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The slotting method is a nondestructive detection method based on the stress release principle to evaluate in-place stress in concrete. By measuring the change in strain of the slotting area using a strain gauge, the in-place stress within the concrete member can be calculated by elastic theory. This paper proposes a multi-step slotting method that combines experimental strain measurements with numerical simulation results. For concrete specimens under unidirectional stress, the effects of compressive stress, slotting spacing, slotting length, and slotting depth on the degree of stress release were analyzed using finite element analysis, and a normalized fitting equation was proposed that can be quickly and accurately applied in engineering detection. The excellent agreement between the experimental results and the numerical simulation (fitted equation) results shows that the slotting method can facilitate the accurate evaluation of the in-place stress in concrete, and the relative error can be reduced to less than 10% when it is calculated using the optimized multi-step experimental data. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) fluids are a new kind of smart vibration mitigation material for vibration control, whose shear yield stress can change in magnetic field, and the change can occur only in a few milliseconds. The rheological properties, anti-settlement stability, and redispersibility are the very important properties of MR fluids. In this paper, a kind of preparation process of MR fluids is introduced and MR fluids with different grain diameter ratios of carbonyl iron particles are produced. Then, the properties of self-prepared MR fluids are tested, including the sedimentation stability test, viscosity test, and shear yield stress test. The results of the MR fluid property tests show that the adding of 10 μm-carbonyl iron particles will improve the magnetic effect of MR fluids, increase the zero magnetic field viscosity of MR fluids, and increase shear yield stress of MR fluids in same magnetic field, but the anti-settlement properties will be degraded. [ABSTRACT FROM AUTHOR]

Both experimental and modeling studies of magnetic field induced viscoelastic properties of magnetorheological (MR) elastomers under different loading cases are discussed. Anisotropic MR elastomer (MRE) samples with different concentrations of carbonyl iron powder, natural rubber and additives are fabricated and four MRE vibration mitigation devices are manufactured to investigate the dynamic viscoelastic properties of MREs under varying magnetic fields, displacement amplitudes and frequencies in the shear mode. The characteristics of the dynamic properties of the MRE devices are obtained in terms of the experimentally determined shear storage modulus and loss factor. These results demonstrate that the MREs exhibit variable stiffness and damping properties. Based on the studies of properties of viscoelastic materials and the experimental results of MREs, a parameter model is proposed to describe MRE performances. The four parameters under various working conditions, such as magnetic field, displacement amplitude and frequency, are identified by using the Matlab optimization algorithm. Comparisons between experimental and numerical results are discussed, and the results show that the proposed parameter model can describe the performances of MRE devices very well. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) damper, a kind of intelligent vibrationmitigation device, can be used to reduce the vibration or dynamic responses of structures. Its damping forces can be adjusted in real-time by updating control currents of the MR damper according to the state parameters of the structure. In this paper, a single-chip microprocessor (SCM) for MR damper coupling sensing and control is developed. The SCM has three main functions: the first one is that it can collect the acceleration responses of the structure by using the acceleration sensor in real-time; the second one is that it can use the segmented control strategy to decide the control currents of theMR damper according to the collected acceleration information; the third one is that based on the PWM technology it can realize to accurately supply power for the MR damper. The developed SCM is tested through experiment. The analysis results of the simulation and experiment show that the SCM can collect the state information of the structure in real-time and realize to choose the currents of MR damper accurately to control the damping forces of the MR damper. [ABSTRACT FROM AUTHOR]

The magnetorheological (MR) damper, a shock absorption device, can be used to reduce vibration or dynamic response of controlled systems. Its parameters can be adjusted in real-time by updating its control current, therefore, it is critical to determine the control current of the MR damper accurately and quickly. This study proposes a fuzzy control strategy based on a neural network forecasting model of the building structure with MR dampers, in which a neural network forecasting model is developed to predict dynamic responses of the system with MR dampers and a fuzzy controller is then designed to determine control currents of MR dampers. A five-floor steel structure with MR dampers using the proposed fuzzy control strategy is simulated by using Simulink. Simulation results of the fuzzy control system are compared with those of the bi-state control system, the passive-on control system, the passive-off control system, and the uncontrolled system. Analysis results demonstrate that the fuzzy control strategy can determine control currents of MR dampers accurately and quickly; furthermore, the fuzzy control strategy reduces seismic responses of structures more effectively than the passive-on control strategy, the passive-off control strategy, and the bi-state control strategy. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) damper has a potential use in the vibration control of large structures due to its lower energy input and fine earthquake mitigation ability. A key problem for controlling structure with MR dampers is choosing the control current quickly and accurately. In order to solve this problem, a new method by using fuzzy controller, namely fuzzy full-state control method, is proposed. Dynamic responses under different inputs of fuzzy controller are compared. At the same time, dynamic responses of the traditional bi-state (BS) controlled structure and the passive full-current (PFC) controlled structure under different earthquake waves are compared with those of fuzzy full-state controlled structure. Through a numerical example about a three-story reinforced concrete structure, it can be concluded that fuzzy control technique can realize choosing of currents of MR dampers quickly and accurately and have good control effect. [ABSTRACT FROM AUTHOR]

Magnetorheological (MR) dampers are increasingly employed to attenuate the harmful vibration in Civil Structures caused by dynamic loadings such as earthquakes and strong winds for their excellent response mitigation capacity. The credibility and precision of dynamic response mitigation capacity of MR dampers are highly dependent on intelligent control strategy. In this paper, a piecewise control algorithm based on the feedbacks of story drift and ground excitation acceleration is adopted through a micro-controller with a digital signal processor chip as the control processor. Shaking table tests are carried out on a three-story steel frame structure which incorporates MR damper with the micro-controller installed between the ground and first floor. The dynamic responses of the real-time online intelligent controlled structure are compared with those of passive-on and passive-off controlled structures under different earthquake waves to evaluate vibration control efficacy of the MR intelligent control system. Test results show that the developed MR intelligent control system can sufficiently reduce the peak and root mean square responses due to earthquake excitations, and the control efficiency of displacement and acceleration responses is higher than the two passive control cases. [ABSTRACT FROM AUTHOR]