design of deteriorating shear buildings considering soil-structure interaction

The current code-conforming seismic lateral load patterns are implicitly derived based on the dynamic solutions of fixed-base elastic structural systems, without considering the effects of hysteretic characteristic and soil-structure-interaction (SSI). Consequently, such lateral force patterns may not be applicable for the seismic design of nonlinear deteriorating structural systems. In this study, the analytical model was constructed using the shear building model. The peak-oriented modified I–K model and sway-rocking (S-R) model were employed to simulate the deteriorating behavior and SSI effects, respectively. A practical optimization design procedure for optimal lateral load pattern was developed based on the uniform damage distribution. The influence of main parameters on the new lateral load pattern was comprehensively investigated, including the parameters of the S-R model and the peak-oriented modified I–K model, ground motion excitations, fundamental period, target ductility, damping ratio and so on. The quantified expression of the new lateral load distribution was proposed as a function of fundamental period, the target ductility, aspect ratio and shear wave velocity. The results show that the structures designed according to the proposed lateral force pattern experienced obviously less damage than the code-conforming pattern.

Bayesian Approach of Model Updating of Structural Parameters with Simulated Modal Data

The present study investigates the effectiveness of Bayesian approach of model updating of structure, using simulated modal data sets as evidence. The importance of the prediction of error implemented in the proposed Bayesian framework to assess its capability in sampling posterior values with improved accuracy has been highlighted. The natural frequencies and mode shapes of the structure are taken only as the evidence. The study highlighted the importance of the likelihood functions corresponding to the prediction of error between the experimental and predicted data. The study also implemented the likelihood functions corresponding to the prediction of error variances of natural frequencies only in sampling posterior values with higher accuracy. The efficacy of the proposed approach in dealing with the issue of incomplete data sets, that makes the problem typically ill-conditioned, is duly addressed. The present work also implemented model reduction technique to synthesise the mode shape ordinates at unmeasured degrees of freedom (DOF) from the reduced-order model. In addition, the efficiency of the proposed model reduction algorithm is explored by adding noises of varying percentages to the measured mode shape values. The proposed methodology is illustrated numerically to update the stiffness parameters of an eight-storey shear building model, considering simulated datasets contaminated by Gaussian error as evidence. Results with both incomplete and complete data sets using the proposed Markov Chain Monte Carlo approach are studied. The accuracy on the synthesis of mode shapes from unmeasured DOF using model reduction algorithm is also studied.

Damage Detection in Initially Nonlinear Structures Based on Variational Mode Decomposition

Nonlinear characteristics in the dynamic behaviors of civil structures degrade the performance of damage detection of the linear theory based traditional time- and frequency-domain methods. To overcome this challenge, this paper proposes a damage detection approach for nonlinear structures based on Variational Mode Decomposition (VMD). In this approach, the measured dynamic responses from nonlinear structures under earthquake excitations are adaptively decomposed into a finite number of monocomponents by using VMD. Each decomposed mono-component represents an amplitude modulated and frequency modulated (AMFM) signal with a limited frequency bandwidth. Hilbert transform is then employed to identify the instantaneous modal parameters of the decomposed monomodes, including instantaneous frequencies and mode shapes. Based on the identified modal parameters from the decomposed structural dynamic responses, two damage indices are defined to identify the location and severity of structural damage, respectively. To validate the effectiveness and accuracy of the proposed approach, a nonlinear seven-storey shear building model with four different damage cases under earthquake excitations is used in the numerical studies. In experimental verifications, data from shake table tests on a 12-storey scaled reinforced concrete frame structure with different earthquake excitations are analyzed with the proposed approach. The results in both numerical studies and experimental validations demonstrate that the proposed approach can be successfully applied for nonlinear structural damage identification.

Study on the Sensitive Factors of Structural Nonlinear Damage Based on the Innovation Series

Constructing a damage-sensitive factor (DSF) is one of the key steps in structural damage detection. In this paper, innovation series extracted from the auto-regressive conditional heteroscedasticity (ARCH) model are proposed to construct a DSF, which is defined as the standard deviation of innovation (SDI). A three-story shear building structure is used to demonstrate and verify the performance of the proposed method, and the results are compared with the standard deviation of the residuals (SDR) based on an auto-regressive (AR) model. In the proposed method, the AR model is established using the acceleration responses obtained from the reference and test states. The residual series are then extracted for fitting the SDR. Subsequently, the ARCH model is constructed based on the residual series from the AR model, and a new DSF of SDI is defined. This study focuses on analyzing the accuracy of fitting AR model and ARCH model to vibration response data via the normal probability distribution, and identifying the characteristics of the residual and innovation series. The mean squared error (MSE) is used as the loss function to calculate the loss on residual and innovation series from the AR model and ARCH model, respectively. The results demonstrate that the SDR can be used for nonlinear damage detection. However, the proposed SDI can provide more accurate nonlinear damage identification and is robust to varying environmental condition and small damages. Thus, the innovation series developed based on ARCH model are promising for expressing and constructing nonlinear DSFs.

Nontarget-Based Measurement of 6-DOF Structural Displacement Using Combined RGB Color and Depth Information

Structural displacement is an important physical quantity that provides essential information regarding the structural conditions and the safety of a structure. To date, a wide variety of displacement measurement methods have been developed. As a noncontact type of measurement, the computer-vision-based approach receives significant attention for its cost effectiveness, measurement convenience, and great performance. However, most existing methods are limited to one- or two-degrees-of-freedom (DOF) displacement measurement and require known dimensions of structural members or predefined target markers attached to the target structure, which limits real-world application. This article proposes a nontarget-based 6-DOF displacement measurement method using the combined RGB and depth information. The proposed method utilizes three-dimensional information of measurement points on the target structure obtained using the RGB-D camera, and suggests a coordinate transform scheme to determine the 6-DOF displacement in the physical domain. The proposed method is validated in two laboratory experiments using a shear building model and a pan-tilt with a measurement plate, in which both translational and rotational displacements are measured.