javad katebi

The tensile strength of high-strength bolts is determined by two test methods. In the first method, the tensile strength of the bolt is determined using a nut. The second method uses the device introduced in ISO instead of the nut. In the tested bolts, two failure patterns are observed,the bolt thread stripping and fracture in the threaded length of bolt. In this research, in addition to the experiment, the elastic-plastic numerical simulation of the bolt failure pattern was also performed in Finite element software. The results of the study show that the frequency of the thread stripping failure pattern is 4% in the bolt tension test with the ISO device and 90% in the bolt tension test with the nut. In addition, the tensile strength obtained from the bolt tension test with a nut is lower than the bolt tension test method with the ISO device. According to the frequency of the failure pattern in each method, the bolt tension test with the ISO device leads to the determination of the tensile strength of the bolt material, and the bolt tension test with the nut leads to the evaluation of the tensile strength of the bolt and nut assembly. Due to the compatibility of bolt and nut performance in steel structure, this research suggests performing tensile test of bolt and nut, in addition to other tests.

In this research, the robustness of the controller designed based on the critically damped condition (CD) is evaluated against parametric uncertainty, time delay, sensor/actuator faults, and the failure of the actuators. Then,  robust controllers are designed in different conditions and the results are compared with the CD method. Linear matrix inequalities and Lyapunov theory are used to design the  controllers, and due to the fact that sparse and large matrices arise in the process of solving, the problem is suboptimally solved. Therefore, Yalmip toolbox and Mosek® solver are used for this purpose.

In this study, a semi-active control system is assessed over a numerically updated model to achieve the most promising numerical results and to keep the performance of the numerical model as close to the prototype behavior as possible. Numerical model updating is performed based on the experimentally captured non-contact sensing data considering uncertainties. The elastic modulus of the jacket elements is specified as the calibration parameter. A mathematical function -optimized using Particle Swarm Optimization (PSO) algorithm- is also employed to reduce the structural uncertainties of the numerical model. Eight MR dampers both in X and Y directions are located in a platform numerical model. Modified Newmark-Beta method besides optimized parameters of instantaneous optimal control algorithm are utilized to predict the response of the system. The performance of the updated model is evaluated under environmental loads. The results indicate the importance of model uncertainty reduction in improving the accuracy of simulation results in a complex system. Based on the results using a non-contact sensing technology such as Laser Doppler Vibrometer (LDV) system is strongly recommended in practical cases due to great sensitivity capabilities and also no direct contact requirements.

The present study has been performed aiming to appraise the efficiency of endurance time method for evaluation of some vibration control methods in comparison with traditional time history dynamic analysis. Endurance Time method is a dynamic structural analysis that evaluates structural responses under different intensities. In this method structure is subjected to an intensifying predefined acceleration function and different damage indices of structure are evaluated through analysis time. The Endurance Time acceleration function have been generated for different spectra, such as ASCE07 design spectrum, in previous researches of ET group. Due to its inherent dynamic nature, there is no restriction on its application and it can be applied to any structure with any plan or height or any degree of freedoms. Furthermore, it can be used in linear or nonlinear analysis also it can significantly reduce computational demand compared to time history analysis. In this research the Endurance Time method has been applied to an isolated bridge with different control systems such as Active, Semi Active and Passive by using classical linear quadratic regulation (LQR) algorithm and Sliding Mode control (SMC). Two approaches including LQR and pole assignment method have been used for determination of sliding surface as an important parameter in SMC algorithm. The effectiveness and robustness of SMC and conventional LQR control to reduction in displacement response of the structure have been verified by different researchers. Viscous dampers with two different dissipation rate of  and have been considered as two passive control mechanisms. When these bridges are subjected to ground motion with large intensity, the deck displacement becomes excessively large so in this study, different control strategies are used to mitigate this phenomenon. Sliding Mode control with LQR approach has provided the best efficiency in dynamic response mitigation. Herein, the column-isolator-deck system has been idealized as two-degree-of-freedom lumped mass system. To evaluate its seismic behavior, a set of seven suitable records is selected and a wavelet-based procedure has been used to match their spectra with a target spectrum. These records are used for the comparison of the results of Endurance Time analysis with nonlinear time history analysis as a verified method. Results indicate that the Endurance Time method is capable of predicting the seismic behavior of isolated bridge with different control systems within acceptable accuracy. Considerable variance in the analyses result under ground motion records necessitates to apply numerous records to get reliable results while it is possible to attain close estimates using endurance time method. Although ground motion records and endurance time method both have resulted in similar trends for structural displacement response with different control approaches, results are more dispersed for different earthquake records with standard deviation of 1.2 up to 3.36 but this parameter decreases using endurance time method to 0.35 up to 1.58 and this method provides an accurate and time saver tool to evaluate the performance of structural vibration control methods under seismic excitations.

