MODARES TECHNICAL AND ENGINEERING
Year:2008 | Volume:- | Issue:33 (SPECIAL ISSUE ON CIVIL ENGINEERING)|Papers Count:11

Foam asphalt IS a mixture of foamed bitumen that is spread onto the aggregates at ambient temperature. Foam bitumen is expanded bitumen that is produced when cold water is injected into hot bitumen with compressed air. The result is the increase of bitumen viscosity and improvement of the ability of the mixture to cover aggregates. As these entire procedures take place at ambient temperature, so these mixtures are classified as cold mixtures.Despite many advantages of the foam mixtures, there is not a standard mixture design established yet. In this research, in order to establish a design for foam bitumen mixtures, some foam bitumen samples were prepared in laboratory and Marshall test and ITS (Indirect Tensile Test) were used to characterize mechanical properties of the samples. After determining the optimum bitumen content, few percentages of lime and/or cement powder were added and the tests were repeated in order to determine their effects. The air voids of the samples were also determined setting up a modified permeability test method. Unconfined Compressive Strength (UCS) test was also performed and from the results, a relationship was established between dry ITS & UCS.

The shear strength of soils is an important aspect in many geotechnical problems. Problems such as the bearing capacity of shallow foundations and piles, the stability of the slopes of embankments, and lateral earth pressure on retaining walls. Furthermore, regarding brine spreading in the earth, there is always probability that the soils be exposed to brine. Therefore, recognition of behavior and interactions of soils due to the sodium chloride solutions can help us to take the best decision about these soils. In this study, the strength behavior of compacted clays exposed to brine in a short period of time and after 40 days regarding the effect of lateral pressure was explored and was differentiated with the sodium chloride permeation effects on shear strength.

Reinforced concrete shear wall with opening is one of the important elements of the structures for resisting earthquake. Therefore, their behaviour has been the concern of many engineers and designers. On the other hand, nonlinear dynamic analysis which can give the real behavior of the shear wall is very complicated, and thus has forced the engineers to use the available linear analysis methods. In order to consider the effects of non linearity of structures in the analysis, the codes used in practice, has recommended the use of the behavior factor.In this paper, behaviour factor and as a result, extra resistance factor, reduce factor due to deformation capacity for shear walls of symetrical 5, 10, 15 and 20 story buildings with different parameters under Naghan and Tabes earthquake were calculated. In fact with different shear wall and earthquake, the effects of different partameters on behaviour factor are considered. As a result, an average behaviour factor obtained, which does not depend on shear walls or earthquake. It could be understood from the analysis results that average behaviour factor of the studied walls with opening varies between 7.9 and 11.27 and average behaviour factor under Naghan and Tabes earthquake is about 9.6 and 10.1. Furthermore, the results are in good agreement with the Iran's standard 2800, and behaviour factor of shear walls with more than one layer of opening is bigger than one large opening.

In this study, results of nonlinear analysis of RC columns confined with CFRP composites at different parts of the column, under different ratios of lateral force to axial load were investigated. To evaluate the strength enhancement of the confined columns, the load-moment curves for the specimens confined with FRP sheets at different parts of the columns' height were drawn. Furthermore, the ratio of the total area under the moment-rotation curve to the area under the linear part of the curve was taken as ductility criterion. Accordingly, the ratio of the ductility for the specimen confined with FRP composite for a balanced section, to that for the specimen with confined core with spiral reinforcement was calculated as 3.06 and 1.09 for columns wrapped with FRP on the whole height and on the plastic zone, respectively. In the meantime, the aforementioned ratios for those specimens compared to the conventional RC columns with no spiral were calculated as 5.99 and 3.75, respectively. Furthermore, performing nonlinear analysis and taking into account the effects of large deformations, the confinement effect due to the wrapping of the composite on the buckling of the column was evaluated. The axial loading on the column with a very low lateral force was continued until occurrence of a sudden large lateral displacement in the column. Accordingly, the confinement of the column wrapped with FRP on the whole height, enhances buckling load up to 64.4%.

In geo-environmental engineering, electrokinetics is one of effective methods for contaminant removal from clayey soils. Even though kaolinite due to its low negative charge has the small capability for contaminant retention, the presence of carbonate causes a noticeable increase on contaminant retention. In spite of several research works which have been perfomled on the efficiency of electrokinetics remediation method, the impact of carbonate on such efficiency in a pilot scale has not been well investigated.In this paper, the effect of carbonate calcium on the process of heavy metals removal by electrokinetics method on kaolinite soil and a clayey soil of liner of waste disposal site of Hamedan in laboratory in a pilot scale are investigated. Based on theoretical considerations, series of electrodes in pilot scale were designed and a series of pilot scale experiments were performed. In laboratory scale, kaolinite specimens were mixed with 4, 10, 15, 20, 25 and 30% calcite. Different concentrations of zinc nitrate were used as a source of heavy metal contamination. Batch tests were performed to define Zn (II) adsorption onto these samples. Series of electrokinetics experiments were carried out on these artificially prepared samples. The study showed that during the electrokinetics experiments, soils which have higher carbonate percentages prevent the development of an acid front. Therefore, an alkaline condition will form throughout the soil. This significantly lowers the efficiency of the method.For pilot scale experiments, the electrodes were designed and made on the basis of theoretical patterns and were arranged in two rows by I-meter distance. The natural soil of clay liner of waste disposal site of Hamedan were artificially contaminated and were used as a soil sample for pilot scale experiments in previously designed site. The experiments were performed for 100 days. Results show that the Zn(II) decontamination was inefficient. This was attributed to the presence of 28% carbonate in the natural soil. Finally, monitoring of Zn distribution is presented.

