Civil Engineering Infrastructures Journal
Year:2011 | Volume:45 | Issue:3|Papers Count:13

Wastewater collection systems play key role in servicing the public and protecting the environment. Construction of these facilities is expensive and needs large investments. Therefore optimization of sewer network construction costs will have an essential effect on early implementation of these plans all over the country. On the other hand, reviewing the experiments of developed countries in the field of maintenance and operation of the sewer networks represents that reducing the maintenance and operation costs is necessary as well as optimizing the construction costs, so designing a sewer network with high reliability and proper performance which is able to transport wastewater without hydraulic overload should be considered. In this study a methodology is developed to optimize sanitary sewer systems with object of minimizing network construction and operation costs and considering system reliability as an optimization constraint by Genetic Algorithm method. For this reason a definition for wastewater collection system reliability has been provided and its applicability has been analyzed by some system performance indicators. The Efficiency of the proposed methodology has been assessed in a case study. It is also observed that with considering reliability and hydraulic performance indicators as optimization constraints, a more reliable collection system with less environmental impacts will be achieved by a reasonable increase in construction costs.

Pile group are vastly used in marine structures for several applications. Loadings exerted to these structures are divided into two main categories: lateral loading and vertical loading. All researchers agree to use vertical piles in the case of pure vertical loading where as the use of batter piles in the case of lateral loading is still in doubt. The behavior of batter piles in a pile group is somehow two-faced. Although batter piles reduce the lateral displacement of the pile group under lateral loading but they also cause stress concentration in batter pile and pile head. Thereby complete understanding of batter and vertical piles is of great importance. In our research, different pile group configurations are analyzed numerically that based on the finite difference method. Soil is modeled as a mohr-coulomb continuous medium obeying model and piles and pile head are assumed to be elastic concrete. To validate the simulation, results from numerical modeling are compared to those from available experimental data and analytical solution.

One of the effective parameters of the behavior of rockfill materials is particle breakage. As a result of particle breakage, both the stress–strain and deformability of materials change significantly. In this article, a novel approach for the two-dimensional numerical simulation of the phenomenon in rockfill (sharp-edge particles) has been developed using combined DEM and FEM. All particles are simulated by the discrete element method (DEM) as an assembly and after each step of DEM analysis, each particle is separately modeled by FEM to determine its possible breakage. If the particle fulfilled the proposed breakage criteria, the breakage path is assumed to be a straight line and is determined by a full finite element stress–strain analysis within that particle and two new particles are generated, replacing the original particle. These procedures are carried out on all particles in each time step of the DEM analysis. Novel approach for the numeric of breakage appears to produce reassuring physically consistent results that improve earlier made unnecessary simplistic assumptions about breakage. To evaluate the effect of particle breakage on rockfill's behavior, two test series with and without breakable particles have been simulated under a biaxial test with different confining pressures. Results indicate that particle breakage reduces the internal friction but increases the deformability of rockfill. Review of the v–p variation of the simulated samples shows that the specific volume has initially been reduced with the increase of mean pressures and then followed by an increase. Also, the increase of stress level reduces the growing length of the v–p path and it means that the dilation is reduced. Generally, any increase of confining stress decreases the internal friction angle of the assembly and the sample fail at higher values of axial stresses and promotes an increase in the deformability. The comparison between the simulations and the reported experimental data shows that the numerical simulation and experimental results are qualitatively in agreement. Overall the presented results show that the proposed model is capable with more accuracy to simulate the particle breakage in rockfill.

The present study examines the use of submerged vanes for reducing local scour at rectangular piers with circular nose. Experiments were carried out with piers aligned and skewed at 5o and 10o to the flow, and with submerged vanes at different arrangements. It was found that effectiveness of submerged vanes reduces by increasing the skew ness of the pier. Maximum reduction of scouring was 45.57, 39.76 and 27.78% for submerged vanes with height 2.5cm on the bed and skewed at 30o to the flow when was aligned, skewed at 5o and skewed at 10o to the flow, respectively.