Model predictive control is one of the optimal control methods for systems based on their behavior on future horizons. One of the salient features of this control method is the optimal consideration of control constraints in the system control process. Accurate states are required to perform an optimal control performance with this technique. On the other hand, state sensors are unable to provide accurate states due to the uncertainty in their structures. This shortcoming causes problems in the optimal control process. In this study, a discrete-time Kalman filter-based model predictive control scheme with actuator saturation consideration is presented. As a state estimator, the Kalman filter is able to provide more accurate states. On the other hand, the application of performance constraints in the control process causes the saturation of the actuators to be optimally regarded. In the present study, to investigate the effectiveness of the proposed control method in reducing seismic responses, a nine-story benchmark steel structure (SAC) under seismic excitation is utilized. Then, the results obtained from the proposed method considering three different control force constraint scenarios are compared with the results of the uncontrolled case. The results of numerical studies demonstrate the appropriate performance of the proposed control process in reducing seismic responses. Also, the replacement of low-capacity actuators with high-capacity ones, while making the control process more economical, do not significantly change the other responses quantity. For example, the highest change in the Drift Ratio Index (J1) for the controlled case with control force constraints to the controlled case without control force constraints for the Elcentro earthquake is by up to 4%, while the same conditions for the maximum control force index (J12) is 78%.

Successful implementation of active control technology requires an appropriate control algorithm to calculate the adaptive control force required by the actuators. Smart structures represent a new engineering approach that integrates the actions of digital sensors, actuators and control circuit elements into a single control system that can respond adaptively to environmental stochastic changes in a useful manner. The mathematical model of the system is an estimation of its actual dynamic behavior. In general, this difference can have a significant effect on the performance and stability of the control system. One of the important issues in active control algorithms is the evaluation of the control systemchr(chr('39')39chr('39'))s robustness to model uncertainties and the actuator saturation. In this paper, a Developed Robust Proportional Integral Derivative controller with uncertainties in the structural stiffness parameter, the sensing noise and saturation windup of the saturation is introduced. the PID control force is obtained in such a way that the infinity norm of the closed loop system transfer function from disturbance inputs to target outputs becomes minimal. By considering the parametric uncertainty in the structural stiffness parameters and multiplicative unstructured uncertainty and the windup phenomenon in the actuator model and existence of noise in the velocity sensor, PID control scheme has been developed in the form of state space. The PID control gains by taking advantage of the Hinfinity mixed sensitivity minimization criterion, are obtained simultaneously by considering the effects of all vibration modes of the building in such a way that the infinity norm of the closed loop transfer function from exogenous inputs to the controlled outputs becomes minimal. To demonstrate the robust performance and stability of the proposed algorithm, the results of numerical simulations on a 4-story structure equipped with an active tuned mass damper are used. The obtained results show the robust performance and stability of the proposed robust PID control scheme in comparison with conventional PID and linear quadratic regulator (LQR) control algorithms, both in time and frequency domains. According to the mean values ​​of performance indices, in average 11 and 7% more reduction in J1 , 7 and 5% in J2  and 10 and 6% in J3  in the proposed robust PID in comparison with the LQR and common PID for three models subjected to far field selected earthquake records. And in average 17 and 10% more reduction in J1 , 12 and 8% in J2  and 11 and 8% in J3  in the proposed robust PID in comparison with the LQR and common PID for three models subjected to near field selected earthquake records. And J4  which related to amount of control effort, for the proposed robust PID, LQR and conventional PID are 1.3e-2, 9.1e-3 and 7.9e-3 in average for the three models subjected to far field and 4e-2, 2.4e-2 and 2.7e-2 subjected to near field selected earthquake records. The obtained results show the robust performance and stability of the proposed controller in the presence of structural stiffness uncertainties, actuator saturation and measurement noise.

