Amirkabir Journal of Civil Engineering
Year:2010 | Volume:41 | Issue:2|Papers Count:18

Minimizing of cement paste volume not only decreases the cost of construction but also improves many of attributions regarding durability in self-consolidating concrete. In this paper, a mixture design method of Self-Consolidating Concrete based on minimum cement paste volume is proposed that descends cost of construction, more over because of creating a systematic modification process, achieving desired mixture is accelerated. It's understood from the results that amount of minimum required cement paste in self-consolidating concrete is dependable on aggregate size distribution and composition of cement paste, more over in self-consolidating concrete, it is probable that minimum amount of required cement paste is needed in aggregate composition that haven't maximum packing density.

Determining the responses of floating structures the sea are the most important concerns in shipbuilding industry. In physical and dynamical principles a ship can be analyzed as a free elastic beam floating in sea without any supports. The analysis of corresponding dynamic equations are difficult and time consuming, thus investigation on the behavior of floating structures can be done numerically using specific software. In this research, instead of using expensive specific software, ANSYS 5.5 as a typical finite element software is used for investigating the effect of various parameters on an assumed floating structure. In this way, after structural modal analysis, modeling and analysis of the structure with variation on its properties under different sea environment have been done and the responses are illustrated Amid-ship moment is one of the most important and effective parameters in ship design. In this paper, due to different ship speed and stiffness of cross section, amid-ship moment beside the shear force of various cross section along the ship are considered and the critical shear cross section is determined.

Running rivers in alluvial plains, always drawn to meandering process. In this paper, according to valley slope and river slope, the relationship between meanders' geometric parameters and sinuosity factor revealed. Based on the field data of Sistan River which is a meandering one, meanders geometric characteristics of this river were calculated and defined on the base of mathematical model.Finally, estimated results were compared with observed measurements in different reaches of Sistan River. This research demonstrates that acquired estimations and field measurements have a good correlation coefficient.

Nowadays one of the primary demands in the design of structures is to provide life safety performance level with minimal of human and financial damage after severe earthquakes. The Iranian seismic standard (2800) has introduces possesses stipulates two hazard levels, the service level and design level. The latter is defined as an earthquake with 10% probability of occurrence in 50 years. Also the “FEMA-356”: define the MCE level as maximum hazard level that refers to an earthquake with 2% probability of occurrence in 50 years.This paper presents research on R.C. tall buildings designed based on the 2800 standard and retrofitted with steel bracing. The selected hazard level in this research is MCE level. The results indicated that unretrofitted buildings collapse at the selected hazard level. Additionally retrofitting of the buildings failed to provide life safety performance level.

The Avaj earthquake in June 22, 2002 with a magnitude of Mw=6.5 occurred in western north of Iran. The requirement characteristics for modelling of strong ground motion such as length and wide of fault plate, strike, dip, focal position, stations position and etc. is defined by field study. These parameters are used in order to generate artificial earthquake based on the semi-empirical Green's function methods for Avaj, Bahar, Kabudar Ahang, Shirin Su and Bakandi stations. Then, some parameters such as peak ground acceleration, effective duration, acceleration response spectrum and root mean square error of the generated earthquake compared with the real records.In this paper, semi-empirical Green's function method is further developed for Iran condition. The results of the study are shown that the method can be applied for the other region with the fault of same mechanism such as Tehran faults.

In welding process, stresses after cooling, which remain in body, are called residual stresses. Sometimes, the magnitude of stresses is high and reduces the strength of welded pieces, moreover, they cause crack in the weld. To predict welding residual stresses, it is necessary to do thermal and mechanical analysis.In this paper, some parameters which influence the welding using ANSYS software are investigated. Results show that even by decreasing the travel speed of torch, it makes no differences in the amount of residual stresses, but preheating causes decreasing the produced stresses about 22 percentages. Suitable welding sequences also, decreases residual stresses up to 25 percentages.

