IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2007 | Volume:31 | Issue:B5|Papers Count:13

Experimental studies show that an indeterminate structure or a continuous concrete beam does not fail when critical sections reach their ultimate strengths. Therefore, if a structure has adequate ductility, stress and moment redistribution will take place in the flexural members by developing plastic hinges at critical sections. This causes the other points of beams to achieve their ultimate strengths and capacities. Besides, moment redistribution allows designers to adjust the bending moment diagram computed by elastic analysis.The usual result is a reduction in the values of negative moments at the support face as well as an increase in the values of positive moments along the span.In the current investigation, a parametric study on moment redistribution in continuous RC beams with equal spans under uniform loading was performed. First, the governing equation for the allowable percent of moment redistribution was extracted using ductility demand and ductility capacity concepts. The effects of different parameters such as the concrete compressive strength, the amount and the strength of reinforcing steel, the magnitude of elastic moment at the support and the ratio of the length to the effective depth of the continuous beam on moment redistribution were then investigated. Furthermore, the allowable moment redistributions were calculated according to the regulations of different codes in each case. The results showed that, whereas the permissible moment redistribution in continuous reinforced concrete beams based on the relevant rules in the current codes is not in a safe margin in some cases, it is rather conservative in most cases.

In this paper, the direct boundary element method in time domain is used for the calculation of local amplifications of seismic waves by real 3-dimensional surface topographies.The presented method is effective for modeling surface irregularities with arbitrary shapes under complex incident wave forms. A real topography with particular importance in Iran, Urmia Hill, which represents a complex surface irregularity with sloping boundaries, is considered as a study case and its seismic behaviour, particularly sloping boundary effects, is studied under SH and SV incident waves with various azimuths and angles of incidence. This method can equally be used for P or mixed P-S incidences. The boundary is modelled using quadrilateral (8-node) elements, and synthetic displacement time history based on the deterministic approach is used for excitation of the model. The results show that the areas located at the end of slopes experience more excitations in some cases, while greater amplifications occur in the nearby flat areas in some other incidences. The amplification pattern is shown to be completely dependent on the wave type and the direction of sloped boundaries with respect to the angle and azimuth of incidence.  

The application of ant algorithms, as any other evolutionary optimisation method, requires a number of controlling parameters to be known a priori. These parameters are often determined by sensitivity analysis as their values dramatically affect the performance of the methods. In addition to these parameters, a penalty parameter is usually to be defined for constrained optimisation problems. An ant algorithm with a minimum number of controlling parameters is introduced in this paper for pipe network optimisation problems. This method uses the interrelation between pheromone change and initial pheromone strength to initialize the pheromone trail strength at the start of the computation. Ant algorithms with an elitist strategy of pheromone updating are known for premature convergence leading to suboptimal solutions. Such suboptimal solutions are avoided by using the concept of pheromone strength limiter introduced in the literature for TSP. The introduction of this concept, however, requires the introduction of a new parameter adding to the number of controlling parameters of ant algorithms. A sensitivity analysis was carried out to find the proper value of the newly introduced parameter. The results suggest that a value in the range of 0.15-0.3 is the best value for the examples considered. The efficiency of the proposed ant algorithm is tested against two benchmark examples in the literature and the results are presented. This method is shown to be capable of locating the best ever solutions obtained for these problems.

In this study, a certain characteristic of neural networks called Self Organizing Feature Maps (SOFM’s) was applied to pollution source identification in the Kor and Sivand Rivers located in Fars Province, Iran. Wastewater quality data from significant industrial pollution sources to these rivers (mainly factories located upstream) were given. Observed sets of water quality data in sampling stations, downstream from the pollution sources, were utilized to identify the most probable pollution source that may have contributed to pollution in these rivers. With the aid of partial semantic maps generated by SOFM’s, different patterns with different likelihoods were recognized in the pollution data. Certain patterns matched that of the pollution sources very closely. In other words, the fingerprints of all pollution sources (which were studied) were identified in the pollution data. Therefore, it is possible to use the maps as an aid to the management and decision support system of these rivers.

Due to decreasing precipitation in recent years, lack of perennial surface water resources, and the high volume of groundwater extraction in the vicinity of Tashk Lake (called Tavabe-e-Arsanjan), the groundwater level decreases, and as a result, salt water from Tashk Lake intrudes into the fresh groundwater coastal aquifers. Several technical countermeasures are used to prevent or retard the groundwater salinization process. One of them is to increase (artificial) recharge in upland areas to enlarge the outflow of fresh groundwater through the coastal aquifer, and thus, to reduce the length of the salt water wedge.In this research, the natural recharge of groundwater is studied using the Cumulative Rainfall Departure (CRD) method with regards to the existing information in the study area. This study focuses on using both revised CRD (R-CRD) and CRD methods to simulate, and consequently predict, transient water table fluctuations. A user-friendly program named GREM, which is written in Visual Basic language, is used to minimize the difference between simulated and observed water table elevations. The simulated water table exhibits good agreement with the observed water table (modeling efficiency = 0.933). The percentage of the cumulative rainfall departure (r), which results in a recharge from precipitation, is estimated to be 33.6. This implies that less than half of the precipitation acts to recharge the water table. The results showed that the natural recharge is not enough to compensate the high volume of groundwater extraction in the study area.The end objective of this study is to provide the foundation for the construction of a regional model of the Tavabe-e-Arsanjan groundwater basin to enable sustained agricultural production while mitigating the impact of salt water intrusion.

