Sharif Digital Repository

In this paper, the dynamic characteristics of skewed bridges are explored analytically. Closed form solutions for translational and torsional periods of free vibration and mode shapes are given for slab-girder skewed bridges. Moreover, the seismic displacement of the deck of skewed bridges is calculated using the response spectrum method and its skew term is compared with the requirement of AASHTO. The effects of seismic force resisting elements, such as elastomeric bearings and end diaphragms are included. It is shown that the skew term in AASHTO's equation can underestimate the seat width requirement for some bridges. A new skew term for the bridge seat width requirement is suggested  

Caspian Sea - the largest enclosed body of water on earth - is the subject of one of the world's most intractable disputes, involving five coastal states of Azerbaijan, Iran, Kazakhstan, Russia, and Turkmenistan. The conflict over the legal status of this multinational water body emerged after the collapse of the Soviet Union in 1991. Since then the parties have been negotiating without reaching an agreement on the ownerships of waters, and the oil and natural gas beneath them. As long as there is no new agreement on how to share the Caspian Sea among the five states, the two old Iran-USSR treaties may continue to govern the Caspian Sea. Based on these treaties, each state's territorial... 

The present study has been conducted to investigate the effect of inlet flow regimes on vertical velocity and concentration profiles of the turbidity current. Experiments carried out on small scale channel and Kaolin with a density of 2.65 kg/m3 and a mean particle diameter of 4.5 μm, was used to generate the currents. Velocities were obtained at a rate of 10 Hz using an acoustic Doppler velocimeter. Using the siphon sampling approach, the acoustic backscattering intensity was calibrated and concentration was determined using a backscattering analysis. Results showed that the ratio of maximum velocity height to the height of the current was around 0.4-0.5 in sub- and super-critical regimes.... 

Stepped spillways have been widely used in Roller Compacted Concrete (RCC) dams in the recent decades. Considering complexity of hydraulics of stepped chutes, their initial design involves pre-selection of some empirical formulae for calculation of flow characteristics and design parameters. In this paper, accuracy of several empirical formulae, proposed for calculating locations of aeration inception (LI), uniform flow (Lu) and rate of energy dissipation (ΔH/Hmax), were compared in relation to results of physical model tests of four stepped spillways and the preferred formulae, providing least amounts of relative errors, were identified. Such a feedback will be helpful for improvement of... 

Water resources limitation in arid and semi arid regions on one hand and water demand increase on the other, have made the optimum utilization of existing water resources and systems necessary. In this context, researchers are trying to increase the accuracy and lag time of prediction by using various statistic and empirical models as well as different local and long-range variables in the last decades. Karoon River is the greatest and most important river in Iran because of agricultural water demand supply and hydroelectric power production. Therefore streamflow prediction of this river has considerable economical and social benefits. In this study the relationship between Karoon stramflow... 

Flood control as an important purpose of reservoir systems faces a wide range of natural, social and political challenges, mainly due to different uncertainties. Over the time, these uncertainties call for necessary changes in the original plan of the systems. Therefore, construction of new flood control systems as well as the storage reallocation and reservoir reoperation of existing ones are essential for adapting the systems to new information, conditions and policies. Furthermore, multipurpose nature of the multi-reservoir systems requires considering conflicts among various purposes. In this paper, a multiobjective optimization model is developed for analyzing such conflicts in a... 

Flood as a natural disaster causes heavy human and economic losses and social unrests in most areas of the world. As flood control cost and flood damage compensation is a heavy burden over countries' budget, traditional flood design methods are being replaced by more reliable risk-based methods employing comprehensive risk analysis. In this respect, flood damage estimation is an important step in flood control systems design and analysis. In large river basins with complex reservoir systems and various land uses, flood damage estimation is complex, data-intensive, time demanding, and uncertain task requiring an intensive hydrologic and hydraulic analysis. In this study a simple approach is... 

Prediction of the vibration response due to defects on rolling element bearings requires having an accurate representative vibration model. In this paper, a new model for vibration generation in the rolling element bearings has been introduced. The proposed model assumes a stochastic source of vibration excitation, which is produced as a result of metallic contact between bearing elements during rolling. This model explains high frequency vibration in the acceleration spectrum clearly. When a defect grows in the bearing, the roughness of the contacting surfaces increases locally and stochastic excitation becomes stronger in the defective area. The increased vibration level at the defective... 

Occurrence of liquefaction in saturated sand deposits underlying foundation of structure can cause a wide range of structural damages starting from minor settlement, and ending to general failure due to loss of bearing capacity. If the bearing capacity failure is not the problem, reliable estimation of the liquefaction-induced settlement will be of prime importance in assessment of the overall performance of the structure. Currently, there are few procedures with limited application in practice for estimation of settlement of foundations on liquefied ground. Therefore, development of a general relationship is important from the practical viewpoint. In this paper, the dynamic response of... 

