دکتر سید مهدی زهرایی

tuned mass dampers are a combination of mass, spring and dampers. tuned mass dampers are set on a specific frequency range, when the structure is subjected to external force in the desired frequency range, TMD reduce the responses of the structure by creating a force against the movement direction of the structure. The most important limitation of TMD is providing a sufficient mass ratio in order to optimally control the structure. The inerter element is an element with two terminals that can produce a force proportional to the acceleration difference created in its two terminals. One of the distinguishing features of this element compared to other structural control tools is the possibility of changing the mass matrix of the structure. Nowadays, extensive research is being done in order to combine the inerter element with structural control systems. Adding an inerter element to conventional tuned mass dampers significantly increases the efficiency of TMD and removes the limitation of TMD to provide a suitable mass ratio. The placement position of the inerter element in the control system is very important. If the inerter element is placed between two inappropriate levels in the system, it will disrupt the function of absorbing dynamic vibrations and cause the responses to intensify. In this research, the optimization of the parameters of the inerter element combination with tuned mass dampers is done using the particle optimization algorithm and with the ability to generalize to all structures

In previous earthquakes, many steel frames suffered damage to their ordinary rigid moment beam-to-column connections. As a result, the use of multi-level control systems in structures has gained attention from engineers in recent years. The main idea in this system is to combine two separate control systems with different stiffness and strength, thus creating dual seismic behaviors. In this study, a two-level friction-yielding damper passive control system is presented for beam-to-column connections, and its cyclic behavior is evaluated using nonlinear static analysis with the finite element method using ABAQUS software. The evaluation results demonstrate that the performance of the samples improves with an optimal ratio of length to thickness. This improvement is reflected in increased stability and area of the hysteresis curves, ultimately leading to higher energy absorption. Additionally, the hysteresis curves indicate a ductile behavior for the proposed damper in the moment connection. Moreover, the obtained hysteresis curves show that the system reliably dissipates energy at different earthquake levels, satisfying the seismic criteria for special moment resistant connections based on the AISC code. The proposed damper serves as an energy dissipating device, effectively dissipating energy at different levels of earthquakes by facilitating slip and yielding, thereby controlling the seismic response of the structure.

In the recent past, the application of various types of passive dampers (e.g., yielding metallic dampers) has become a common practice for improving seismic performance of the under-construction buildings and rehabilitation of existing constructions. In this study, a new elliptical metallic damper was introduced to improve the seismic behavior of existing steel structures. Among other parameters, geometrical characteristics are known to affect the seismic performance of the constructions rehabilitated with the proposed elliptical damper. Accordingly, the performance of the proposed damper was investigated through accurate numerical studies on various types of dampers considering various damper dimensions, ellipse major and minor axes length-to-plate thickness ratios, and placements of elliptical shear diaphragm. To study the proposed elliptical damper in terms of its effect on the seismic behavior of rehabilitated buildings, three benchmark structures with 3, 9, and 20 stories were used. Further, far-field and near-field earthquake records were used to undertake nonlinear dynamic analyses. In this work, the proposed elliptical damper was verified by the Abaqus finite-element software, and nonlinear time-history analyses were conducted in the SAP2000 software to check for seismic performance of rehabilitated structural frames with the considered damper. Results of the nonlinear dynamic analyses indicated the appropriate performance of the proposed elliptical damper in terms of reducing the seismic responses of the rehabilitated structures and suitable behavior of the proposed elliptical damper in dissipating the imposed earthquake energy to the structures. Based on these results, upon rehabilitation with the proposed damper, the 3-, 9-, and 20-story structures exhibited smaller maximum lateral roof displacements by 66, 64, and 31%, respectively.

Roller compacted concrete is a dry, hard concrete with zero slump, typically used in mass concrete structures where casting is done in stages with time intervals between each stage. However, the formation of joints in these concretes increases the penetration of destructive ions, leading to eventual failure and instability of mass concrete structures. This study aims to evaluate the impact of replacing part of cement with zeolite in reducing the destructive effects of joint formation in roller compacted concrete structural members.Samples were made with hot, warm, and cold joints, with zeolite replacing cement at percentages of 0, 15%, 30%, and 40%. Results showed that at 15% replacement percentage, samples had the highest compressive strength, so roller compacted concrete samples were made with 15% zeolite to test for Rapid Chloride Permeability Test (RCPT), water penetration depth, water absorption, ultrasonic pulse velocity (UPV), and electrical resistivity. The tests showed that replacing 15% of the cement weight with zeolite improves compressive strength in warm joint areas and reduces destructive effects of warm and cold joints on durability properties. The electrical resistivity test revealed that replacing 15% of cement with zeolite significantly reduces the permeability of specimens. Zeolite also reduces the permeability of roller compacted concrete specimens based on the results of water penetration depth, RCPT, and electrical resistivity tests, but increases water absorption and decreases UPV.

