• Smart Structures and Systems
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• v.29 no.4
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• pp.549-560
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• 2022

The optimum damping and tuning frequency ratio of the tuned mass damper-inerter (TMDI) for the base-isolated structure is obtained using the numerical searching technique under stationary white-noise and filtered white-noise earthquake excitation. The minimization of the isolated structure's mean-square relative displacement and absolute acceleration, as well as the maximization of the energy dissipation index, were chosen as the criteria for optimality. Using a curve-fitting technique, explicit formulae for TMDI damping and tuning frequency for white-noise excitation are then derived. The proposed empirical expressions for TMDI parameters are found to have a negligible error, making them useful for the effective design of base-isolated structures. The effectiveness of TMDI and its optimum parameters are influenced by the soil condition and isolation frequency, according to the comparison made of the optimized parameters and response with different soil profiles. The effectiveness of an optimally designed TMDI in controlling the displacement and acceleration response of the flexible isolated structure under real and pulse-type earthquakes is also observed and found to be increased as the inertance mass ratio increases.

• Journal of Electrical Engineering and Technology
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• v.3 no.1
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• pp.101-107
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• 2008

We introduce an optimization of fuzzy set-fuzzy systems based on IG (Information Granules). The proposed fuzzy model implements system structure and parameter identification by means of IG and GAs. The concept of information granulation was coped with to enhance the abilities of structural optimization of the fuzzy model. Granulation of information realized with C-Means clustering helps determine the initial parameters of the fuzzy model such as the initial apexes of the membership functions in the premise part and the initial values of polynomial functions in the consequence part of the fuzzy rules. The initial parameters are adjusted effectively with the help of the GAs and the standard least square method. To optimally identify the structure and the parameters of the fuzzy model we exploit GAs with successive tuning method to simultaneously search the structure and the parameters within one individual. We also consider the variant generation-based evolution to adjust the rate of identification of the structure and the parameters in successive tuning method. The proposed model is evaluated with the performance of the conventional fuzzy model.

• Smart Structures and Systems
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• v.10 no.6
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• pp.517-546
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• 2012

In this paper, vibration-based methods to monitor damage in foundation-structure interface of harbor caisson structure are presented. The following approaches are implemented to achieve the objective. Firstly, vibration-based damage monitoring methods utilizing a variety of vibration features are selected for harbor caisson structure. Autoregressive (AR) model for time-series analysis and power spectral density (PSD) for frequency-domain analysis are selected to detect the change in the caisson structure. Also, the changes in modal parameters such as natural frequency and mode shape are examined for damage monitoring in the structure. Secondly, the feasibility of damage monitoring methods is experimentally examined on an un-submerged lab-scaled mono-caisson. Finally, numerical analysis of un-submerged mono-caisson, submerged mono-caisson and un-submerged interlocked multiple-caissons are carried out to examine the effect of boundary-dependent parameters on the damage monitoring of harbor caisson structures.

• Geomechanics and Engineering
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• v.16 no.5
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• pp.527-538
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• 2018

The study on the performance of the nonlinear friction tuned mass dampers (FTMD) for the mitigation of the seismic responses of the structures is a topic that still inspires the efforts of researchers. The present paper aims to carry out a numerical study on the optimum tuning of TMD and FTMD parameters using a multi-objective particle swarm optimization (MOPSO) algorithm including soil-structure interaction (SSI) effects for seismic applications. Considering a 3-story structure, the performances of the optimized TMD and FTMD are compared with the uncontrolled structure for three types of soils and the fixed base state. The simulation results indicate that, unlike TMDs, optimum tuning of FTMD parameters for a large preselected mass ratio may not provide a best and optimum design. For low mass ratios, optimal selection of friction coefficient has an important key to enhance the performance of FTMDs. Consequently, a free parameter search of all FTMD parameters provides a better performance in comparison with considering a preselected mass ratio for FTMD in the optimum design stage of the FTMD. Furthermore, the SSI significant effects on the optimum design of the TMD and FTMD. The simulation results also show that the FTMD provides a better performance in reducing the maximum top floor displacement and acceleration of the building in different soil types. Moreover, the performance of the TMD and FTMD decrease with increasing soil softness, so that ignoring the SSI effects in the design process may give an incorrect and unrealistic estimation of their performance.

• Advances in nano research
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• v.14 no.2
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• pp.141-154
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• 2023

Effects of viscoelastic foundation on vibration of curved-beam structure with clamped and simply-supported boundary conditions is investigated in this study. In doing so, a micro-scale laminate composite beam with two piezoelectric face layer with a carbon nanotube reinforces composite core is considered. The whole beam structure is laid on a viscoelastic substrate which normally occurred in actual conditions. Due to small scale of the structure non-classical elasticity theory provided more accurate results. Therefore, nonlocal strain gradient theory is employed here to capture both nano-scale effects on carbon nanotubes and microscale effects because of overall scale of the structure. Equivalent homogenous properties of the composite core is obtained using Halpin-Tsai equation. The equations of motion is derived considering energy terms of the beam and variational principle in minimizing total energy. The boundary condition is assumed to be clamped at one end and simply supported at the other end. Due to nonlinear terms in the equations of motion, semi-analytical method of general differential quadrature method is engaged to solve the equations. In addition, due to complexity in developing and solving equations of motion of arches, an artificial neural network is design and implemented to capture effects of different parameters on the inplane vibration of sandwich arches. At the end, effects of several parameters including nonlocal and gradient parameters, geometrical aspect ratios and substrate constants of the structure on the natural frequency and amplitude is derived. It is observed that increasing nonlocal and gradient parameters have contradictory effects of the amplitude and frequency of vibration of the laminate beam.

