Maximum Absolute Acceleration Research Articles

FUZZY SLIDING MODE CONTROL OF A STRUCTURE BASED ON HEDGE ALGEBRAS CONTAINING INPUT TIME DELAY

In this paper, the authors present the sliding mode control problem of a structure using hedge-algebras-based fuzzy controller considering the impact of time delay (de-sHAC). Controlled model is a structure subjected to earthquake excitations. Numerical simulations are implemented in order to show advantages of the proposed controller. Obtained results include: variation of maximum displacement and maximum absolute acceleration versus time delay; time responses of displacement, absolute acceleration and control force of the structure in the uncontrolled case, the controlled case using the hedge-algebras-based fuzzy controller with input time delay (de-HAC) and the de-sHAC.

Parametric study of seismic pounding between RC buildings with aligned slabs

This paper presents a parametrical study on seismic pounding between pairs of RC frames with 3 and 5 stories and aligned slabs. The performance indices are the maximum inter-story drift, absolute acceleration, and story shear force, and the cumulated hysteretic energy. The distinctive features are the selection of parameters and of performance indices, the soil-structure interaction, a modified Kelvin-Voigt pounding model, and, the careful selection of the discretization period. The findings of this study are the corroboration of remarks from previous researches and the formulation of new conclusions.

Numerical Study of the Circumferential Fuses Used in Steel Repairable Buildings with Seesaw Motion

Abstract Structural fuses and rocking system are used in order to reduce the building response to earthquakes and damage guidance. In the proposed seesaw motion system, which is similar to the rocking system, the building columns, in top of the foundation, have been removed and a central support and structural fuses are used around the building instead of them. The main purpose of creating this system is that the structural components remain elastic during the earthquake and nonlinear deformations occur in circumferential structural fuses it means that, it is possible to replace damaged fuses after the earthquake and exploit the building in a short time and at a lower cost than the construction cost of the whole building. In this research, the specification of a kind of structural fuse have been investigated and its application in the building with a seesaw system is studied under the influence of the near-field earthquake. After reviewing the fuses, it was observed that, the maximum absolute acceleration of roof and the base shear are significantly reduced in this system; however, the relative drift of floors in some buildings has increased but is lower than the permitted limit.

Automatic determination of LQR weighting matrices for active structural control

This paper presents a method for the automatic selection of weighting matrices for a linear-quadratic regulator (LQR) in order to design an optimal active structural control system. The weighting matrices of a control performance index, which are used to design optimal state-feedback gains, are usually determined by rule of thumb or exhaustive search approaches. To explore an easy way to select optimal parameters, this paper presents a method based on Bayesian optimization (BO). A 10-degree-of-freedom (DOF) shear building model that has passive-base isolation (PBI) under the building is used as an example to explain the method. A control performance index that contains the absolute acceleration, along with the inter-story drift and velocity of each story, is chosen for the design of the controller. An objective function that contains the maximum absolute acceleration of the building is chosen for BO to produce optimal weighting matrices. In the numerical example, a restriction on the displacement of the PBI is used as a constraint for the selection of weighting matrices. First, the BO method is compared to the exhaustive search method using two parameters in the weighting matrices to illustrate the validity of the BO method. Then, thirty-three parameters (which are automatically optimized by the BO method) in the weighting matrices are used to elaborately tune the controller. The control results are compared to those for the exhaustive search method and conventional optimal control, in terms of the control performance of the relative displacement, absolute acceleration, inter-story-drift angle, and the story-shear coefficient of each story. The damping ratio for each mode, and the control energy and power are also compared. The comparison demonstrates the validity of the method.

Damage boundary of structural components under shock environment

This paper studies the damage of structural components (solid structures and electronics) under severe shock environment introduced by intensive impulsive loads. Two types of critical states of shock response spectrum (SRS) are identified, i.e. the critical SRS state governed by the maximum relative displacement and absolute acceleration, and the critical SRS state governed by the maximum pseudo velocity. The damage boundary of a given component under shock environment is determined analytically in a wide range of frequency domain, which shows good agreement with experimental and numerical results. The proposed method can be used to guide the shock environment adaptability design of aerospace and other structural components.

