جستجوی مقالات مرتبط با کلیدواژه « passive control » در نشریات گروه « عمران »

In this study, the authors present the performance spectrum (P-Spectra) for an idealized shear SDOF equipped with two types of passive negative stiffness devices. The first device includes a pre-compressed spring, gap springs at the bottom, and a combination of frame elements and plates that hold the parts together. The other device consists of three gears designed to control the movement of the primary gear and affect the response of the structure. Negative stiffening devices are used to reduce the stiffness of the system and increase the displacement of the structure. To prevent displacement increase, a viscous damper with 20% damping is used in parallel to the negative stiffness device. The SDOF structure has a post-yield stiffness of 5% pre-yield stiffness. Using the NLA method, P-Spectra for 0.5 to 2.5 periods are plotted for different mechanical parameters of negative stiffness devices. To construct the performance spectrum, dimensionless parameters of spring stiffness ratio to structural stiffness and yield strength ratio of the device and structure to the structure are used. The performance spectrum is investigated in designing the parameters of the negative stiffness device and its effects on reducing the response of structures. The authors also use a benchmark highway bridge structure in MATLAB software to investigate the effectiveness of systems designed using this method. The obtained target parameters demonstrate the desired results of this method in designing negative stiffness systems and reducing the responses. The presented findings suggest the potential of using negative stiffness devices as an effective solution to reduce structural response during seismic events.

The probabilistic analysis could effectively apply the effects of uncertainty in the structural analysis, where fragility curves are a well-established technique for the probabilistic evaluation of the structural performance. Notably, incremental dynamic analysis (IDA) is one of the most common analytical methods for obtaining fragility curves. In this study, the statistical and probabilistic seismic performance of 3- and 9-story steel buildings are investigated under 22 pairs of far-fault records introduced in FEMA P695. The seismic performance of both uncontrolled and controlled buildings with LRB is studied using IDA. Then, a general mathematical equation corresponding to each structure will be determined for all damage states known as the probabilistic seismic demand model (PSDM) of the structures. Using this equation, the collapse fragility curve of the structures will be determined for both uncontrolled and controlled structures with LRB. To evaluate the possible impact of different levels of seismic intensities on the performance of the isolated structure, the collapse fragility curves for three different levels of intensities of the benchmark records are presented. According to the collapse fragility curves, in addition to the effect of different levels of seismic intensity on the seismic performance of the structure, it is possible to see the positive effect of the LRB in reducing the probability of collapse. Also, the collapse margin ratio (CMR) in the 3- and 9-story buildings has increased by 100% and 81%, respectively, which indicates the better performance of the LRB isolators in low-rise structures.

Passive control of the structure is a system that dissipates the input energy caused by lateral loads without the need for an external energy source. Improvement of seismic performance of the structures equipped with a damper, lies in increasing the energy dissipation and decreasing the vibration of the structure. For this purpose, Toggle Brace Damper system can be used to follow design guidelines. This paper aims to compare the results obtained from SAP2000 software for two structures equipped with Toggle Brace Damper (TBD) and Diagonal Brace Damper (DBD). In this research, time-history analysis is used by applying the El Centro, Kobe and Tabas earthquake records. The dampers used in all models are the same pipe dampers selected from the hysteretic type. The results suggest that the roof displacement of the TBD system in the 2 and 5-story frames decrease in average 77 and 42 percent respectively compared to that of DBD system. The drifts of the floors in the TBD system for 2-story frame are 82 and 78 percent in the 1st and 2nd floors respectively and for the 5-story frame are 53, 46, 41, 35 and 30 percent in the 1st to 5th floors respectively, lower compared to those of DBD system. Magnification factor (ratio of axial damper displacement to floor displacement as ductility capacity) of the 1st story in the TBD and DBD systems for 2-story frame are 1.83 and 0.74 percent respectively and in the 2nd story of TBD and DBD systems for 5-story frame are 1.46 and 0.73 percent respectively.