Active control acts as an effective strategy to improve the seismic behavior of structures by calculating and applying the external forces and leads to the adaptive change in dynamic properties of the structure during the earthquake. In the LQR method as the most common control algorithm, the second-order performance index has been optimized to establish a balance between response and control force reduction. In defining the performance index, the relative importance of response reduction and control force reduction is regulated by the selection of Q and R weight matrices. Q and R are the weight matrices for the response and control forces, respectively, and their values indicate the relative importance of response or control force decrement. There is no systematic way to determine these matrices so far these weights are chosen based on trial and error and designer experience. This study has concentrated on metaheuristic algorithms in optimal active control of structures. In this paper, to facilitate the process of controller design, R and Q weighting matrices are considered as design variables and wavelet-based performance index as objective function of metaheuristic optimization. Imperialist competitive algorithm (ICA) as a socio-politically motivated algorithm, differential evolution (DE) as an evolutionary method, bat (BA) and firefly (FA) as natural-inspired algorithms, colliding bodies (CB) as physics-inspired algorithm and harmony search (HS) as music-inspired metaheuristic are used in this study to compare different aspects of metaheuristics in dealing with the optimal active control problem. Some of these metaheuristics have not been explored in control problem yet. In this study, in order to enhance the controller performance, DWT has been applied to decompose the excitation into different frequency bands. For decomposition process, signal is decomposed using Daubechies wavelet of order 10 (db10) mother wavelet in five levels. Defined wavelet-based performance index has been selected as objective function and weighting matrix elements considered as design variables of optimization process. Then, metaheuristic algorithm has been employed to search the optimum weights for each frequency band to calculate the control force in each domain. In addition to wavelet-based LQR performance index used as objective function of optimization, nine benchmark indices obtained from the results are calculated to evaluate the controller-performance by reduction of different design parameters such as interstory drift, story displacement, acceleration, base shear and needed control force compared to the uncontrolled cases. The best solution, convergence rate and computational effort of aforementioned optimization methods for a three-story structure under different artificial earthquakes have been compared. According to the results of simulations, the effectiveness of each algorithm in vibration reduction through various seismic excitations has been evaluated by numerical simulations. This formula is able to be easily performed with any metaheuristic algorithm providing the great flexibility in the active controller design. The results for active control of structures have shown the potential of wavelet and metaheuristic algorithms in vibration control for building structures depending on the user to select the appropriate algorithm or on the problem types and its requirements such as the quality of solution, convergence rate, computational effort, and consuming time. The results indicate the effective role of metaheuristic methods in reducing responses and control forces simultaneously over the LQR method. Considering total cost value, CB, ICA and DE have produced better results compared to all the mentioned algorithms. FA and BA have good convergence tendency compared to other algorithms. Each metaheuristic algorithm has advantages and disadvantages in solving active control problem, whiles the superiority of CB, ICA and DE over other methods in finding the optimal responses for active control problem has been shown as well.

