Sharif Digital Repository

Dynamic compaction is a widely used soil deep improvement method in dry and/or saturated soils. Despite its vast application, numerical and /or experimental modeling studies of dynamic compaction due to impact are little. In order to clarify the ambiguities in process and to present a comprehensive design approach, numerical modeling of dynamic compaction in dry soils with PISA (A fully coupled dynamic finite element code: Program for Incremental Stress Analysis) has been done. Because the geometry and loading configuration are symmetric around the falling tamper (load centerline), a two-dimensional axisymmetric simulation has been used. Here for sake of simplicity, initial velocity of... 

In recent decades, most of the codes have placed a high value on Performance Based Design of structures; however, these methods are computationally complex and time-consuming, and caused researchers to seek new and efficient methods to investigate performance of structures under different intensities of seismic loading. This issue is much more obvious when optimum design of structures, which requires repetitive analysis, is investigated. In the present research, using Endurance Time analysis, we are trying to provide better insights into the dynamic behavior of structures in continuous performance levels. Then, as a first step, we will use the verified method to find the optimum outline of... 

Road network expansion is a well known problem in the world, particularly in developing countries. One approach in financing this development is to charge the users for the services rendered. Recent studies prove the merits of private sector participation in road investment and revenue collection. Public sector may cooprate with private sector in permitting it to build the roads, operate and maintain them for certain period of time, while taking advantage of the revenues collected. The road will, then, be transferred to the public sector when that period of time is over. This study presents an extension to a previous model in this area. It presents a bi-level programming network design... 

Increasing of public transit market share in urban transportation is one of the major policies of urban system improvement. Lessening emission and fuel consumption are outstanding achievements of designing and operating effective public transit systems. As rapid transit systems play a major role in urban transit network, feeder bus lines can play as their complementary role in the urban transit scene. Feeder bus network provide a better accessibility and coverage for passengers. In spite of its important role, feeder bus network design is studied in a small number of publications in transit network design. In this study, a mathematical program model is presented to state feeder bus network... 

General strategies for seismic design of structure include increasing the rigidity and strength, increasing the energy absorption capacity by implementing energy dissipating devices and reducing the seismic demand by isolating the structure from its base. Isolation system provides the required ductility of the structural system by concentrating its displacements mainly on the isolator level, and separates the structure from the horizontal components of the ground motion. That would create a system whose its main frequency is much lower than the dominant frequency of the earthquake records and the natural frequency of the equivalent fixed-base structure. Because of growing tendency towards... 

This thesis investigates the performance of concentrically braced frames through numerical simulation approaches. During a moderate to severe earthquake, the bracing members and their connections are expected to undergo significant inelastic deformations into the post-buckling range. Recently, provisions for special concentrically braced frames (SCBFs) were developed to exhibit stable and ductile behavior in the event of a major earthquake. Special Concentrically Braced Frames (SCBFs) are distinguished from Ordinary Braced Frames in that they possess improved post-buckling capacity. Performance based evaluation of SCBF system as well as ordinary concentrically braced frame (OCBF) system... 

Improving synchronization in a bus network has a profound effect on reducung waiting times and increasing satisfaction of system’s users. By doing so, the scheduler create a more attractive transit system that generates the opportunity for increasing the number of riders. In this research, the problem of creating timetables with maximum synchronization is modeled as a mixed integer programing (MIP) problem. The objective of this model is to minimize the total waiting times of passengers at transfer nodes. For this purpose, the model take advantage of uneven headways. Some of features that distinguish this research are more realistic objective function, and considering adjacent departures... 

The use of unbonded post-tensioned precast concrete walls with horizontal joints as the primary lateral load resisting system in seismic zones has been considered in several previous studies. These walls are constructed by post-tensioning precast wall panels across horizontal joints using post-tensioning steel which is not bonded to the concrete. The behavior of the unbounded post-tensioned precast structural wall under lateral loads strongly depends on base panel geometry and concrete confinement properties. In this research an analytical parametric investigation on base panel design parameters is conducted using DRAIN-2DX software. Fiber beam-column elements are used to represent the... 

Despite of existing advanced routines and concepts of Maintenance, which are imported along with Metro System hardware, and valuable experience of maintenance personnel, which has been gathered during years of operation, there are some undeniable shortages in current Maintenance Policy of Tehran Metro. These shortages can be classified in two major groups: first, lake of reasonability in performing maintenance tasks and second, general reluctancy about runnig scientific works. Treating those two deficiencies, can improve the performance of Tehran Metro Maintenance System dramatically. Above mentioned shortages can be seen in whole Maintenance System of Tehran Metro, for the reason of having... 

This work investigates the possibility of developing suitable design guidelines for aircraft flying in very low altitude as well as terrain following flights (TFF). The work aims to highlight the TFF mission in the early stages of design process; as oppose to other mission conducted by the aircraft. Current approach in TFF relies heavily on efficient Flight Control System (FCS) regardless of the overall configuration of aircraft. However, in this work, we show not all aircraft in the service could conduct TFF and maneuverability of airplane is very important. In fact, we investigate the overall impact of TFF on the wing loading (W/S) and thrust loading (T/W); if we were to design an aircraft... 