The fracture toughness and deformation mechanism of PP/CaCO3 (15 wt.%) composites were studied and related to load-bearing capacity of the particles. To alter the load-bearing capacity of the particles, different particle sizes (0.07-7 μm) with or without stearic acid coating were incorporated. The fracture toughness of the composites was determined using J-Integral method and the deformation mechanism was studied by transmission optical microscopy of the crack tip damage zone. It was observed that the load-bearing capacity of the particles decreased by reduction of particle size and application of coating. A linear relationship between normalized fracture toughness and inverse of... 

Angular contact ball bearings are the most commonly used types of bearings. Although simple in appearance, these bearings have a complicated and nonlinear behavior, and have significant effect on the dynamics of a rotating system. Accounting for high speed effects adds to the complexity of their behavior. The governing equations of the bearing amount to the solution of a set of nonlinear equations for each rolling element at each iteration, which represents a tedious and expensive solution. In this work, a simplified model for angular contact ball bearings under the action of arbitrary loading including high speed effects and preload is presented. The model considers five degrees of freedom... 

In this work, the development of a two-dimensional Direct Simulation Monte Carlo (DSMC) Program for pressure boundaries using unstructured cells and its applications to typical micro-scale gas flows are described. For the molecular collision kinetics, variable hard sphere molecular model and no time counter collision sampling scheme have been used. Applications to micro-scale gas flows include micro-nozzel, nano channel and slider air bearing.The aim is to further test the treatment of pressure boundaries. For slider air bearing gas flows of the computer hard drive, the simulated gas pressures, at different rotating speeds, have a very good agreement with previous studies. The applicability... 

In this research, a combination of the physical model based on Paris law and probability method is proposed for remaining useful life prediction of rolling element bearings. Level crossing is used as a feature that represents a linear relationship with defect size. Considering this linear relationship and using Paris law, a new model has been developed for bearings that follow degradation pattern with two stages. In this pattern, a bearing starts working in the healthy condition. Then it starts slow degradation stage and finally it goes to fast degradation stage until it reaches to the failure threshold. Considering a normal distribution for transition point from the slow degradation to the... 

In this paper, a seismic reliability-based approach is proposed to design inelastic steel moment frame structures isolated by lead-rubber bearing (LRB) systems. An equivalent two-degree-of-freedom system is assumed in which a bilinear behaviour is assigned to both the superstructure and the base. Furthermore, uncertainties associated with the equivalent superstructure mass, stiffness, and yield properties are taken into account by employing proper probability density functions. The proposed design approach is twofold: 1) Reliability curves that return the key design parameters of the inelastic base-isolated structure including: the period of the superstructure, the target base displacement,... 

In this paper, a modeling procedure is carried out to numerically analyze the end bearing capacity of drilled shafts in sand. The Mohr-Coulomb elastic plastic constitutive law with stress dependent elastic parameters is used for all numerical analyses performed in this study. The numerical results are compared with the available experimental equations. It is seen that numerical results are in good agreement with experimental equations. The variation of the end bearing capacity of drilled shafts versus embedment depth is also studied. Numerical results show that with increase in pile embedment depth, the end bearing capacity increases. However, the rate of increase becomes smaller as the pile... 

In this paper a new approach to determine the size of defects in rolling element bearings is proposed. This approach is based on the statistical characteristics of the vibration signals generated by rolling element bearings. Although some traditional statistical parameters such as r.m.s. and kurtosis have some diagnostic capabilities, these parameters are not suitable for quantifying the defect size. The proposed new model was validated experimentally for both inner and outer race defects and it is concluded that the newly proposed model can determine the defect length of rolling bearings  

In this research, Al 3003/Zn sheets with different Zn layer thicknesses (as filler layer) have been soldered to the monolithic Al 3003 sheets. The effects of Zn layer thickness and soldering time at the peak temperature on the joint strength of soldered Al 3003 alloy by pure Zn filler (as the soldering sheets) have been evaluated. Furthermore, microstructure and fracture mechanism of Al 3003/Zn/Al 3003 soldered joints have been studied. The results indicate that by decreasing the Zn layer thickness and increasing the holding time at the peak temperature of soldering, the joint strength improves. Additionally, microscope examinations show that the fracture type of the Al 3003/Zn/Al 3003... 

In this paper an analytical model is proposed to study the nonlinear dynamic behavior of rolling element bearing systems including surface defects. Various surface defects due to local imperfections on raceways and rolling elements are introduced to the proposed model. The contact force of each rolling element described according to nonlinear Hertzian contact deformation and the effect of internal radial clearance has been taken into account. Mathematical expressions were derived for inner race, outer race and rolling element local defects. To overcome the strong nonlinearity of the governing equations of motion, a modified Newmark time integration technique was used to solve the equations... 

This paper investigates a hybrid structural control system using tuned liquid dampers (TLDs) and lead-rubber bearing (LRB) systems for mitigating earthquake-induced vibrations. Furthermore, a new approach for taking into account the uncertainties associated with the steel shear buildings is proposed. In the proposed approach, the probabilistic distributions of the stiffness and yield properties of stories of a set of reference steel moment frame structures are derived through Monte-Carlo sampling. The approach is applied to steel shear buildings isolated with LRB systems. The base isolation systems are designed for different target base displacements by minimizing a relative performance...