Year:2007 | Volume:41 | Issue:1 (103)|Papers Count:15

Ritz method is one of the techniques for reduction of the degrees of freedom. Efficiency of Ritz method depends on used vectors. The Ritz method uses load depended vectors in spite of modal method and for this reason it is expected to give better results than modal method. This is the advantage of Ritz method. It is worth mention that the mode shapes are independent of loading. The vectors that are calculated based on spatial distribution of loads are load dependent vectors. Humar et.al. have introduced a new type of vectors that are dependent not only on spatial distribution of loads but also on frequency of those This type of vectors is named frequency dependent vectors. In this paper a new style of vectors is proposed that can replace both. previous types. It is shown that these vectors are linearly independent. Various examples utilizing new Ritz vectors in two and three dimensions are analyzed. It is observed that this method is effective and efficient.

Short-term water demand modeling plays a key role in urban water resources planning and management. The importance of demand prediction is even greater in countries like Iran with frequent periods of drought. Short-term water demand estimation is useful for planning and management of water and wastewater facilities such as pump scheduling, control of  reservoirs and tanks volume, pressure management and water conservation programs.This helps the network managers to decrease vulnerability of the system and consumers and to increase network reliability. Exact prediction of short-term water demand which is a function of different complex parameters is difficult, time consuming and even impossible. In this research Artificial Neural Networks method (ANN) with back propagation algorithm is used to develop a model for daily water demand prediction of the city of Tehran (center of Iran) using climate parameters and previous daily water consumption records.Several structures were considered with one and two hidden layers and 0- 50 neurons. Also different linear and nonlinear functions were tested for the layers and finally nonlinear function was chosen for the hidden layers and linear function for the output layer.Furthermore, each year was divided into two parts and different models were constructed for hot and cold months. About four years data for Tehran daily water consumption was available. The model was calibrated by daily data for two years period. At the learning stage, in order to establish the optimal structure of the ANN model, the case of two hidden layers and seven neurons produced the best results and therefore, it was applied for water demand prediction in this city. Results indicate that ANN models can be used to predict Tehran short-term daily water demand, properly. Model evaluation showed that the correlation coefficients for demand prediction are more than 80% for both learning and testing data and the average of error is only 2%.Comparison of the results from ANN and Fuzzy models showed that the ANN outputs are more accurate. Furthermore, a simple formula was proposed to evaluate daily water demand of Tehran using results of a one layer one neuron ANN model with just two input parameters of the last day temperature and water consumption. The results showed good correlation with the measured values with mean error of less than 3%. It can be concluded that a useful model and a simple formula have been produced as the outcomes of this research which can help Tehran water company Decision makers for better operating of the system.

Roundabout is one of the most effective intersection control methods in the world. Although, they have often been used in Iran, but, the methods which are proposed to analyze roundabouts are very old and new regulations are not implemented for analyzing modern roundabouts. There are strong needs to apply new modern analyzing methods for studying roundabouts in Iran. Also, these methods should be compared with other methods for controlling intersections. The results from previous studies show that roundabouts perform better than the intersection with two-way stop and all-way stop control in various cases. The most important aim of this research is to compare the capacity and delay of roundabout with signalized intersection at the same conditions. In this paper, the methods which are applied in the developed countries for calculating the capacity and delay of roundabout are considered and the most effective and suitable one is chosen for using in Iran. The method of Australia was selected and proposed for analyzing roundabouts. For analyzing the capacity and the delay of signalized intersection the HiCAP software was used. This software works based on HCM2000 theoretical model. Two signalized intersection of Isfahan city were selected for the case study. The roundabout plan was used in the same situations with the same space and traffic data. The diagram of entrance delay and capacity of roundabout and signalized intersection was obtained and analyzed. One of the main results of this analysis is that a two-lane roundabout in same space intersection with inscribed circle diameter of 55 to 60 meter can pass about 3400 vehicles per hour with lower delay comparing to intersection. Another result is preference of roundabouts in low and medium volumes comparing to intersections. In such volumes roundabouts have very low delays comparing to intersections. As an important point, this research shows capability of the selected method for analyzing roundabout and represents formula calibration with regard to Iran conditions.

