Volume 2 : Issue 5, September 2012

Table of Contents, 25 September, 2012

Research Title/ Field

Article (Abstract)

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Effects of a Locally Sourced Water Reducing/Retarding Admixture on Concrete


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Original Article, B30
Oladiran A, Aderinlewo, Tanimola M.
Journal. Civil Eng. Urban.
2(5): 170-175. 2012.

ABSTRACT:The results of experiments to determine the effects of a water reducing/retarding admixture locally sourced from orange tree leaves on concrete are presented in this paper. The admixture was added to the concrete mix in percentages of 1, 2, 5, 10 and 15 by weight of cement. The results showed that the workability of the mix improved while the water cement ratio reduced gradually as the admixture content was increased from 1% to 15%. Cube crushing tests performed showed that the 28th day compressive strengths of the concrete increased considerably as the admixture content increased from 1% to2% up to 5% beyond that of the control. Thereafter, the compressive strengths dropped at 10% and 15% admixture contents. The percentage increase in compressive strengths of the concrete with 1%, 2% and 5% admixture contents were 6.58%, 14.07% and 23.53% respectively above that of the control.
Keywords:
water reducing, retarding, admixture, workability, crushing tests, compressive strengths.

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Optimization of Clay Core Dimensions in Earth Fill Dams Using Particle Swarm Algorithm


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Original Article, B31
Roshani E, Farsadizadeh D.
Journal. Civil Eng. Urban.
2(5): 176-181. 2012.

ABSTRACT: The flow rate from earth fill dam body mainly depends on the dimensions and characteristics of the clay core. Thus, finding the optimized dimensions for clay core in non-homogeneous earth fill dam is essential. In order to decrease water loss, the clay core should be expanded this leads to dramatic increment in construction volume and costs. The novelty of this issue could be expressed as an optimization material in which the total cost of lost water and earthwork should be minimized. The method serves us a simpler and an accurate solution for an earth fill dam to be in optimised dimensions. The objective function is consisting of two parts. The first part is to calculate the water seepage volume through the dam core with a combination of finite element method and artificial neural network (ANN) and the second part encounters the costs regarding to the volume of earth works. Finally the best answer from the economical view will be chosen according to the amount of seepage and core volume. Since calculating water seepage through soil using finite element method is time consuming, first a combination of 600 different potential shapes of the core has been modelled by finite element and then the result have been used to train an artificial neural network. Comparing this model with linear and logarithmic regression models proved that ANN evaluates water flow rate with more precession. Output data, including flow rate, entered to the particle swarm optimization (PSO) algorithm and the optimized dimensions were achieved. The proposed model for optimizing the clay core dimension can be applied for non-homogeneous earth fill dams with impervious foundation. Allavian earth fill dam was chosen to show the benefit of using the proposed optimization method in a real world case study. The results indicated that the construction cost could be dramatically less than what has been already spent on the case study.
Keywords:
Optimization, Clay core, Artificial neural network, Particle swarm optimization.

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Strengthening of Steel Slab-On-Girder Bridges by Increasing Torsional Stiffness, Case Study:

Karkhe Bridge

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Original Article, B32
Gharighoran A, Rafizadeh A.
Journal. Civil Eng. Urban.
2(5): 182-186. 2012.

ABSTRACT:A field investigation is conducted to strengthening of Karkhe Bridge with type of steel slab-girder in Khouzestan, Iran that it was damaged due to unusual loading and had been extra vibration. In the first, two types of truck are assigned that one of them has loading of Iranian code (40-ton-truck), and other has unusual loading (90-ton-truck) that used in field for transportation of materials. In the next step, this bridge is analyzed by finite element method under these two types of loading, and load distribution factors for different modes are determined. According to these factors, flexural and torsional moment and also displacements of bridge are calculated. In order to strengthening of bridge, fin sections are used to increasing the flexural stiffness for girders, and lateral bracings are used to increasing the torsional stiffness. Finally, results of analysis after strengthening of structure are compared with results before strengthening, that it shows improving in distribution of load between girders and decrease of displacements for bridge deck.
Keywords:
Steel Bridge, Slab-on-girder, Torsional stiffness, Unusual load, Finite element method

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Sensitivity Analysis of Movable Bed Roughness Formula in Sandy Rivers


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Original Article, B33
Fuladipanah M, Majediasl M.

Journal. Civil Eng. Urban.
2(5): 187-190. 2012.

ABSTRACT:Sensitivity analysis as a technique is applied to determine influential input factors on model output. Variance-based sensitivity analysis method has more application compared to other methods because of including linear and non-linear models. In this paper, van Rijn’s movable bed roughness formula was selected to evaluation because of its reasonable results in sandy rivers. This equation contains four variables as: flow depth, sediment size, Bed form height and Bed form length. These variable’s importance was determined using the first order of Fourier Amplitude Sensitivity Test. Sensitivity index was applied to evaluate importance of factors. The first order FAST based sensitivity indices test, explain 90% of the total variance that is indicating acceptance criteria of FAST application. More value of this index is indicating more important variable. Results show that bed form height, bed form length, sediment size and flow depth are more influential factors with sensitivity index: 32%, 24%, 19% and 15% respectively.
Keywords:
Sensitivity Analysis, Variance, Movable bed roughness formula, Sandy River.

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Investigating the Distribution and Orientation of Steel Fiber Reinforced Concrete

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Original Article, B34
Zandi Y.
Journal. Civil Eng. Urban.
2(5): 191-195. 2012.

ABSTRACT:The distribution functions of fiber location variables were investigated that can be used to produce an analytic model to predict the mechanical properties of SFRC. Considering the effect of surrounding boundaries and distribution function, theoretical expressions were derived for the number of fibers per unit cross sectional area in SFRC. A comparison between empirical results and the theory were done to confirm the analytical results. Fibers are usually used in concrete to control cracking due to both plastic shrinkage and drying shrinkage. The amount of fibers added to a concrete mix is expressed as a percentage of the total volume of the composite (concrete and fibers), termed volume fraction (Vf). Vf typically ranges from 0.1 to 3%. Fibers with a non-circular cross section use an equivalent diameter for the calculation of aspect ratio.
Keywords:
steel fiber reinforced concrete; steel fibers; vibration, distribution function.

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Aeration in Bottom Outlet Conduits of Dams for Prevention of Cavitation


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Original Article, B35
Kolachian R, Abbaspour A, Salmasi F.

Journal. Civil Eng. Urban.
2(5): 196-201. 2012.

ABSTRACT:The more necessity of human communities to water resources demand leads to establishing and development of high dams and hydraulic structures with high capacities. With increasing in dam height, the water velocity in bottom outlet conduits increases. In the case of decreasing of local pressure due to sudden change in flow area or the passage slope the possibility of cavitation occurrence through the structure increases. Experiences showed that the flow aeration can decrease the risk of cavitation damages effectively. The investigations of flow characteristics by numerical methods along with physical hydraulic models can be effective in choosing the best choice for aeration and also decrease extra cost and time of physical modelling. In this research, first, the cavitation occurrence in bottom outlet of Sefidroud dam was evaluated in different gate openings by Fluent software in 3D mode and then after the comparison results of numerical and physical model, a method for aeration of this structure consist of aerator ramps on floor and side walls of conduit is suggested and investigated by numerical model. For this purpose the VOF model was used for flow simulation in tunnel and the water surface profile, mean velocity, static pressure and cavitation index were investigated before and after aeration. The results showed the relative capability of numerical models in flow simulation in bottom outlet conduit of dam and improving the flow conditions after aeration.
Keywords:
Aeration, Bottom outlet conduit, Cavitation, Fluent

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