Year:2003 | Volume:37 | Issue:2 (80)|Papers Count:12

Traditionally the height datum's of the countries has been derived from tide gauge observations. Nowadays due to scientific and technological developments reconsideration of the definition of height datum has become a must! Especially the removal of the country boarders (Unification of the Europe) and the inter-countries activities require unification of height datum's. In this paper we are aiming at a new method for unification and of height datum's and sea surface topography (SST) computations. Our computation is based on (i) Tide gauge observations, (ii) Precise GPS observations at the tide gauge station, (iii) high degree/order spherical/ellipsoidal harmonic expansion. These observations are used according to following methodology: (i) From tide gauge observations Mean Sea Level (MSL) is determined. (ii) Using precise GPS observations and spherical/ellipsoidal harmonic potential at the level of MSL is computed. (iii) The difference of the potential of MSL and geoids potential value W0 is computed. (iv) The computed potential difference is converted into height unit via nonlinear ellipsoidal/spherical Bruns formula. (v) The computed height difference in step (iv) is Sea Surface Topography (SST) at the tide gauge stations. (vi) Knowing the SST at the reference tide gauge stations of various country, unification of height datum's can be performed. As the case study SST at 4 tide gauge stations at main harbors of Iran along Persian Gulf and Oman Sea are computed. The theoretical details of the method and results the case study is presented.

Clogging is one of the main disadvantages of artificial recharge projects. This situation is occurred because of high density of suspended solids in flooded water used in these projects. This paper investigates the effects of different soil mattes on infiltration rate of recharge basins. In a test site near the river Kan (north west of Tehran) 12 pools were built and variations of permeability rate for three different soil mattes (composite, gravel inverse filter and cotton wastages) with three different suspended solid densities were investigated. In the first step, it was observed that soil with gravel inverse filter had higher infiltration rate. Also, both gravel inverse filter and cotton wastages mattes showed higher permeability rate after sedimentation. In the last step, after removing 5 cm of the soil top layer, a higher infiltration rate was observed for compost mat, in comparison with the other two covers. As expected, the higher the density of suspended solids, the permeability rate was lesser.

This paper presents a new approach for reliability-based optimization of water distribution networks. The approach includes three sub models (a steady state simulation model, a reliability model and an optimization model). In this method, nodal and system reliabilities in critical conditions (such as excessive of demands, shortfall in minimum desirable nodal pressures, pipes failure, etc.), are considered as a constraint. Reliability is defined as the ratio of the available outflow to the total demand considering probability of any mechanical and hydraulic failures. The innovation of the algorithm is in the use of a pure head driven simulation model to simulate pressure deficient conditions, properly. This model relates the available outflows to the available nodal pressures, which produces available nodal outflows efficiently. These values are the best input for the reliability model. The optimization model uses external penalty and gradient functions to obtain the least-cost configuration of the network. Finally by presenting two test network, the efficiency of the method is illustrated.

Preparation of Iso-Velocity and Iso-Depth maps for different shear wave velocities in Tehrans alluvium is the main subject of this paper. In this regard, data obtained through geoseismic and geotechnical investigations was used. The collected geotechnical data of about 1000 boreholes including results of 26 new drilled boreholes are considered and combined with the results of 95 refraction surveys and 9 down hole surveys in the studied area. Furthermore the combination of geoseismic surveys, collected geotechnical data and in-situ measurements in drilled boreholes are used to propose a new classification of Tehrans soils based on shear wave velocity and N(SPT). A comparison also is made between results of Standard Penetration Test (SPT) in drilled boreholes and shear wave velocities obtained from geoseismic surveys. The new correlations established between N (SPT) and shear wave velocity for different types of fine-grained soils in south of Tehran are proposed.

