Sharif Digital Repository

In this paper, considering horizontal components of seismic excitation, an algorithm for the nonlinear multi-component analysis of building structures by the Endurance Time (ET) method is proposed, and results of the ET method for various steel moment frames with one to seven stories are verified by comparing with the results from Nonlinear Time History Analysis with use of two different sets of ground motions. In addition, several parameters such as eccentricities and irregularities in structure, rotational and lateral stiffness, effect of hysteresis type and ductility have been considered for sensitivity analysis on results, obtained by ET method. Results show that on the basis of... 

This paper deals with the problems of attitude determination, parameter identification and reference sensor calibration simultaneously. An LEO satellite's attitude, inertia tensor as well as calibration parameters of Three-Axis-Magnetometer (TAM) including scale factors, misalignments and biases along three body axes are estimated during a maneuver designed to satisfy the condition of persistency of excitation. The advanced nonlinear estimation algorithm of Unscented Kalman Filter (UKF) is a good choice for nonlinear estimation problem of attitude determination, but its computational cost is considerably larger than the widespread low accurate Extended Kalman Filter. Reduced Sigma Point... 

Based on special properties of metal dampers such as high energy dissipation, stable hysteric cycles, simple application, low cost, insensitivity to changes of temperature and the ability to substitute after the occurrence of earthquakes, they are being used for structural control. One of these metal dampers which has been of special interest is the tapered steel slit damper (TSS). When shear forces are applied, this damper yields and enters the plastic zone. The TSS damper is made of pieces of standard wide flanges where slits have been extracted from their web. These dampers are connected to the top of the chevron braces and under the middle of the beams. In the endurance time (ET) method... 

This paper deals with attitude determination, parameter identification and reference sensor calibration simultaneously. A LEO satellite's attitude, inertia tensor as well as calibration of Three-Axis-Magnetometer (TAM) are estimated during a maneuver designed to satisfy persistency of excitation condition. For this purpose, kinematic and kinetic state equations of spacecraft motion are augmented for the determination of inertia tensor and TAM calibration parameters including scale factors, misalignments and biases along three body axes. Attitude determination is a nonlinear estimation problem. Unscented Kalman Filter (UKF) as an advanced nonlinear estimation algorithm with good performance... 

Micro-electro-mechanical systems (MEMS) such as sensors and actuators are rapidly gaining popularity in a variety of industrial applications. Usually these systems are constructed by a cantilever beam or plate along with a fixed substrate. The movable beam or plate deflects due to applied voltage between the plates. Pull-in voltage and contact time are the most important characteristic of these systems. Allowing the substrate to be movable in vertical direction pull-in voltage in comparison with the fixed substrate is expected to be much smaller. In this paper the pull-in voltage and the point at which pull-in takes place for a fully clamped microplate is evaluated. The nonlinear... 

In the analysis of micro structures, due to proximity of the elements Van der Waals forces plays an important role on the dynamics of the structure. In the modeling process a similar approach should be considered for the capillary effect caused by the moisture in the environment. Microplates and microbeams are used widely in the design and manufacturing of sensors and actuators. These structures are usually made of a cantilever beam or plate along with a fixed substrate. The cantilever beam usually deflects due to applied voltage. By increasing the voltage the pull-in phenomenon takes place. It is believed that the short contact time is one the important characteristic of any micro switches.... 

A third-order asymptotic analysis is conducted to study the three-dimensional resonant interaction between a monochromatic progressive surface wave and two oblique interfacial waves in an open, lightly viscous, two-layer fluid of intermediate depth. By solving the evolution equations of the waves, the short- and long-term behaviors of the interfacial waves are studied. The analysis provides a correction to the second-order theory. The results indicate that the third-order analysis predicts a much lower limit on the growth of the interfacial waves than the second-order theory. Furthermore, in the long term, viscous effects cause the interfacial wave amplitudes to approach a constant value.... 

The equilibrium equations of the first-order nonlinear von Karman theory for FG circular plates under asymmetric transverse loading and heat conduction through the plate thickness are reformulated into those describing the interior and edge-zone problems of the plate. A two parameter perturbation technique, in conjunction with Fourier series method is used to obtain analytical solutions for nonlinear behavior of functionally graded circular plates with various clamped and simply-supported boundary conditions. The material properties are graded through the plate thickness according to a power-law distribution of the volume fraction of the constituents. The results are verified with known... 

In this paper a continuous-time state-space aerodynamic model is developed based on the boundary element method. Boundary integral equations governing the unsteady potential flow around lifting bodies are presented and modified for thin wing configurations. Next, the BEM discretized problem of unsteady flow around flat wing equivalent to the original geometry is recast into the standard form of a continuous-time state-space model considering some auxiliary assumptions. The system inputs are time derivative of the instantaneous effective angle of attack and thickness/camber correction terms while the outputs are unsteady aerodynamic coefficients. To validate the model, its predictions for... 

Endurance Time (ET) method is a time history based method for seismic evaluation of structures using intensifying dynamic excitation as the loading function. In this paper, application of this method in the analysis of steel tanks has been investigated. A methodology for practical application of ET method in seismic assessment of storage tanks has been presented. This methodology has been applied in three-dimensional nonlinear analysis of a particular anchored steel tank using Finite Element method, and results are compared with conventional codified design procedures. Results of the analyses indicate reasonable accuracy of the proposed method in estimation of seismic responses of steel... 

