Sharif Journal of Civil Engineering
Year:2009 | Volume:25 | Issue:48.1|Papers Count:8

One of the most important design parameters of columns is their effective length in buckling. In the past, because of lack of analytical solution for differential equation of deformation of a tapered column, determination of its effective length was done by numerical methods which result in approximate solutions. In recent years, due to development of very powerful mathematical software’s, one can obtain analytical solution of equation of deformation and accurately find the coefficient of effective length. It will also facilitate to evaluate the values of errors of the past methods. The structure considered in this research is a one- bay gabled frame with tapered members that are solved for state of free to sway with hinged bases.In this research by equating the external work on the structure with its internal flexural strain energy of buckling, and imposing the boundary conditions and compatibility conditions, an equation is found from which the critical load of the structure and accordingly the coefficient of effective length of its columns is obtained. After analysis and obtain of precise graphs, that are more simple to use than graphs of AISC code of practice, the results are compared to the results of previous approximate methods.

The most significant tool for project manager in order to make decision about control and management of project is information obtained from reports prepared by project planning and control team. The common reports of project control cannot present a clear perspective of the project due to lack of updating capability, dynamic analysis of project information and forecasting the available obstacles of the project. Also lack of a stable baseline for measuring the activities progress in any time, re-planning and re-scheduling for some activities in order to mitigate the obstacles in reaching to project purposes would result in mitigating the schedule variances of other activities of project and could cause in connivance of the postponed activities. According to present study, the most successful system of control management of projects all over the world is the earned value management system. Applying this innovative system, the project manager can diagnose the difficulties and obstacles in project performance in least possible time and by perfect understanding of present state of project and forecasting the future difficulty, he would be able to present effective solutions for managing the project to approach determined purposes.

The Discrete Element Method (DEM) was initiated in 1971 by Cundall, who studied the dynamic behavior of rock masses. In his method, each single particle is treated as a distinct element. The new concept of DEM, in which each block of a soil mass is considered as an element, was presented by Chang, in regard to different geotechnical problems. In this research, DEM is used to analyze metal-strip reinforced soil structures. The whole reinforced earth wall is divided into trapezoidal elements; each one containing reinforcement. Normal and shear Winkler springs are considered at the sides of the elements to model interaction with adjacent soil blocks. Also, there are two other springs for the effects of metal strips in each element. The stiffness of the reinforcement's normal springs is calculated by considering the friction of the soil and metal strip surfaces. The sheer force is obtained by considering the equation of an elastic bending and by replacing the soil with a series of elastoplastic springs. Then, the stiffness matrix can be obtained and, by applying the external force vector, displacements are found. The internal forces at the sides of each element can be calculated by multiplying the stiffness of the springs with the relative displacements of that side. A FORTRAN program is written to model different cases of reinforced earth walls. In order to verify DEM results, several examples have been analyzed and compared with other methods. In contrast with the difficulties and uncertainties of conventional methods, DEM can easily model the static and dynamic analysis of reinforced earth walls.

In recent years, the Anzali harbor has been developed as the most important port at the northern border of IRAN. Geotechnical investigations play an important role in the design and construction of offshore and onshore projects. Due to the existence of loose saturated sand in the Anzali subsurface deposits, any earthquake occurrences may lead to liquefaction. The consequence of this may cause damage to structures, due to loss of bearing capacity, settlement and lateral spreading. For observation of Anzali sand behavior, a transparent chamber was built, including a glass tank, a vibration table system and a hydraulic platform. By utilizing this apparatus, one is able to study and observe the different conditions for static and dynamic liquefaction phenomena in sand which has been poured into the glass tank. Equivalent accelerations, ranging from 0.15g to 0.35g, with amplitudes of 0.6 to 0.9 cm, were imposed on the sand with different sets of density in the chamber. According to the developed excess pore water pressure and instability conditions noted during the test procedures, few criteria for liquefaction and instability have been concluded.

This paper is concerned with the problem of a plane strain hydraulic fracture transverse to a borehole. Compressibility and near borehole effects are considered to explain the early unstable phase of the fracture growth observed in laboratory experiments, which are potentially applicable to micro fracture experiments conducted in order to determine in-situ stresses. The fracture grows in an impermeable elastic material. A solution is obtained in terms of fluid net pressure, fracture length and opening. It is shown that the problem depends only on a dimensionless viscosity and an evolution parameter that are related to the compressibility and borehole effect. Instability is identified in the problem after breakdown for an in viscid fluid. The potential for unstable growth depends on the initial flow length, the fluid compressibility, the volume of the fluid and the material elastic modulus.

Using colored substances like Fluorescent and Nigrosine crystals which produce dye streaks in water is one way of obtaining velocity profiles of a fluid. In this study the effects of a large sill on the selective withdrawal of a two-layer fluid through a line sink is examined experimentally.The flow field upstream of the sill was measured using dye streaks method and the results were compared with the predictions of a numerical model. The comparison of the discharges and velocity profiles indicates a good agreement between the measured velocity profiles and the predictions.