Using a Tuned Mass Damper (TMD) in a structure, is a reasonable solution for absorbing its movements caused by external forces. However, when designing a TMD on the grounds of passive control, it is a challenging task as this device can be tuned once and for a specified range of frequency. Employing more than one TMD is another option; although this will lead to higher cost and might increase the base shear of the structure. In this paper, to provide a wide range of frequency and mode shapes in the analysis, nine types of steel structures are designed, having the story number of 4, 8, and 12, respectively, and then subjected to 22 acceleration records of FEMA-P695; These records, are a suitable choice for generating statistical results as they provide a wide range of magnitudes. Three of these structures are uncontrolled, and the remaining are equipped with a TMD on their roof, being of 0.5% and 1% mass ratio and considering the first mode frequency for the TMD design. The design of the TMDs is carried out via Den Hartog's formula.Using incremental dynamic analysis (IDA), fragility curves are created with constant 0.1g steps for PGA intensity measure. In addition, for considering the uncertainties in the performance of the TMD and the structure due to the changes in frequency, a 10% error is applied for the first mode frequency in the nonlinear design of the structures. The maximum drift ratio is used as a damage measure due to its simplicity and comprehensive coverage. Multiple earthquake recordings and their statistical characteristics, such as mean, median, 16%, and 84% of the recorded amplitudes and their more robust components, are utilized to examine the IDA curves to eliminate any ambiguity about structure response. This paper presents its novelty by applying a statistical method for choosing the mass ratio of TMD, considering the possible real-world quantities for this parameter and a wide range of frequencies for the excitations; therefore, limiting the TMD stroke. Subsequently, verifying the linear and non-linear behavior of the model used in this paper is carried out by modeling a 40-story steel structure equipped with a TMD situated on its roof and tuned based on its first mode under the Kobe Earthquake. Furthermore, the displacement response of the 4, 8, and 12-story structures, being equipped with a single TMD of 0.5% and 1% mass ratio, respectively, are compared to their uncontrolled state by exposing them to the Landers earthquake.Results show that using TMD reduces the maximum drift ratio of the structures. Considering the first 16% of the acceleration records, as expected, a 12-story steel structure equipped with a TMD of 1% mass ratio on the roof, presents the best results of maximum drift improvement ratio of 2.54%. Moreover, for reducing computational effort, another alternative is applying a limited number of earthquakes to the structure. By using the median for the duration and PGAs of all FEMA-P695 data to estimate this earthquake record, the maximum drift improvement ratio is then 1.61% for the twelve-story structure resulting in decent numbers compared to the first method. Moreover, all types of the 4, 8, and 12-story structures (uncontrolled, controlled with a TMD of 0.5% mass ratio, and controlled with a TMD of 1% mass ratio) were subjected to the Kobe earthquake, and their average roof displacements were compared. Among these three types of structures, the 12-story structure was recorded to have the highest rate of maximum roof displacement compared to its uncontrolled state, being 3.47%.

In this paper, a new energy dissipative device named elliptical damper was introduced for passive control of structures. In the proposed damper, the energy dissipation capacity is provided by the shear deformation of the elliptical ring. To investigate the behavior of the proposed damper, a sample of this damper was tested experimentally. The results showed that the proposed damper had stable hysteresis loops and good energy absorption. Also, the finite element model was developed by considering nonlinear behavior, large deformation, and material damage. The results of the numerical model were verified through experimental results. The results showed that the numerical analysis could predict the cyclic response and damage location of the experimental sample. A parametric study was performed to investigate the changes in the cyclic behavior of the elliptical damper with its dimensions. Four independent parameters considered for this study are the greater diameter of the elliptical ring, the ratio of its diameters, the ratio of the thickness of the elliptical ring to its greater diameter, and the ratio of the height of the connection area to the greater diameter of the elliptical ring. Among the studied parameters, the thickness of the elliptical ring had the greatest effects, and the height of the connection area had the smallest effects on the cyclic response of the proposed damper. By increasing the thickness of the damper, the maximum strength and energy dissipation capacity increase, but its ductility decreases. The proposed damper has stable hysteresis loops, excellent ductility, and high energy dissipation capacity. The elliptical damper is simple in terms of construction technology and provides excellent energy dissipation capacity for the structure compared to the cost spent for its construction. According to the results, the proposed damper can be used as an appropriate energy dissipation device for passive control of structures.

