Seismic behavior of special moment-resisting frames with energy dissipating devices under near source ground motions

Mahmoud Bayat,Mahdi Bayat 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.16 No.5

In this study, the performances of the SMRF building equipped with energy dissipating devices are studied. Three types of these structures with different heights are considered. The Added Damping and Stiffness (ADAS) devices are used as energy dissipating devices in these structures. The behavior of these structures with ADAS devices subjected to near source ground motions are investigated. Three SMRF buildings with five, ten and fifteen-story, with ADAS devices were chosen. The nonlinear time history analysis was used by applying the near source ground motions with PERFORM 3D.V4 and conclusions are drawn upon an energy criterion. The effect of PGA variation and height of the frames are also considered based on the energy criterion.

Application of power spectral density function for damage diagnosis of bridge piers

Mahmoud Bayat,Hamid Reza Ahmadi,Navideh Mahdavi 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.71 No.1

During the last two decades, much joint research regarding vibration based methods has been done, leading to developing various algorithms and techniques. These algorithms and techniques can be divided into modal methods and signal methods. Although modal methods have been widely used for health monitoring and damage detection, signal methods due to higher efficiency have received considerable attention in various fields, including aerospace, mechanical and civil engineering. Signal-based methods are derived directly from the recorded responses through signal processing algorithms to detect damage. According to different signal processing techniques, signal-based methods can be divided into three categories including time domain methods, frequency domain methods, and time-frequency domain methods. The frequency domain methods are well-known and interest in using them has increased in recent years. To determine dynamic behaviours, to identify systems and to detect damages of bridges, different methods and algorithms have been proposed by researchers. In this study, a new algorithm to detect seismic damage in the bridge’s piers is suggested. To evaluate the algorithm, an analytical model of a bridge with simple spans is used. Based on the algorithm, before and after damage, the bridge is excited by a sine force, and the piers’ responses are measured. The dynamic specifications of the bridge are extracted by Power Spectral Density function. In addition, the Least Square Method is used to detect damage in the bridge’s piers. The results indicate that the proposed algorithm can identify the seismic damage effectively. The algorithm is output-only method and measuring the excitation force is not needed. Moreover, the proposed approach does not need numerical models.

Nonlinear vibration of oscillatory systems using semi-analytical approach

Bayat, Mahmoud,Bayat, Mahdi,Pakar, Iman Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.4

In this paper, He's Variational Approach (VA) is used to solve high nonlinear vibration equations. The proposed approach leads us to high accurate solution compared with other numerical methods. It has been established that this method works very well for whole range of initial amplitudes. The method is sufficient for both linear and nonlinear engineering problems. The accuracy of this method is shown graphically and the results tabulated and results compared with numerical solutions.

Analytical solution for nonlinear vibration of an eccentrically reinforced cylindrical shell

Mahmoud Bayat,Iman Pakar,Mahdi Bayat 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.14 No.5

In this study we have considered the governing nonlinear equation of an eccentrically reinforced cylindrical shell. A new analytical method called He’s Variational Approach (VA) is used to obtain the natural frequency of the nonlinear equation. This analytical representation gives excellent approximations to the numerical solution for the whole range of the oscillation amplitude, reducing the respective error of angular frequency in comparison with the variation approach method. It has been proved that the variational approach is very effective, convenient and does not require any linearization or small perturbation. Additionally it has been demonstrated that the variational approach is adequately accurate to nonlinear problems in physics and engineering.

Nonlinear frequency analysis of beams resting on elastic foundation using max-min approach

Bayat, Mahmoud,Bayat, Mahdi,Kia, Mehdi,Ahmadi, Hamid Reza,Pakar, Iman Techno-Press 2018 Geomechanics & engineering Vol.16 No.4

In this paper, nonlinear vibration of Euler-Bernoulli beams resting on linear elastic foundation is studied. It has been tried to prepare a semi-analytical solution for whole domain of vibration. Only one iteration lead us to high accurate solution. The effects of linear elastic foundation on the response of the beam vibration are considered and studied. The effects of important parameters on the ratio of nonlinear to linear frequency of the system are studied. The results are compared with numerical solution using Runge-Kutta $4^{th}$ technique. It has been shown that the Max-Min approach can be easily extended in nonlinear partial differential equations.