Steel plate shear walls have been used in structures as a lateral load resisting system since 1970. Main advantage of thin steel plate shear wall is buckling of steel plate under tension field action. Generally, there are two methods to delay the steel plate buckling, using stiffeners or concrete cover which attached to the steel plate by shear connectors.In the present study, a numerical approach has been used to investigate the shear behavior of composite shear walls under lateral loading. Furthermore a geometrical optimization analysis was carried out by changing the concrete cover thickness and distance between shear connectors. The results of numerical analysis, show increasing concrete cover thickness will result decreasing stress concentration in steel plate and distributing them. Furthermore the result show that decreasing distance between shear connector will result increasing the strength and stiffness of shear panel. Finally studying the models deformation the optimum concrete cover thickness and distance between shear connectors are proposed.

One of the main challenges in designing of thin-walled open section beams is lateral-torsion buckling mode. Due to the access for piping, electrical and other devices, inserting cut-outs in web are inevitable.This paper deals with the effects of different parameters in lateral-torsion buckling of plate girders. Lateral-torsion buckling loads of more than 700 plate girders are calculated with opening in different shapes, dimensions and locations by Ansys 5.4. The study is performed using numerical approach and the results are compared together. Three kinds of cut-outs including square, circular and hexagonal are selected. An extensive parametric studies is conducted to study the influence of cut-out dimensions, thickness, area, location and distribution along the beam length. Finally optimum scheme is obtained in order to have better estimation load carrying capacity of open-section beam.

To design the engineering structures properly, some relevant information is required main part of which can only be obtained from modeling them. Physical modeling, if carried out carefully, can present such valuable information in connection with structural behaviors that may implement to calibrate the numerical modeling or to verify the designing assumptions. In geotechnical problems however, the physical modeling, due to their inherent complexity and dependency to many factors, are of great importance and may submit very useful and crucial data.In this paper, a new physical model capable for studying the behavior of strip footings on reinforced soil under monotonic and cyclic loadings is presented. The design criteria and specification of different parts of the model are explained and discussed. In order to control the ability and accuracy of the model, regarding the responses of strip footings subjected to different static and cyclic loadings, the results of some tests have been compared with other empirical and theoretical data. The consistency between the results shows the reliability of the developed model.

In this paper, test and evaluation of torsional strength of concrete beams reinforced with longitudinal rebars and without transverse reinforcement, is considered. Most of concrete codes dose not consider any post cracking torsional strength for concrete element which are not reinforced with torsional reinforcement. It seems that ordinary concrete elements, reinforced for bending, have a post cracking torsion strength (TC), due to aggregate interlock and dowel action. According to the test results, beams which were reinforced by a moderate ratios of longitudinal rebars, showed a ductile torsional behavior in relatively high torsional rotations. A post cracking strength about 50 percent of (Tcr) is suggested for these beams.

This study considers mobilization and desorption effects of biosurfactant produced in biodegradation of hydrocarbon-contaminated soils. 88 erlens with 100cc volume containing slurry contaminated kaolinite soil with 10000ppm and 50000ppm crude oil concentrations used as reactors. Mixed culture microorganisms were isolated from contaminated soils collected from Tehran refinery with total petroleum hydrocarbon then cultured in mineral solution. Results indicated that production of biosurfactant by microorganism cause to desorption and mobilization of hydrophobic hydrocarbon compounds. Further more shaking and aeration have been negligible effect on desorption and mobilization. Results also have shown that 19% of total reduction of TPH (about 40%) in twenty days concerns biosurfactant effects for 50000ppm samples. This effect is about 7% for 10000ppm samples.

