AMIRKABIR
Year:2005 | Volume:16 | Issue:62-C|Papers Count:17

The post-buckling behavior of rectangular frames in elastic domain is studied in depth. In analysis, unsymmetrical geometry, sway possibility and support conditions are considered in order to find their influences on load- deflection path and non-linear deformations. The static perturbation technique is used for analysis and discussion. The first, second and third order perturbation problem, as an accuracy measurement, for the frame are solved and the solutions are compared with previously published papers. The results reveal that the symmetric frame with sway movement, due to non-axial force in beam, has symmetric bifurcation point in the first order perturbation analysis. However, the post-buckling behavior of un-symmetric frames with or without sway is bifurcated in an asymmetric manner.        

The grindability of ores is a very significant parameter which is used in size reduction equipments design and selection. The Hardgrove Index (HGI) is a normal approach for measuring the coal sample grindability which is calculated using hardgrove machine. The coals specification such as humidity, ash content, volatile matter and heating value are analytical parameters which could change the HGI amount of coal samples. In this study it has been attempted to define the coal HGI values. on the basis of sink-float experimental data. An empirical equation was defined with applying regression technique on the data of above parameters to estimate HGI values.    

In this research, the interaction of blast-induced stress wave with the surrounding media is investigated by the UDEC code. The stress wave resulting from the explosion of a cylindrical charge is simulated by a triangular pulse which is the result of an overpressure equivalent to 1860 MPa. This pressure is applied to the blasthole wall as a uniform load. Numerical results are compared with published empirical data for blasting in a granite rock mass. A good agreement between numerical and empirical results was achieved.      

Recovery of elemental components of cutting tools, i.e. WC and Co is started from last decade. At the moment, about 35 percent of produced cemented carbide scraps are recovered. Usually, recovery of these scraps is carried out using melted zinc. . In this research, the cemented tungsten carbide scraps were dissolved by selective electrolytic process. By plotting linear polarization curves, different parameters such as electrolyte, additives, current density, time, and temperature were studied and the best conditions for selective electrolysis of cemented carbides components were determined.            

The main object of invention and further development of fuzzy set theory was its applicability to solve the decision making problems. Three decades after its invention, it is applied in various subjects. Application of this theory in multi criteria decision making is one of them. In this study we use this technique to evaluate various Bauxite deposits. In order to determine the priority order of twenty different Bauxite deposits for further exploration, this theory was applied. This had to be done because the data obtained about these deposits were not at the same accuracy level. Ore Reserve, Bauxite Quality, Stripping Ratio, Type of Overburden, Road Accessibility and the Market Distance were the selected common influential criteria. Decision Making Function and appropriate operators together with Membership Function of each of the selected criteria were determined and finally the desirability degrees of the possible alternatives were determined, using their appropriate Fuzzy Values. The obtained fuzzy values were used as the priority indicates for establishment of priority list of the studied Bauxite deposits.

The Sabzevar complex ophiolite as a part of Khorasan ophiolite belt is located in 175 Km Northwestern of Sabzevar (L., 560 50' 20" and A., 360 35' 30"). These complexes are including igneous rocks consist of both peridotites (lherzolite, dunite and harzburgite), serpentinite, gabbros and a volcanic sequence composed of basalts, andesites, rhyolites and basanites. Based on the geochemical characteristics and petrographic observations, the mentioned rocks have been classified both in terms of tectonic settings and the chemistry. According to this research, it is proven that the basic to intermediate igneous rocks are very similar to that of Arc Island type setting rocks, and also very similar to each other in terms of genesis. It means, they are formed from unit melt segregation. But, the ophiolite complexes are very close to that of ocean ridge basalt-like composition, in the extrusive units of Neo-Tethyan. All of this rock unites could be the result of the oceanic spreading center development activities, when, through changing the extension regime to the compression one, it could penetrate into the previous continental plate to form colored mélange.        

A large number of algorithms have been developed for optimization of mining limits in open pit boundaries, however, little amount of research is available for underground cases. This is mostly due to variability of the underground mining methods, complexity of economic factors in underground mines and lack of acceptability of computer algorithms among the underground mine design practitioners. This paper presents a new algorithm to optimize ultimate stope geometry, using the dynamic programming technique. The algorithm employs a conventional 20 economic block model, called the "primary model". The minimum stope height and length are imposed to the primary to construct intermediate and final models. The dynamic programming algorithm is then applied on the final model to maximize the stope total net value. The task is performed through a recursive formula, which consists of two criteria. The proposed dynamic programming algorithm is best suited for vein type orebodies using any type of underground mining methods.    

By immersing initially nitrided steel into low temperature salt bath with ferrovanadium powder additive, a hard and wear resistant vanadium carbonotride coating will be produced, known as the Thermo-Reactive Diffusion and Deposition (TRD) method. The aim of this project is to evaluate the effect of different coating parameters on producing vanadium carbonitride coating on DIN 1.2510 steel using low temperature TRD method. Results indicate that the structure of the coating consist of vanadium carbonitride in the form of V(C,N) + V2(N,C) and Iron-vanadium carbonitride in the form of (Fe-V)(C,N). Increasing ferrovanadium content in the bath along with the use of finer ferrovanadiul11powder and increasing nitriding time, results in a thicker layer with decreased surface hardness. However, increasing time in conjunction with higher temperature results in increased surface hardness. Hardness distribution from surface to substrate is diffuse, producing a good compatibility between coating and substrate.

