نشریه مهندسی عمران و محیط زیست دانشگاه تبریز
سال چهل و یکم شماره 2 (پیاپی 65، زمستان 1390)

Urmia Lake is the largest lake in Iran and the second largest saline lake in the world. This ecosystem is the habite for different species of birds and animals. Due to various aspects like economy, sociality, and ecology Urmia Lake has important role in the country. In fact, because of the high salinity of the lake, number of visiting birds is reduced significantly and thousands of them died. Unfortunately, this ecosystem faces many problems nowadays. Because of droughts, overuse of surface water resource, and dam construction, water level has been decreased and one quarter of the lake is changed to saline area within the last 10 years. The important aim of this research is to determine the effect of decrease in surface water on the lake's level. Therefore, in order to investigate the probability of lake's water level decrease in the result of each scenarios, a simulation model based on the system dynamic is developed for the Urmia Lake basin. Results show that between two factors, constructing 4 dams has 25%, and overuse of surface water resource has 65% effect in decreasing the lake's level in recent years respectively.

Flood prediction is one of the important issues in water resources management. The produced information from the flood prediction has a key role in planning of water resources. The goal of this research is the prediction of flood hydrograph with Grey system theory. For this purpose, rainfall-runoff model was analyzed using Grey theory, MATLAB software and hydrometery and rainfall gauge data for Shaharchay watershed. Differential hydrological Grey model (DHGM) was calibrated by four recorded circumstances and the model was evaluated for two other circumstances. Finally, sensitivity analysis of model parameters was accomplished. High values of correlation coefficients (R2>0.74) and low values of error coefficients showed the ability of model for flood prediction with acceptable accuracy. The results of sensitivity analyses specified the role of any Grey parameter in forming of predicted hydrograph. Change results in model parameters showed that this change has an important role in output hydrograph from Grey model.

This paper investigates the effects of the partial and total mode components for strain energy release rate (ERR) in strengthened reinforced concrete beams (SRCBs) by fiber reinforced polymer (FRP) sheets. External bonding of FRP sheets in regions under tension is a general method of strengthening of RC beams. If the debonding phenomenon occurs along the FRP and concrete interface, a sudden failure of structures may be produced. Previous experimental results and analytical methods show that six types of failure due to debonding phenomena exist in the interface of reinforced concrete structures strengthened by FRP sheets. In this paper, two of the most important and common debonding types have been chosen. These two types of debonding are: 1) the separation between FRP sheet and concrete beam at the end of their connection, and 2)- the intermediate crack which is an essential problem in debonding phenomena. This type of debonding has called shear-flexure crack. The present paper provides a parametric study method in realization of debonding phenomena and its effects on behavior of concrete structures strengthened by FRP sheets using mixed mode debonding analysis. The obtained results prove that the effect of mechanical and geometric parameters on the partial and total mode components of strain energy release rate are much more considerable in soffit plate with respect to adhesive layer.

Organic soil is one of the important problematic soils in construction industry. The effect of organic materials on engineering features of soils is variable depending on the type and content of organic matter. The main purpose of this study is to investigate the effects of organic matter on the strength and physical properties of organic soils and its improvement. One of common improvement methods in this type of soils is chemical stabilization with lime, cement, etc. For this purpose, organic matter (peat) was added to inorganic clayey soil at three levels (3%, 6%, 9% by weight). The physical properties of the mixtures were determined by conducting a series of laboratory tests including Atterberg limits, compaction, unconfined compressive strength, and swell characteristics tests. The results showed that with increasing organic matter content, the percentage of lime required to modify the soil, changed too dramatically. Also results indicate that by increasing three percent in organic matter, the amount of required lime increases by two percent. The study of plasticity and swelling in each three soil types shows that these parameters are decreased after stabilization, but with increasing amount of organic matter, the rate of reduction can be reduced. To evaluate the mechanical properties of these soils, unconfined compression strength (UCS) test was carried out on lime treated samples. The results show that in all samples after 28 days of curing, the UCS has been increased noticeably. This growth in strength decreases with increasing organic matter content. pH of all samples has been reduced after 28 days of curing and the amount of reduction has been increased with higher organic matter. Considering the results, with increasing organic matter content from 0 to 9%, only soil with organic matter of 3% suitably stabilized.

The paper describes the development of a very rapid test that measures the permeability of concrete to chloride ions. Once sample conditioning has been done, up to 15 concrete samples can be tested in an hour using a single conductivity cell. The test involves saturating a concrete sample with a 30% NaCl solution, before measuring the conductivity of the sample. By saturating samples with a highly conductive solution, they have virtually the same pore water conductivity. Different concrete samples yield different conductivities primarily because of differences in their pore structure. The measured conductivity is related to the diffusibility ratio as well as to the chloride diffusivity of the concrete.

Two kinds of hangers are used in suspension bridges: vertical and inclined hangers. Inclined hangers provide a damping system in the bridge structures to reduce vibration produced by lateral loads, whereas this kind of damping is not available for vertical hangers. Some of inclined hangers become slack because of their arrangement in bridges and some others are overstressed under external loads. In this paper a case study of a suspension bridge with inclined hangers has been investigated. Special attention has been made to reduce internal forces and fatigue in inclined hangers, as well as to eliminate slackness problems in hangers. A horizontal cable, attached to existing hanger system, has been proposed by the authors. The attached horizontal cables transfer the tension forces from overstressed hangers to the adjacent slack hangers. A Finite Element program in FORTRAN language has been provided to analyze the bridge. The results of analysis of the bridge with this program show that the modified system has improved the behavior of the bridge.

Estimation of the first-order reliability method (FORM) for computation of structural failure probability is possible by using mathematical optimization methods. Computational time and global convergence of various optimization methods are criteria for evaluating an appropriate optimization method in the reliability analysis. In this paper, the Nonlinear Conjugate Gradient (NCG) methods have been established for determination of the structural reliability index for the first time. Seven NCG methods have been proposed based on appropriate formulation of the reliability analysis for calculation of the reliability index of structures. The ability and efficiency of these methods are checked in several examples. The convergence and CPU run-times of examples are compared together. The results illustrated that the NCG methods successfully are applied for computation of the reliability index and these methods have suitable efficiency and convergence for estimation of the failure probability of structures. In the basis of problem property has been obtained irregular convergence and run-times of various NCG methods.

There are different methods for treatment of composting leachate. Parameters dictating which method to be chosen include quantity of the leachate, required amount of treatment and economical issues. In treatment of composting leachate existence of organic matters, heavy metals, sulfates and other inappropriate material with high concentration should be considered. Adsorption by GAC is one of the appropriate methods for treatment of these kinds of leachates. In this study, after complete identification of GAC’s specifications as an adsorbent, its application in final treatment of leachate was investigated via batch reactor experiments. According to the conducted experiments in pH=8 and in presence of 200 gr /liter adsorbent, removal rate of 42% was achieved at the equilibrium time of 30 minutes. In addition, in this research, experimental data of adsorption equilibrium was compared with freundlich and langmuir isotherm models. The results indicated that equilibrium data of adsorption is highly compatible with freundlich and langmuir models. Moreover, maximum capacity of adsorption for the adsorbent, in optimized condition, was estimated to be 3 mg of pollutant per each gr of GAC.