Seismic evaluation of isolated skewed bridges using fragility function methodology

M. Bayat,F. Daneshjoo,N. Nisticò,J. Pejovic 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.4

A methodology, based on fragility functions, is proposed to evaluate the seismic performance of seismic isolated 45° skewed concrete bridge: 1) twelve types of seismic isolation devices are considered based on two different design parameters 2) fragility functions of a three-span bridge with and without seismic isolation devices are analytically evaluated based on 3D nonlinear incremental dynamic analyses which seismic input consists of 20 selected ground motions. The optimum combinations of isolation device design parameters are identified comparing, for different limit states, the performance of 1) the Seismic Isolated Bridges (SIB) and 2) Not Seismic Isolated Bridge (NSIB) designed according to the AASHTO standards.

Probabilistic sensitivity analysis of multi-span highway bridges

M. Bayat,F. Daneshjoo,N. Nisticò 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.19 No.1

In this study, we try to compare different intensity measures for evaluating nonlinear response of bridge structure. This paper presents seismic analytic fragility of a three-span concrete girder highway bridge. A complete detail of bridge modeling parameters and also its verification has been presented. Fragility function considers the relationship of intensities of the ground motion and probability of exceeding certain state of damage. Incremental dynamic analysis (IDA) has been subjected to the bridge from medium to strong ground motions. A suite of 20 earthquake ground motions with different range of PGAs are used in nonlinear dynamic analysis of the bridge. Complete sensitive analyses have been done on the response of bridge and also efficiency and practically of them are studied to obtain a proficient intensity measure for these types of structure by considering its sensitivity to the period of the bridge. Three dimensional finite element (FE) model of the bridge is developed and analyzed. The numerical results show that the bridge response is very sensitive to the earthquake ground motions when PGA and Sa (Ti, 5%) are used as intensity measure (IM) and also indicated that the failure probability of the bridge system is dominated by the bridge piers.

Mathematical solution for nonlinear vibration equations using variational approach

M. Bayat,I. Pakar 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.15 No.5

In this paper, we have applied a new class of approximate analytical methods called Variational Approach (VA) for high nonlinear vibration equations. Three examples have been introduced and discussed. The effects of important parameters on the response of the problems have been considered. Runge-Kutta’s algorithm has been used to prepare numerical solutions. The results of variational approach are compared with energy balance method and numerical and exact solutions. It has been established that the method is an easy mathematical tool for solving conservative nonlinear problems. The method doesn’t need small perturbation and with only one iteration achieve us to a high accurate solution.

Vibration of electrostatically actuated microbeam by means of homotopy perturbation method

Bayat, M.,Pakar, I.,Emadi, A. Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.6

In this paper, it has been attempted to present a powerful analytical approach called Homotopy Perturbation Method (HPM). Free vibration of an electrostatically actuated microbeam is considered to study analytically. The effect of important parameters on the response of the system is considered. Some comparisons are presented to verify the results with other researcher's results and numerical solutions. It has been indicated that HPM could be easily extend to any nonlinear equation. We try to provide an easy method to achieve high accurate solution which valid for whole domain.

Accurate analytical solution for nonlinear free vibration of beams

Bayat, M.,Pakar, I. Techno-Press 2012 Structural Engineering and Mechanics, An Int'l Jou Vol.43 No.3

In this study, Hamiltonian Approach (HA) is applied to analysis the nonlinear free vibration of beams. Two well-known examples are illustrated to show the efficiency of this method. One of them deals with the Nonlinear vibration of an electrostatically actuated microbeam and the other is the nonlinear vibrations of tapered beams. This new approach prepares us to achieve the beam's natural frequencies and mode shapes easily and a rapidly convergent sequence is obtained during the solution. The effects of the small parameters on the frequency of the beams are discussed. Some comparisons are conducted between the results obtained by the Hamiltonian Approach (HA) and numerical solutions using to illustrate the effectiveness and convenience of the proposed methods.

