Scientia Iranica
Volume:19 Issue: 3, 2012

Phenomena related to the fatigue behavior of pavements are among the most important concerns confronting pavement designers. Damage caused by pavement fatigue requires large amounts of money to be budgeted for the maintenance and rehabilitation of highway and airport pavements, and this expenditure motivates research into methods to reduce the fatigue damage. One of these proposed solutions is the inclusion of waste materials in the material used for pavement construction to increase its strength against dynamic loading. Many models have been developed for predicting the fatigue behaviour of asphalt concrete pavements, but none exist for asphalt mixtures modified by the addition of waste materials. This paper presents the first model of the fatigue behaviour of glass-asphalt (glasphalt) mixtures, which is able to describe the fatigue behaviour of glasphalt under dynamic loading. The proposed model is then compared with a number of previously suggested models for the behaviour of Hot Mix Asphalt (HMA). Glasphalt concrete mixtures are shown to have a longer fatigue life than HMA.

Cyclic loading-induced pore water pressure and degradation in the stiffness and strength of saturated soils are most important in dynamic stability analyses of soil structures, because they highly influence the behavior of soils. Conducting laboratory tests for the study behavior of soils is time-consuming, requires huge effort, and is usually expensive. Thereby, the prediction of soil behavior using analytical models can be utilized in the feasibility studies of projects, early decisions in the field, parametric analytical evaluations, etc. Therefore, some efforts have been made to model the excess pore water pressure and degradation characteristics of sandy and clayey soils due to cyclic loading; however, mixed clayey soils have not been examined in detail. This article offer regression analysis-based models to determine the cyclic loading-induced pore water pressure and degradation index of mixed clayey soils using laboratory tests data. The major parameters of the models are the number of loading cycles, cyclic strain amplitude, granular material content, and effective confining pressure. To establish functional relationships between variables, some linear and nonlinear regression tools are used. Residual analyses of the models illustrate that they are superior in establishing meaningful correlations and can be employed effectively, in practice, in the range of parameters used in conducting laboratory tests.

In the presented work, the compressive behavior of circular cylinders, having certain size ratios and containing a notch with various configurations, was investigated through experimental and numerical studies. Nonlinear finite element analysis, using ABAQUS software, was conducted to evaluate the ultimate strength of the cylinders. The results were compared to those observed experimentally. The comparison of the numerical and experimental results showed that the nonlinear analysis results were more accurate than those established based on a linear analysis. The study also focuses on the deformed shape and stress distribution of the critical region in a notched cylinder for further consideration, e.g. repairing purposes.

In this study, the effects of using blast furnace slag, ground basaltic pumice and blast furnace slag + ground basaltic pumice as fine aggregates, on the durability of concrete pipes, were investigated. Blast furnace slag, ground basaltic pumice, and equal amounts of blast furnace slag and ground basaltic pumice were used at 5%, 10% and 15%, by weight, in place of fine aggregate, in mixes. The durability of concrete pipes has been tested, according to standard procedures. The sulfate resistance and permeability of the reference specimen and the specimen with admixtures were investigated. It was observed that the ultimate load of specimens depends on the type and percentage of admixtures. The maximum ultimate load was obtained in concrete specimens containing 5% blast furnace slag and 5% ground basaltic pumice, which was 20% larger than that of the reference concrete specimens. Furthermore, concrete specimens with 10% ground basaltic pumice were found to have the highest sulfate resistance.

This paper presents a two-phase, hybrid, Cellular Automata–Linear Programming (CA–LP) method for both size and topology optimization of planar truss structures, in order to achieve the minimum weight of the structure under stress, nodal displacement, cross-sectional area and kinematic stability constraints. The optimization process is carried out in two phases. In the first phase, the optimal topology of the structure is obtained by replacing the topology optimization problem with a proper sizing problem. In the second phase, the topologically optimized truss obtained from the first phase is solved to determinate the optimal sizing of the structure. The resulting non-linear sizing problem is solved using a recently introduced CA–LP approach. This method uses the nodal displacements and internal forces of the truss structure as decision variables, instead of the cross sectional areas, and the resulting problem is solved iteratively, with two solution stages at each iteration. In the first stage, the internal forces are kept fixed, and nodal displacements are found using a CA approach. In the second stage, a linear programming problem is defined and solved, using a Simplex method, to find the set of internal forces for the fixed nodal displacements obtained at the first stage. The efficiency and effectiveness of the proposed method is evaluated using some benchmark case studies. The results show that the proposed method achieves the same optimization level of some available methods in the literature with much reduced computational effort.