In this research using finite volume method a two dimensional mathematical model is developed for predicting the changes of river morphology. The developed computer package can be used specially for calculating bank erosion and sedimentation in meander loops. In the prepared model first by solving the energy, velocity diffusion and momentum equations, flow parameters including main and secondary velocities, main and secondary shear stresses and critical velocity and shear stresses are determined. Then by comparing the critical flow velocity with the longitudinal flow velocity, the rates of sediment transport in longitudinal direction for each sub-section are computed. The transversally sedimentation (or erosion) rate is calculated, afterwards, through comparing the calculating bed shear stresses in the two main directions, together with determined sediment exchange among the subsections based on mass continuity equations. In this manner, the erodibilty parameter is calculated for each river section and by using periodic wave model the river plan changes is predicted. This investigation has indicated that: - The most suitable grid for dissolving the equations is 50*20 grid. - The finite volume method can be suitably used for analysis of natural river morphology problems. - To dissolve the questions, the point-by-point method, in spite of its simplicity, has shown a more suitable accuracy. - The best numerical methods for dissolving the equations (least time, accuracy of answer) are point-by-point (PBP) and line-by-line up to down (LBLUTD) methods, respectively. - Ghezel-Ouzan River has a parabolic velocity distribution and the exponent of the suggested equation varies between 3 to 8. - The maximum displacement of Ghezel Ouzan River is different in various places and it depends on discharge and slope. The prepared model is very sensitive to the variation of discharge and slope.

The construction of Latiyan Buttress Dam was finished in 1968. The result of dam instrumentation indicated that till July of 1970 the dam was in a suitable situation. However at that time vertical cracks were observed on the walls of buttress 10/11, for the first time. These cracks were located on both sides of the gate control room, which extend from the crest level down to the floor of control room. The rehabilitation operations were done by injection of epoxy into the crack openings in winter 1970, but it did not work properly and the cracks opened again in summer 1971. Measurement of opening and closing of cracks shows a cyclic loop behavior affected by seasonal variations in temperature. The latter seems to be the major cause of cracking. In this study finite element analysis of crack propagation has been done by use of Nonlinear Fracture Mechanics concepts and Smeared Crack Method. In this method its suggested that the crack will be replaced by a continuum with changeable physical properties. If the failure criterion is met, cracking takes place in the direction normal to the maximum principal stress. After cracking, the stiffness of concrete normal to the crack plane is reduced and concrete model becomes orthotropic. Therefore by propagation of crack in the structure the finite element mesh will not change while the material behavior relation changes. At first we find the distribution of temperature in the dam body by Heat Transfer Analysis for both summer and winter. Then by applying different static load combinations, the load combination that produce the crack is found. The result of static analysis demonstrates that applying the following load combination would cause high tensile stresses in the cracked region: Dam Weight + Hydrostatic Pressure + Summer Temperature Load + Lateral Pressure of Adjacent Blocks By analyzing of the model under cyclic temperature loads it is concluded that after a while the results should become steady and increasing the loading cycles does not make major differences in the results. We can conclude that by applying static loads the crack pattern wont propagate and the dam wont get in danger. It means that to keep services of this dam it is not necessary to do rehabilitation operations to resist static loads and the dam is safe in the normal loading conditions.

A three-dimensional slope stability method based on limit analysis is proposed to investigate the pore water pressure effects. A rigid-block translational collapse mechanism is considered, with energy dissipation taking place along planar velocity discontinuities. The failure mass is assumed to be symmetrical and homogeneous. The approach can be considered as the modification and extension of the procedure proposed by Farzaneh and Askari in. Results are compared with those obtained by other researchers in two and three dimensional cases.

In this paper, an evaluation on liquefaction potential of a part of South-West of Tehran City, based on the simplified method proposed by Seed and Idriss (1985) is presented. PGA was estimated for the return period of 475 years, life time of 50 years and an earthquake with Magnitude of 7.5 in Richter scale. The studied area was divided into 1km 1 ×km grids and geotechnical profile was evaluated for each grid. The Liquefaction Index determined for each grid using method proposed by Iwasaki et. al (1982) and liquefaction hazard was evaluated based on this Index.

