Scientia Iranica
Volume:21 Issue: 4, 2014

Damage detection and estimation in structures using incomplete static responses are presented in this study. In the proposed approach, damage location and severity is determined by solving an optimization problem using pattern search algorithm. Therefore, the objective function is formulated using incomplete static responses. Because of limitation in using sensors and difficulties in sensing all degree of freedoms, the effect of using incomplete responses has been evaluated. The performance of the proposed method is evaluated using three numerical examples, namely a simply supported beam, three-story plane frame and plane bridge with and without noise in measured displacement and containing one or several damages. The results indicatedthat proposed method is effective and robust in detection and estimation of damage in spite of the incomplete responses.

The purpose of this paper is to put forward the effect of different turbulence closer models on an enhanced Moving Particle Semi-implicit (MPS) method for solving continuity and momentum equations of viscous fluid. MPS method is a mesh- free Lagrangian method capable of solving non-linear governing equations and simulating complex free surface flow circumstances. Various turbulence closer models are added to a MPS program and applied it to different fluid mechanic problems to investigate the effect of these types of closure. Dam break simulation outcome indicates that two-equation turbulence model improves free surface estimation accuracy most. It also shows that type of utilized Kernel function has no significant efficacy on stability when the effect of turbulence is included. Further, an algorithm called Incomplete Conjugate Cholesky Gradient (ICCG) is applied for computing pressure implicitly. Applying developed model to well-known sample problems cited in the literature represents that using turbulence closure models can enhance the prediction of developed model as well as stability of the simulations.

In this study laboratory testing of e ectiveness of cement treatment has been made on geotechnical parameters of problematic soils encountered in southern coast line of Caspian Sea, Iran. Gorgan loess, Rasht clay, and Anzali sand were selected in this research. Addition of cement was found to improve workability and increased uncon ned compressive strength, and elastic modulus of soils signi cantly. Triaxial test results indicated that cement treatment not only improved shear strength remarkably, but also it changed the type of failure greatly from ductile to brittle behavior. The large scale direct shear test results showed signi cant improvement in shear strength and shear modulus. Besides, the brittle behavior of cement treated samples was observed. Eventually, it was found that the trend of failure envelope of cement treated samples was non-linear, and some failure criteria such as modi ed Grith theory, Hoek-Brown theory, and the Johnston criterion can describe the soil cement behavior satisfactorily.

The study aimed at presenting the leadership characteristics of Nigerian construction professionals involved as team leaders on building projects. Sixty construction project managers who were based in the Nigerian cities of Lagos and Abuja were selected for the study. A questionnaire was designed to collect data on 11 variables pertaining to the leaders including professional grouping, age, educational and professional qualifications, industrial experience, overseas training, overall training, personality, leadership style, style range and effectiveness. Descriptive statistics were used for the analysis of the data obtained. One way analysis of variance and Chi-square were used to test the study hypotheses. Notable findings include: Majority of the project leaders exhibited consensus leadership style, overwhelming majority style range support high task/high relationship behaviour;there was no significant relationship between the project leader’s professional background and his leadership style, and there was no significant relationship between project leader’s professional background and effectiveness.

Nonlinear nite element analysis of RC beams under combined shear and torsion to extract linear and curvilineThe use of non-linear nite elements to assess the e ect of transverse reinforcement amount on the shape of shear-torsion interaction curve for RC beams is addressed. At rst, FEM results for specimens under pure torsion and combined shear and torsion were validated with previous outcomes. Secondly, reference specimens were made with the minimum required transverse reinforcement at rst. Each specimen was analyzed with the nite element method and tested under similar conditions in the laboratory, and the results, including the cracking pattern, cracking and ultimate loads, and shear-torsion interaction curves, were found to be in very good agreement. Finally, the transverse reinforcement amount was increased to certain extents and similar results were determined. FEM interaction curve stood below the experimental curve. It was also deduced that, from a certain increase in the transverse reinforcement, the shear-torsion interaction curve transforms from linear to elliptical.ar ranges of interaction curves.

Equivalent linear one-dimensional site response analysis, which approximates the nonlinear soil behavior within the linear analysis framework, is widely used in estimating local site effects. In this analysis, soil behavior is often assumed to be independent of the frequency of seismic loading. However, the large scale triaxial test results on rockfill material have shown that the shear modulus, and especially the damping ratio, are influenced by the loading frequency. A series of one-dimensional equivalent linear analyses were performed on 30m and 90m thick profiles of the studied rockfill material to evaluate the frequency-dependent soil behavior under several well-known near-fault ground motions. The analyses are carried out for three base acceleration levels, namely, 0.1 g, 0.35 g, and 1 g, using the simple time history scaling method. Results show that the frequency-dependent shear modulus and damping ratio can have a pronounced influence on propagated ground motions. The frequency-dependent soil behavior is also dependent on the thickness of soil profile,amplitude, equivalent no. of cycles at 0.65τmax, and frequency content of the input ground motion.

