Sharif Digital Repository

The dynamic deformation of a geometrically nonlinear rectangular simply supported plate under a moving lumped mass is evaluated using mode expansion method. The governing differential equations of motion for a largely deformable rectangular plate are derived using Lagrange method based on appropriate in and out-of-plane spatial functions which satisfy the proposed boundary conditions. Although the proposed procedure is applicable for any arbitrary edge boundary conditions, only the simply supported plates are addressed in the present work. On the other hand, all inertial components of the moving mass are included in the derivation of the equations of motion. A numerical example is used to... 

Various researchers have contributed to the identification of the mass and stiffness matrices of two dimensional (2-D) shear building structural models for a given set of vibratory frequencies. The suggested methods are based on the specific characteristics of the Jacobi matrices, i.e., symmetric, tri-diagonal and semi-positive definite matrices. However, in case of three dimensional (3-D) structural models, those methods are no longer applicable, since their stiffness matrices are not tri-diagonal. In this paper the inverse problem for a special class of vibratory structural systems, i.e., 3-D shear building models, is investigated. A practical algorithm is proposed for solving the inverse... 

The governing differential equation of motion of a thin rectangular plate excited by a moving mass is considered. The moving mass is traversing on the plate's surface at arbitrary trajectories. Eigenfunction expansion method is employed to solve the constitutive equation of motion for various boundary conditions. Approximate and exact expressions of the inertial effects are adopted for the problem formulation. In the approximate formulation, only the vertical acceleration component of the moving mass is considered while in the exact formulation all the convective acceleration components are included in the problem formulation as well. Parametric studies are carried out to investigate the... 

This paper discusses the time-varying characteristics of the output signals resulted from Linear Time Variant (LTV) systems using level-crossing properties. These systems, used for generating synthetic records based on a target record, contain two identification processes: 1) amplitude modulating function; and 2) time-varying Impulse Response Function (IRF) parameters. To track the IRF parameters efficiently, the zerocrossing and positive minima/negative maxima cumulative curves are usually utilized as the measures of the instantaneous spectral power. Using spectral moments, analytic relations for zero-crossing and positive minima/negative maxima cumulative count are developed with respect... 

This article introduces a new time-varying model to generate synthetic non-stationary acceleration records using the modified Kanaii-Tajimi model with time-variant parameters. The proposed method can capture two different dominant frequencies per time which makes it suitable for synthesizing the near-field no-pulse earthquake records. A number of closed-form relationships are developed to describe the frequency dependent time-domain level crossings of the simulated records under white noise excitation. The model parameters are optimized using the crossing and Arias intensity properties of the synthetic and target records. The efficiency of the proposed model is demonstrated using a data base... 

In this study, the performance of a proposed friction damper with two slip loads in controlling the seismic response of steel moment resisting buildings structures under moderate and intense earthquake excitations is investigated. The proposed friction damper initially operates with a smaller slip load and could shift to the higher slip load after a certain amount of slippage when subjected to intense ground motions. In this regard, the hysteresis behavior of the proposed double slip loads (DSL) friction damper is modeled and after necessary verifications is imported to the material library of OpenSees software to be used for parametric study. To evaluate the performance of the proposed DSL... 

Seismic response of a Single Degree of Freedom (SDOF) system containing a rigid circular cylindrical liquid tank under the earthquake excitations is considered in the presence of fluid/structure interaction. The governing differential equations of the system is derived considering the first three liquid sloshing modes (1, 1), (0, 1) and (2, 1) under different strong ground motions. The dynamic response of the system is investigated in the neighborhood of 1:1 and 1:2 internal resonances between the SDOF system and the liquid sloshing modes. These internal resonances take place by tuning the frequency of the first asymmetric sloshing mode of the liquid to the fundamental frequency of the SDOF... 

The governing differential equation of motion for an undamped thin rectangular plate with a number of bonded piezoelectric patches on its surface, and arbitrary boundary conditions are derived using Hamilton's principle. A moving mass traveling on an arbitrary trajectory acts as an external excitation for the system. The effect of moving mass inertia is considered using all the out-of-plane translational acceleration components. The method of eigenfunction expansion is used to decouple the equation of motion into a number of coupled ordinary differential equations. A classical closed loop optimal control algorithm is employed to suppress the dynamic response of the system by determining the... 

The seismic performance of diagrids equipped with buckling restrained braces (BRBs) is investigated. In that regard, the effects of BRBs on the seismic performance characteristics of diagrids such as response modification factor, R, overstrength factor, Ω0, ductility ratio, μ, and median collapse capacity, S^CT, are evaluated. To this end, 6 three dimensional diagrid structures with various heights and diagonal angles are modeled using OpenSees program and are equipped with BRBs in a novel arrangement. Utilizing nonlinear static analysis, the seismic performance factors of models are evaluated. Subsequently, the median collapse capacity (S^CT) of the models are determined by performing... 

In the present paper, a decentralized control algorithm is considered for actively controlling the response of flexible tall building structures under earthquake excitations. Sliding mode control is used as a base control algorithm and a decentralized scheme of that is presented. In the proposed approach, the building is divided into several substructures and for each subsystem a separate local control algorithm is designed. The control algorithm consists of the sliding surface and the reaching law equations. A numerical example is used to demonstrate the efficiency of the control algorithm in guaranteeing the system's global stability under the effects of subsystem interconnections and... 