The use of control methods in the design of structures has received more attention. Separators, reduce damage by reducing the vibration transmitted to the structure. In this research, modeling of 7 and 11 story steel flexural frames with and without separators has been used and the effects of separators on the structural safety have been measured using nonlinear time history analysis. The modeling was performed under the record of the El-centro earthquake and the results show that the isolators are very effective in reducing the shear and acceleration parameters. With 67% reduction of the base shear in the middle structure and 44% reduction in the high structure, using this control system, reduces the possibility of damage due to relative displacement. Also, according to the study of the process of plastic joint formation in the models, structures with separators mostly remained in the elastic stage. Plastic joints formed in unseparated structures were also in the range of life safety. The isolators, have a good effect on the process of reducing the floor shear, acceleration and relative displacement.

One of the common methods in controlling the seismic response of structures is the use of seismic isolators. Isolators reduce the base shear as well as the relative displacement of the floors by increasing the period of the structure. Typically, extreme deformation of the isolator level occurs due to severe environmental factors, which can lead to damage to the isolators; As a result, there is a possibility of permanent deformation in the isolator and also the collision of the structure with adjacent buildings. Therefore, to prevent damage to buildings equipped with base isolations due to severe ground motions, it is important to identify damage at the isolators. In this study, assuming the linear behavior of the main structure, a proposed subspace-based method for identifying the stiffness of the base isolation with a limited number of sensors is presented. For this purpose, using the compression technique, the structure equipped with a separator with a large number of degree of freedom (DOF) is transformed into a two DOF structure; So that the stiffness associated with the first DOF in the reduced system corresponds to the stiffness of the Isolator level in the original structure. Then, using the identified Markov parameters of the system, the reduced structural stiffness is identified. Numerical examples are used to evaluate and compare the performance of the proposed method. The results show that even in the presence of noises in the measured responses, the proposed method detects the amount of damage at the isolator level with acceptable accuracy.

One of the aims of structural engineers is to improve the behavior of structures and reducing their responses under dynamic lateral loads. The structural control systems are advanced techniques to reduce the structural responses against vibration, and Tuned Liquid Damper (TLD) is a well-established tool for the control of structures. In this study, the effect and behavior of TLD under 7 far-field earthquakes and 7 near-field earthquakes was investigated in ANSYS software. To assess the performance of TLD on the control of structural responses including displacement, acceleration, and velocity, the effect of four different design parameters i.e., tank length, water height, water ratio, and mass ratio (with 27 different designed alternatives based on closed-form relationships proposed in the literature) were studied. The results showed that when the water ratio and the mass ratio of the cubical container are equal to 0.375 and 5 percent respectively, The TLD had the best performance under near-fault records. Also, the designed TLD with a 5 percent mass ratio and 0.125 water ratio outperforms other designed alternatives under far-fault records. In general, and among the considered alternatives, the performance of the damper with a higher mass ratio improves all studied performance criteria. Also, the well-designed TLD could reduce the acceleration better than velocity, and velocity better than displacement.

Respect to the concept of the control structures, the author of this study recently suggested a novel hysteresis damper with named nested-eccentric-cylindrical shells damper (NESD) for increasing the damping in structures.According to the greater ability of the shell structures versus the plate structures, the NESD is designed based on the shell structures. The configuration of the shells in the NESD is designed in such a way that it can be increasing the performance and stability of the device. These members are as well as the multi-springs with the combination of series and parallel form. Also, the configuration of this device is designed by the simple form and with an easy way to install in structures. However, to evaluate the seismic performance of the proposed damper, the NESD used into the structures with various heights with four, eight, and twelve floors and analyzed by dynamic nonlinear time history. The seismic analyses are run with eleven records by particular geography characteristics of seismic hazard zone. In this evaluation, the efficiency of this damper in damping seismic energy and reducing the displacement and base shear responses is approved. In the seismic analysis, Therefore, by modeling this damper in structures, it was found that by using this damper in structures could be a damping of up to 35% of the seismic energy in the structures and reduce an average of 50% in displacement and could cause a reduction of 7 to 27% in the base shear for the structures. However, it was found that the NESD could be better behavior for reducing the response of mid-rise structures.