Time integration of nonlinear models of dynamic structural systems is in general involved with responses improper convergence. In this paper, this undesired phenomenon is studied in mathematical detail. The consequence is the fact that in the above- mentioned analyses the main reason for responses improper convergence is a special kind of consistency between additional errors induced by iterative non-linearity solutions and time integration inherent errors.

There is evidence documented in numerous case histories, which indicate that, when earthquake occurs, presence of soil media underlying the base of structures and dynamic soil-structure interaction may increase the seismic forces applied on structures, which at many cases may result in the collapse of structures. In this research, the approach is to evaluate and discuss the nonlinear soil behavior effects on dynamic response of high-rise buildings, considering dynamic soil-structure interaction. This evaluation is necessary, because of its effects on the estimation of seismic applied forces on the structure, and consequently on the design of the structural elements. To this end, various models of dynamic soil-structure interaction systems, with different geometrical, behavioral parameters, and seismic environments are assumed and analyzed with the well-known Subtraction Substructure Method. Having performed the mentioned analyses, variation of spectral acceleration response of the structure, versus the dominant parameters of the problem, such as the ratio of structure stiffness to soil stiffness and maximum input acceleration is evaluated, and the obtained results are compared with conventional dynamic response analysis results. The outcome of aforementioned studies quantitatively indicates that dynamic nonlinear behavior of soils underlying the base of structures, particularly for high-rise buildings constructed on soft soils, may considerably increase the dynamic response of structures. At some cases, this increment is so large that for evaluation of seismic applied forces on structures, it is required to perform dynamic soil-structure interaction analysis; while restricting oneself to the results obtained from conventional dynamic response analysis approach may lead to unreliable design of structures.

Until now, studies on the behavior of reinforced concrete joints have been limited to some experimental studies with variation of a few parameters. Therefore, a comprehensive study is needed to clarify the precise effect of design parameters on the behavior of joints. To reach this purpose, in this paper, 432 reinforced concrete exterior connections were analyzed using finite element method. The variable parameters were as per followings: the longitudinal reinforcement ratios of beam and column (1% and 2% for beam, and 1% and 4% for column), the transverse reinforcement of beam and column (3 ratios), the transverse reinforcement detail of beam and column (9 combinations), and dimension of beam and column. In the current study, the effect and role of each parameter on the ultimate resistance moment, ultimate rotation and performance of connections were studied. Finally, connections were classified in four categories; rigid-full strength, rigid-partial strength, semi rigid-full strength and semi rigid-partial strength.

In hot-mix asphalt the shape and surface texture of fine aggregate particles have a vital effect on the resistance to permanent deformation of the mix. Due to availability and cheapness in comparison with crushed sand, there is a tendency of using as much natural sand in pavement construction, which under poor jon inspection is sometimes used without perfect washing. The aim of this research was to investigate the effect of using natural sand, particularity in a soiled (as-dig) state, on the properties of asphalt concrete, and also to evaluate the sufficiency of the current method of design and control of asphalt mixes in this relation. Four types of aggregate blends with the same grading and a 60/70 penetration grade asphalt were used in the study to produce asphalt mixes. Aggregate blends were prepared using constant coarse and different fine fractions. Fine aggregates which their shape and surface texture characteristics were determined by following standard laboratory procedures include one lype of crushed sand, one type of natural river sand and a sand type consisting of a blend of the crushed sand and the natural sand. Results obtained from Marshall Method of Mix Design indicates that this design method does not comprise the sensitivity required to indicate the maximum allowable percentage of natural sand in asphalt mixes and so, further relevant complementary tests are needed. Results obtained from mix design tests, and also from unconfined compressive strength tests indicate that using natural sand particularly in a soiled state causes a reduction in the bearing and energy absorption capacity of the asphalt mixture, and intensifies the risk of occurrence of permanent deformation and bleeding in the asphalt concrete surfaces.