AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2015 | Volume:47 | Issue:2|Papers Count:8

Solubility of alunite increases in acids and bases by calcinations. This process includes two main steps which are dehydroxylation and desulphuration. In this paper, after characterization of Haft Sandogh alunite ore, kinetics of dehyroxylation and desulphuration were studied. According to the results of thermogravimetric and weight loss, dehydroxylation of alunite occurs at 508 to 577°C and desulphuration takes place at temperatures above 680˚C. It was observed that the dehydroxylation and desulphuration reaction rates increased with increasing temperature. Different kinetics models were used to evaluate kinetics data. By regression analysis and normalized standard deviation (NSD), the Avrami model was found to give the best fit to kinetic data. The reaction rate of both calcination processes were found to be less than one (i.e., n<1). This finding along with the high activation energy value (i.e., 117.4 kJ mol-1 for dehydroxylation and 215.4 kJ mol-1 for desulphuration) indicate that both reactions are controlled by chemical mechanism.

Preparation of site-specific spectra for alluvium and design of tall and special structures are needed. Due to placement of the city of Ardabil on the alluvium and developing of construction in the central part of the city, preparing of site-specific design spectra is inevitable and worthwhile. In this paper, according to the geotechnical boreholes and tests to a depth of 40 meters in different parts of the city, beside probabilistic risk analysis, site- specific spectra for central part of the city are developed. Based on the distribution of boreholes, the area is divided into 15 districts, with an area of one square kilometer. Through the probabilistic risk analysis, design acceleration of 0.32g is obtained for earthquakes with a return period of 475 years, which is 6% higher than that proposed by Building Design Codes for Earthquakes- Standard 2800.Design spectra are obtained using three methods of ground response analysis, statistical analysis of different earthquakes and uniform hazard spectra. Using the data from geotechnical measurements, soil types in the different areas of the city center is designated. The soil types in the most parts of studied area are classified as type III of the standard 2800 classification. Comparison of the obtained spectrum with the proposed spectrum of standard 2800, showed that in the range of constant acceleration, the values of site-specific design spectra is 25% higher than those proposed by the standard 2800.

Due to many advantage of Autoclaved Aerated Concrete (AAC) such as lightweight, low thermal conductivity and fire resistance its usage is increasing day by day. In this paper first the compressive and shear strength of mortar and blocks was given then the result of three wall specimens with dimensions 120 × 120 ×25 cm under diagonal loading was studied. In spite of suitable shear resistant of mortar, sliding did not occur at mortar/blocks interface. In all wall specimens, failure occurred on the blocks because block's shear resistance is less than mortar.

To describe nonlinear behavior of MR dampers as established semi-active devices employed to control vibrations, various models have been proposed which could be classified in hard and soft computing fields. However, only some could mimic hysteretic and highly dynamic characteristics of MR dampers appropriately directly and inversely which is a principle control attribute; more precisely, choosing a qualified invertible model plays a prominent role in a semi-active control, which has not come into sharp focus so far. Thus in this article, first, some best-proposed hard computing (parametric) MR damper models are chosen and identified by genetic optimization under the same conditions. Second, two fuzzy-genetic and neuro-fuzzy models using soft computing techniques are constructed. Then a pseudo static model is proposed, which unlike to accurate dynamic models, have no differential equations and is invertible. Finally, all models subjected to filtered Iranian and foreign earthquakes would be compared. During all phases, experimental data is generated utilizing a benchmark program equipped with large-scale MR dampers, which is proposed by American Society of Civil Engineering (ASCE). Comparisons bring two results: the fuzzy-genetic model is more precise than hard computing ones; and the proposed model performs more effectively than dynamic ones, as it not only demonstrates desirable accuracy and much higher rate, but could easily be inverted.

In this study, several drained and undrained triaxial tests were conducted on the reconstituted samples of Babolsar sand under isotropic and anisotropic consolidation. This sand is widely distributed over the southern bank of Caspian Sea. The tests data have been analyzed in order to investigate the steady state strength and liquefaction susceptibility of this sand within a wide range of initial relative density and principal effective stresses. It is shown that the initial stress anisotropy can profoundly affect the potential of volume change and pore pressure generation. The steady state line, however, remains identical for the isotropically and anisotropically consolidated specimens. It is shown that there exists reasonable correlation between peak values of excess water pore pressure and the corresponding state parameters.

Subgrade reaction modulus (Ks) is a conceptual relationship between soil pressure and deflection, which is widely used in structural analysis of various foundations. Values of Ks are assessed by relating them to intrinsic parameters of soil such as elastic modulus (Es) and California bearing ratio (CBR). The small-strain stiffness (Gmax) is a fundamental soil parameter, applicable to all types of geomaterials for static and dynamic loading. In-situ direct estimation of maximum stiffness or Gmax of soil are more accurate and reliable than the stiffness derived from resistance-based correlation or laboratory tests. This paper has provided a new method to estimate Ks based on Gmax. In order to validate the proposed method, results of the survey of loading tests and seismic geophysical tests of several sites were evaluated and compared. The results indicated that the proposed method in this study could be effectively used to predict the Ks of granular soils. This is much more accurate than the predictions of conventional methods.

Morphology properties, such as surface roughness, have a very important role in the minerals processing. Thus, understanding the relationship between surface roughness of the particles and their Bond work index is important. In this study, pyrite, barite and quartz with the work index of 4.73, 8.93 and 13.57 kwh/st are examined respectively. Results showed that with decreasing of particle size, particle roughness increased. Also surface roughness in the all size ranges is as following: barite> pyrite> quartz. Consequently surface roughness of the particles decreases with increasing of their bond index. Maximum particles roughness for barite, pyrite and quartz occurred in range of +177- 147 microns, that are equivalent to 193.41, 84.63 and 23.09 (dimensionless), respectively.