By the concept of control structures a new shell configuration for a steel energy dissipative device designed for earthquake protection of structures is proposed in this study. This device is named a nested-eccentric-shells damper (NESD). This device is made of a large cylindrical shell that surrounded three small cylindrical shells. The conventional methods of welding or metal casting can be applied in constructing this damper. The configuration of the shell-type components is designed in such a way that to be able as a combination of series and parallel springs. To assess the performance of this damper, numerical analysis and full-scale testing are run. Hysteretic loops obtained from the analysis with highly ductile performance are applied to determine the behavior of this proposed damper. The results indicate that the nested-eccentric-shells damper is of a stable behavior in hysteretic loops, and can provide appropriate damped energy subject to cyclic loading. However, in order to improve the performance and interaction of the internal members of this damper, a thickness ratio is proposed for the inner shells and the usefulness of using this modification in numerical analysis has been proven in this study.

Nowadays, the use of control systems in buildings has been increased and the importance of vibration reduction of structures is considered more than ever. In addition to improve the dynamic behavior of buildings, control systems can be installed between adjacent buildings as activated, semi-active and inactivated systems. Fluid viscous dampers are one of the most important approaches for inactivated control systems in which the dynamic response of two adjacent buildings reduces according to the high resistance of the viscous fluid. The main purpose of this study is the use of control systems in two similar adjacent buildings to reduce the entire system response which will be the analytical study of the impact of viscous dampers to control system performance. In order to provide the analysis and to study the dynamic behavior improvement of different adjacent buildings connected with dampers, two models of the original sample was investigated. All examples are different from each other and response analysis and time history was provided using SAP 2000 software. According to the acquired results, the effect of fluid viscous dampers for tall buildings is less than the shorter ones. Moreover, these dampers are more efficiently working for adjacent buildings with different heights rather than buildings with the same height.

In this study, to investigate and compare the performance of the single mass damper in the maximum modal displacement (roof) and multiple mass dampers vertically distributed in the height of the structure, based on the modal analysis, two linear and nonlinear models of a 40-story structure were selected. The structure has been modeled in OpenSees software using seven acceleration time histories. The analysis results for applied earthquakes under the maximum acceleration of 1.0g show that the control of the linear structure by multiple tuned mass dampers (MTMDs) tuned to the first and second modes have more appropriate behavior than others, and the average reduction of the maximum displacement of the Roof applying this type of dampers is 14.5%, which is about 2 times more than reduction of the STMD tuned to the first mode and the MTMDs tuned to the first or second modes, systems. However, due to the assumption of tuning the design parameters of the dampers corresponding to their elastic behavior, the performance of single and multiple mass dampers slightly decreases in a nonlinear model of the structure while structural responses are still controlled. Also, for the 10% error caused by misadjusting of the dampers, the behavior of MTMDs is more appropriate.

In this research, numerical analysis of the hybrid lead rubber bearing system with shape memory alloy was investigated by Abaqus software and the effectiveness of various parameters on its performance was examined. The parameters studied are the bearing dimensions, the type of shape memory alloy and its cross-sectional area, the lead core diameter, the thickness of the rubber layer and the compressive stress. In this hybrid bearing, memorable form shape memory alloy are used as a recovery unit and lead core is used as a unit of energy dissipation. For this purpose, a finite element model of the bearing is modeled using the Abaqus software and the effect of the various parameters mentioned on the bearing performance has been investigated. The results show that the structures equipped with this bearing have better seismic performance than lead rubber bearing. Finally, depending on what kind of performance is required from the bearing, the parameters can be obtained optimally. As a result, in order to achieve a combination of behavior, both the suitable absorption capacity of lead and the recentring property of the shape memory alloy, it is necessary to balance the stiffness between the lead core and the shape memory alloy wire.

