Civil Engineering Infrastructures Journal
Year:2012 | Volume:45 | Issue:7|Papers Count:9

This paper deals with the dynamic interaction of a massless rigid circular plate and a transversely isotropic full-space in frequency domain. The plate is located in an arbitrary place in the full-space in such a way its normal vector is in the direction of the axis of material symmetry of the domain, and undergoes a vertical displacement with a frequency of. Using potential representation and Henkel integral transform, and satisfying the continuity and regularity conditions, the governing equations are transformed to dual integral equations, which can be changed to a Fredholm integral equation of second kind. The Fredholm integral equation is solved analytically in the static case, where is zero, and is numerically evaluated in the general dynamic case. The results are shown to be identical with the simple case of isotropy in both analytical form and numerical evaluation.

Application of simulation-optimization models to the problem of optimal design and operation of multi-reservoir hydropower systems with control on the reliability of meeting the system’s energy yield could be a suitable approach to solve the resulting mixed integer nonlinear, nonconvex optimization model. An optimization-simulation model has been developed in this study by integrating MODSIM river basin simulation model and Particle Swarm Optimization (PSO) algorithm. First, the possibility of defining an energy demand-node and applying a hydropower standard operating policy (HSOP) in MODSIM was provided. Then the extended simulation model (MODSIMP) was linked to the PSO algorithm with the objective function of maximization of the net benefit from the system’s design and operation over its projected life period. In the developed model, each objective function evaluation of PSO is performed by running MODSIMP. Analysis of the PSO-MODSIMP model results was done through its application to the problem of optimal design and operation of the Khersan multireservoir hydropower system as a real case study. Computational efficiency of the MODSIMP in simulating the operation of multireservoir hydropower systems and the flexibility of the PSO algorithm in considering the model nonlinearity has provided a promising modeling tool in tackling the problem of optimal design and operation of multi-reservoir hydropower systems.

In this paper, the influence of joint roughness on the support requirements for the stabilization of highway tunnels constructed in jointed rock is investigated. For the numerical analysis, UDEC program which is based on distinct element method (DEM) is used. Several models are included in UDEC including elastic model, Mohr Coulomb model and null model for the blocks and point contact, area contact and Bandis-Barton model for the joints. Mohr Coulomb model is used for the blocks and area contact model is used for the joints in this research. Two joint sets dipping 70 and 130o with spacing of 1m are considered and it is assumed that all base characteristics of the joints remain the same in various analyses except the roughness of joints. The analyses are carried out both for single and twin tunnels. The distance between the twin tunnels have been selected in such a way that they do not affect each other. For the support system, a combination of shotcrete and rockbolt is used.The results of the analyses indicate that the increase in joint roughness leads to the decrease in support requirements to a certain degree which are discussed in detail both for single and twin tunnels. It is also concluded that in general, twin tunnels each comprising two lanes for one direction require less support compared with the equivalent single tunnel.

In this paper, semi-active vibration control of a single degree of freedom (SDOF) system under seismic excitation using magnetorheological (MR) damper is investigated. A Proportional-integral-derivative (PID) controller is used as the control algorithm. The present study just addresses the results of the numerical simulations performed in SIMULINK. The models of uncontrolled and controlled systems are made. For the controlled system, three different cases are considered: (a) ideal active control, (b) ideal semi-active control and (c) real semi-active control. Comparison of the results reveals that a properly designed semi-active control can considerably reduce the vibrations of the controlled system which is comparable to that of a fully active control.

In this study, the effect of temperature, binder content and compaction on the resilient modulus of hot mix asphalt (HMA) were studied. The samples were prepared by using gyratory compaction method. The resilient modulus of samples that were prepared with different binder content and compaction effort were determined by Indirect Tensile Method (ASTM – D4123). To increase the accuracy, the tests were conducted on two similar samples and the results were discussed by using both tests. The results show that with increasing temperature, decreasing binder content and increasing compaction effort, the resilient modulus of hot mix asphalt increase. Based on the results of this study, the variation of resilient modulus with temperature, binder content and gyration number was estimated by using a mathematical model. Comparison of the prediction of this model with experimental results shows that the model is acceptable.

There has been a dramatic growth in asphalt recycling and reclaiming as a technically and environmentally preferred way of rehabilitating deteriorated pavements over the last couple of decades. One of the latest asphalt recycling techniques is cold in-place recycling using foamed bitumen. In recent years, there have been a number of successfully implemented cold in-place asphalt recycling projects in Iran; and it seems that the utilization of this method is gaining more acceptances amongst the road authorities and the contractors. At the same time, endeavors to evaluate the performance properties of foamed bitumen mixes were started and are still in progress. The present research, studies the mechanical and the performance properties of foamed bitumen mixes. In the first phase of the project, the effect of aggregate grading, bitumen and cement content and compaction efforts, on resilient modulus and indirect tensile strength (ITS) of 144 foamed bitumen specimens (of various curing conditions) has been investigated and analyzed. In the next phase, the effect of above parameters on resilient modulus and unconfined compressive strength (UCS) of 108 different samples was studied. Results indicate that for the tested materials, changing the aggregate grading from coarse to fine didn’t have a significant effect on resilient modulus, ITS, UCS and the moisture susceptibility of the specimens. Also the effect of increasing bitumen content from two to four percent is negligible. On the contrary, adding one percent cement and increasing it to two percent considerably improved the moisture susceptibility and the mechanical properties of the mixes. Based on the obtained data, a regression model between resilient modulus and ITS of the foamed bitumen mixes was developed to facilitate the prediction of the resilient modulus based on the corresponding ITS values.

Inversion analysis of dispersion curves for surface waves is one of recent and important applications in surface soil explorations. This is a challenging problem for linear inversion procedures to be used in evaluation of surface soil mechanical properties due to a highly non-linear nature of soil and to the possibility of large numbers of local minima and maxima of the objective function (multi-modality) in any inversion procedure. As the important outcome of the current study, Genetic algorithm (GA) method is utilized in optimizing the inversion of measured dispersion curves. The main objective of application of Genetic Algorithm in this study is to estimate unknown shear-wave velocity profile of soils in such a manner that the most conformity achieves between experimental dispersion curve obtained by Array measurements of microtremors and the theoretical dispersion curve obtained by the relations which are presented by Haskell (1953) based on wave-propagation theory in layered medium. GA firstly assumes random values for unknown parameters and then by using Selection, Crossover, Mutation and Elitism operators and producing new estimation for these parameters improves the results so that the results in each generation becomes more accurate. The effectiveness of the presented method is considered by an example presented in this study. The results of provided example show acceptable coincidence between the theoretical and experimental dispersion curves. Also, the shear-wave velocity profile of the example site obtained by the new method agrees well with the profiles which are obtained by another alternative method of determination of shear-wave velocity profile.

In this paper, non-linear behaviors of structures with special moment resistant frame were studied and possibility of using knee bracing for retrofitting of those structures was examined. For this aim, the structures that have been designed according to the second edition of Iranian seismic code (2800), were selected. Those models have 3, 5 and 7 stories. To evaluating and retrofitting of models, non-linear static analysis and capacity spectra (ATC-40) method were applied and providing of the expected performance levels in FEMA356 was studied. Results showed that the response of structures that designed according to the previous edition of code (second edition) is not compatible with the criteria of third edition. The knee bracing system was used to seismic retrofit of those structures. It would be concluded that the using of knee bracing increases lateral stiffness and improves their energy dissipating capacity. Furthermore, the results showed that the shorter knees have the highest stiffness and ductility in the structures.