Recent research has indicated that even though construction materials and components may constitute more than fifty percent of total project costs, existing methods for managing them still depend on human skills. This traditional data collection is time and labour-intensive, error-prone, and unreliable, due to the reluctance of workforces to monitor and record the presence of large numbers of material. Automating the task of identifying and tracking construction materials can provide timely and accurate information on materials available to the manager. This paper investigates a new approach for integrating the latest innovations in ADC technologies for real-time data collection in construction. In this approach, the combination of Radio Frequency Identification (RFID), Global Positioning System (GPS), and General Packet Radio System (GPRS) technologies can facilitate extremely low-cost, infrastructure-free, and easy-to-implement solutions to uniquely identify materials, components, and equipment. The presented system is fully automatic and will lead to their location and tracking in three phases, namely, production sites (off-site), en-route (shipping), and construction job sites (on-site), almost instantaneously.

A total of 27 large scale direct shear tests have been conducted to investigate the shear strength and dilatancy of well graded sand-gravel mixtures. This paper focuses on the differences in behavior between three soils: sandy gravel with a specified gradation as the base soil, and two other ones with equivalent scalped or parallel gradations. Direct shear tests were conducted on three considered soils. Maximum grain size is 25.4 mm in base soil, and is limited to 12.5 mm for equivalent scalped and parallel gradations. Test results are considered in terms of frictional and dilatancy contributions to the shear strength as a function of relative density and applied surcharge pressure. According to the results, the gradation of tested soils affects their shear strength by a change in maximum friction angle, which can be related to both dilatancy at failure and the constant volume friction angle. Scalped gradation is found as a better approximate gradation compared to the parallel one for determination of peak shear strength for coarse grained soils. Finally, empirical equations are developed to relate the shear strength characteristics of the base gradation to scalped and parallel ones.

The concept of beam on an elastic foundation has been extensively used by geotechnical engineers for foundation design and analysis. However, most numerical solutions for beam on an elastic foundation are obtained by mesh based methods, such as finite element or finite difference methods. Mesh based methods suffer from some deficiencies, mostly related to mesh definition. In this paper, a mesh-free method, called the radial point interpolation method, is implemented for the analysis of a beam on two parameter elastic foundation. The beam and the elastic foundation are modeled separately. The geometry of the beam is simulated by a set of nodes that are aligned on two or three parallel lines. The displacement field along the beam is constructed by radial basis functions, and the discretized system of equations is derived by substitution of the displacement field into the weak form of the governing equation. The elastic foundation is simulated by the concept of the linkage element and there is no need for nodes or elements in the traditional sense. The stiffness of the foundation has been taken into account by defining normal and tangential stiffness coefficients along the foundation layer. The displacement of each point across the foundation layer is tied to the displacement of the beam nodes. The final system of equations is derived by a combination of equations for both the beam and the elastic foundation in the global coordinate. Based on the derived equations, a computer code has been developed and the results of analysis with the mesh-free method are compared with the results of the exact solution and results obtained from finite element analysis.

In this paper, the optimum design of some floor systems, including composite slab, one way waffle slab, and the formwork of a concrete slab, is performed via recently developed meta-heuristic algorithms, namely, the Charged System Search (CSS) and the Enhanced Charged System Search (E-CSS). The CSS is a multi-agent approach based on some principles of physics and mechanics. Each agent, called a Charged Particle (CP), is a sphere with uniform charge density that can attract other CPs by considering the fitness of the CP. Here, optimum designs are based on LRFD-AISC and ACI 318-05. The objective function for each structure is the cost function. This function includes materials used and the construction cost of the structure. The considered structures are also optimized by the Improved Harmony Search (IHS) algorithm and the results are compared to those of the CSS.

In this paper, a new approach combining the features of the homotopy concept with the variational approach is proposed for describing and predicting analytical approximations of a conservative oscillator with strong odd-nonlinearity. The new technique does not depend upon small parameter assumptions, and incorporates salient features of both methods of homotopy perturbation and the variational approach. The cubic–quintic duffing oscillator is analyzed to illustrate the usefulness and effectiveness of the proposed technique. Four approximate formulas for the frequency are established for small, as well as large, amplitudes of motion. The results of applying this procedure to the cubic–quintic duffing equation are compared to those analytical and exact solutions, in order to substantiate the accuracy and correctness of the approximate analytical approach. The approach can be easily extended to other nonlinear oscillators.

Slope stability analysis is a branch of geotechnical engineering that is highly amenable to probabilistic treatment. Probabilistic analysis of slope stability has received considerable attention in the literature, and has been used as an effective tool to evaluate uncertainty that is so prevalent in variables. In this research, the jointly distributed random variables method is used for probabilistic analysis and reliability assessment of the stability of infinite slopes without seepage. The selected stochastic parameters are internal friction angle, cohesion and unit weight, which are modeled using a truncated normal probability distribution function. The geometric parameters, such as height of slope and angle of slope relative to horizontal, are regarded as constant parameters. The results are compared with the Monte Carlo, Point Estimated, and First Order Second Moment methods. Comparison of the results indicates the superior performance of the proposed approach for assessment of reliability.