Civil Engineering Infrastructures Journal
Year:2012 | Volume:45 | Issue:6|Papers Count:10

Recently there have been many researches on the subject of soil-contaminant interaction. However, there are very few researches on the potential of nano-clays to increase the contaminant retention of soils. In addition, reviewing the previous studies shows that the application of nano-clays in geo-environmental engineering has not been taken into consideration. The main objective of this paper is to indicate the special potential of nano-clays for heavy metal contaminant retention. To achieve this purpose, a series of geo-environmental experiments were performed to establish the fundamental aspects of nano-clay and contaminant interaction. To compare the geo-environmental behavior of nano-clay and bentonite, different concentrations of calcite were laboratory added to nano-clay samples. Series of batch equilibrium testing, and buffering capacity experiments were performed and were compared with the experimental results on bentonite, before and after addition of carbonate to nano-clay samples. It is shown that mixtures of nano clay and 8% carbonate have more contaminant retention than that of bentonite sample. In the other part of this paper the process of nano-clays and heavy metal contaminant interaction were investigated by application of XRD analysis. In addition, it is shown that even though carbonate has more impact than surface area on contaminant sorption by soils, the large specific surface are of nano clays is responsible for their very high contaminant retention ability. Therefore, the enhanced nano-clay with carbonate will be very capable for use in geo-environmental projects. The achieved results of this paper show that among bentonite, kaolinite, and four Cloisite nano-clay samples, the order of contaminant retention of samples are as follows:Bentonite>Cloisite®Na+>Kaolinite>Cloisite®30B>Cloisite®20A> Cloisite®15A However, with addition of laboratory added carbonate to the nano-clay samples, the above order will be changed according to the following order:Cloisite®Na+>Cloisite®15A³Cloisite®20A>Cloisite®30B>Bentonite This shows a larger retention by mixture of nano-clays/8% carbonate in comparison with bentonite.

This paper presents analytical and experimental studies on the cyclic behavior of modified moment connection of I-beam to double-I built-up column. Traditional connection of I-beam to double-I built-up column, due to flexibility of the column cover plates, acts in a semi-rigid manner. In addition, it does not provide the required strength and ductility for a special moment frame connection. In this paper, it is suggested to reinforce the column cover plate in critical areas by substituting the column cover plate with a thicker and wider plate. To investigate the cyclic behavior of this proposed connection, non-linear finite element numerical analysis and experimental test were carried out on full-scale models. Both analytical and experimental results indicate that this modified connection has sufficient strength and ductility to be used in special moment frames. Its stiffness is also in the range of a fully restrained connection.

Most of structural parameters, such as material properties, geometric parameters, loads, and analytical models, are random in nature. Recent advances in stochastic structural analysis have made it possible to analyze the behavior of structures in which such parameters are modeled as spatially varying random processes or fields rather than as random variables. This article, applies a probabilistic nonlinear dynamic analysis of portal frames in which volume mass, modulus of elasticity and section dimensions are considered as random variables. The Monte Carlo method is used to simulate the random variables. Each variable is simulated for three kinds of probability density function (PDF) with three different coefficients of variations (COV). The objective of this paper is to evaluate the sensitivity of dynamic responses to the kind of PDFs and COVs. In doing so, the nonlinear dynamic analysis of structure portal frame with uncertain parameters is performed using numerical methods and the safety of the structure is investigated.

In order to obtain a precise modeling method that would be comparable with experimental results, the specification of grains such as form, size, elasticity, plasticity should be modeled carefully. Since the shape of the grain affects tremendously the mechanical behavior of total grains like shear resistance, the appropriate modeling of the grain shape is considered to be very important. In most cases of modeling that have been applied so far, the grain form is either circular, elliptical, polygonal modeled which none of them is a direct model of the irregular shape of the grain, hence will not project the mechanical behavior as expected. So, it seems to be worthy that direct modeling of grains with irregular shapes be accomplished. The method that is employed in this paper, is in fact a direct modeling of grain’s shape. In this method, the real shape of grain is modeled by combining arbitrary number of overlapping circular elements which are connected to each other in a rigid way. In order to measure the effects of grains shape on mechanical properties of granular soils three types of grains, highangular grains, medium angular grains and round grains are considered where several biaxial tests are performed on assemblies with each of grain types. The results emphasize that the angularity of grains is considerably affecting the behavior of soil. Also, the results are compared against experimental measurements in a qualitative manner which show a reasonable conformity.