Worldwide experience repeatedly shows that damages in different kind of slopes caused by earthquakes are highly dependent on site condition and epicentral distance. In this paper, a potentially sliding slope in Alborz region was selected as an example to investigate these two effects. In order to verify the analysis software, a hemicycle valley was first modeled and its amplification response to the Ricker wavelet was compared with the results of previous studies. The numerical model of the well-known Shafarood landslide located in the Reservoir of Shafarood dam was prepared and dynamic analysis of the model was performed. Eight far and near field acceleration time histories of different earthquakes in Iran was selected as input motion. Then, the average acceleration time history of the sliding block to each input excitation was calculated and the permanent Newmark displacement was evaluated using MATLAB software. The results demonstrate that the permanent displacement of the potentially sliding block in near field earthquakes is less than that for far field ones. Besides, it was concluded that the frequency content of the records has more influence on the Newmark displacement than the epicenter distance.

Short time interval rainfall data (e.g. hourly data) serve as inputs to a range of flood and pollution transport models. However, they are not usually available. Due to availability of daily data as measured values, in this study an attempt is made to examine the suitability of a random cascade model for transformation of observed daily rainfall data measured at the rain gauge station situated on the Amameh catchment, north of Tehran, Iran. A random cascade model was proposed for the first time by Olsson (1998). The cascade model presented here is based on exact conservation of rainfall volume together with the rainfall seasonality. Having applied this model to the data measured with the mentioned rain gauge, 45-minute data were simulated and compared with its corresponding measured data for the same period of daily data. It was observed that the modelling procedure employed and used in this study can simulate the 45-minute peak values much better that the previous models such as the Olsson one. The potential for the better estimation of peak discharges is, therefore, has the potentiality to be used in storm design purpose as far as the application of rainfall-runoff models for flood estimation are concerned.

In this paper, an algorithm for calculation of active lateral pressure on retaining walls at seismic condition is presented. In this algorithm, that its formulation is based on lower bound of limit analysis method, by considering a stress discontinuity and finding the acceptable stress fields on its two sides, active force is calculated. Soil cohesion and internal fraction angle, also the cohesion and friction between the soil and wall are considered. Results are compared with other researchers and the algorithm validation is confirmed.

Modified bituminous materials can bring real benefits to highway maintenance/construction, in terms of better and longer lasting roads, and savings in total road life castings. This paper present the effect of there novel modifier as Precipitated Calcium Carbonate (PCC) and Nanoclay on engineering properties of asphalt concrete. Various empirical and fundamental tests such as Marshall test, indirect tensile strength, resilient modulus, dynamic creep and diametric fatigue have been investigated in this research. These tests have been conducted at different temperature and various lording forms. The results show that nanoclay modifier can improve cohesive and strength of the mix by increase in marshal stability, indirect tensile, resilient modulus but has non proper response in fatigue behaviour. Precipitated Calcium Carbonate can improve fatigue response of the mix but has not salient effect on marshal stability and indirect strength.

The elasticity theory and numerical method has been used to determine the lateral earth pressures on retaining walls due to surcharge. Initially, Boussinesq (1876) presented a relationship based on the elasticity theory to estimate the lateral pressure induced from point load. This was then extended for line, strip, uniform, …, surcharges. Experimental results showed that there exists difference between Boussinesq equation and experimental results. For example, Spangler (1936) performed large scale experiments and recorded the lateral stresses. He found stresses twice the lateral stress estimated by Boussinesq equation. Mindlin (1936) related this phenomenon to “mirror effect” but some of researchers such as Bowels does not agree with this. In this paper, PLAXIS software has been used for calculating lateral earth pressure exerted on retaining walls from line and strip surcharges. Three values of 0.3, 0.40, and 0.45 have been used for the soil Poisson ratio. The numerical results have been compared with those obtained from Boussinesq equation. The horizontal distance between surcharge and retaining wall has been taken as a variable. At a given depth, the ratio of lateral pressure determined from PLAXIS divided by that obtained from Boussinesq equation has been drawn. The results show that the horizontal distance between surcharge and retaining wall has a negligible effect on results. In addition, the ratio of PLAXIS result to that given from Boussinesq equation for line and strip surcharges is about 1.5. Moreover, the Poisson ratio has a negligible effect on results. While only line and strip surcharges are considered in this paper, the extension of analysis to other surcharges is straightforward.