Accurate analytical solutions for nonlinear oscillators with discontinuous

Bayat, Mahdi,Bayat, Mahmoud,Pakar, Iman Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.2

In this study, three approximate analytical methods have been proposed to prepare an accurate analytical solution for nonlinear oscillators with fractional potential. The basic idea of the approaches and their applications to nonlinear discontinuous equations have been completely presented and discussed. Some patterns are also presented to show the accuracy of the methods. Comparisons between Energy Balance Method (EBM), Variational Iteration Method (VIM) and Hamiltonian Approach (HA) shows that the proposed approaches are very close together and could be easily extend to conservative nonlinear vibrations.

Probabilistic seismic demand of isolated straight concrete girder highway bridges using fragility functions

Bayat, Mahmoud,Ahmadi, Hamid Reza,Kia, Mehdi,Cao, Maosen Techno-Press 2019 Advances in concrete construction Vol.7 No.3

In this study, it has been tried to prepare an analytical fragility curves for isolated straight continues highway bridges by considering different spectral intensity measures. A three-span concrete isolated bridge has been selected and the seismic performance of the bridge has been improved by Lead Rubber Bearing (LRB). Incremental Dynamic Analysis (IDA) is applied to the bridge in longitudinal direction. A suite of 14 earthquake ground motions from medium to sever motions are scaled and used for nonlinear time history analysis. Fragility function considers the relationship of earthquake intensity measures (IM) and probability of exceeding certain Damage State (DS). A full three dimensional finite element model of the isolated bridge has been developed and analyzed. A wide range of different intensity measures are selected and the optimal intensity measure which has the less dispersion is proposed.

Forced nonlinear vibration by means of two approximate analytical solutions

Bayat, Mahmoud,Bayat, Mahdi,Pakar, Iman Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.50 No.6

In this paper, two approximate analytical methods have been applied to forced nonlinear vibration problems to assess a high accurate analytical solution. Variational Iteration Method (VIM) and Perturbation Method (PM) are proposed and their applications are presented. The main objective of this paper is to introduce an alternative method, which do not require small parameters and avoid linearization and physically unrealistic assumptions. Some patterns are illustrated and compared with numerical solutions to show their accuracy. The results show the proposed methods are very efficient and simple and also very accurate for solving nonlinear vibration equations.

An accurate novel method for solving nonlinear mechanical systems

Bayat, Mahdi,Pakar, Iman,Bayat, Mahmoud Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.3

This paper attempts to investigate the nonlinear dynamic analysis of strong nonlinear problems by proposing a new analytical method called Hamiltonian Approach (HA). Two different cases are studied to show the accuracy and efficiency of the method. This approach prepares us to obtain the nonlinear frequency of the nonlinear systems with the first order of the solution with a high accuracy. Finally, to verify the results we present some comparisons between the results of Hamiltonian approach and numerical solutions using Runge-Kutta's [RK] algorithm. This approach has a powerful concept and the high accuracy, so it can be apply to any conservative nonlinear problems without any limitations.

On the large amplitude free vibrations of axially loaded Euler-Bernoulli beams

Mahmoud Bayat,Iman Pakar,Mahdi Bayat 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.14 No.1

In this paper Hamiltonian Approach (HA) have been used to analysis the nonlinear free vibration of Simply-Supported (S-S) and for the Clamped-Clamped (C-C) Euler-Bernoulli beams fixed at one end subjected to the axial loads. First we used Galerkin’s method to obtain an ordinary differential equation from the governing nonlinear partial differential equation. The effect of different parameter such as variation of amplitude to the obtained on the non-linear frequency is considered. Comparison of HA with Runge-Kutta 4th leads to highly accurate solutions. It is predicted that Hamiltonian Approach can be applied easily for nonlinear problems in engineering.