Landslides in the hilly terrain of Sefidargoleh area in Semnan province cause many damages to residential area, roads, ...every year. To address this problem, a statistical method called multiple logistic regressions has been used to create a landslide hazard map for study area. Data included digitized geology, slope, aspect, DEM, landuse, precipitation and buffer of faults manipulated using SPANS in GIS environment. Logistic regression relates predictor variables to the occurrence or nonoccurrence of landslides within geographic cells. This information was used to produce a map showing the probability of future landslides. Results indicated that slope and litology are the most important variable for estimating landslides. Precipitation and buffer of faults were excluded from the final analysis because these variables did not add the predictive power of the logistic regression.      

One of the most important factors leading to the success of a cement plant is its location. A multicriteria decision-making method is used to rank alternative plant locations. The set of criteria is established and corresponding criteria should be established for each case study, although this multicriteria decision-making approach has broader applicability. In this paper, Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) with five criteria is used to develop a location evaluation for Alumina - cement plant in East- Azerbaijan province of Iran. Five alternatives for the plant location are evaluated. The main criteria are transportation consideration, water supply, power supply, fuel supply and land consideration. Other criteria have the same importance as for five alternatives. Finally, Alternatives are ranked and the best site is proposed.

In rock engineering practices, understanding the most effective parameters and their relationships is important in order to obtain an optimum engineering design. The applications of rock engineering system (RES) in the analysis of complicated rock engineering processes have been widespread. In this method, the main parameters are located along the diagonal of the matrix, and their interaction is quantified by assigning values in the off-diagonal elements. Then, this matrix is used to assess the amount of cause and effect of each parameter within the whole system. In this paper, firstly, the fully coupled model of coding the interaction matrix is reviewed. Then, RES is applied to the analysis of a plane failure risk in a rock slope for both saturated and drained situations. In order to recognize the optimum stabilization technique, three different alternatives are studied considering a safety factor of 1.5. These are: 1) reducing height of the slope by keeping the slope angle unchanged, 2) reducing the slope angle by keeping the slope height unchanged, and 3) changing both slope height and angle simultaneously. The results indicate that drainage reduces the failure risk by 25 percent. Comparing three different alternatives, the second method was chosen as the optimum stabilization technique.        

This paper presents a force (flexibility) based formulation for nonlinear static analysis of reinforced concrete plane frames. Nonlinear behavior of concrete and steel fibers based on a simple one-dimensional constitutive law is considered. Navier- Bernoulli theory is accepted in different sections and the effect of bond-slip is, thus, neglected. The section flexibility and stiffness matrices are extracted by direct integration of tangential modulus of materials all over the sections. Flexibility, stiffness and residual force vector of elements are estimated, using principle of virtual work and based on a force (flexibility) formulation. An iterative algorithm used to satisfy the proposed convergence criterion. Presented samples show accuracy and efficiency of the proposed method in contrast to other existing numerical and experimental results.    

Highways work zone areas due to their traffic lane restrictions impose excess user costs mostly additional travel time, fuel consumption, air pollution, accident as well as wear and tear of vehicle. In this paper, mathematical functions for calculation of costs caused by delay, fuel consumption and air pollution are developed and a final function covering all of these factors is presented. For this study, entry traffic volume to work zone area, vehicle travel time during the peak morning hours and peak afternoon hours were collected and by applying the FRESIM simulation program, work zone traffic behaviors were modeled. The amounts of delays in lanes adjacent to the closed lane were obtained as a function of closed lane length and vehicle speeds. The results indicate that in the upper portion of the closed lane, the amounts of delays are an exponential function of entry flow rate, heavy vehicles proportion of traffic volume, and close lane length. Comparisons of different factors indicated that delay was the major contributor of the total cost.      

The freezing and thawing is one of the major problems of the concrete industry in cold climates. There are many parameters that effect the durability of concrete under freezing and thawing cycles; some of them are water content, cement content, water-to-cement ratio, curing condition, air content, and the number of freezing and thawing cycles. The aim of this study is investigation of the effects of some of these parameters to extract some experimental relation to explain the frost resistance of normal concrete (NC). To do so, the effect of three key parameters, i.e. the role of water- cement ratio (0.5, 0.6, 0.7 and 0.8) and air content (3, 4.5, 6 and 7.5%) in addition to number of freeze-thaw cycles was studied on the normal concrete under freezing. Totally, 288 normal concrete specimens were cast and cured; then tested based on ASTM C666B under 45, 100 and ISO cycles of freezing and thawing. Finally using the experimental data, some expressions were proposed regarding the durability of normal concrete under freezing.