IRANIAN JOURNAL OF SCIENCE AND TECHNOLOGY TRANSACTION B- ENGINEERING
Year:2006 | Volume:30 | Issue:B4 (CIVIL ENGINEERING)|Papers Count:13

In this study, the vibration and stability of orthotropic plates, moving on elastic foundation or elastic supports and subjected to in-plane forces, are investigated by classical plate theory. Firstly, a solution based on the exact finite strip method is developed for multi-span moving plates on an elastic foundation. Then a formulation which is an extension of the approximate finite strip method is presented for axially moving plates on discrete or distributed elastic supports. By some examples, the reliability of both proposed methods is investigated for the stability and the vibration analysis.

In this study, an analysis of fiber reinforced, symmetrically laminated composite plates containing circular holes has been carried out. First, the stress state of a layer in a laminated plate is studied. After obtaining the stress state for each layer due to the uniaxial loading of a plate, the stress concentrations around a circular hole are studied. A number of diagrams are drawn to show the stress concentrations around a hole for layers having different oriented fibers using different material pairs with different E1/E2 ratios (ratio of elasticity modulus of fiber direction to that of transverse direction). Graphs are given for various E1/E2 values for the circumferential stress values around the hole versus angular location of points for two different fiber orientation angles. Second, the failure of the laminated composite plate is studied. To determine the “first–ply failure” of a laminated plate, Tsai-Hill failure criterion is employed to find minimum bearing circumferential stresses and where they occur as a function of the fiber orientation angle.

The focus of this research is on presenting an optimized structural design for priestesses concrete sleeper type B70. In approaching this optimized design, current practices in the design of concrete sleepers, assumptions and design criteria are surveyed and then the sensitivity analysis with SAFE software is made based on 5 criteria. 40 sleepers with different dimensions are put in this analysis. Having chosen the one with the best geometrical condition among those 40 sleepers, the priestesses concrete design method is used for determining the number and the place of rebars. Finally, the designed sleeper is analyzed and a comparison between the proposed sleeper and the current B70 with regard to the structural strength and the construction costs is presented.

The load displacement relationship of shallow rigid strip anchors embedded in sands and subjected to uplift pressures has been examined by using the finite element method. The soil medium is modeled as a linear elastic-perfect plastic material following Mohr-Coulomb failure criterion and an associated flow rule. The computed load displacement response is presented in non-dimensional form. The ultimate failure load is expressed in the form of non-dimensional uplift factor Fg, the variation of which is plotted as a function of soil friction angle (f) and the embedment ratio (l) of the anchor. The magnitudes of Fg, as well as the displacements of anchor at failure are found to increase with the increases in the values of the anchor embedment ratio and the angle of shearing resistance of soils. In all the cases, it was seen that even at complete collapse, the soil mass lying just vertically above the anchor remains more or less non plastic. The failure of the anchor occurs on account of the development of a thin curved plastic shear zone emerging from the bottom of the anchor and then extending up to the ground surface.

An adaptation of the Newton Method is used to solve the combined system of ordinary differential and algebraic equations that describe the spatially varied flows that occur from lateral inflow with periodic outflow along open channels. The application selected is lateral inflow into gutters with periodically spaced grates in its bottom through which the accumulated flow is discharged. The occurrence of critical flow may allow the lateral inflow to be solved as a separate problem, and the outflow to be handled separately. Where subcritical flow exists, the composite system of differential and algebraic equations resulting from a series of gutter-grates must be solved simultaneously. Solutions to such example applications are given.

Resistance to flow is an important and primary parameter in the determination of water surface elevation. A variety of bed forms, especially dunes, have a sensible effect on total roughness. Because of the complexity of bed form development, previous methods differ drastically from each other in predicting dune bed forms. In this paper, laboratory experiments were conducted to investigate the geometry of dunes in a sand-bed channel and its influence on total channel resistance. The experiments were performed in a flume in the hydraulic laboratory of Shiraz University using sand particles. Simple relations were sought for dune dimensions via some dimensional parameters, and previous methods were compared to each other in light of this new data.

In this study a simple simulation model for the design of microcatchment water harvesting systems for rain-fed tree cultures in the Bajgah area, Fars province, I. R. of Iran, was developed. The actual daily evapotranspiration was calculated during the years 1984 to 1987. This model has been calibrated based on 34 measured volumetric soil water contents at depths of 120 cm, and soil water at depths of 0-120 cm in the study area. To calculate the daily actual evapotranspiration during these years, daily crop coefficient, the coefficient of evaporation from the soil surface, mean daily soil water stress coefficient for four years (1984-1987) and the Penman-FAO method for the calculation of reference crop potential evapotranspiration (ETo)   were used. The results indicated that the total amounts of actual evapotranspiration (ETa) for growing seasons were 407, 346, 376 and 362 mm (mean value of 373 mm). Also, the values of yearly ETa were 537, 472, 488 and 485 mm (mean value of 496 mm). Furthermore, a simple method based on Type III Pearson distribution and Penman-FAO ETo was used to estimate the amount of actual evapotranspiration for different probabilities of occurrence in each month of the year. So, the total amount of actual evapotranspiration during the growing season can be obtained for different probabilities of occurrence. Moreover, by using the yearly actual evapotranspiration and yearly rainfall with different combinations of probabilities, the microcatchment areas were estimated for different probabilities of occurrence. These data were used in a simple equation for determining the microcatchment area based on the probability of annual rainfall and yearly ETa. The results indicated that with 50 % probability of annual rainfall and yearly ETa, the microcatchment area (sum of cropping and runoff areas) was estimated to be about 8.7 m2 (cropping area=1.8 m2 and runoff area=6.9 m2). According to the indigenous knowledge of the local farmers, the microcatchment size in the study area is also 9 m2, which is similar to the microcatchments size with a 50 % probability.