Although GA optimization is among the most effective with the best performance optimization methods, the method may not be successfully employed in all cases due to slow down in process and some other unknown parameters including the number of generations, cross over ratio, mutation ratio, and the selection process which cause local optimized points. In this paper a new approach is proposed to perform GA for optimization of cross section and topology of trusses that reduces such problems. A complete system with different sub sections, called island, is used to search in the design space. In each island, different operators and parameters are used separately. After some generations, depending on the migration ratio, the best chromosomes from each island alter the chromosomes with lower fitness in other island. Based on the proposed method, GA is continued until the global optimum with the least dependence on the GA parameters is achieved. The results were evaluated with some standard examples.

The performance of buildings designated as very high importance buildings (such as hospital buildings) according to Iranian Seismic Code (Standard 2800) is that, these buildings maintain their operational level in major seismic ground motions (design level earthquake) without major structural damage. This paper discuses the design requirements to reach the purposes in this code and shows that the code regulations can not provide the enough strength for the buildings to operate acceptable during sever earthquakes. To evaluate the code requirements, some R/C moment resistance frames with difference in stories numbers (designated according to standard 2800) was selected and their strength was evaluated based on Instruction for Seismic Rehabilitation of Existing Buildings (No. 360), by pushover analysis. The results indicate that the buildings designated as very high importance according to standard 2800, do not remain operationally after sever earthquake.

Noise causes to decrease the performance of simulation models. Data disturbance and inefficient simulation models are two important roots of noise. Data disturbance is resulted by errors which occur in observations and measurements. Kalman's approach in filtering the data disturbance is well-known method to reduce the noise of modeling procedure. Nowadays, the extended Kalman filters are applied to both linear or nonlinear state space and arbitrary data disturbance. In this paper, the authors applied the Kalman filter to improve two classical classes of run-off routing methods in a reach with 63.2 Km length, between Bamdej and Harmaleh stations in Khouzestan province. The results of comparing two approaches, fully adaptive and Kalman filter, showed noticeable improvement in application of filtering regarding to run-off simulation and reducing the error of computation versus observation.

The present research focuses on the development and verification of a computational procedure and relevant code capable of predicting the water cavitation effects on dynamic response of concrete dam-reservoir coupled systems. Because of the catastrophic consequences of a dam failure, dynamic analysis of dam-reservoir system should include the effects of significant nonlinearities in the response of these systems. The objectives of this paper are summarized as follow: 1- Present a numerical hybrid model to capture acoustic cavitation in the reservoir of dams. 2- To develop a nonlinear fluid-structure coupling code for studying the water cavitation effects on the response of concrete dam- reservoir system subjected to earthquake ground motion. 3- Perform a study of typical concrete dam-reservoir systems to determine the effects of reservoir cavitation on dam response. Finally, for investigate water cavitation effects on seismic response of concrete dams, two typical gravity dam- reservoir and arch dam-reservoir systems are modeled. Based on the results presented in this paper the following conclusion can be drawn: 1- The coupling phenomena are found to have great significance in the case of dam– reservoir interaction analysis. 2- Once the cavitation takes place, the interaction process is quite different from what is predicted by a model that does not consider cavitation. Strictly nonlinear phenomenon will dominate and a proper cavitation model is required to define fluid behavior. 3- Reservoir cavitation does not affect the response of concrete dams considerably.