Reducing undesirable vibrations of planar linkage mechanism with joint clearance

An optimization design method is presented to reduce the undesirable vibrations caused by clearance for planar linkage mechanism. A clearance joint is defined and considered a contact/impact force constraint. Contact and impact force models for the clearance joint are established using a normal contact force model based on Hertz model with energy loss and a tangential friction model based on modified Coulomb model with dynamic friction coefficient, respectively. In view of the clearance joint, dynamic equations and optimization method for a planar four-bar mechanism are then presented as an application example. The optimization aims to minimize the maximum absolute acceleration peaks of the mechanism by determining the link lengths of the planar linkage mechanism. Finally, the optimization design is solved by a generalized reduced gradient algorithm. Results show evident decrease in vibration peaks of the mechanism and obvious reduction in the contact forces in the clearance joint, which contribute to a good performance of planar linkage mechanism systems.

Seismic Performance of Base‐Isolated Precast Concrete Shear Wall Structure with AHW Connections

To improve the seismic performance and seismic reliability of precast concrete shear wall (PCSW) structure with improved assembly horizontal wall connections (AHW connections), base isolation technology was proposed to be applied in the PCSW structure. Two 1/4‐scaled structure models using the improved AHW connections were constructed: a lead‐rubber bearing (LRB) base‐isolated PCSW structure model and a base‐fixed PCSW structure model. Shaking table tests were conducted on these two models with three strong ground motions to assess the seismic performance of the structures. It was found that the improved AHW connections in the base‐isolated PCSW structure are useful and effective and that they fulfil the requirements to be met by the connections to withstand an earthquake. In addition, the maximum absolute acceleration and base shear force of the base‐isolated PCSW structure model were less than those of the base‐fixed PCSW structure model, and the isolation effect on the absolute acceleration responses and base shear responses increased with increase in the intensity of ground motions. In a word, the seismic performance and seismic reliability of PCSW structures can be effectively improved using base isolation technology. After this investigation, the seismic responses of the base‐isolated PCSW structure model were numerically simulated using OpenSees software. There was a reasonable agreement between the numerically simulated results and test results; thus, the numerical simulation method and analysis model used for the base‐isolated PCSW structure model were verified.

Modeling method of element Rayleigh damping for the seismic analysis of a 3D FEM model with multiple damping properties

Damping modeling is important for the accurate evaluation of the seismic response of structures. Our group previously reported a damping modeling method using element Rayleigh damping and evaluated the effectiveness using a simple lumped-mass model with multiple damping properties; however, the effectiveness of the method was not evaluated for three-dimensional (3D) finite element method (FEM) models with multiple damping properties. Moreover, further studies showed that the method needed to be improved to be applied to 3D FEM models. Therefore, the method has been improved to enable application to the seismic analysis of 3D FEM models, and the effectiveness of the method has been evaluated. The proposed method uses a weighted least-squares method to automatically determine the coefficients of element Rayleigh damping. The weighted least-squares method minimizes the differences between the modal damping ratios to be modeled and those given by element Rayleigh damping. Although all modal damping ratios in a simple lumped-mass model were used for damping modeling in our previous study, obtaining them for 3D FEM models is impractical because these models have more natural modes than simple lumped-mass models. Therefore, we used modal damping ratios below a cut-off frequency. The effectiveness of the proposed method was evaluated by comparing it with conventional methods in terms of the modeling errors related to the modal damping ratios and the maximum absolute acceleration. The proposed method tended to have lower errors than the conventional methods and is concluded to be more effective for the seismic analysis of 3D FEM models with multiple damping properties. The proposed method can automatically determine the coefficients of element Rayleigh damping and can more accurately model the damping properties of analysis models, indicating that the proposed method is a powerful tool for the seismic analysis of 3D FEM models with multiple damping properties.