Detection of Broken Bars in Induction Motors, Using Neural Network

M. Ebrahimi,M. Moradian,M. Danesh,M. bayat 전력전자학회 2006 JOURNAL OF POWER ELECTRONICS Vol.6 No.3

This paper presents a method based on neural networks to detect the broken rotor bars and end rings of squirrel cage induction motors. At first, detection methods are studied, and then traditional methods of fault detection and dynamic models of induction motors by using winding function model are introduced. In this method, all of the stator slots and rotor bars are considered, thus the performance of the motor in healthy situations or breakage in each part can be checked. The frequency spectrum of current signals is derived by using Fourier transformation and is analyzed in different conditions. In continuation, an analytical discussion and a simple algorithm are presented to detect the fault. This algorithm is based on neural networks. The neural network has been trained by using information of a 1.1 KW induction motor. This system has been tested with a different amount of load torque, and it is capable of working on-line and of recognizing all normal and ill conditions.

Vibration of electrostatically actuated microbeam by means of homotopy perturbation method

M. Bayat,I. Pakar,A. Emadi 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.48 No.6

In this paper, it has been attempted to present a powerful analytical approach called Homotopy Perturbation Method (HPM). Free vibration of an electrostatically actuated microbeam is considered to study analytically. The effect of important parameters on the response of the system is considered. Some comparisons are presented to verify the results with other researcher’s results and numerical solutions. It has been indicated that HPM could be easily extend to any nonlinear equation. We try to provide an easy method to achieve high accurate solution which valid for whole domain.

Bayesian demand model based seismic vulnerability assessment of a concrete girder bridge

Bayat, M.,Kia, M.,Soltangharaei, V.,Ahmadi, H.R.,Ziehl, P. Techno-Press 2020 Advances in concrete construction Vol.9 No.4

In the present study, by employing fragility analysis, the seismic vulnerability of a concrete girder bridge, one of the most common existing structural bridge systems, has been performed. To this end, drift demand model as a fundamental ingredient of any probabilistic decision-making analyses is initially developed in terms of the two most common intensity measures, i.e., PGA and Sa (T₁). Developing a probabilistic demand model requires a reliable database that is established in this paper by performing incremental dynamic analysis (IDA) under a set of 20 ground motion records. Next, by employing Bayesian statistical inference drift demand models are developed based on pre-collapse data obtained from IDA. Then, the accuracy and reasonability of the developed models are investigated by plotting diagnosis graphs. This graphical analysis demonstrates probabilistic demand model developed in terms of PGA is more reliable. Afterward, fragility curves according to PGA based-demand model are developed.

Membrane/sorption-enhanced methanol synthesis process: Dynamic simulation and optimization

M. Bayat,Z. Dehghani,M.R. Rahimpour 한국공업화학회 2014 Journal of Industrial and Engineering Chemistry Vol.20 No.5

In this study, a dynamic mathematical model of a Membrane-Gas-Flowing Solids-Fixed Bed Reactor (Membrane-GFSFBR) with in-situ water adsorption in the presence of catalyst deactivation is proposed for methanol synthesis. The novel reactor consists of water adsorbent and hydrogen-permselective Pd-Ag membrane. In this configuration feed gas and flowing adsorbents are both fed into the outer tube of the reactor. Contact of gas and fine solids particles inside packed bed results in selective adsorption of water from methanol synthesis which leads to higher methanol production rate. Afterwards, the high pressure product is recycled to the inner tube of the reactor and hydrogen permeates to the outer tube which shifts the reaction towards more methanol production. Dynamic simulation result reveals that simultaneous application of water adsorbent and hydrogen permeation in methanol synthesis process contributes to a significant enhancement in methanol production. The notable advantage of Membrane-GFSFBR is the continuous adsorbent regeneration during the process. Moreover, a theoretical investigation has been performed to evaluate the optimal operating conditions and to maximize the methanol production in Membrane-GFSFBR using differential evolution (DE) algorithm as a robust method. The obtained optimization result shows there are optimum values of inlet temperatures of gas phase, flowing solids phase, and shell side under which the highest methanol production can be achieved.

Analytical approach on nonlinear vibration of dry cask storage systems

M. Bayat,V. Soltangharaei,P. Ziehl 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.75 No.2

In this paper, a novel analytical method, Max-Min Approach (MMA), has been presented and applied to consider the nonlinear vibration of dry cask storage systems. The nonlinear governing equation of the structure has been developed using the shell theory. The MMA results are compared with numerical solutions derived by Runge-Kutta’s Method (RKM). The results indicate a satisfying agreement between MMA and numerical solutions. Parametric studies have been conducted on the nonlinear frequency of dry casks. The phase-plan of the problem is also presented and discussed. The proposed approach can potentially ca be extended to highly nonlinear problems.