Showing 5 results for F. Nateghi
F. Nateghi-A and N.a. Hosseinzadeh,
Volume 20, Issue 2 (4-2001)
Abstract
This paper presents a methodology for the assessment of ductility and strength capacities in low-rise buildings. This method utilizes the characteristics of force-displacement for the lowest story level or considers the weakest story in any given low-rise building for its primary analysis. Calculations are based on two levels of earthquake motions, namely strong earthquakes (PGA=0.3 g), and very strong earthquakes (PGA=0.45). Failure mechanism for the structure is established based on three criteria which are: a) bending mode, b) shear mode, and c) shear-bending mode. Evaluation is then performed using a five step procedure starting with a: modeling the building, b) developing the non-linear properties of the model, c) strength calculations, d) ductility calculations, and finally, e) assessing the safety of the building under consideration. All these evaluations are performed based on a matrix format, which simplifies the whole procedure. Developed equations and step-by-step procedure are presented and described in this paper Satisfactory results are obtained from the use of the method developed.
Keywords: Strength, Ductility, Failure mechanism, Low-Rise R. C. Buildings
N.a. Hosseinzadeh, F. Nateghi-Alahi and F. Behnamfar,
Volume 22, Issue 2 (1-2004)
Abstract
The objective of this study is to design a robust direct model reference adaptive controller (DMRAC) for a nonlinear cardiovascular model over a range of plant parameters representing a variety of physical conditions. The direct adaptive controllers used in thisd study require the plant to be almost strictly positive real (ASPR) that is, for a plant to be controlled there must exist a feedback gain such that the resulting closed loop system is strictly positive real. We designed a new compensator so that the system composed of the cardiovascular plant and the compensator satisfy the ASPR condition.
Numerous studies in the past have considered a small range of gain variations of the cardiovascular system. In most cases, the controller was designed based on variations in either time delay or plant gains. Many of these workers treated the cardiovascular system as a single-input single output (SISo) plant in which the control output was Mean Arterial Pressure (MAO). We treated the cardiovascular system as a multi-input multi-output (MIMO) plant in which both the MAP and Cardiac Output (CO) are simultaneously controlled.
In this study, a new linear model is presented that provides a better approximation thanthe one the original linear model does. By doing so and utilizing the DMRAC algorithm, we could satisfy the stability conditions for the nonlinear model while satisfactory responses obtained under every possible condition for the cardiovascular nonlinear model.
A. F. Nateghi, A. Vasseghi, and V. L. Shahsavar,
Volume 25, Issue 1 (7-2006)
Abstract
Bridges are potentially one of the most seismically vulnerable structures in the highway system during earthquake
events. It is known that the seismic performance of transportation systems plays a key role in the post-earthquake emergency management. Hence, it is necessary to evaluate both physical and functional aspects of bridge structures. The physical aspects of the seismic performance of bridges are evaluated by seismic fragility functions or damage probability matrices of transportation facilities. The fragility curves represent the probability of structural damage due to various levels of ground shaking. The fragility curve describes a relationship between a ground motion and a level of damage.
In this paper, the fragility curves (F.C) are developed. The vulnerability of a railway prestreed concrete bridge is assessed using fragility curves derived from dynamic nonlinear finite element analysis. A software package is developed in MATLAB to study the results obtained. Modeling of the bridge using 3D nonlinear models and modeling of abutments, bearings, effect of falling of girder on its bearings, and nonlinear interaction of soil-structure are some of the advantages of this research compared to previous ones. Reliability curves developed in this study are unique in their own kind. The proposed method as well as the results are presented in the form of vulnerability and structural reliability relations based on two damage functions.
M. Motamedi, F. Nateghi-Elahi, M. Ziaeefar, and M. Karimi,
Volume 25, Issue 1 (7-2006)
Abstract
Energy absorber systems like metallic dampers for controlling the structural vibrations due to earthquake have witnessed considerable development in the past few decades. Also there are some studies on the energy absorption of thin-walled tubes due to impact load. Thin-walled tubes have a large deformation capacity and are suitable energy absorbers in the structure during an earthquake provided that a suitable inelastic buckling mode obtains. This paper deals with the study of energy dissipation in accordion thin-walled tubes and their behavior due to axial cyclic loads. For this purpose, experimental and analytical studies have been performed. Experimental studies were conducted on specimens available in the market by dynamic tension and compression actuator. Analytical studies are based on finite element methods and nonlinear inelastic dynamic analysis. These studies are focused on the effects of mechanical and geometrical parameters of these tubes like shape, thickness, diameter, length and material type of tube on the amount of energy dissipation and axial stiffness. The results show that accordion thin-walled tubes exhibit satisfactory energy absorption behavior and that proper selection of the parameters yields the optimum design of this metallic damper.
F. Nateghi, and A. S. Ghods,
Volume 25, Issue 2 (1-2007)
Abstract
An effective approach for strengthening masonry buildings is to apply shotcrete reinforced with mesh on the surface of the wall. It is not possible to assess the behaviour of coated walls solely using analytical approaches based on simple equations of theory of elasticity without the use of numerical methods. Unreinforcced masonry wall is modelled in this study using the finite element software “ANSYS” to assess the behavior of walls strengthened with reinforced jacket. The accuracy of the model is ensured by calibrating the model against results obtained from laboratory tests. Then the calibrated model is
generilized to model the strengthed wall and, finally, the analytical results obtained from masonry walls and strengthed walls are compared and evaluated.