In this paper, the interference effects of neighboring large structures located at upstream of the cooling towers group were numerically investigated. In order to assess the computed pressure field, the concept of using equivalent sand-grain roughness is utilized to simulate the physical effects of external ribs. The numerical solution results are compared with a set of reported laboratory measurements as well as VGB code of practice. Having a verified numerical model, the interference effects of a group of cooling towers were considered. In order to investigate the grouping effect, the lay out of a set of three cooling tower Kazeroun power station (South west of Iran) was used. The computed wind pressures on cooling towers in a group with irregular arrangement present different distribution from the pressure values suggested by VGB guideline The effects were found more pronounced for lower parts of the cooling towers by considering the interference effects of upstream large structures.

In the present paper flow pattern at a constriction in an open channel is studied experimentally. A constriction as a model of bridge site is constructed in a flume 73.5 cm wide and with erodible bed. Measurements were carried out after the scour hole was reached to its equilibrium condition. Tests were conducted with one flow discharge and two tail waters. Flow velocity was measured in 3 directions simultaneously with an ADV. Based on instantaneous velocities, turbulence intensity was also calculated and analyzed. The effect of constriction on flow pattern was then studied based on velocity and turbulence measurements in x, y and z directions.

Humans are social creatures who interact with others in doing their activities. The social activities occur in space and time. Therefore, a proper model of human activities must consider the two dimensions of space and time simultaneously. This paper attempts to model human activities in spatio-temporal domain to improve the efficiency of group activities. For this purpose, Hagerstrand theory is evaluated and extended for managing human team activities in space and time. The suggested model can be implemented in a Geospatial Information System and helps resolving multidimensional problem in their proper environment. To assess the proposed model, activities of two teams: life-detection and collapse lifting in two forms of normal and simulation were assessed. The proposed strategy improved the activities by a factor of 18.83.

This paper presents a recently developed automated pullout apparatus for soil-geogrid strength and deformation behavior investigation. The new apparatus is capable of applying load/displacement controlled monotonic/cyclic loads at different rates/frequencies, different wave shapes and loading patterns, through a computer closed-loop system. An extruded uniaxial geogrid and silica sand are used throughout the experiments. The effects of normal pressure (surcharge) and relative density are investigated on displacement distributions and pullout capacity of the geogrid in both monotonic and cyclic tests.In monotonic tests, it is observed that with increase in relative density and surcharge, pullout resistance has increased. In cyclic tests, despite some minor observations of post-cyclic strength increased, no specific comment can be made at this stage on the post-cyclic strength.

The compressibility characteristics of reconstituted clays are used as a basic frame for interpreting the corresponding characteristics of natural sedimentary clays. Intrinsic properties are especially used for reconstituted soil which, are independent of natural state. Void index is a parameter which relates the reconstituted parameters of different clay soils. Burland 1990 suggested that the natural properties of clay soil may be different from that of reconstituted ones due to the influence of soil microscopic and macroscopic texture (fabric and bonding).In this research, clay specimens from Tehran region were prepared by water to 1.5 times the liquid limit and then reconstituted. The amount of additional water depends upon the clay content and the development of adsorbed water (diffuse double layer).Plotting the results in Burland's framework, show the SCL lies well below the ICL. This is related to the rates and modes of deposition of alluvium when, a freshet (high water) from wide valleys of Alborz Mountain spread out the flood plain providing deposits of low to insensitive clay soil. In this study the compressibility parameters were correlated as an aid to site investigation interpretation.

Abutments and foundation are among the most vulnerable parts of arch dams therefore, understanding their defects are of high priority. As far as seepage forces have a great effect on abutment stability, understanding the seepage in rock masses has a great importance. Joints hydromechanical interaction is a phenomenon that is not studied sufficiently. In this research, an effective algorithm is devised so that the mechanical behavior of jointed rock mass has been described and modeled by an equivalent continuum rock model with multilaminate concept and the hydraulic behavior assuming laminar flow with cubic law for joint systems. The hydromechanical interaction is thus modeled for a hypothetical arch dam and the effect of the phenomenon is studied on the stresses, their redistribution and in the rock mass abutments. It is concluded that disregarding the seepage effect or the H-M interaction may introduce significant errors in displacements and shear stresses of dam abutments.