Panel zone is one of the most important elements for transferring the lateral load to other elements in Steel Moment Resistant Frames. To some extent, this element through its suitable ductile behavior with beams, that. themselves have been known as ductile elements, can increase the overall ductility of SMRF. The suitable design procedure for this element and details, can highly affect the performance of SMRF. Present research, specially on panel zone with unequal beam depth on two sides of panel zone and their effect on panel zone when monotonic load acting on SMRF is limited. Therefore, main aim of this paper is considering ductility of panel zone individually with unequal beams depth on two sides.The research method is based on verifying the analytical model, built in ANSYS Finite Element Software, with experimental model in laboratory test. This verification permits us to make different models with variety of geometric parameters of Panel Zone (i.e. depth of beams and thickness of column flange).Then the partial ductility ratio that is driven from backbone curve of cyclic behavior of panel zone used for comparing to presence standard rehabilitation code (fema 274).The obtained results from this research in all of geometric cases will not demonstrate constant ductility ratio as stated in standard rehabilitation code (fema274). Current partial ductility ratio in standard rehabilitation code (fema274) will be overestimated. When the depth of one of the two beams is shallower than the other, the partial ductility ratio of panel zone will decrease .In case of exterior columns (which are connected to only one beam) this ratio will be minimum and in a case of interior column with equal or approximately equal beams depth this ratio will be maximum.

In this research, using the Modified Compression Field Theory (MCFT), a new model is proposed to predict the behavior of reinforced concrete coupling beams. The model is able to consider the effects of shear and axial forces and bending moment, simultaneously. The proposed model includes a non Hnear shear spring, an axial spring and some nonlinear springs for considering bending deformations. In the experimental part of the research, six specimens with different reinforcing layouts were manufactured and tested. In order to consider the constraining effect of slab diaphragms, three specimens were constrained, axially. The results of the proposed model were compared with the test results reported by other researchers. Good agreement was obtained between the test results and calculated values. The test results of the axially constrained specimens show that axial rigidity may change the behavior of coupling beams, considerably.

In this paper the effects of uncertainties in the estimation of seismic hazard parameters is considered. These uncertainties are the result of the intricacy of the matter, restriction in identifying the interfering factors and lack of ability in determining the effective elements. One of the methods in estimating the seismic hazard potential is probabilistic method. In this method with the hypothesis of an appropriate probable distribution for the site and distance; where the earthquake happens, from the considered site and by considering a probable time base distribution, we can determine the probability of various levels of a acceleration (or other seismic parameters).in present time," the most appropriate method for determining the seismic parameters is a method named maximum likelihood. Although the basic methodologies used in seismic hazard analysis are well established, but the complex process of earthquake occurrence in a region and uncertainty in hazard modeling based on probabilistic method have some problems such as Simplification in modeling (without theoretical and experimental evidence) and Qualification in data(data with different level of noise). In this article is tried to pay the most attention to the problems and uncertainties of this method.

Population growth, land-use development, and car ownership increasing in -cities would enhance trip demand and volume of passing vehicles in urban streets dramatically. In case of traffic congestion, travel time in urban transportation network is one of the major problems of mega cities. It is noteworthy that an important portion of travel time is caused by control delay at signalized intersections, so study of control strategies and methods is necessary. Furthermore, intelligent control methods would increase variety and ability which are result of -investing on the manner of signalized intersection control.Using fuzzy logic as a means of control in engineering problems has a successful history. This approach of control has proved its efficiency in practical problems. Fuzzy logic, similarly, is used in transportation engineering problems. In this study, an appropriate environment for evaluation of different control algorithm of signalized intersections is provided. In addition, a new method based on fuzzy control is proposed and evaluated. Also, various tests in this simulation environment are applied for different volumes and geometric conditions. In fact, applying this algorithm can improve performance indices, specially, in comparison with fixed and traditional vehicle actuated methods. On the whole, using two contemporary fuzzy variables and new method for determination of membership function are remarkable differences between this study and formers.

In this paper a new approach to formulation of active control of structures based on energy concepts and use of Linear Quadratic Regulator (LQR) has been proposed. The suggested method eliminates the trial and error procedure in finding appropriate gain matrices in active control of structures. In this method the gain matrix is obtained by considering the energy of the structure and it remains constant for all types of earthquake input.To show the efficiency of the proposed method, a three-story building with two active tendons in the first and third floors is considered. The proposed gain selection and other techniques reported in the literature for LQR controllers have been used to compare the response of the structure for three accelerograms. A comparison of the displacements and control forces shows that although the maximum displacement in the proposed method is negligibly more than classical LQR methods, but the control forces are considerably less than the classical methods. Comparison of the results for an earthquake with various levels of scaling also shows that the proposed method is not sensitive to the intensity of input earthquake.

The SIMP approach is one of the most frequently used methods for topology optimization of structures. In this method, the relative density is expressed as a function of coordinates and varies from 0 to 1 within the design domain. Relative densities of 0 and 1 are associated to the existence and nonexistence of the material, respectively. The finite element approach is usually utilized to analyze the problem while considering a constant relative density within each element. As a result, relative densities of the elements are assumed as the design variables. A common deficiency of such an approach is the introduction of the so-called checkerboard pattern, which is an indication of numerical instability. In this paper, a new algorithm is proposed to overcome this source of instability which is based on the concept of stress and strain smoothing. Benchmarks and practical problems are simulated and discussed in order to verify the proposed approach and to assess its performance.

