MODARES TECHNICAL AND ENGINEERING
Year:2009 | Volume:- | Issue:35 (SPECIAL ISSUE ON CIVIL ENGINEERING)|Papers Count:14

The aim of this paper is to present an applicable and practical model and to suggest an algorithm for shape optimization of concrete arch dams to enhance their seismic performance. In this research, dam body volume has been considered as the objective function and in order to increase the consistency with practical conditions, a great number of geometrical and behavioral constraints have been included in the mathematical model. Three loading conditions, i.e., gravity loading, dominant static loading and dynamic loading have been studied. In seismic loading, dynamic interaction of dam-foundation system and effect of the reservoir under longitudinal component of Operating Basis Earthquake spectrum have been considered. Capabilities of ANSYS Parametric Design Language (APDL) are applied for modeling the Dam-Foundation-Reservoir (DFR) system and sequential nonlinear approximation procedure is used for the optimization analysis. Each cycle of optimization problem have been solved by the SQP method using the DOT software package. This technique has been successfully applied to an existing arch dam in Iran. Results obtained from this example show that the modification and optimization of shape could make considerable reduction in the dam body volume and costs; furthermore, it has a quite important role in increasing the safety against dynamic design loads by improving the stress distribution in the dam body.

In this paper, first, the process of incremental-iterative methods for solving non-linear finite element equations having limit points is studied from a new point of view. Some of incremental-iterative parameters are introduced and based on these residual parameters, techniques for correcting the iterative part of the process are proposed. This will show that the correcting schemes of the residual parameters along with incremental length and displacement parameters yield the best method. Finally, numerical examples for evaluating the ability of the suggested techniques are considered.

In this paper multi -surface yield with kinematic hardening is considered. The model is a type of Von Mises yield surface criteria with associated flow rule. Prager's translation rule is implemented for movements of yield surfaces. Our algorithm is based on elastic prediction and plastic correction with kinematic hardening of each of the surfaces by use of the Prager's rule. Ability of the algorithm and model has been showed for uniaxial and multiaxialloadings in some numerical examples. The results show that the accuracy of the approach is increased with the increase of number of yield surfaces, while the accuracy of Mroz or Garud's rules is decreased with the increase of number of yield surfaces. Based on the proposed algorithm, acceptable results have been obtained under cyclic loading.

Interest in the ability to monitor a structure and detect damage at the earliest possible stage is pervasive throughout civil, mechanical, and aerospace engineering communities. Research in vibration-based damage identification has been rapidly expanding over the past few years. The basic idea behind this technology is that modal parameters (frequencies and mode shapes) are functions of the physical properties (mass and stiffness) of the structure. Therefore, changes in the physical properties will cause detectable changes in modal properties.The purpose of this research is to review some existing method and define a new method to predict location and severity of damage in structures using changes in modal characteristics. This new method is a combination of existing methods. Based on this method, a computer software is developed that can perform the damage detection process.

In Iran, a special kind of connection, named Khorjini connection, is common in steel structures. Despite their widespread use, the performance of these connections against dynamic loads is not satisfactory. Hence, in the recent decades various researches have been conducted in this area with the aim of understanding and enhancing the behavior of these connections. In this paper an improved version of this connection with peripheral angles has been introduced and compared with the state of the art in this area. Furthermore, it has been shown that the proposed connection, with a relatively simpler detail, could be acknowledged countrywide as an advantageous connection.

Urmia lake is located in the north-west of Iran. It was divided into two North and South basins in 1979 when an east-west dike type causeway began to be constructed almost in the middle of the Lake. An opening of about 1.25 km allows for water circulations between the North and South basins. High water salinity (more than 200 g/lit) singles out the Urmia lake from other similar water ecosystems. Fluctuation range for the salinity may reach 50 g/lit annually. Other researchers have already addressed the flow regime in the lake using 2D numerical models. This paper deals with a 3D simulation of flow in the lake as it seems that depth-dependent parameters are also important in the flow regime. The employed 3D model presents good correlation with limited field data available. The current study shows that the velocity and the direction of flow very significantly by water depth. However, stratification as that caused by variations in the water salinity and its density down the water depth has not been observed.

In this paper a comparison of ordinary braced frames behavior subjected to displacement control pushover analysis has been made. In our analysis, post-buckling behavior of bracing members has been considered. In this regard, for a specific geometry of buildings, different types of bracing system are designed and pushover analysis of frames is performed using SNAP-2DX software. Roof displacement versus base shear and plastic hinge locations of the frames has been compared. It is observed that frame lateral resistance highly degraded after bracing buckling. To prevent having plastic hinge in columns, it is suggested to design column besides bracing members and beams supports V and IN. V bracing members based on bracing member strengths.