The goal of the present research is to propose a novel adaptive fractional order PID (AFOPID) controller whose parameters are tuned online by five exclusive multilayer perceptron (MLP) neural networks using the extended Kalman filter (EKF). An MLP neural network that is trained using the Back Propagation (BP) error algorithm is considered to identify the structural system and estimate the plant. The Jacobian of the model estimated online is utilized to apply to the controller. Considering the adaptive interval type-2 fuzzy neural networks (IT2FNN) and this issue that the compensator is tunned by EKF and feedback error learning strategy (FEL), the stability and robustness of this controller are increased against the estimation error, seismic disturbances, and some unknown nonlinear functions. In order to validate, the performance of the proposed controller is investigated on a 3-story nonlinear benchmark building equipped with semi-active dampers under far and near field earthquakes. In order to evaluate the effectiveness of the proposed controller equipped with a compensator in reducing seismic responses, the evaluation indices were discussed and compared with previous studies. The numerical results represent the substantial efficiency of the proposed adaptive controller (AFOPID) over the previous controllers such that J2 in the Hachinohe and Northridge earthquakes enhanced by up to 35% and more than 40%, respectively. In general, all indices ( J3  to J6 ) have experienced a considerable enhancement using the proposed method.

Use of passive control systems causes reduction in seismic demand and prevents damage to the main components of the structure. Yielding dampers are among the common tools used for dissipation of earthquake energy entering the structure. The main goal of the present research is introduction of a novel pseudo elliptical yielding damper for improvement of the seismic performance of the existing steel structures. Considering the impact of geometric parameters of the pseudo elliptical damper on its stiffness and strength, a precise numerical study was performed on the ratio of diameter to thickness and other dimensions of the damper in this research.  For evaluating the impact of proposed damper on the seismic performance of existing steel buildings, use was made of three benchmark structures with 3, 9 and 12 stories which were retrofitted by this type of dampers. Also, the nonlinear time history analysis has been performed using the near field and far filed accelerometers to evaluate the analyses results at different seismic states. The results of numerical analyses indicated the good performance of propose pseudo elliptical yielding damper in terms of dissipating the earthquake energy entering the structure and reduction in the seismic responses of retrofitted benchmark buildings by this type of dampers. It was found that on average, the maximum inter-story drift in the 3, 9 and 20 story benchmark buildings were reduced by 66, 69 and 67%, respectively.

To reduce the seismic response of steel frames, energy dissipation devices can be placed at connections. These connections can be modeled as a rotational spring and damper in parallel. In this paper, an attempt is made to estimate the best distribution of the connections, by time-history analysis and optimization operation. Although in the previous studies, these connections were distributed uniformly, in this research the combination of these connections in rigid frames is proposed. Two 9 and 20-story frames with sections and dimensions based on SAC benchmark structures are studied. Seismic performance of optimized structures with connections equipped with dampers and rigid connections is evaluated and compared with that of the moment frame with uniformly placed such connections. It is observed that performance of hybrid structures, despite having less dampers in connections, is much better than the structure with uniform distribution of this type of connections. On the other hand, linear and nonlinear behavior of elements and connections in structure is developed. Also, in optimal condition, 62 and 68% of the connections in linear and 58 and 61% in nonlinear behavior have been equipped with dampers respectively for 9 and 20-story structures.