Today connections are playing an important role in the steel frames subjected to lateral seismic loading. The steel extended end-plate moment connection can play an important role in the steel frame when subjected to seismic loadings. In the past, this type of connection has been under investigation mainly when it was subjected to monotonic loading. After major recent earthquakes and failure of number of traditionally practiced moment connections in US, it seems that the extended end-plate moment connections can be qualified as a suitable semi rigid type connection to be used in the heavy steel frames.In this article, the seismic behavior of the extended moment connection is investigated. Using the nonlinear finite element method of analysis and with the help of yield line analysis, the behavior of the connection, with the emphasis on the column depth and end-plate thickness effecting on the panel zone as well as the connection as a whole, is obtained and then the results are compared with those obtained from tests by University College of Engineering, University of Tehran 5 other researchers. Plastic moment versus plastic rotation hysteresis, stress contours of the pertinent part of the connections and displacements are part of the results of this study. The difficulties arising in modeling and analysis technique, exists in such connection, is also discussed.

At the moment, Moshanir loading code which has been provided by Tavanir Company in 1998 is used for loading transmission line towers. Also ASCE52 are applied for designing these structures. In the above Moshanir loading code, loading parameters such as, maximum yearly ice thickness, maximum monthly ice thickness, maximum yearly wind speed and maximum monthly wind speed have been considered as certain values and partial safety factors are determined without attention to uncertainty in these random variables.In the present paper, load and resistance parameters that are involved in designing transmission towers, have been considered randomly, and based of this assumption reliability indices have been calculated for 230 KV towers members in two limit states function (Compression (Buckling) and Tension) for four selected city (Bandare Abbas, Yazd, Tehran and Shahre Kord) of Iran.At the next step, by using attained results, Target Reliability Indices, have been calculated in the above limit states, and after that load and resistance factors have been calibrated so that reliability indices for new designed members be as near as possible to selected target reliability index, therefore this way would cause uniform safety for all members.Finally, the results show that by using new load and resistance factors designers can make uniform safety for members. Also by this theory the weight of towers would be considerably decreased and therefore, towers can be designed economically and more realistic.

This paper discusses the possibility of application of Performance-Based Design (PBD) procedure in analysis and design of segmental lining of funnels. Interaction of lining with surrounding media, nonlinear behavior of media, as well as lining connections and influence of construction stages in the modeling of the system make this analysis too complicated. Therefore a simplified nonlinear approach to evaluate the interaction of lining and media may be useful to be applied. On the other hand there are similarities in concepts of convergence confinement method with capacity-spectrum method in PBD. The ground convergence response to the excavation will provide a demand on the lining and can be compared with the lining capacity to reach the - performance point. Using this concept, the PBD of segmental lining of tunnels is suggested to consider the nonlinear behavior of medium and lining connectionless. However, the non-uniform pressure around the lining needs some special considerations which have also been proposed. The results of the estimated deformations and lining internal forces are compared with numerical solution, using some examples. Good agreement of results shows the accuracy of the proposed method.

The interaction of fluid-shell surface of tanks built on roof of buildings and the resulting damage during an earthquake is of great importance. The existence of containers on buildings in large cities with high earthquake risk has caused many critical problems during past earthquakes. In addition to financial losses, it might induce uncontrolled fire, water cut and local or global failure of the structure. Moreover, the influence of this interaction on structure dynamic behavior can cause structural failures. Therefore, it is important to become assured of the behavior of structures with such tanks during an earthquake. The seismic response of a structure depends on its dynamic characteristics, including its frequency, mode shapes and damping effect. The first step in analyzing the structural response to an earthquake is the calculation of frequencies and trembling periods. Dynamic characteristics of a structure are highly influenced by presence of fluid in the vicinity of the structure. In this study, the dynamic interaction of water containers built on roof of structures, is investigated during an earthquake by means of nonlinear software based on Finite Element Method. In this paper, the compound system of structure, tank and water has been examined under seismic excitements simultaneously. The analytical method used is the Finite Element Method, and calculations have been -done with the aid of ANSYS software. The tank shell and its water have been modeled as a composite system and the interaction of container and water have been examined. This seismic control system with its limited potential capability as a tuned liquid damper (TLD) has been employed and investigated for 5 -story building structure, subjected to two various earthquakes. The significant influence of earthquake frequencies and type of stations used for seismic accelerometers on structural trembling and effect of such tanks on structures are among the main conclusions drawn from this study. The results gained from the present study can be helpful in investigating the tank's support conditions and its installation. It has been found that, in structures with few stores (or lower period) the importance of accelerometer type is more. Therefore, for low-story buildings, definite statement about structural seismic behaviors is quite difficult.Conversely, for tall buildings such statement can be done with more certainty. Based on the numerical results obtained in this paper, frequency content and other earthquake characteristics highly affect the role of water tanks on the seismic performance of lower rise buildings.