USE OF BOUNDING ANALYSES TO ESTIMATE THE PREFORMANCE OF A SEISMICALLY ISOLATED STRUCTURE

Current design approach for seismic isolated structures is to perform bounding analyses. These analyses provide an envelope for the response of the seismic isolated structure rather than focusing on the actual performance. In this study, the success of bounding analyses to estimate performance of a seismic isolated structure, in which the isolation is provided by means of lead rubber bearings (LRBs), is evaluated in a comparative manner. For this purpose, nonlinear response history analyses were performed under the effect of bidirectional ground motion excitations. In bounding analyses, non-deteriorating hysteretic representations were used to model the hysteretic behavior of LRBs. On the other hand, to estimate the actual performance of both the superstructure and isolator units, deteriorating hysteretic idealizations were employed. The deterioration in strength of LRBs was defined as a function of temperature rise in the lead core. The analyzed structure is an existing seismically isolated hospital building and analytically modeled in accordance with its reported design properties for both isolation units and superstructure. Results obtained from analyses where LRBs are idealized by both deteriorating and non-deteriorating hysteretic representations are used in the comparisons. The response quantities used in the comparisons are maximum isolator displacement, maximum isolator force, maximum absolute floor acceleration, and maximum relative story displacements. In an average sense, bounding analyses is found to provide conservative estimates for the selected response quantities and fulfills its intended purpose. However, it is revealed that there may be individual cases where bounding analyses fails to provide a safe envelope.

Single precast concrete rocking walls as earthquake force‐resisting elements

SummaryPrecast concrete walls with unbonded post‐tensioning provide a simple self‐centering system. Yet, its application in seismic regions is not permitted as it is assumed to have no energy dissipation through a hysteretic mechanism. These walls, however, dissipate energy imparted to them because of the wall impacting the foundation during rocking and limited hysteretic action resulting from concrete nonlinearity. The energy dissipated due to rocking was ignored in previous experimental studies because they were conducted primarily using quasi‐static loading. Relying only on limited energy dissipation, a shake table study was conducted on four single rocking walls (SRWs) using multiple‐level earthquake input motions. All walls generally performed satisfactorily up to the design‐level earthquakes when their performance was assessed in terms of the maximum transient drift, maximum absolute acceleration, and residual drift. However, for the maximum considered earthquakes, the walls experienced peak lateral drifts greater than the permissible limits. Combining the experimental results with an analytical investigation, it is shown that SRWs can be designed as earthquake force‐resisting elements to produce satisfactory performance under design‐level and higher‐intensity earthquake motions. Copyright © 2016 John Wiley & Sons, Ltd.

Effectiveness of resettable energy dissipating devices in seismic response modification of elastic SDoF systems

SummarySemi‐active variable stiffness resettable devices can reduce seismic demands and damages in structures. Despite their advantages, variable stiffness resettable devices are under‐utilized mainly because of the shortage of fundamental research in quantifying the sensitivity of key seismic response parameters, and losses, in structures that use such systems for seismic hazard mitigation. Within this setting, the research summarized herein measures the effectiveness of semi‐active resettable energy dissipating devices in the Single‐Degree‐of‐Freedom domain aiming at quantifying the sensitivity of their seismic response to variation in control parameters and generating the required knowledge to utilize such semi‐active devices in the Multi‐Degree‐of‐Freedom domain. The performance (i.e. maximum relative displacement and peak absolute acceleration demands) of Single‐Degree‐of‐Freedom systems with an array of semi‐active control logics under various dynamic excitation regimes is studied. Two sets of 40 ground motions representing various seismic loading conditions (i.e. pulse‐like and rock‐site ground motions) are used, and an efficient control logic for mitigating these seismic demands is proposed. Numerical results show that proposed control logic enables a decrease of 40–60% for both maximum relative displacement and seismic base shear and 15–25% decrease for peak absolute acceleration. Copyright © 2016 John Wiley & Sons, Ltd.