Low-cement roller compacted concrete is one of the special types of concrete that has a low amount of cement in its mixture proportion in order to reduce the heat caused by the hydration reaction. This increases the permeability of roller compacted concrete compared to conventional concrete. The increase in permeability also leads to the entry of destructive ions into concrete of mass structures and ultimately the instability of these structures. Cement supplementary materials such as zeolite can reduce permeability, so in this research, the effect of replacing a part of cement with zeolite on durability and mechanical properties of roller compacted concrete has been investigated. First, chemical analysis and pozzolanic activity of zeolite were investigated. Then, in order to evaluate the effect of zeolite on the properties of concrete, samples of roller compacted concrete were made in four mixture proportions with replacement percentages of 0%, 15%, 30% and 40% of cement with zeolite and subjected to compressive strength, water penetration depth, water absorption, Rapid Chloride Permeability Test (RCPT), electrical resistivity, Ultrasonic Pulse Velocity (UPV). The workability of the roller compacted concrete mixtures was also determined by the V.B. table test. The results showed that according to RCPT, water penetration depth and electrical resistivity tests, replacing 15% of cement weight with zeolite reduces permeability and significantly improves durability properties of roller compacted concrete. Also, increasing the percentage of zeolite reduces the compressive strength of the specimens.

Base isolation is an effective technology for reducing seismic damage to structural and non-structural components as well as building contents, allowing buildings to maintain their function during and after a rare, high-intensity earthquake. This makes it an ideal seismic response correction system for importance buildings. The main advantage of isolated structures is that seismic responses can be easily and effectively reduced by prolonging the period and increasing damping. Therefore, the natural period of the structure isolated from the base is longer. In this paper, a new energy balance method is used to design a lead rubber bearing (LRB) isolator. Energy balance method is an analysis method to evaluate seismic resistance based on the balance of seismic energy input to buildings due to ground motion and energy absorbed by the building. In other words, the energy balance method is a response prediction method to approximate the seismic response of buildings isolated from the foundation. This method is effective for determining the relationship between ground motion, seismic isolation period and the effect of reducing the reaction of dampers. In this method, the specifications of the isolation system, including stiffness, yield shear force and viscous damping ratio, are adjusted in such a way that the maximum shear and maximum displacement in the isolation system do not exceed a certain value determined by the designer. This allows the designer to limit the maximum displacement at the isolation level to a certain amount when there is a constraint on the supply of separation distance around the building and the isolated level. Also, by limiting the maximum shear of the isolators, it is possible to use the base isolation system for retrofitting the existing structures that have a certain lateral capacity.
This design method was first proposed and used in Japan. This method has been recently proposed in the Iranian regulations (which is being drafted) and has not been used much in this country so far. Its advantages include no need for trial and error in the design process, the possibility of designing a rubber and frictional type of seismic isolator, the possibility of using a viscous or hysteretic damper, or a combination of both at the isolator installation site. To evaluate the accuracy of this method, three 5, 10 and 15-story steel structures with an ordinary concentric braced frames in both directions for clinic usage have been modeled and under eight near and far-field earthquakes in the by the nonlinear time-history analysis method have been analyzed. The results obtained from the time-history analysis are in good agreement with the estimated results of the energy balance method. The error percentage related to the displacement of isolator compared to the value assumed at the beginning of the design for 5, 10 and 15-story structures is 3.4%, 2.57% and 2.12%, respectively. Also, the percentages of error related to the maximum shear of isolator compared to the value obtained from the performance curve for 5, 10 and 15-story structures are 11.08%, 12.61% and 13.98%, respectively.

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.

The selection of appropriate membership functions for fuzzy control systems has always been a topic of discussion among researchers and has been generally determined by trial and error based on the experience of the control system designer. In this study, the control performance of type-1 and type-2 fuzzy systems with different membership functions in semi-active fuzzy control of three- and nine-story structures under seismic excitation of the El centro, Kern County, Northridge, and Kobe earthquakes at different maximum accelerations Will be discussed. In this study, two fuzzy systems have been used considering the type of membership function as well as the number of defined membership functions for each input. The examined membership functions are defined symmetrically and at the same intervals for comparison. The results of the control systems used for the type-1 and type-2 fuzzy algorithms are examined and compared to the uncontrolled mode by considering the triangular, Gaussian, and trapezoidal membership functions. The results obtained from the defined evaluation criteria show that in general, type-2 fuzzy systems perform better than type-1 fuzzy systems, due to the consideration of uncertainties and the use of membership functions intermittently. is Fuzzy control systems with triangular membership functions have the best performance compared to other membership functions and the Gaussian membership function has shown close control function close to triangular function. Also, when more membership functions are used to determine the degree of membership of fuzzy language values, the fuzzy system becomes less sensitive to the type of membership function used.