Small-strain shear modulus, G0, is an important fundamental soil property. Although many studies have been conducted on this property for clean sands and pure clays,small-strain behavior for mixtures of sand and fines has been less addressed. Thispaper presents the results of a comprehensive laboratory study on G0 value of sandcontaining various amounts of different fines. To this aim, bender elements wereintegrated into a conventional triaxial apparatus, and shear wave velocity wasmeasured on samples of sand with different amounts of highly-plastic, medium- plastic, low-plastic, or non-plastic fines at different void ratios. Measuring the shearwave velocity and thus obtaining G0 at different void ratios and effective stresses, theintrinsic parameters that characterize G0 were determined for the tested materials.This allowed the effects of fines type and content on the G0 value of sand to beevaluated in a systematic manner. The G0 values of different sand-fines mixtureswere compared based on different density parameters. Results show that G0 of siltyand clayey sands is affected by both fines content and fines type. Therefore, in orderto estimate G0 of sand-fines mixture, not only the fines content but also theirplasticity needs to be properly accounted.

A novel and robust approach is proposed to find the optimum shape of concrete arch dams located on any unsymmetrical shape of the valley. The approach is capable to find the optimum shape for any given valley type in suitable time based on the abutment stability analysis against thrust forces from arch dam. The behavior and stability of the concrete arch dam is strongly dependent on the bedrock that dam rests on it. Stability of abutment is considered as a constraint in proposed approach. In addition a new objective function is introduced to decrease the final volume of the arch dam. Furthermore, a computer program was developed which can take effect of the dam foundation system into consideration and can model the most loads that applied to arch dams. The optimization problem is solved via both the Particle Swarm Optimization (PSO) and classical methods. Several practical factors have been considered to make the approach more feasible and effective in practical projects. The results show the efficiency of the proposed method and the final shape satisfy all constraints.

A dependable long-term prediction of tunnel surrounding rock displacement is an effective way to predict the rock displacement values into the future. A multi-step-ahead prediction model, which is based on support vector machine (SVM), is proposed for tunnel surrounding rock displacement prediction. To improve the performance of SVM, parameter identification is used for SVM. In addition, to treat with the time-varying features of tunnel surrounding rock displacement, a forgetting factor is introduced to adjust the weights between new and old data.At last, the data from the Chijiangchong tunnel are selected to examine the performance of the prediction model. Comparative results were presented between SVMFF (SVM with a forgetting factor) and artificial neural network with a forgetting factor (ANNFF) show that SVMFF is generally better than ANNFF. This indicates that a forgetting factor can effectively improve the performance of SVM, especially for the time-varying problems.

The sustainable practices in the built environment are based on conservation of resources, such as minimum use of material, energy and water. Disposal of construction waste poses major challenge to the municipal administration of the developing countries. The fast urbanization and rapid construction in these countries has generated substantial volume of construction wastes. There are many options for the disposal of construction wastes. One of such options is to utilize these wastes as aggregates for concrete. The reuse of such aggregates in the concrete would reduce the disposal costs of construction wastes on one hand and burden on natural resources in terms of resource harvesting on the other hand. In this research work, the construction wastes collected from the municipal sources have been segregated, graded and utilized as aggregates in cement concrete. Considering different percentages of recycled aggregates, various concrete mixtures were prepared and tested to determine their compressive strengths for evalauating suitability of the concrete mixtures for construction purposes. The test results indiacte that the recycled aggregates can be used for producing plain concrete mixtures for mass concreting and construction of pavements and walkways.

Composite aluminum-SiC foam was manufactured by injection of air and addition of reinforcement particles into the liquid aluminum. Microstructure and mechanical properties of the Al/SiC foams were investigated by scanning electron microscopy and compression tests. Results showed that both the cell size and the wall thickness augmented with increasing of the SiC reinforcement particles; while SiC particles resulted in the reduction of the plateau border length. With more SiC particles, plateau stress became larger; but maximum plateau strain became smaller. The stress-strain curves exhibited serrations in the plateau region due to addition of the SiC particles.

In a group of installed piles, the stresses applied from one pile to soil may have overlaps with another pile which leads to the changes in bearing capacity and settlement of each individual pile. In order to predict the performance of those piles, interaction coecients, based on elasticity theory proposed by Mindlin, are widely applied. In this paper, the e ect of soil relative density and also toe condition on the interaction between two similar piles in sandy soil is presented using centrifuge modeling. To achieve this objective, 22 tests have been conducted to investigate the e ect of soil relative density and another 11 tests were performed to study the contribution of pile toe and shaft in the interactions. The results showed that the value of soil relative density has an important role in the coecient of interaction which has not been considered in previously reported correlations. For this reason a modi cation has been proposed for the Randolph and Wroth equation to consider soil relative density. Accuracy prediction of the new modelwas compared with the Randolph and Wroth equation with the aid of di erent statistical parameters. This comparison indicated the superiority of the proposed model over previous methods.