In the present work, a feasibility study has been carried out in order to investigate the suitability of the use of skeletal double layer grid systems as the ceilings and walls of residential, educational, hospital, commercial and administrative buildings in seismic areas by a series of the nonlinear static as well as dynamic time history analyses of representative models. In the case of the sample single story buildings designed in accordance with the common Allowable Stress Design methods, the pushover analysis results have indicated that a lighter structure with higher stiffness and lateral load carrying capacity can be achieved compared with a similar building composed of the moment resisting frame system. It has been demonstrated that with the imposition of appropriate limitations on member slenderness ratios for a few critical members, the ductility of the structure can be improved considerably. Also, the influence of the slope of the post buckling curve representing the member behavior has been found to be remarkable. A comparison of the response of the structure under the influence of three translational components of ground motion with single component excitation has demonstrated the significance of the consideration of the vertical component of ground motion in the analysis and design of such building structures. With due consideration of the lightweight and high indeterminacy of the structural system under consideration, the preliminary investigation carried out here has revealed that the proposed system is a potential candidate for the mass production of common types of building structures in seismic areas and hence deserves further theoretical and experimental investigations.

The kinematic method of limit analysis approach is applied to study stability of reinforced slopes. The amount and length of reinforcement required to prevent the slope to collapse are determined based on different mechanisms. A new method consisting of horizontal blocks is used in translational mechanism. The failure wedge is divided into a number of horizontal slices involving reinforcements. The reinforcements do not intersect the slices. Thus, they have no direct influence on the inter-slice forces. The presented method can reduce difficulties of stability analysis for reinforced slopes. In this paper, the seismic stability of slopes reinforced with geosynthetics is investigated. The seismic analysis procedure is substituted with pseudo-static horizontal forces. While such an approach ignores the acceleration history of a structure, it is routinely used in practice. It has been assumed that the geosynthetics are uniformly distributed in the height of slope. Based on these assumptions, different possible failure mechanisms are considered and necessary analytical expressions for determining the design parameters are derived for each mechanism. The results of these analyses are presented to illustrate the influence of different parameters such as geometrical parameters of slopes, soil characteristics, and seismic forces on the stability of reinforced earth structures.

The growing increase in the number of roller compacted concrete (RCC) dams in all over the world due to their economy and construction speed in one hand and the considerable costs of their construction, new ideas on the construction and material selection for these structures are proposed continually. Since the number of horizontal construction joints in RCC dams is almost five to seven times the corresponding number in traditional dams and considering the fact that the shear stresses under static and dynamic loads are one of the most important stresses in this type of dams, and the joint retrofitting costs-which is almost ten percent of the total costs of the dam, this study aims at evaluation of the optimum place of these joints through nonlinear time history analysis of the finite element model of a prototype RCC dam. The analysis considers the soil-fluid-structure interaction between the dam and its foundation and reservoir. No need for seismic retrofitting of some joints, is one of the considerable outcomes of this study.

After observing some phenomena like liquefaction and flow failures which generally occur in loose and saturated sands, extensive investigation have been conducted in sands and effective parameters on their critical state behavior. Preliminary conducted researches have mainly been focused on clean sand or its mixtures with non-plastic fines and the critical state of clayey sands have not been much paid attention. May be it was thought that plastic properties in clay, prohibit occurring flow behaviors and liquefaction. However, carried out researches after some earthquakes like Northridge 1994, Kokaeli 1999, Chi Chi 1999 and Niigata 2004 indicated that notable settlements have been observed where soils included considerable amount of clay, resulting notable damages. These studies demonstrated that more detailed investigations should be undertaken to determine the critical state behavior of clayey sands. Previous researches have shown that a surface called state boundary surface can be defined for loose sands in the three dimensional space that determine the shape of stress path after collapse and strain softening. Unsteady states that sand show at this condition, may lead to occur phenomenon such as liquefaction and flow behaviors during the undrained loading. This research is aimed at evaluating existence of boundary state surface for 161 Firoozkooh sand and its mixtures with different plasticity clays. In fact, the main objective is to assess the effect of fine percent and its plasticity on characteristics of boundary state surface in the three dimensional space through employing proper parameters and mathematic equations. The obtained results indicated that state boundary surface characteristics depend mainly on the fine percent and its plasticity. Since state boundary surface characteristics mainly determine the behavior characteristics of soil sample in the critical state, the effect of changes in the shape and characteristics of this surface on critical state soil behavior has been investigated in the next step. In this way, valuable results have been obtained about the effect of fine percent and its plasticity on the behavior characteristics and liquefaction potential of clayey sands.

This paper assesses three definitions of eccentricity employed in the description of asymmetric multistory buildings. Other definitions of static eccentricity in multistory buildings fall essentially into one of the above categories. Using the three approaches, formulae are developed to evaluate the asymmetry of shear-type buildings where the deformation is governed by the lateral and rotational rigid-floor displacements arising from the seismic design loadings. Finally by modelling three concrete buildings according to Iranian concrete code (ABA) and investigating these three definitions and comparing them, the best method for representing Iranian 2800 Standard was selected. Simple comparisons and comments on the alternative approaches are presented with the aid of these appropriate examples. This clarification of the definition of eccentricity isneeded for improved understanding of the application of codified torsional design procedures. It is also a prerequisite for advanced studies of the inelastic seismic response of multistory shear buildings.