Damages caused by the impact of adjacent structures in past major earthquakes have shown the importance of structural control systems to reduce the seismic risk of the impact of structures. Connecting energy dissipation devices to adjacent buildings is a practical and effective approach to prevent collisions as well as reduce the seismic responses of structures, and this issue has been an active research field in recent years. One of the semi-active control methods is the use of MR dampers. These dampers use a magnetic fluid that produces large damping forces in a piston-cylinder system that can be controlled instantly by changing the applied voltage to the damper. The Bouc-wen model has been used to take advantage of the unique properties of MR damper as well as to consider its inherent nonlinear behavior. In this study, to evaluate the performance of MR dampers using a fuzzy control system, three- and nine-story standard structures under seismic excitation of two near-field earthquakes including Kobe (1995) and Northridge (1994) and two far-field earthquakes including El centro (1940) and Kern county (1952) with maximum accelerations of 0.1g to 1g are investigated.The MR damper is connected to the third floor level of the two structures and can produce a controlled force equivalent to 1000 kN. The fuzzy system is designed based on the displacement of the third floor of two structures to reduce the risk of collision of structures as well as reduce seismic responses. the benchmark buildings have been modeled in OpenSees and the fuzzy control system was implemented in MATLAB software. The displacement responses of the third floor of structures are considered as the input value of the fuzzy system and the required voltage of MR damper is considered as the output value of the fuzzy system. In addition, triangular membership functions have been used to determine the degree of membership of input values. In general, the control system designed under far-field earthquakes has shown better performance in reducing the responses of two structures compared to near-field earthquakes. According to the results obtained from the dynamical analysis, the fuzzy system used under far-field earthquakes compared to near-field earthquakes and based on evaluation criteria of J1 (maximum roof displacement), J2 (maximum roof acceleration), J3 (maximum Base shear) and J4 (maximum relative displacement of floors) in three-story building 17.35, 4.94, 3.58, 12.17% and in nine-story building 7.93, 7.05, 0.67, 9.13%  showed better performance, respectively. Also, according to the evaluation criterion of J5, which is related to the minimum required gap between two buildings, the fuzzy system used under far-field earthquakes has shown 9.71% better performance than near-field earthquakes.

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%.

Statistical collection of existing buildings, especially in Tehran, and their classification can be a great help in identifying crisis management in order to reduce earthquake damage. Modern architecture is widely used due to its economical and practical benefits. In this architecture, the infills on the ground floor are generally removed. In Iran, most infills are constructed in such a way that they are connected to the corner of the frame by bricks, mortar, and other elements. For this reason, they are considered structural elements and will affect the lateral stiffness and lateral strength of the structure. Many studies have been conducted on buildings with this style of architecture designed based on gravity loads, which show their poor performance due to the formation of the soft story. In this study, first, statistical information is collected from recently built buildings in regions No. 9 and 11 of Tehran that are designed and constructed based on seismic criteria and are classified based on the reasons for the formation of the soft stories. Most of the buildings in these regions are RC moment-frame structures and have 6-8 stories and 2-3 bays in each direction. The first story in these buildings is used as parking. Therefore, assuming the correct constructions, the factor of removing the infills on the ground floor can cause the formation of a soft story in these structures.Next, a six-story concrete building with similar architecture in accordance with the results of statistical studies, is modeled in a three-dimensional mode in the OpenSees to evaluate the seismic behavior of the structure in different scenarios of infills arrangement on the ground floor and earthquake at different angles. To better cover all angles and reduce analysis costs, through the LHS sampling method, the selected angle for analysis is determined. Due to the lack of laboratory studies in three-dimensional mode and the importance of the axial-flexural interaction in the column in this research, structural modeling in this study was considered through the fiber model. The model of two compression struts placed diagonally in the panel is used to model the infills, and the numerical modeling is verified with experimental research.In this research, the probable formation of the soft story is evaluated based on three criteria: the ratio of the lateral linear stiffness of the stories, mode shapes, and distribution of the nonlinear lateral drift of the stories. The linear analysis results show that because these infills have high initial linear stiffness, the mode shape and lateral linear stiffness of these buildings are like soft-story buildings. However, the results of the nonlinear dynamic analysis show that since these structures are designed based on seismic criteria and the height of the ground floor is smaller than others, the infills have low ductility. Therefore, the removal of infills in this story does not necessarily lead to a soft story and instead can improve the performance of the structure by uniformly distributing damage across all floors. On the other hand, in the case that infills are evenly distributed in all floors, the behavior of the structure is similar to the moment frame and the damage is concentrated in the middle stories. This type of infill distribution increases the lateral stiffness and reduces the capacity of the structure. Therefore, it has even poor performance in comparison with building without infills in the first story. Also, different scenarios of infill arrangements on the ground floor change the behavior of the structure. Applying earthquakes at different angles indicates the building will experience varied behavior at each angle so that for some angles the building even collapses while for others not. Therefore, according to the numerical results, this modeling and analysis method will help show the actual behavior of the structure during an earthquake to prepare capacity curves for design.