In this study a new method using Artificial Neural Networks has been used to predict design parameters of grouting. In this method, a single layer perceptron, one of the most practical kinds of artificial networks, is used. For learning and test of network, data of Ardabil dam is used and by using mean - standard deviation and linear transfer methods, data has been normalized. Using assessment criteria, the optimum number of neurons for middle layers is chosen. Depth parameter, RQD, water pressure and lugeon for input parameters, and grouting duration, grouting pressure and cement usage for output parameters are applied into the network. Although this prediction is available for new holes in the same dam, it can be applied to other dams with different foundation properties.

Contamination of soil and water with total petroleum hydrocarbons (TPH) has caused many problems. One of the most effective measures for removal of contaminations from soil and water is bioremediation. The aim of this study is to evaluate the ability of mixed culture microorganisms in biodegradation of TPH which have existed in contaminated soils around the storage tanks of Tehran refinery in liquid and slurry phases. Results have shown that inoculation of mixed culture microorganisms, which are isolated from the Tehran refinery's contaminated soils, have shown best Anthracene removal efficiency. It would contaminate with indigenous microorganisms metabolic activities and reduce their TPH biodegradation rate. Mixed culture microorganisms in sterilized slurry system are able to biodegrade only 21.34% of petroleum hydrocarbons during 81 days, whereas the slurry system which contains only indigenous microorganisms in the same period of time, has ability of reducing 67.8% of petroleum hydrocarbons. Addition of mixed culture microorganisms has resulted in reduction rate of biodegradation to be 61.89% in 81 days. In unstrill liquid system, inoculation of mixed culture microorganisms has caused removal of 12.23% of the petroleum hydrocarbons during 81 days, whereas in the same period of time, the liquid system which only contains indigenous microorganisms, has shown petroleum hydrocarbons biodegradation rate of 29.03%.

Shell foundations are structural elements which can be economical alternatives to flat foundations. Since few investigations have been done on these foundations, specific relations are not presented for determination of bearing capacity of these foundations. In this paper a comprehensive formulation for ultimate bearing capacity of conical shell foundation is presented based on experimental investigations and the Buckingham theory. Therefore, at first, by using the Buckingham theory the general shape of ultimate bearing capacity relationship is determined. Then constants are estimated via laboratory results. Finally, the proposed formulation was checked with other test results which show good agreement.

An experimental study on the variation of bed topography in 90 degree channel bends at Tarbiat Modares University was carried out. The main objective of this study was to compare the bed topography in different flow conditions. Experiments were conducted under live bed (1.24<U/Uc<1.33), clear-water (U/Uc<1) and near threshold conditions in straight channel inlet reach (l <U/Uc<1.1). Results show that the flow intensity (U/Uc where U and Uc are mean approach velocity and mean approach velocity at the threshold condition respectively) has a great influence on bed topography in the bend. It was observed that in clear-water conditions (U/Uc<1) two point bars are formed in the bend, first at the inner side wall at about 45 degree from the beginning of the bend and the second near the exits of the bend. Moreover one scour hole along the outer side wall near the exits of the bend was observed. In the live bed condition (1.24<U/Uc<1.33) two point bars were observed at positions similar to clear water with two scour holes at the front of the point bars. When (I <U/Uc<1.1) both of the two scour holes are much close together. Variation of bed topography shows that the slope of bed increases by increasing Froud number. The influence of Froud number and flow intensity on depth of scour was also investigated. A relation for prediction of lateral variations of bed topography along the bend was introduced.

Considering that many parameters are measured in the quality analysis of water, the water quality index has the highest degree of usage among the other general water quality adjustments, and it has been used for adjusting quality index of watershed of Latian dam. Determining the condition of water in Jajrood river and Latian dam as one of the most important drinking water resources of Tehran with its increasing population and special aspects, is of great importance. In this research, according to the results of measurements carried out by Tehran Water and Sewage Company and by the Research Center of Water & Energy, three methods of quality adjustment of Jajrood river and the water going out of Latian dam have been separately used. The results of these quality indices have been analyzed and compared with each other.According to the obtained results, the most suitable method for calculating the water quality index is the method introduced by the National Sanitation Federation Water Quality Index. Also, according to the results of this water - quality index, the water in the river is of average quality. The quality of water near some populated areas, such as Meygoon is low because of the contaminating bacteria and microbes, suspended particles in water, and the low level of clearness of water is not so good.