Ferdowsi Civil Engineering
Year:2014 | Volume:25 | Issue:1|Papers Count:11

The intakes usually have been used in water distribution networks, irrigation channels, sewage networks, and the water/wastewater treatment facilities, etc. Lack of sediment control entered to the intake channel is the main reason of entering sediments to the installation systems, which makes many problems for different parts. Due to suspended particles in water, the facilities used such as pumps and turbines are damaged. In this study, first, numerical simulation of sediment flow in an intake from a rectangular channel using SSIIM2 is investigated. Among the main parameters affecting the flow the channel cross-section, main channel and intake slope, and the entrance form are supposed to be constant. Then, the effects of the deviation angles 45-90 degree, ratio of diverted discharge 0.2-0.57, and Froude Number 0.32-0.48 on ratio of sediment entering to the intake have been investigated and obtained numerical results were compared with experimental results that good agreement has been observed. Then for numerical investigation of sediment control methods the effects of the submerged vanes, spur dike length, and spur dike distance from the front intake entrance for different ratios of diverted discharge were investigated. The results showed that the effective performance of the vanes increased and consequently eliminated the bed sediment ingestion into diversion with a single spur dike at opposite side of the intake. Also an average reduction of 36% in sediment ingestion into diversion was observed when a spur dike located at a distance of twice intake width from the centre line. Then obtained numerical results have been compared with experimental results that good agreement has been observed.

The seismic analysis of structures in the past relied on the assumed soil desirable effects as the elongation of excitation period with higher damping. Therefore, imposing earthquake loading at the foundation level fulfilling higher safety requirements was the common practice until occasional movement amplifications demanded more rigorous research. The goal of the current study is to scrutinize the effects of length to diameter and spacing to diameter ratios on the response of soil-pile group-structure systems of 2×2 and 3×3 arrangements. The mentioned parameters' increase in the kinematic interaction study resulted in higher transfer functions. Such changes lead to decrease in the real part and increase in the imaginary part of the impedance functions in the inertial interaction study.

Channel flows have three components of velocity, 1component in flow direction and 2components in spanwise of Channel. Because of heterogeneity of velocity undulations, in the channel section the vortices are formed that are nominated "Secondary Current Cells". These cells cause the lateral shear stress in the channel walls and introduce the erosion and scour of the channel walls. Heterogeneity of the turbulency is caused due to boundary conditions of the bed, side wall and free surface, the aspect ratio and the geometry of the channel. The mechanism of secondary currents can be expressed by longitudinal vorticity equation. In this research, the flow in trapezoidal channels has been modeled using the "Computational Fluid Dynamics" (CFD) with "ANSYS CFX" soft ware, and additional to investigation of sufficiency of CFD in modeling of secondary flow cells, depth averaged velocity and boundary shear stress distributions are perused. For this purpose, the experimental model of Tominaga, and analytical model of Shiono and knight has been used to verify the numerical results. The numerical results are in agreement with the experimental and analytical models.

Nowadays, the use of high performance concrete is rapidly increasing due to its capability of being a good substitute for poorly constructed structures and also concrete structures in corrosive environments which suffer from short life span and immature failure. However, in the last decades the pozzolans are greatly used in order to produce concretes with improved mechanical properties and durability. One of the most usable pozzolans is silica fume and metakaoline. In present paper, the mechanical properties and durability of high performance concretes containing metakaolin of 5, 10 and 15% of cement replacement is compared to those containing silica fume with 5, 7.5 and 10% of cement replacement using compressive strength test, water absorption, void volume, sorptivity, electrical resistance and gas permeability tests. According to the results, metakaoline showed better results compared to silica fume regarding improvement of mechanical properties and durability of high performance concretes and it is found that the optimum content of metakaoline is about 10 to 15% of cement replacement which can make it a good substitute for silica fume.

In this paper, the weighted average flux (WAF) method is used to investigate the development and propagation of roll waves in inclined steep channels. In fact, the WAF method improves the accuracy of the classic HLL scheme in evaluating numerical interface fluxes. The present shallow water solver is capable of efficiently capturing flow discontinuities associated with roll waves. In addition, it provides a robust approach to eliminate the numerical instabilities due to small water depths usually encountered in roll wave modeling. The simulated free surface profile and flow velocity show very satisfactory agreement with available analytical solution. The numerical results for time evolution of wave amplitude under different undisturbed Froude numbers are compared with those obtained by another numerical model. Comparisons are also made between water depth time histories computed by these two models. The observed agreement implies the efficiency and accuracy of the present scheme while it is relatively simpler in computer implementation and consumes shorter simulation run times.