Many researchers have incorporated the effects of rock fragments in soil erosion studies to improve the prediction of erosion by raindrop impact and overland flow. According to the Box- Simanton approach, the effect of rock fragments should be incorporated into the crop factor of USLE, C, whereas the Poesen-McCormack and Sepaskhah et al. approaches include the rock fragments in the soil erodibility factor K. For this study we investigated which approach was most suitable for our research basins. This study is based on a comparison of observed sediment concentration data out of a representative agricultural watershed in the south of Iran with the output of ANSWERS model. Preliminary results reveal that there is no meaningful statistical difference between the Poesen-McCormack and Box-Simanton approaches. Nevertheless, when the runoff coefficient exceeded 0.3, the Poesen-McCormack approach was more accurate, but under high antecedent soil moisture conditions, the Box-Simanton approach gave more accurate results. Finally, a comparison of the Sepaskhah et al. approach with other methods showed that,  in general, the Sepaskhah et al. method is more practical and reliable than the other approaches.

BRI-STARS (Bridge Stream Tube model for Alluvial River Simulation) program was used to investigate the scour depth around bridge piers in some of the major river systems in Iran. Model calibration was performed by collecting different field data. Field data are cataloged on three categories. The first group of bridges having river beds formed by fine material (i.e., silt and lay), the second group of bridges having river beds formed by sand material, and finally, bridges having river beds formed by gravel or cobble materials. Verification involved application and comparison of the model to different known real-life cases. The results of this comparison determine the validity and quality of the calibration. Verification was performed with some field data in Fars Province. The scour depths of various bridges located in Iran during significant floods were calculated. The bridges are located in three different locations with different bed materials such as: the Ghadir Bridge on the Zayanderood River, the Khan Bridge River and the Chame Sohrabkhani Bridge on Kor. Results show that for wide piers, computed scour depth is more than the measured depth. In gravel bed streams, the computed scour depth is also greater than measured scour depth, the reason is due to the formation of the armor layer on the bed of the channel. Once this layer is eroded, the computed scour depth is close to the measured one.

An investigation was conducted to detect the change-point years in the Southern Oscillation Index (SOI) and precipitation time series in Iran for the period 1951-1999 (49 years). Due to the unavailability of data, the record length of the precipitation time series was not consistent for all stations, varying from 34 to 49 years. The Pettitt-Mann-Whitney and Mann- Whitney-Wilcoxon tests were applied to determine the significance of the detected changes. The difference in SOI and precipitation amounts for the period before and after the change years was investigated. The coincidence of change-point years in the SOI time series and precipitation data was explored to evaluate the possible forcing effects of the El Nino-Southern Oscillation (ENSO) phenomenon on the suppression or enhancement of Iran’s hydrological cycle. The results indicated that the mid 1970s are the most probable change-point years in the time series of Southern Oscillation Index (SOI) data. The frequency and intensity of El Nino events have increased since then. Consistent with this finding, precipitation data from both south-western and northern parts of Iran have also shown significant change years in or around the mid 1970s. Compared to the period before 1975, annual precipitation over most of the studied regions has increased. This increase was found to be more considerable in southern rather than northern districts. Seasonal precipitation amounts in southern regions have generally increased during autumn and winter and decreased in spring. On the other hand, for northern regions, precipitation has increased during summer and autumn and decreased throughout winter and spring. The most enhanced portions of the hydrological cycle in the southern and northern regions were centred on March and May, respectively.

Multiplicative seasonal autoregressive integrated moving average models are appropriate for the monthly stream flow of the Zayandehrud River in western Isfahan province, Iran, through the Box and Jenkins time series modeling approach. Among the selected models interpreted from ACF and PACF, seasonal multiplicative ARIMA (1,1,0) × (0,1,1) satisfied all tests and showed the best performance. Seasonal moving average parameter in the model indicates periodicity, and long memory in the streamflow, while a nonseasonal autoregressive parameter indicates the linearity of the monthly streamflow. The model forecasted streamflow for 24 leading months showed the ability of the model to predict and forecast statistical properties of the streamflow.