ABSTRACTMost of the steel moment resisting frames, damage at the beam-to-column connections during seismic loads. Application of passive dampers in order to prevent damages to the main components of structure has been an interesting subject for many researchers recently. In this present study, performance of the metallic yield damper is slit steel damper (SSD) on the steel beam-to-column connection is carried out using finite element model. Thus, first this damper and its connection is simulated. After validation of results, the effect of various dimensional parameters including radius slot, of damper on the performance of damper and its connection was investigated. Then various forms of this damper simulated and their effect on the performance of damper and the steel beam-to-column connection is studied. Moment- rotation, Hysteresis curves and plastic strains for each size of radius slot and different shapes extracted from the analysis were compared. Furthermore base shear force for steel frames with and without slit dampers in term of energy absorption and deformation are compared together. Findings indicated seismic behavior fitted to such dampers. The results indicate that the slit damper shows a proper function in absorbing energy. Recommendation for appropriate size and shape of slit steel dampers proposed.

In the present paper, the efficiency of combined tuned liquid damper (CTLD) in controlling the dynamic responses of offshore jacket platforms under the earthquake and sea wave excitation is investigated. This type of damping system consists of one or more tanks containing a fluid, generally water or oil, which can be installed on the topside (superstructure) of the platform. During the excitation, hydrodynamic action induced by the sloshing of the water in the tank acts as a resistant force against the vibration and controls the structural response. In fact, due to the oscillation of the structure, the fluid inside the tank begins to oscillate in the opposite direction. During this process, most part of the fluid has a wave-like oscillatory motion, while the part adjacent to the tank’s floor experiences a rigid-type displacement and exerts impact pressures to the tank’s walls. In order to attain maximum decrease in the structural response, the oscillation frequency of the fluid inside the tank should be near the natural frequency of the structural free vibration which can be determined by performing a modal analysis. Hence, one of the objectives of the present study is to adjust the frequency of fluid’s oscillation based on the natural frequency of the jacket structure. In other words, the aim is to find a frequency range in which the maximum decrease can be achieved in the amplitude of structural responses. In this research, using the FE software ANSYS, a jacket-type platform having dimensions appropriate for the Persian Gulf climate (case study: SPD1 platform) was modeled and then dynamically analyzed by the modal and time-history approaches subjected to the records of El Centro and Tabas earthquakes as well as 10 cases of wave loading with different height and period. The CTLD system was optimally designed and after the verification of FE results, the dynamic responses of the jacket-type platform with and without CTLDs were compared.

A passive control strategy is the use of Tuned Mass Dampers (TMD). In a simple form, the TMD consists of 1 to 10 percent of the structure eective mass connected to the main structure through a spring and a dashpot (viscous damper). The design is based on tuning the frequency of the TMD to the predominant frequency of the structure. So, when the structure is excited, the secondary mass vibrates in resonance with the structural motion, with 90 degrees of phase shift, and the TMD damping dissipates the input energy; consequently, a signi cant reduction in the response of the structure is achieved. Although the design process of the TMD, which includes determining its parameters, i.e., mass, stiness and damping, is simple, nding optimum parameters has always been a challenging area in its analysis and design. In most optimization studies on tuned mass dampers, tuning and damping ratios are optimized and the damper mass is a pre-assumed parameter in design, because its optimum value is large and economically unjusti able in real structures. In this paper, on the basis of the structure energy balance equation for a single-degree-of-freedom model and an iterative formula that tends to minimize the kinetic energy of the structure, a wise (targeted) method has been developed to nd the optimum mass of the damper that reduces the maximum response of the system under harmonic and earthquake base accelerations. Eventually, good agreement was seen between the results of the present study and the ones obtained by previous related studies, which provides the possibility of optimal design of the damper through a simple iterative process. Also, the eectiveness of the optimum TMD in a nonlinear structure has been investigated. It was shown that when the structure behaves nonlinearly, the eectiveness of the TMD in reducing the peak response decreases, but, it provides damage reduction, and, for more severe input, protects the structure from collapsing compared to an uncontrolled structure.