Journal of Garmsar Science and Engineering

Abstract The current research examines the resistance of the bolted tree connection against progressive Collapse. This type of steel connection is used due to many benefits including ease and speed in installation, better quality of beam-to-column connection welding due to implementation in the factory and lowering the high percentage of welding errors. The research aimed to investigate the strength of the tree column connections under progressive collapse using finite element method with the scenario of column removal and deformation control, which has been simulated in ABAQUS. At first, the verification was done using the results of an experimental research. The results of the research show that the use of steel with higher yield stress in the column and the tree beam caused the plastic joint, In the place of reduction of the beam away from the weld, the connection of the tree beam to the column has occurred and the possibility of failure in the weld has been greatly reduced and it has provided a stable displacement with high plasticity during the removal of the column, which further improves the behavior in this type of connection. In general, by examining the results of the analyzes and comparing the behavior of the tree-column connection, it can be said that the use of the tree-column connection has provided a stable force-displacement curve with high ductility during the removal of the column.

Abstract Fractal geometry was first introduced in 1975 by Mr. Mandelbrot. Fractal shapes are used to model natural phenomena that cannot be expressed by Euclidean geometry, such as clouds, tree leaves, sea shores, etc. The characteristic of fractal shapes is that these shapes are self-similar, so that each part of these shapes is actually a small scale of the whole shape. Trees are a clear example of this feature, the stems and branches of trees and even leaves are actually a smaller scale than the tree itself. Today, the use of fractals in physics, chemistry, biology, economics, geology, image processing, computer graphics, antenna design, etc. is widespread. The use of fractal geometry in electromagnetic problems has become a new and interesting topic. The research and study for the use of these mathematical functions in scattering problems, array techniques, improvement of input impedance matching, size reduction and multiband antennas. Recently, it has been tried to use fractal geometry in the design of antennas. The use of fractals in the design of antennas has advantages that encourage designers to use them. In this article, some examples of fractal structure have been introduced and their application in antenna design has been reviewed.

Abstract One of significant features of the impact test that has been less used so far is determination of the natural frequency of the tested specimen. The purpose of this research is to measure experimentally the natural frequency of tested steel using drop weight tear test (DWTT). For this purpose, wavelet transformation was used for the first time (in research field of high pressure gas transportation pipes) to analysis the acceleration signal from impact test. The acceleration signals during fracture test of the API X65 steel specimens were captured by an accelerometer and analyzed then using the wavelet transformation. The DWT tests were performed according to the API 5L standard using three Chevron Notched specimens. The specimens were cut from a spirally welded steel pipe and machined then to standard dimensions. Next, the acceleration signal was denoised using the universal threshold method on the detail coefficients. After each impact test, the captured acceleration signal which was highly noisy was decomposed into low and high-frequency bands using discrete wavelet transform from which wavelet coefficients obtained. By applying continuous wavelet transformation (cwt) on the denoised acceleration signals, the natural frequencies of tested samples were found. The average natural frequency obtained from three specimens for API X65 steel was 2.598 kHz. Furthermore, the natural frequency time interval was obtained which was in the first millisecond of the experiment. The comparison of obtained results with available data showed the capability of WT for accurate measurement of the natural frequency in drop weight tear testing.

Abstract The current research was conducted with the aim of evaluating the impact of sidewalk architecture on the level of pedestrian satisfaction. This research is exploratory in terms of the nature and method of data collection and practical in terms of purpose. The research has been done by two methods: questionnaire and statistical analysis. Questionnaire method was done using SPSS software. The main method of data analysis is using descriptive and inferential statistics. Also, through correlation tests, Friedman, Chi-2 and t-tests, the residents' satisfaction with Tajrish Street's sidewalk construction has been evaluated in terms of physical, economic, social and environmental aspects. The results showed that Tajrish sidewalk users were satisfied with this sidewalk in physical, social, economic and environmental dimensions. From the point of view of pedestrians, the physical dimension has the highest priority in creating the satisfaction of pedestrians. Also, the appropriate width of the sidewalk from the sub-set of the physical dimension has had the greatest effect on the level of citizens' satisfaction with the sidewalk.

Abstract The Markowitz model, known as modern portfolio theory, operates based on the principles of diversification, risk, and return, aiming to reduce the overall risk of a portfolio while achieving higher returns. One of the main advantages of the Markowitz model is its ability to manage risk through the combination of different assets in the portfolio optimization problem. This model allows financial analysts and investors to create portfolios that not only meet their financial needs but also assist in optimizing financial performance using mathematical and statistical methods. This research examines and analyzes the Markowitz stock portfolio optimization model and reviews previous studies in this field. The aim of this research is to better understand the Markowitz model and its applications in optimizing investment portfolios, identifying and analyzing the strengths and weaknesses of this model, and comparing it with other models and approaches to stock portfolio optimization. The results of these examinations show that the Markowitz model, despite various limitations and challenges, remains one of the foundational and effective models for optimizing investment portfolios.