Hysteretic Modeling of Unbonded Posttensioned Precast Segmental Bridge Columns with Circular Section Based on Cyclic Loading Test

The seismic performance of unbonded posttensioned (PT) precast segmental bridge columns (PSBCs) with circular sections was investigated. Two precast segmental columns with/without energy dissipation (ED) bars were tested under quasi-static cyclic loading. Their damage patterns and hysteretic curves were compared. Three single-degree-of-freedom hysteretic models were formulated with the key parameters identified from the tests. Cyclic loading analyses of the two tested specimens were conducted using these hysteretic models. Time history analyses were also conducted utilizing the proposed three hysteretic models to observe their applicability in modeling the dynamic responses of PSBCs. Finally, parametric analyses of PSBCs were performed under the excitation of an ensemble of 20 history ground motions to study the influences of relative yield force, elastic period, and energy dissipation coefficient on the earthquake responses of displacement ductility demand, maximum absolute acceleration, and maximum absorbed energy.

Nonlinear dynamic response of a base-excited SDOF oscillator with double-side unilateral constraints

The aim of this paper was to study the dynamic response of a single-degree-of-freedom (SDOF) oscillator exited by a base acceleration and constrained by two unilateral constraints (bumpers). The coupled equations of motion are formulated in dimensional and dimensionless form for the case in which both SDOF oscillator and bumpers exhibit a nonlinear behavior. Two possible states characterize the system’s response: flight, when the mass of the oscillator is not in contact with the bumper, and contact, when the mass touches the bumper. When the system is in the flight state, the independent time evolution of the bumpers’ response is also considered in equations of motion. In the numerical investigations, a viscoelastic SDOF oscillator and viscoelastic perfectly plastic bumpers subjected to a harmonic base excitation are considered. First, the transient versus steady-state dynamic response is considered, and afterward the only steady-state dynamic response is studied by means of pseudo-resonance curves of maximum absolute acceleration and relative displacement excursion of the SDOF oscillator. Furthermore, the continuation technique is applied in some cases in order to highlight in the system’s dynamic response hysteresis ranges, jumps between multi-periodic orbits, and super-harmonics. The dynamic analysis with and without bumpers is compared to observe how unilateral constraints modify the dynamic response of the SDOF oscillator with respect to the absence of bumpers and when their presence may be beneficial with respect to response mitigation.

Simultaneous optimization of structural shape and control system of large-scale space frame based on sine wave inputs

This paper proposes a simultaneous optimal design method of asymmetric large-scale space frames with tuned mass dampers (TMDs). The objective function is defined by the maximum absolute acceleration response of the structure to input ground motions of sine waves. Sine waves of periods with the five natural periods having large modal participation factors of the structure are input, and the maximum responses are calculated by time-history response analysis to evaluate the objective function. The shape of the space frame, i.e. nodal coordinates of the space frame's joints, is described by a Bezier surface to reduce the number of design variables. The change from the initial values of the nodal coordinates is constrained to preserve the initial design shape, which is provided by an architect. The method employs a genetic algorithm in optimization. In addition, a case study is conducted for an asymmetric steel space frame of a vault-like shape. The results confirm the reduction of maximum absolute acceleration responses in the optimal shapes not only to the five sine waves but also to four scaled ground motion records. Moreover, the presence of TMDs enables the reduction of the peak response value and maintains similarity to the initial shape. Keywords architectural design, Bezier surface, earthquake engineering, genetic algorithm, optimiza- tion, seismic control, structural engineering, structural shape, space frame, tuned mass damper Language: en

The Seismic Performance Analysis for the Ceramsite Concrete Frame – Shear Wall Structure

The paper focused on the seismic performance of ceramsite concrete frame—shear wall, which conducted the modal analysis and elasto-plastic time history analysis for 6 layers ceramsite concrete frame—shear wall and ordinary concrete frame—shear wall by software SAP2000. Then compared the results, which showed that the periods of ceramsite concrete frame—shear wall structure was longer than the ordinary concrete frame—shear wall structure, while the inter-storey drift ratio and the maximum absolute acceleration are less than ordinary concrete frame—shear wall. Besides, the largest base shear of ceramsite concrete frame—shear wall structure was less than ordinary concrete frame—shear wall structure. And the seismic performance of ceramsite concrete frame—shear wall showed was better than ordinary concrete frame—shear wall structure.

