mohsen mehrjoo

The spatial structure of cities depends on the different and mutual relationships of all forces and factors in the city. These factors include market forces, activities, urban infrastructures and various services, which always have a complex and reciprocal relationship. In today's world, one of the basic challenges in cities is to create a balanced spatial structure that plays an important role in sustainable development. Development and creating an efficient multi-core spatial structure in metropolises like Tehran requires a balanced spatial distribution of population and activity cores. The factors of population and activity are the main elements of the spatial structure that have a direct and main effect on the creation or non-creation of desirable urban cores. The Aim of this research is to evaluate and analyze the spatial structure of Tehran metropolis from the perspective of population and activity indicators in order to determine the state of balance or imbalance of the spatial structure as well as the state of urban functional cores.

The research method is descriptive-analytical and based on spatial statistics calculations. The information and data used are collected from official and library sources and include information related to urban activities in the field of employment. The activities are listed in seven (7) main industrial, commercial, administrative, educational and recreational, cultural and medical categories and are considered as functional cores. In order to analyze the distribution of functional cores of activities and the population of Tehran and the spatial patterns of activities, the methods of mean center, standard deviation ellipse, nearest neighborhood mean and geographical weighted regression (GWR) have been used.

The results of this research regarding the distribution of the spatial structure of the city of Tehran based on the indicators of activity and population and the relationship between these two indicate that the activity nuclei are in the form of a single nucleus and in some components in the form of multiple cores and the pattern of distribution of functional cores in the city has a cluster pattern.

Based on the results of geographic regression, there is an effective relationship between functional cores and population distribution in the city of Tehran, and this situation causes and aggravates traffic problems and congestion in the metropolis of Tehran. In this regard, it is necessary to strengthen the functional role of areas in which the relationship between these two indicators is weak (Region's 15-22-5-18) in order to reduce the burden of traffic and congestion in other saturated areas of the city (Region's 3-6-7-11-12) And also be strengthened the multi-core spatial structure of the city.

In this paper, a crack detection method is presented to detect Euler-Bernoulli beams containing arbitrary number of transverse cracks. The proposed method uses the time domain signal of the free vibration response to provide the position and depth of cracking of the Euler-Bernoulli beam that is modeled with a modified stiffness using the Spring model, with high accuracy and precision. The time history responses used in this paper are nodal computational accelerations at certain points of the beam exposed to impact load. The acceleration of the nodes is calculated with the Newmark beta method at the edge of the elastic beam`s superelements. Initially, using the computational time history of the damaged beam and the analytical model of the Euler-Bernoulli beam, the objective function of the failure detection problem, to be optimized by particle swarm algorithm, is defined and, intensity and location of transverse cracks are calculated by solving the optimization problem in Matlab environment. In order to determine the accuracy of the proposed method, three beam samples with different cracks and loadings are considered. In the first sample, the crack supposed to be in the superelements of beam and the beam considered to be with four elements as superelements. The second one has ten elements and same loading as previous. The third one has twenty elements and the loading is on the second element. All of the loadings are impulse loads. The comparison of the results of a four elements beam with the primitive conditions shows that accuracy of the deducted results were exactly matched. For the ten element beam, the results were satisfying but in the twenty element beam with asymmetric loading, obtained results indicate imprecise match.</div>

To determine the accuracy of the developed model in real environmental conditions, different percentages of noise were added to the data of all three samples. These noise addition to data, contain 1, 3, 5 Percentages of noise.  The results show that the model presented in the presence of noise also provides accurate results and the model is not sensitive to the presence of noise in the data applied to three samples. Considering different number of elements in each sample, no convergence was observed, Also the results were not sensitive to the location of impact load applied on the samples.</div>

The results of this study indicated that asymmetric cracking and loading variation are very effective in predicting beam failure. The results also indicate that variable reduction is very effective on the accuracy of results.</div>

Having more cracks and therefore more elements to analyze will yield to less accurate results. To lessen these inaccuracies, it can be practical to achieve better results by assuming the location of crack is constant in the element length if the depth of crack be the matter of importance.</div>

The number of iterations that have been executed, indicate that the pace of convergences in the developed process is less than when PSO deployed solely. This speed rate for obtaining results makes the developed method practical for solving crack detection problems in structures.</div>
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Decreasing the losses caused by earthquakes in order to increase seismic resistance, is mainly focused on construction methods of buildings. But coping with earthquake is beyond the technical principles for earthquakeresistant buildings and in fact the entire city should be planned to reduce vulnerability to the earthquakes. This study seeks to find the common aspects of the renovation, urban planning and disaster management. Access to this method is the most important goal of this study. The research method used in this study is case study done through analysis and induction. At first, it studied the old urban texture and the theory of urban planning and strategic planning and then the gathered data from urban organizations were analyzed using the SWOT technique. Burnout of urban contexts and renovation in urban areas has provided a proper opportunity to perform urban development plans which can be considered simultaneously with the disaster management measures and reducing vulnerability. Suggestions for organizing and urban development on regional scale were finally recommended.