In this experimental investigation, three damaged reinforced concrete frames are repaired with infill masonry bricks. Frames are built in 1:2 scale and tested by pseudostatic method. The frames are subjected to cyclic displacement controlled loads. Then, different response parameters such as lateral stiffness, strength and energy dissipation are investigated. The results of studies show that masonry infill improves frames behavior and increases its lateral stiffness, ultimate strength and energy dissipation capability.

The transport of leachates and contaminants to the sub-layers of waste disposal sites and further contamination of underground water is a common problem in geo-environmental engineering. The use of sand enhanced bentonite (SEB) mixtures, as a layer to prevent contaminant transport, is very common in these projects. These mixtures have very high adsorption characteristics and very low hydraulic conductivity. Previous researches indicate that the variation of hydraulic conductivity of soils is a function of plasticity properties of soil. In the current research the impact of two heavy metalions (HMs), Pb and Zn, which can be found in many industrials waste disposal sites, on plasticity behaviour of soils are investigated. Samples of mixtures of sand-bentonite, at different sand-bentonite ratios, were exposed to different concentration of heavy metal ions. After equilibrium condition, the atterberg limits of those samples were determined. In addition, the effect of Pb and Zn ions on the pH of samples is monitored. Furthermore, the impact of heavy metal ions on the soil structure is assessed by the use of SEM micrographs. Results show that the presence of heavy metal ions causes a reduction on the plasticity behaviour and pH of the samples. These reductions are attributed to the adsorption of HMs to the bentonite, the flocculated structure due to the low pH, and decrease of the thickness of the double layer. For restriction of these impacts it is suggested that only 20% bentonite is used in SEE.

Field testing of bridge vibrations induced by passage of vehicles is an economic and practical form of bridge load testing. Data processing of this type of tests is usually carried out in a system identification framework using output measurements techniques which are categorized as parametric or nonparametric methods. These methods are based on the theory of probability. Learning theory which stems from two separate disciplines of statistical learning theory and neural networks, presents an efficient and robust framework for data processing for such tests. In this article, ADALINE- Adaptive Linear Neuron networks- with LMS (Least Mean Squares) learning rule have been adapted for strain and displacement sensors fusion of a railway bridge load test. The trained NN has been used for structural analysis and finite element (FE) model updating.

For buildings to resist and properly dissipate energy during earthquake, suitable connections are those which allow plastic hings develop in beam neither connection elements or welds should fail or break, nor panel zone should be damaged during earthquake. Buttress connection is one that meets all such requirements. A full scale model of this connection is tested in the University of Berkeley. During the research the connection is modeled by finite element method with special consideration of post buckling effects and calibrated with experimental data. Two buttress plates in the top and bottom of beam as well as web stiffeners of beam and column are arranged in the form of a truss and created a rigid zone so plastic hinge is developed in the beam, the elements of connection do not fail, stress concentration in weldes is low and weldes do not damage during loading and plastic zone remained elastic. The effect of buttress plates in top and bottom and web stiffener of beam is studied. For studying, any of these plates are removed and under a new connection is loaded. The results show that if buttress plates are removed, even though plastic hing is developed in the beam but stress concentration is increased in the weld, connection zone is damaged and plasticity is developed in panel zone. If web stiffener of beam is removed, plastic hinge is developed in connection zone and the connection fails.

Wavelet transform (WT) is a relatively new mathematical tool that does not have disadvantages of the Fourier transform (FT). In recent years enormous interest on its applications in the solution of problems in engineering has been observed. This technique is particularly suitable for non-stationary processes for which FT is useless. The WT allows exceptional localization both in time and frequency domains. This technique has been successfully implemented in signal and image processing, solution of differential equations, numerical analysis, dynamic analysis and other fields. The continuous wavelet transform (CWT) of a signal can represent the time and frequency domain content at the same time. In the WT the use of a fully scalable window solves the signal-cutting problem. The window is shifted along the signal, and for every shift the spectrum is calculated. This process is repeated with a slightly shorter (or longer) window for every new cycle. At the end of the process, we have a collection of time-frequency representations of the signal, all with different resolutions. The CWT is used for decomposition of earthquake records in time-frequency localization. The CWT shows the time of occurrence for each frequency component in the earthquake records. Numerical results show that this approximation is a powerful technique and the error involved in CWT is small. A number of earthquakes have been decomposed and the results are compared with that of the fast Fourier transform (FFT) method.

One of the major stresses which develop in concrete pavements is the thermal stresses. Since concrete is less able to deform in response to temperature changes than bituminous materials, thermal stresses have to be taken into account as well as traffic stresses in analysing the behavior of concrete pavements. Temperature stresses in concrete slabs can be divided into three categories namely, end restraint compressive stress, foundation restraint compressive and tensile stress and partially or completely restrained warping stresses. Since the concrete has a high compressive strength, the first category does not take into account, but developing the two other kinds of thermal stresses in concrete pavements are inevitable and when added to traffic stresses here are called combined stresses. The combination of these can cause cracking and failure in pavements. The conclusion of this investigation showed that the day time combined stresses have an adverse relation to the length of slabs while the night- time combined stresses are directly proportional to the slab's length. From comparing the various results it was concluded that the results from Westergaard equations normally overestimate the curling stresses for both day and night times by 17% and 30% respectively.