Ferdowsi Civil Engineering
Year:2012 | Volume:23 | Issue:2|Papers Count:8

In the realistic manner, piles are similar to the slender columns that soil around them acts as a lateral support. The piles situated in the liquefiable soil layers, loss their lateral supports due to the liquefaction resulted from the seismic ground motion. In this case, pile has the potency of axial instability similar to the unsupported columns. This instability can lead to the lateral buckling of the piles in the eak direction and creating the plastic hinges in the pile’s badly. Many failures that acurr in the piles and their supported structures, due to the lique faction of soils after earthquakes has been reported. These piles ere designed based on the credictable codes such as JRA and NEHRP. So it seems that the behavior and analysis methods of piles are still unknown. This research attempts to predict the buckling capacity of the piles in layered liquefiable soils, using a numerical method in which Rayleigh-Ritz approach was employed to minimize total potential energy. Furthermore, a new practical approach has been presented to calculate effective buckling length of pile in liquefiable soils. By the means of this approach the buckling capacity of pile could be obtained while the stiffness of pile and soil are accessible. This method can be also applied to the extended pile shafts in the bridge piers.

With respect to the new aspects of earthquake engineering in the area of performance besed design, accurate estimation of structural response becomes more important. This requires precise recognizing of relevant parameters in the behavior of structures and using proper methods for applying the effects of distribution of these parameters in the desired response. In this study the effect of distribution of existing uncertainties on the important parameters corresponds to the behavior of reinforced concrete frames is studied. For this purpose by using sensitivity analysis of tornado diagram and first-order second-moment approximation method, the important parameters in different behavior states of structure are recognized and by using first-order second-moment approximation method and Monte Carlo simulation, the effects of uncertainties in the selected response are combined together and results of these two methods are compared.The results indicate acceptable accuracy of first-order second-moment approximation method for combining the effects of uncertainties on the desired response and efficacy of this method for classification of uncertainties.

This article is devoted to the simultaneous optimization of shape and topology of shell structures. The optimum shape is obtained together with the optimum layout for the reinforcement layers at the both sides of the shell surface. To solve this problem the finite element method is employed. It is assumed that each element is comprised of a porous media with microscopic rectangular voids where the density of the material in each element is a function of the geometric parameters of the voids. These parameters are also considered as the design variables of the topology optimization problem. The geometry of the shell structure is defined by using Non-Uniform Rational B-Splines (NURBS) technique and the control points of the NURBS’ surfaces are considered as the design variables of the shape optimization problem. For solution the Method of Moving Asymptotes (MMA) is employed. To demonstrate the efficiency of the method a few examples are presented and the results are discussed.

In this paper the response modification factor due to ductility and saved strength of cylindrical concrete elevated and ground tanks is obtained using finite element method and nonlinear push over analysis considering the lateral effective modes of tanks. To modeling the behavior of the tank materials, the five parameters William-Warnke and prefect elastoplastic models are used for concrete and reinforcement rebars respectively. In the calculations the reinforced bars are modeled both exactly and as percentage of concrete surface area. In addition it is assumed that the foundation of the structure is absolutely rigid and contained water has linear behavior. The response modification factor is obtained for different performance levels by changing different parameters such as height, thickness, radius, and percentage of the rein forcementbars of the shaft and shell, thickness and dimensions of stiffener and water level. The obtained results show that the factor for the elevated tanks changes between 4and 5 and the factor for the ground tanks varies between 1 and 2.5 these changes depend on the performance levels for the tanks.

Regarding the increasing demand for lightweight concrete especially lightweight structural concrete, and safety requirements underlined in 2800 Iranian standard, research to achieve the optimized results in lightweight concrete production seems inevitable. Since, one of the commonly used methods for producing the light eight concrete, utilizes the light weight aggregates with significant role in the concrete strength, proposing the optimized mix-design for the light weight concrete appears to be important. In this paper, concretes made from leca, perlit and scoria, are investigated. By using the light weight concrete, 120 cubic specimens were constructed and tested by compression and twist-off methods. In addition to the relationships between the results of compression tests and twist-off method, effects of the additives on the properties of the lightweight concretes are presented.

Excessive production and stockpile of scrap tires cause some environmental and sanitary risks throughout the world. To manage these materials, possible use of soil-tire mixtures has been recently propounded in civil engineering projects. A few studies previously have been conducted to evaluate behavior of clay-tire mixtures, while swelling properties, consolidation and settlement characteristics of this type of mixtures are not known admirably. For this purpose, a number of clay-tire chips mixtures were prepared (by adding 10%, 20%, and 30% tire-chips to the clay), and compaction and oedometric consolidation tests are carried out on them. The results show that adding tire-chips to the clay, reduces swelling potential of the mixtures, while the free swelling and swelling pressure of specimen consist of 30% tire-chips is negligible.Also, size of the tire-chips may affect the values of free swelling and swelling pressure. In addition, the results of oedometric consolidation tests indicate that when the tire content increases, compression and swelling indices of the specimens decrease and increase, respectively. Moreover, the settlement behavior of the specimens depends on the tire-chips content and size of the chips.

In this research, failure mechanism, soil deformation and effect of reinforcement below a strip foundation were studied using physical modeling and PIV method. For this purpose, a comprehensive set of tests were undertaken on dense and loose sands and different geosynthetic materials such as geotextile and geogrid for soil reinforcing. In each step of loading, digital image of deformed soil was captured and image processing was applied with GeoPIV software. The experimental results showed that using of geogrid and geotextile leading to increase bearing capacity considerably, reduce settlement and change the failure mechanism of sand. The test results showed also that geogrid has an effective performance in comparison with geotextile in sand at the range of small strains.

Pavement design using mechanistic-empirical methods is often carried out based on the some assumptions for pavement layer's properties (thickness, elastic modulus, Poisson's ratio and ….), loading properties (axial weight, tire coordinates, number of repetitions and …) and also the failure mechanism for different materials. Fulfillment of these assumptions for evolution of pavement performance during service life is impossible. This is because of the uncertainty in the traffic preaiction of different vehicles, problem of precise determination of material specifications due to high cost of some tests and also errors and limitations in the construction phase. The error Existance in the estimation of input pavement design parameters leads to the probabilistic procedure. for the pavement design This helps the designer to study the influence of uncertainty of input parameters on the pavement performance parameters and finally controlling the design reliability. Because of the complicated computations for pavement analysis and its performance prediction, classical methods based on the deviation are not applicable to the reliability analysis of pavement performance. In this paper, the effect of the error in estimating the different input parameters of pavement design (elastic modulus, thickness and tire pressure) on prediction error of the fatigue and rutting life is studied using Monte Carlo Simulation method. For this purpose, three pavement sections with different structural capacity were considered and importance of each input parameter on prediction error of fatigue and rutting life have been prioritized. The possibility of using Monte Carlo simulation to develop some relationships to estimating the pavement rutting and fatigue life error has been explored. These relationships can be applied for future reliability analysis without using simulation.