• Communications of the Korean Mathematical Society
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• v.34 no.2
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• pp.465-475
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• 2019

Let X be a Banach space and $X^*$ be its dual. In this paper, we give relationships among some parameters in $X^*$: ${\varepsilon}$-nonsquareness parameter, $J({\varepsilon},X^*)$; ${\varepsilon}$-boundary parameter, $Q({\varepsilon},X^*)$; the modulus of smoothness, ${\rho}_{X^*}({\varepsilon})$; and ${\varepsilon}$-Pythagorean parameter, $E({\varepsilon},X^*)$, and weak orthogonality parameter, ${\omega}(X)$ in X that imply uniform norm structure in X. Some existing results are extended or approved.

• Structural Engineering and Mechanics
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• v.82 no.6
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• pp.785-799
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• 2022

The effect of earthquakes in earthquake resistant structure design stages is influenced by the highest ground acceleration value, which is generally a strength-based approach in seismic codes. In this context, an energy-oriented approach can be suggested as an alternative to evaluate structure demands. Contrary to the strength-based approach, the strength and displacement demands of the structure cannot be evaluated separately, but can be evaluated together. In addition, in the energy-oriented approach, not only the maximum effects of earthquakes are taken into account, but also the duration of the earthquake. In this respect, it can be said that the use of energy-oriented earthquake parameters is a more rational approach besides being an alternative. In this study, strength and energy-oriented approaches of earthquake parameters of 11 different periods of single degree of freedom systems were evaluated over 28 different earthquake situations. The energy spectra intended to be an alternative to the traditional acceleration spectra were created using the acceleration parameter equivalent to the input energy. Two new energy parameters, which take into account the effective duration of the earthquake, are proposed, and the relationship between the strength-oriented spectral acceleration parameters and the energy parameters used in the literature is examined by correlation study. According to the results obtained, it has been seen that energy oriented earthquake parameters, which give close values in similar period situations, will be a good alternative to strength oriented earthquake parameters. It was observed that the energy parameters were affected by the effective duration of the earthquake, unlike the strength-based parameters. It has been revealed that the newly proposed energy parameters considering the effective duration give good correlations. Finally, it was concluded that the energy parameters can be used in the design, and the newly proposed effective energy parameters can shorten the analysis durations.

• Structural Engineering and Mechanics
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• v.70 no.6
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• pp.703-710
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• 2019

While fiber-reinforced plastic (FRP) materials have been largely used in the retrofitting of concrete buildings, its application has been limited because of some problems such as de-bonding of FRP layers from the concrete surface. This paper is the part of a wide experimental and analytical investigation about flexural retrofitting of reinforced concrete (RC) columns using FRP and mechanical fasteners (MF). A new generation of MF is proposed, which is applicable for retrofitting of RC columns. Furthermore, generally, to evaluate a retrofitted structure the nonlinear static and dynamic analyses are the most accurate methods to estimate the performance of a structure. In the nonlinear analysis of a structure, accurate modeling of structural elements is necessary for estimation the reasonable results. So for nonlinear analysis of a structure, modeling parameters for beams, columns, and beam-column joints are essential. According to the concentrated hinge method, which is one of the most popular nonlinear modeling methods, structural members shall be modeled using concentrated or distributed plastic hinge models using modeling parameters. The nonlinear models of members should be capable of representing the inelastic response of the component. On the other hand, in performance based design to make a decision about a structure or design a new one, numerical acceptance should be determined. Modeling parameters and numerical acceptance criteria are different for buildings of different types and for different performance levels. In this paper, a new method was proposed for FRP retrofitted columns to avoid FRP debonding. For this purpose, mechanical fasteners were used to achieve the composite behavior of FRP and concrete columns. The experimental results showed that the use of the new method proposed in this paper increased the flexural strength and lateral load capacity of the columns significantly, and a good composition of FRP and RC column was achieved. Moreover, the modeling parameters and acceptance criteria were presented, which were derived from the experimental study in order to use in nonlinear analysis and performance-based design approach.

• Applied Microscopy
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• v.41 no.1
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• pp.75-79
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• 2011

For quantitative analysis of nano-crystal structure, we reported the accuracy improvement method of lattice parameters measured from electron diffraction. For calculation of Au lattice parameters used as a standard crystal structure, it was considered two different acquisition methods (detector and enegy-filter) and three different calculation methods (conventional, least-square and regression fit). As a result, the measurement reliability could be enhanced by using CCD camera which gives higher performance, while energy-filtering did not affect the improvement the camera constant accuracy. Also, the accuracy of lattice parameters could be improved up to $10^{-4}$ order by regression fitting with correction formula. Finally, it is expected that the combination of regression fitting and intensity extraction from energy-filtered precession electron diffraction gives a solution of quantitative structure analysis for unknown nano-crystals.

• Smart Structures and Systems
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• v.24 no.6
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• pp.683-692
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• 2019

Traditional damage detection methods for nonlinear structures are often based on simplified models, such as the mass-spring-damper and shear-building models, which are insufficient for predicting the vibration responses of a real structure. Conventional global nonlinear finite element model updating methods are computationally intensive and time consuming. Thus, they cannot be applied to practical structures. A decentralized approach for identifying the nonlinear material parameters is proposed in this study. With this technique, a structure is divided into several small zones on the basis of its structural configuration. The unknown material parameters and measured vibration responses are then divided into several subsets accordingly. The structural parameters of each subset are then updated using the vibration responses of the subset with the Newton-successive-over-relaxation (SOR) method. A reinforced concrete and steel frame structure subjected to earthquake loading is used to verify the effectiveness and accuracy of the proposed method. The parameters in the material constitutive model, such as compressive strength, initial tangent stiffness and yielding stress, are identified accurately and efficiently compared with the global nonlinear model updating approach.