Dynamic Optimization Design of Sand Milling Collection Machinery Suspensions

Sand milling collection machinery is a kind of large machinery to collect the surface soil containing ores. The suspension system of milling machines directly affects the ride comfort and driving safety for the operator; for this end, the design of suspension system has been optimized so as to satisfy the requirements of reliability and comfort by making the console and operator set at the maximum station and minimum absolute acceleration and the amplitude within the range. This paper first established a suspension system model of milling collection machines and set up the state equation of suspension system by applying Lagrange equation. On this basis, this paper conducted the optimized calculation encouraged bt the pavement with sine rule change and obtained an optimal suspension system parameters ki and ci.

Semi-active fuzzy control for seismic response reduction of building frames using SHD dampers

SUMMARY In this paper, a fuzzy rule-based semi-active control of building frames using semi-active hydraulic dampers (SHDs) is presented. The SHDs are installed between the top of a Chevron bracing and the upper beam on each story to prevent damage to the structure from severe earthquakes. The set of Chevron brace and SHD is modeled as a Maxwell element that consists of a damping element in series with a spring. The rule extraction strategy for semi-active fuzzy control is carried out by genetic algorithm (GA). The objective is to minimize both the maximum inter-story drift and absolute acceleration responses of the structure. Interactive relationships between structural responses and damping coefficients of SHDs are established by using a fuzzy controller. GA is employed as an adaptive method to design the fuzzy controller, which is here known as a genetic fuzzy controller (GFC). To illustrate the efficiency of the proposed intelligent control strategy in application, numerical simulation for a 3-story and a 10-story building frame equipped with multiple dampers is presented. Copyright © 2011 John Wiley & Sons, Ltd.

PREVENTING ACCIDENTS ON BUILDING CONSTRUCTION SITES

The risks of falling at construction sites are primarily caused by a lack of physical stabilities of the workers. In order to ensure their safety and develop better safety guidelines, this study evaluated the various aspects of high-risk activities involved with scaffolding steps by measuring not SD (semantic differential value) but three physical quantities; latitude between minimum and maximum absolute acceleration value, fractal dimension, vacillate value lead from small, wearable and three-dimensional accelerometers.The findings are as follows:1) Avoid rushing up and down the stairs.2) Take an extra precaution right before entering the stairs.3) Make the height between each step as small as possible.Furthermore, the evaluation method based on the three physical quantities proposed above seems useful in terms of ensuring safety at construction sites.

Shock isolation using an isolator with switchable stiffness

A semi-active control strategy is presented for the shock isolation of resiliently mounted equipment where the isolator has light damping. This is achieved by switching the stiffness of the isolator between a high-state and a low-state. The control strategy involves two stages: the first stage involves the displacement control of the equipment during the shock, and the second stage involves suppression of the subsequent residual vibrations. The performance of the switchable isolation system is illustrated using a base-excited single degree-of-freedom system. It is characterized in terms of the maximum absolute acceleration and displacement of the isolated mass, the relative displacement between the base and the mass, and the effective damping ratio of the system. Provided that the damping in the isolator is light, it is found that the semi-active system can outperform a linear passive system during both stages of control.

EVALUACIÓN APROXIMADA DE LA ACELERACIÓN ABSOLUTA PARA UNA FORMA MODAL EN SISTEMAS DE MÚLTIPLES GRADOS DE LIBERTAD

Se presenta una propuesta para la estimación de la aceleración absoluta máxima en los diferentes niveles de un sistema de múltiples grados de libertad en función de la forma modal y del espectro de respuesta de aceleraciones, que tradicionalmente se propone en los reglamentos. La propuesta está basada en la combinación de una respuesta modal con la señal de excitación cuando estas se consideran armónicas. El error promedio de la propuesta presentada cuando se compara con la solución exacta calculada usando series de tiempo es de aproximadamente 7%, que contrasta con errores promedio del orden de 20% y mayores en otras tres propuestas presentadas en códigos de diseño sísmico actualmente vigentes.