Zipper braced frames are an innovative bracing system for steel structures. Conventional inverted-V-braced frames exhibit a design problem arising from the unbalanced vertical force generated by the lower story braces when one of them buckles. This adverse effect can be mitigated by adding zipper columns or vertical members connecting the intersection points of the braces above the first floor. In this paper anumerical study has been performed to estimate and to compare seismic performance of zipper braced and special chevron braced frames. For this purpose nonlinear pushover static analysis and nonlinear dynamic time history analysis have been performed on typical building structures with different number of stories under several earthquake ground motions. According to the analysis results, the ductility and response modification factors of chevron braced frames computed from nonlinear static analysis were generally smaller than the values obtained for zipper braced frames and the distribution of inter-story drifts ratio and maximum story drifts obtained from nonlinear time history analysis, demonstrates the efficiency of the zipper struts in achieving a more uniform damage distribution over the height of the structure, and generally satisfies allowable inter-story drift ratio limits.

Compacted Low strength material (CLSM) made with material such as fly ash and recycled aggregates is used as filler at city infrastructure canals without compaction need. Experimental small specimens and large canals were casted with this concrete and tested to give several results. Test results of compression strengths on 12 different designs shows that this concrete with high workability and w/c ratio over 2 can be replaced with low compacted filled soils and can reduce asphalt settlement over city pavements. Large CLSM canals inside and outside of laboratory tolerated concentrated loads from 3.5 to 7 ton about standard 45-ton Truck (at Bridge and pavement design codes) with low settlement after two months and showed acceptable structural behavior.

Several relationships to assess at-rest pressure coefficient in retaining walls, have been developed by different researchers. These suggested relationships are generally a function of mechanical soil parameters such as internal friction angel, Poison Ratio and over-consolidation ratio. In integral bridges, however, this coefficient is also a function of many other parameters other than soil characteristics. The deck of this type of bridges is subjected to the horizontal movement, which results in cyclic load to be applied to the bridged wall. In the present research, the influence of this cyclic loading on the lateral earth pressure is investigated. A prototype laboratory model of a retaining wall, with cohesionless backfill, was developed in which different cycles of lateral displacement with various amplitudes were applied to the wall. The model was instrumented by small pressure cells to measure the earth pressure at-rest, active and passive conditions. Additionally, the applied load and displacement to the wall were measured, using load cell and LVDT. The results of this study indicate that the variation of at-rest earth pressure coefficient with depth is not linear and it is not only a function of internal friction angel but dependent to the depth and number of cycles. Finally, it could be concluded the cyclic loading causes the backfill material becomes stiffer and stiffer so that an arching is formed. This results in a reduction in lateral earth pressure in the lower parts of the wall.

One of the main factors of premature deterioration of concrete structures is the corrosion of reinforcements. Chloride penetration of concrete is one of the main reasons of this phenomenon. Therefore, to have durable structure, it is necessary to have concretes with low permeability. There are various methods to evaluate permeability of concrete. Finding a relationship between them can be useful for understanding the mechanism of corrosion. Concrete resistivity test is a suitable indicator for concrete penetration and chloride ion permeability. It is a non-destructive, simple, rapid and cheep method that can also be used in site. In this study, various permeability and resistivity tests were carried out on different types of concrete to find a relationship between them. In addition, the main factors affected the resistivity are disgusted and the major constraints of relation between resistivity and permeability of concrete are illustrated. Finally, a new method is recommended to eliminate these problems.

Performance seismic evaluation is an important topic in earthquake engineering. In this regard, several methods have previously been developed and used. The main objective of present research is to evaluate two methods including "Capacity Spectrum Method (CSM)" and "Improved Capacity Spectrum Method (ICSM)" in determination of seismic performance of concrete frames. For this purpose, several sample frames are subjected to several different earthquake records, seismic performance of them are evaluated using these two methods. It was demonstrated that CSM and ICSM methods underestimate displacement at seismic performance level. Based on the numerical results of this study, it was concluded that the ICSM method is more accurate than the CSM Method.