The plate girders used in bridges usually have a deep and relatively thin web, therefore, the buckling of the web is one of the important factors in the design of such girders. While the limit state of web buckling dominant design, Longitudinal and transverse stiffeners are used to increase cross-sectional strength. The location of stiffeners in flat girders has been extensively studied, which has led to the most effective placement for longitudinal and transverse stiffeners. In the case of curved beams in the plan is not as extensive as in the case of flat girders, especially in the case of longitudinal stiffeners in the asymmetric section. Summarized herein is a study that explored single span, horizontally curved, plate girders having a yield stress of 50 ksi (345 MPa) to investigate their flexural behavior as a function of the position of a single longitudinal stiffener at various locations along the depth of the web. The studies were conducted using ABAQUS with the girder cross-sections under high vertical bending moment and low shear. As a result of these studies, recommendations are made for positioning longitudinal stiffeners on horizontally curved:-Placement of longitudinal stiffener at distances D/4, D/5, D/6 from the compression flange can control the flexural buckling of the web. -Among the above-mentioned locations, the location of the longitudinal stiffener at a distance of D/4 from the compression flange has the best shear response in the beam. Therefore, in this study, the optimal location of the longitudinal stiffener at a distance of D/4 from the compression flange.

Using control devices to enhance system identification and damage detection in a structure requiring both vibration control and structural health monitoring is an interesting yet practical topic. In recent decades several independent research studies have been conducted on the semi-active vibration control and health monitoring of the civil structures subjected to earthquakes, whereas both require similar software. Therefore, where there is a need for both vibration control and health monitoring systems in a building structure, integrating both systems using common equipment would be economical. Application of the viscous dampers for control of buildings, due to their proper seismic performance, lack of significant increase in the structural mass, and least interference with the present situation of the building is rapidly increasing. For this reason, the main goal of this research is to present a new integrated procedure for simultaneous health monitoring and semi-active control of the building structure using the viscous dampers with variable damping coefficients. Next, a scheme is presented for updating the building characteristic matrices and identifying the structural parameters. Finally, according to the updated system matrices, the efficiency of semi-active viscous dampers is investigated. For this purpose, a linear quadratic regulator optimal control algorithm is used for a building subjected to seismic excitations. The results show that the structural parameters are accurately identified; and, at the same time, the building structural vibration is significantly reduced.

Typical braced frames, in comparison with rigid frames, have higher stiffness but they have low ductility. On the other hand, rigid frames have high ductility but due to their low lateral stiffness, they maintain large displacements throughout earthquake, which is not favorable. Furthermore, in rigid frames, the beam to column connection is a critical area that often experiences damage during earthquake. In this research, the objective is to create a lateral load-carrying system and improve the seismic performance of steel frames using placement of arch segments cut of steel plates at the corner of simple steel frames and their yielding. Due to the eccentricity, these components are subjected to an interaction of axial and flexural forces and like yeielding dampers absorb the major part of the input energy. In this study, first, hysteresis curve of arch segments made by ST37 steel was achieved using finite element software, ABAQUS. Then this damper was modeled in SAP software to create the same hysteresis curve. Then, 3, 6 and 9-story bare rigid frames and simple frames with arch segments were modeled and subjected to time-history analysis of 12 different earthquakes. Based on achieved results, maximum roof displacement and maximum story drifts of frames, in simple frames with arch segments compared to bare rigid frames in average reduced 22 and 8%, respectively. Also in simple frames with arch segments in average 46% of input energy was absorbed by arch segments that indicates relatively good performance of this system.