Epistemic uncertainty in seismic hazard analysis is traditionally addressed by utilizing a logic-tree structure with subjective probabilities for branches. However, many studies have argued that probability is not a suitable choice for addressing epistemic uncertainties; in particular in addressing the background knowledge supporting the probabilities. In this regard, the application of imprecise probability (IP) is investigated. It is discussed that IP could provide a flexible tool for a more objective presentation of experts' knowledge. Moreover, the importance of addressing the strength of knowledge and surprises relative to knowledge in seismic hazard analysis along with methods to do... 

The performance of several regression methods is investigated to estimate the distribution of engineering demand parameters conditioned on intensity measures (EDP|IM) for small record sets. In particular, the performance of the multivariate ordinary least squares (OLS), a simultaneous mean-variance regression (MVR) done by a penalized weighted least-square loss function, and a mean-covariance/variance regression based on expectation maximization method (EM) are assessed. The efficiency of the introduced methods is compared with FEMA-P58 methodology. Performance assessment of EM and MVR methods shows that the overall increase in efficiency is about 25–45% for maximum inter-story drift ratios,... 

In this study, a frequency domain model updating method is presented using power spectral density (PSD) data. It uses the sensitivity of PSD function with respect to the unknown structural parameters through a decomposed form of transfer function. The stiffness parameters are captured with high accuracy through solving the sensitivity equations utilizing the least square approach. Using numerically noise polluted data, the model updating results of a truss model prove robustness of the method against measurement and mass modelling errors. Results prove the capabilities of the method for parameter estimation using highly noise polluted data of low ranges of excitation frequency. Copyright ©... 

This paper introduces an efficient stochastic method to produce fully nonstationary records having multiple peaks in power spectrum. The zero-crossing characteristics of the acceleration, velocity, and displacement time histories of the output signal are used to estimate the model parameters. This procedure is utilized to resimulate 252 non-pulse-like, horizontal near-field records with rupture distance of less than 10 km and strike–slip mechanism. The model parameters are regressed against moment magnitude, rupture distance, hypo-central depth, and shear wave velocity, enabling the scenario-based simulation of the records. The response spectra of the simulated records are compared with... 

This study aims to optimize, design, and predict the MTMDs performance in SDOF systems using spectral analysis, and then apply their results to MDOF structures. Given the importance of spectral analysis in the design of new engineering structures, achieving a method for designing TMDs based on this theory can be of great importance for structural designers. In this study, several convenient combinations of MTMDs in an SDOF system are first considered to minimize the maximum displacement. For calculating the frequency ratios of dampers, an innovative technique is adopted in which the values of different modal responses obtained from the spectral analysis are approached together. This... 

An integrated probabilistic framework is proposed with a set of probabilistic models that are compatible with the reliability methods used in resilience-based design (RBD). Previous seismic resilience estimation frameworks primarily have used conditional probabilities and total probability integration to compute the expected seismic resilience index while considering the effects of only a few types of uncertainty. However, a high level of uncertainty is associated with seismic resilience estimation. This study presents a probabilistic framework and models that can consider the effect of unlimited uncertainties when calculating the probability distribution of the seismic resilience index for... 

In this paper, the dynamic response of the anchored and unanchored flexible on-grade storage tanks under near-fault input ground motions has been investigated. For numerical analysis, an oil storage tank with its content has been modeled with the displacement-based elements using a general-purpose finite elements program. The fluid-structure interaction has been taken into account using the constraint equations. Non-linear behavior caused by the base uplift in unanchored tanks has been considered by implementing the gap elements between the tank base and the ground level. The results indicate that the non-linear behavior caused by the base uplift, leads to remarkable changes in most of the... 

The governing differential equation of the Duffing's oscillator with time varying coefficients is addressed. It is shown that the response of a flexible nonlinear plate can be simulated by such equation. Existence of the periodic behavior that is the most important regular solution is illustrated using Banach's fixed-point theorem  

In this paper, the time-varying auto regressive moving average (ARMA) process is used as a simple yet efficient method for simulating earthquake ground motions. This model is capable of reproducing the nonstationary amplitude as well as the frequency content of the earthquake ground accelerations. The moving time-window technique is used to estimate the time variation of the model parameters from the actual earthquake records. The method is applied to synthesize the near field earthquakes, Naghan 1977, Tabas 1978, and Manjil 1990 recorded on dense soils in Iran, as well as the Mexico City 1985 earthquake recorded on a site with soft soil. It is shown that the selected ARMA (2,1) model and... 

This paper presents a synthesis strategy for impact force localization and identification of framed structures in time-domain using a two-step wavelet-based fitness evaluation scheme in conjunction with genetic and water cycle algorithms. For this purpose, a straightforward approach is developed for sensitivity analysis of accelerations and spatial signal connecting the peak values. The proposed scheme is capable of using diverse scales of wavelet functions at considerably small sampling rates. A decimal genetic algorithm (GA) coding system and a recently developed water cycle algorithm (WCA) are improved to be used for impact localization and identification, respectively. The fitness...