Nowadays, innovative processes especially processes with integrated growth (combined attached and suspended growth) such as moving bed biofilm reactor (MBBR) and integrated fixed film activated Sludge (IFAS) are being used successfully for new construction and upgrading existing wastewater treatment plants. Increasing the hydraulic capacity, COD and nutrients removal from the effluent are the two main targets of applying these processes. In this research the efficiency of a new version of IFAS reactor was studied at pilot plant scale in Ekbatan municipal WWTP in Tehran, Iran. In this new reactor (which is called H-IFAS reactor) aerobic, anoxic and anaerobic zones were designed in a single reactor and, as a result, the conditions of doing nitrification, denitrification, phosphorus removal and increasing BOD removal rate in the reactor were optimized in comparison with IFAS and MBBR. The media used in this reactor was Bee-Cell2000 with a total specific surface area of 650 m2/m3. In optimum conditions, the organic degradation rate of the anaerobic and aerobic zone with an average temperature of 23.48 °C OLR=22.5 kg COD/m3 day for the anaerobic zone and OLR 8.66 kgCOD/m3 day for the aerobic zone, was equal to 3.56 and 6.22 kgCOD/m3 day respectively. Nitrification and denitrification rate of media with an average temperature of 23.48 °C, HRT=1.26 hr was equal to 532.77, 723.42 and 168.4 gN/m3 day respectively. Biological phosphorus removal rate of the reactor at the best operational conditions with a phosphorous loading rate of 243 g P-PO4 /m3 day, an average temperature of 23.48 °C, and HRT 27 min was equal to 168.4 g P-PO4 /m3 day.

The effect of synthetic leachate on the hydraulic conductivity of a clayey soil in the Urmia city landfill site, Iran, was investigated using a triaxial permeability apparatus. The bladder accumulators were fabricated for flexible wall triaxial permeability apparatus to facilitate synthetic leachate permeation in the apparatus. The landfill soil was tested and classified as silty clayey sand (SM-SC) and did not fulfill the requirements as a soil for landfill liner. Hence, the landfill soil was mixed with 12% of a clayey soil from a nearby location to bring the index parameters of the mixed soil into a range specified for a landfill liner soil. The synthetic leachate was prepared with three different Ca++ concentrations. The mixed soil was compacted wet of optimum water content and permeated with tap water. After equilibrium, the tap water was replaced with synthetic leachate with three different Ca++ concentrations. The hydraulic conductivities of 1.33×10-8 cm/s, 1.81×10-8 cm/s, and 1.77×10-8 cm/s were obtained for the soil permeated with synthetic leachate, compared with the average hydraulic conductivity of 1.52×10-8 cm/s when permeated with tap water for tests A, B, and C, respectively. The synthetic leachate with a 1000 mg/L Ca++ concentration caused about a 13% reduction in hydraulic conductivity in test A which could be due to the decrease in the void ratio because of the consolidation of the sample. The percentages of increase of hydraulic conductivity for tests B and C, in comparison with the values for tap water permeation, were 18% and 20%, respectively, which is attributed to double layer contraction and increased pore space, resulting from the adsorption of divalent cations into the soil matrix.

Various parameters affect the number of household trips, therefore it can be claimed that the first step in the modeling of trip-generation is identification of the most important of these parameters. In this research the effective parameters on trip-generation are determined and evaluated by using the rough-set approach as a modern mathematical method. The primary purpose of the present paper is to find the smallest sets of attributes having quality equal to the general quality of the defined characteristics in the information system. So, the number of parameters used in the modeling is reduced. To evaluate the results, the best algorithm of the defined attributes in the information system is identified by making use of the stepwise (stepwise linear regression) method and then compares the results with each other. The results of the research indicate that the rough-set theory has a better and stronger operational capability in identifying the effective parameters in trip-generation modeling. By taking advantage of these results, the amount of necessary data for trip-generation modeling is decreased and the speed and effectiveness of information processing are increased considerably.

Crushed tile is an industrial waste that causes environmental pollution. Therefore the possible utilization of this material would reduce environmental pollution. The utilization of crushed tile as a coarse aggregate in concrete would have a positive effect on the economy. In concrete production, Portland cement, river sand, 4-32 mm in size crushed stone and crushed tile as coarse aggregates in the replacement ratio of 0, 50 and 100 % were used. Mechanical and physical tests were conducted on specimens. The strength and unit weight of crushed tile aggregate concrete were decreased compared to the control concrete. Absorption and capillarity coefficients were increased compared to the control concrete.

This work presents a computer-based analysis of semi-rigid steel frames. The geometric nonlinearity of the structure and the material nonlinearity of the connections are considered in the analysis. The critical load has been searched as a suitable load parameter for the loss of stability of the system. Several examples are presented to demonstrate the validity of the analysis procedure.

This study was undertaken to determine the mechanical behavior of lime- stabilized clayey sands. The variations of compressive and tensile strengths of materials were investigated. Uniaxial and indirect tensile tests were performed and the results of stress-strain diagrams were used to present a simple nonlinear elastic model. The results show that a simple parabolic elastic model can predict the stress-strain relation before failure. A matrix of elastic coefficients is then presented based on the suggested model and the stress level.  

A recently proposed meshless method, which is called the radial basis point interpolation method (RBPIM), is used for the mechanical analysis of reinforced soils. The media of reinforced soil is divided into three parts: soil, reinforcement and interface layer. The displacement field in each part is constructed by point interpolation. A code has been developed based on RBPIM and the validity of this code has been investigated by solving some examples at the end of the paper.