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 study, to improve the efficiency of TLD, a Variably Baffled Tuned Liquid Damper (VBTLD) was used. The baffles are so that they divide the tank into three equal parts when they are fully closed. Furthermore, when they are open or partially closed, they can serve as some obstacles and improve the energy dissipation parameters. When this damper meets an excitation with a specific frequency, the baffles can be tuned to make the frequency of sloshing equal to that frequency. VBTLD used in this paper could be set for frequency range from 1.73 to 3 times of a specific frequency. Compared to a simple TLD, VBTLD can be tuned to a range of frequencies and improve the performance of structure against external excitation. At first, the benchmark building was modeled in OpenSees, then the performance of the device was verified by previous test results. To examine performance of VBTLD, Tuned Mass Damper (TMD) with optimal parameters was used in this study. Results show that when the baffles are at the best angle, VBTLD with water depths of 42 mm has maximum response reduction for the numerical model subjected to the Kobe earthquake at intensities of 2, 4, 6 and 8% of the Initial maximum acceleration of the earthquake (PGA=0.87g). The improvement of structural behavior compared to the optimal mass damper at maximum acceleration are respectively 23.1, 22, 14.6 and 10.5% while for damper with water depths of 63 mm, they are respectively 8.2, 9.5, 6. 7 and 6.8%.

The fragility curves are used to indicate the probability of damage to buildings during the earthquakes with different intensities. The main objective of this study is to present a new design procedure for exploring the effectiveness of using viscous dampers in the seismic rehabilitation of steel structures using the seismic fragility analysis. In addition, a straightforward formula is presented to determine the effectiveness of seismic rehabilitation of steel structures with viscous dampers. The inter-story drift as one of the effective parameters for assessing the safety of buildings after an earthquake is used in this study as a damage index. To compare the damage probability of buildings with and without damper, three 3, 9 and 20-story benchmark buildings are used. Furthermore, the earthquake records corresponding to three levels of seismic hazard are used for the nonlinear dynamic analysis. Comparison of the fragility curves between the steel structures controlled and the buildings without the damper shows a significant decrease in the damage probability after the rehabilitation with the viscous dampers. The results of numerical analysis showed that although seismic rehabilitation in all benchmark buildings led to the improved seismic performance, the decrease in the response of the 9-story structure is higher compared to the other buildings.

Tuned Mass Dampers, TMDs, often reduce the displacement response of structures by influencing their first mode of vibration. The structure of these dampers consists of three main parameters: mass, damping, and stiffness. Since the parameters of TMDs are constant during the vibrations, optimal tuning of these parameters is very important. Finding the optimal values of the key parameters for a TMD in nonlinear structures using numerical methods involves numerous nonlinear dynamic analyses; therefore, the computations would be time-consuming. Recent studies, carried out on the application of TMDs in building structures, have mainly focused on reducing the lateral displacements of building structures. However in this research, the application of TMDs and their effectiveness are investigated for cables of the power transmission tower in both lateral and vertical directions simultaneously. In order to numerically study the behavior of the power transmission tower, the structure of the telescopic steel tower is modeled in the OpenSEES software and to reduce the volume of computation, a numerical search method is used to find the optimal values for the parameters of the TMDs to minimize the lateral displacement in the middle of the cable span. The mass ratio of the TMDs is equal to 0.5% of the total mass of the structure. Using this mass ratio, numerical analyses of the system indicate that the maximum reduction of lateral displacement at the middle of the cable mitigated due to implementing TMDs is about 50% under the applied earthquakes with 0.5g maximum acceleration.

Dynamic vibrations of mechanical equipment affect the magnificent performance of themselves, and the other structures installed on them. The gradual increasing of their angular velocity leads to some rare occurrence such as Resonance, Pseudo Resonance, Beating, Pseudo Beating phenomenon and so on, when it has gone on angular velocity of mentioned structures. Therefore, dynamic responses of these structures should be declined. In this study, active and semi-active control approaches have been used to going down the responses of a single degree of freedom structure subjected to the above-mentioned probabilistic phenomenon. In addition, some existence optimum functions have been applied to determining the TMD’s frequency and damping parameters. These parameters of semi-active TMD are predicted utilizing two different strategies, the Fuzzy Logic system and Ground-Hook algorithm. The logic of making alteration to damping ratio is based on regaining the equilibrium of structure as it vibrates. Copping with different phenomenon, results of this investigation indicate the advantages of semi-active tuned mass damper usage to drop dramatically the system displacement by 32 to 47 percent. Moreover, using of fuzzy logic systems in order to set damping parameters of TMD, results in 1.5 to 6.2 percent more downward trend in comparison to Ground-Hook algorithm. The done analysis for a wide range of optimal frequencies illustrate that fuzzy logic system is lowly sensitive to determination of TMD’s optimal frequency.