Although there are several popular and standardized mix design methods for hot-mix asphalt, there is no universally accepted mix design method for cold in-place recycling (CIR). The varieties of recycling machinery, materials, quality control limitations, etc. have contributed to this problem. Most of CIR laboratory mix designs are based on 4-inch molds and maximum aggregate size of 1inch. The use of single unit train, which is the most common machinery used for CIR, results in poor control of aggregate gradation, especially when distresses such as fatigue cracking exist. This may lead to presence of aggregate sizes larger than 1 inch. In this case the use of 4-in mold is no longer... 

Design of complex systems requires different challenges to be met simultaneously. Yet the current methods lack a sound theoretic framework and thus designers normally rely on heuristic or empirical methods; based on available experiences. Such approaches to the system design entail both technical and business risks and subsequently increase the probability of long-term problems. In this research, along with the theoretical framework of the systems design concepts, we discuss number of important models. The main concentration of the work, however, is to; somehow, correlate Axiomatic Design Matrix (ADM) with Design Structure Matrix (DSM). Here we exploit mathematical model based on sets and by... 

Although Pulsed Plasma Thruster (PPT) has first been utilized in a space mission in 1964 but after more than four decades, it is still a space rated technology which has performed various propulsion tasks from stationkeeping tasks to three-axis attitude control for a variety of former missions. With respect to the rapid growth in the small satellite community and the growing interest for smaller satellites in recent years, PPT is one of the promising electric propulsion devices for small satellites (e.g. CubeSats) as the following advantages: simplicity, lightweight, robustness, low power consumptions, low production costs and small dimensions. In spite of the fact that the issues relating... 

In order to reduce structural and nonstructural damages and associated financial losses during intense seismic events such as Bam earthquake, seismic retrofitting of existing structures should be considered as a special issue. In this regard, for quantifying the seismic performance of structures a guideline termed “instruction for seismic rehabilitation of existing building No.360” is issued which is mainly borrowed from performance-based assessment procedures FEMA 356. In contrast to conventional seismic design methods which are based on controlling stress ratio for different load combinations, in performance-based earthquake engineering methodology, the displacement control of structural... 

Functional Requirements (FR) are traditionally known to be "input" as far as an engineering process is concerned. However, for a Systems Engineer (SE), this is not the case. A well-known task of a SE is, in fact, to develop FRs from what is considered as the customer needs. The traditional approach to develop suitable FRs involves an algorithmic procedure; which mostly relies on the skills, knowledge, attitude, and experiences of the SE or experts members of design team. It is therefore an ad-hoc method which results in quite a few numbers of trial-errors and its effectiveness only reveals itself as time goes on. The current work aims to address such a shortcoming in Systems Engineering... 

Considering ever expanding applications of embedded systems in all aspects of human life, reliability and fault tolerance of these systems have become vital. To increase the reliability in a microprocessor as the most critical component of an embedded system, one may notice the essential role that is offered by its register bank. In fact the register bank is the most critical subcomponent of an embedded system, greatly affecting the reliability of the overall system. The operation of the embedded system is further critically affected through optimal and efficient usage of power as most systems relay on battery. In this project, to evaluate the availability of register banks various... 

Transportation networks are considered as complex systems, and in many cases they behave in such an irregular and unexpected manner. Such complexities cause problems in studying the behavior of these systems. An example of such complexities is chaos in the network flows. On the other hand, the behavior of these networks is highly affected by the incidents like accidents and bad weather. Such events affect the level of service and travel time reliability of the networks. In this research, a dynamical approach to traffic assignment has been chosen to model chaos and uncertainties in the network. By using this approach for modeling flow evolution, edge of chaos and uncertainty in supply and... 

The aim of the present research project has been techno-economical analysis of using a CCHP (Combined Cooling Heating and Power) technology at the building of Sharif Energy Research Institute (SERI). The CCHP at SERI is supposed to supply energy required at the building. Useful energy demand at the building include heating in winter, cooling and air conditioning in summer, lighting and power requirement of electric appliance and equipments. Since there are many technologies that could be utilized as CCHP, an optimal model of energy supply system of the building has been developed in order to identify the most appropriate technology. The application of model has enabled techno logical... 

Taking into consideration of optimization methods has been increased recently. Optimization methods in engineering that consumes a lot of time and cost have been developed. Optimal design of structures is a matter that grabbed the attention of civil engineers and due to the deficiency of classical methods the modern approaches are being developed. One of the most important structures that are constructed for industrial and transportation purposes are truss structures.Structural control under support excitation is constraining the structure to some structural limitations. The final target in this paper is to apply the modern methods to get the optimal weight of structure under seismic loads.... 

Following the recent developments in the field of decision making, a considerable number of problems involved with stochastic systems can be thought of whose analysis depends on a set of intricate mathematical relations. In such cases, simulation is one of the most popular tools that can be applied toward analysis of behavior of such stochastic systems. Not only does not the simulation model rely on such intricate mathematical relations, it also enjoys the added advantage of being free of any restricting assumptions which may normally be considered in a stochastic system.To analyze such problem, one may aim at determining the best combination of input variables to optimize the system...