One of the most important goals of optimal control of structures is the achieving the desired reduction in responses using minimal control forces. In many research efforts that have been studied over the past few decades in the field of active control, several control algorithms have been proposed that most of them calculates the required control forces by optimizing a second-order performance index. There are simplifying assumptions in formulation of these classic algorithms and constraints in mathematical optimization techniques that have been used in optimizing the performance index, for example, because of unknown nature of earthquakes, the LQR classic controller don’t consider the external forces such as earthquake excitation in calculation of control signal. This may make difficult to finding the optimal solution in optimization process and obtained relatively optimal solutions for optimization problem. Metaheuristic optimization methods, such as differential evolution are modern algorithms and because of their special capabilities in finding global optima are powerful tools that can be used in solving of complex problems. But despite the many advantages, these methods has not been used extensively for solving civil engineering problems especially in field of active control of structures. In this paper we considered the active control of structures as an optimization problem and proposed a controller that used the differential evolution metaheuristic algorithm for finding gain matrix elements of active control problem. The gain matrix elements were globally searched by differential evolution algorithm to minimizing the LQR performance index. Because of the proposed method is repetitive and does not need to solve the Ricatti differential equation; it is possible to consider the effect of external excitation in finding the gain matrix and calculation of control signal. The controller was applied on sample 2DOF and 10DOF structures and responses of these structures under the excitation of several historical earthquake records were obtained by MATLAB programming. In addition to the performance index, the maximum control force and maximum control displacement, 9 benchmark indexes that measured in controlled structures are calculated in this study. These indexes represented the reduction of controlled maximum and average responses of structure in comparison with uncontrolled responses. In order to evaluate the effectiveness of the proposed controller, these 9 performance index for 2DOF and 10DOF examples against 7 historical earthquakes for proposed and LQR controller was calculated and compared. The simulation results indicate that the proposed method is effective in keeping the controlled responses of structures in desired range and reducing the vibrations of structures with lower need to control energy in comparison with LQR algorithm. Because of great capabilities of DE algorithm in searching large spaces and the iterative nature of controller unlike the LQR method, this controller consider the effects of external forces in control process. Numerical simulation showed that the performance of the presented control algorithm is better than the LQR controller approach in finding of optimal displacements and control forces. Therefore, metaheuristic algorithms such as differential evolution can be used in active control of structures to achieving more efficient results in comparison with classic controllers.

Magnetorheological (MR) fluid damper shows great promising in semi-active control of civil engineering structures, in which, fault-safe, low-power consumption, force controllability and rapid response are its advantageous. However, a major drawback that hinders its application rests with the non-linear force/displacement and hysteretic force/velocity characteristics. With regard to building control, it is crucial that a tractable model of the MR damper should be available before any design in realizable controller. There are several MR damper models proposed in the literature using a range of techniques. Models obtained by a deterministic approach include Bingham, phenomenological, Bouc-Wen models. The Bingham model cannot represents nonlinear behavior of MR damper and may be considered as a simple model for the hysteresis characteristic. The Bouc-Wen model uses a differential equation to depict the non-linear hysteresis with moderate complexity and is widely applied in building controls [1]. Nonlinear dependent relation between damper control force, floors displacement and velocity does not allow to solve governing equation of motion which makes the structure response analyzing impossible. There are a few new methods for estimating the response of structure with MR damper. In the present study modified Newmark-Beta method base on the instantaneous optimal control algorithm is used to estimate the response of the coupled system with MR damper, for the first time.

Convergent braces are usually used for stability of frames against lateral forces in seismic design. According to the seismic design philosophy, it's expected that convergent bracing systems could show a non-elastic and steady response under intense earthquakes. In such frames, braces are connected to beams and columns by a plate and non-elastic deformation occurs at the time of yield of the member by tensile and non-elastic buckling. The new experimental tests show that the seismic performance of convergent braces improves by connection plate design and permitting connection plate to yielding. In this research, the connection plate effects and its changes and also the inelastic finite element model and analysis methods are investigated and compared with experimental results. Important details in frames connection are including the effect of brace plate in rigidity of the column-beam connection, shape and thickness of connection plate and analysis of non-elastic deformations. The proposed results will lead to improve the shape and details of this type of connections.

Quantitative Feedback Theory, QFT, is frequency-domain-based robust control design methods that can conquest to structured uncertainty. In the last few years, its application to several control systems design such as flight control, hydraulic actuator control, etc., has been widely investigated but this theory has not been developed in the structural control field. The QFT method offers a direct design technique for satisfying a set of robust performance and stability objectives over a given range of plant parameter uncertainty based on Nichols Chart. In this paper firstly the QFT design methodology is presented through one illustrative example in order to make easy understanding of the basic principles and characteristics for single-input single-output system. Afterwards, feasibility and the efficiency of new structural control method are demonstrated by numerical simulation in multi degree of freedom structure and compared with the robust design approach. Simulation results show that the lower order of QFT controller is important feature of QFT controller in civil engineering.