There are two different ways of using SMA wires as actuators for shape control of flexible structures; which can be either embedded within the composite laminate or externally attached to the structure. Since the actuator can be placed at different offset distances from the beam, external actuators produce more bending moment and, consequently, considerable shape changes with the same magnitude of the actuation force comparing to the embedded type. Such a configuration also provides fast convection which is very important in shape control applications that require a high-frequency response of SMA actuators. Although combination and modeling of externally-attached SMA actuator wires and... 

Aboveground steel tanks are widely utilized in residential and industrial areas, and assurance of their seismic safety is a very important engineering consideration. In this paper, nonlinear response of these tanks using a new dynamic pushover procedure called Endurance Time (ET) method along with conventional nonlinear response history (RHA) is studied. The comparison between the results of RHA and ET method shows reasonable consistency. Based on the level of accuracy observed in this research, it is concluded that ET method can effectively be used in predicting seismic performance of anchored tanks. By considerably reducing the number of required response history analyses for estimating... 

A new method, based on the concepts of matrix analysis as well as the learning capabilities of neural networks, for the analysis of nonlinear trusses under dynamic loading is presented. The method can be applied to static trusses too. While there have been attempts in the past to use neural networks to identify and model different structures based on data measured on structural response directly, the main feature and advantage of this new method is in its capability to model a nonlinear truss by assembling the data collected on the response of its members. The basics of the method are: (1) for each truss member, a neural network is trained to learn and simulate its loadresponse behavior, (2)... 

In this paper, application of a new dynamic procedure called Endurance Time (ET) method in seismic analysis of steel frames is explained. In this method, structures are subjected to gradually intensifying ground shaking and their performance is assessed based on their response considering relevant design criteria at each intensity level. By considerably reducing the number of time history analyses for assessment of structural response at different intensities, this procedure tends to pave a way for practical performance based design of structures. The accuracy of ET method in predicting the response of structures in linear and nonlinear analysis is investigated by considering a set of steel... 

The endurance time (ET) method is a time history based dynamic analysis in which structures are subjected to gradually intensifying excitations and their performances are judged based on their responses at various excitation levels. Using this method, the computational effort required for estimating probable seismic demand parameters can be reduced by an order of magnitude. Calculation of the maximum displacement or target displacement is a basic requirement for estimating performance based on structural design. The purpose of this paper is to compare the results of the nonlinear ET method with the nonlinear static pushover (NSP) method of FEMA 356 by evaluating performances and target... 

In this study, simple analytical expressions are presented for large amplitude free vibration and post-buckling analysis of functionally graded beams rest on nonlinear elastic foundation subjected to axial force. Euler-Bernoulli assumptions together with Von Karman's strain-displacement relation are employed to derive the governing partial differential equation of motion. Furthermore, the elastic foundation contains shearing layer and cubic nonlinearity. He's variational method is employed to obtain the approximate closed form solution of the nonlinear governing equation. Comparison between results of the present work and those available in literature shows the accuracy of this method. Some... 

In Endurance Time (ET) method gradually intensifying acceleration functions are created in a manner that the linear and nonlinear response spectra of them, while being proportional to average of real earthquakes spectra, intensifies in a uniform manner with time. These functions are used as input functions for nonlinear time history analysis of structures and performance of structures is assessed based on the maximum time duration that they can meet the specified performance objectives. In this paper, application of the ET method in nonlinear seismic analysis of structures has been investigated. Numerical procedures and optimization techniques that are used for the production of acceleration... 

This study is about the performance assessment of steel moment resisting frame structures under nearfield strong ground motions. A number of 3 and 9-story, 3-D structural models being designed using the strength method, are considered. A set of 7 near-field earthquake records, scaled according to ASCE- 7(05), are considered for nonlinear dynamic time history analyses using OpenSees program. Park and Ang damage index is considered for quantitative measurement of the performance of structural models. Maximum values of inter-story drifts along with the local and global damage indices are determined to be used in the performance assessment process. Considering the average results of different... 

In order to estimate the seismic demands at the performance level, the inelastic behavior of concrete structures should be considered. Incremental dynamic analysis (IDA) based on a nonlinear response time history analysis (NL-RHA) is considered to be the most accurate method in seismic demand calculations. However, modal incremental dynamic analysis (MIDA), based on the equivalent single-degree-of-freedom (SDF) oscillator, is also often used in studying structural engineering performances. As the MIDA method has usually not been applied to reinforced concrete (RC) structures, in this study an attempt is made to investigate the performances of RC frames and to compare the results obtained... 

In this paper, simple analytical expression is presented for large amplitude thermomechanical free vibration analysis of asymmetrically laminated composite beams. Euler-Bernoulli assumptions together with Von Karman's strain-displacement relation are employed to derive the nonlinear governing partial differential equation (PDE) of motion. He's variational method is employed to obtain a simple and efficient approximate closed form solution of the nonlinear governing equation. Comparison between results of the present work and those available in literature shows the accuracy of presented technique. Some new results for the nonlinear natural frequencies of the laminated beams such as the effect...