AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2016 | Volume:48 | Issue:1|Papers Count:12

This research investigates the effect of using multi-walled carbon nanotube (MWCNT) on flexural and compressive strengths, ultimate displacement and energy absorption capability of standard cement mortar. Different weight percentages of nanotubes as well as different dispersion methods were studied. The key issue of adding nanotubes to the composites is their proper dispersion, which was considered by comparing the results of two different dispersion methods. According to the test results and SEM images, the method using functionalized MWCNTs in combination with ultrasonication was pointed out as an appropriate dispersion method. Using nanotubes resulted in a significant increase in the flexural strength and energy absorption capability of cement mortar that represents the ability of properly dispersed nanotubes in bridging and closure of the micro cracks.

The use of Carbon Fiber Reinforced Polymer (CFRP) laminate systems, for strengthening of structures has gained popularity in recent years. Previous researches indicate that one of the difficulties facing this system is its behavior under high and freezing temperatures. this study investigates the behavior of concrete beams strengthened by CFRP fabrics and laminates, under high and freezing temperatures. in this studies, 24 non-reinforcement concrete beams of 30 x 100 x 100 mm sizes were cast using three different concrete strength. After curing, these beams were strengthened using both flexible and hard CFRP sheets. After setting and hardening of the glue used to adhere the CFRP sheets on to the concrete beams, they were exposed to -20°C, +50°C and +80°C temperatures, before undergoing the four point flexural test. Results of study indicate that while the failure of the CFRP sheets at room temperature seems to be due to the flexural cracking, the mode of failures at very low and high temperatures is due to the shear stresses. It may be said that, in addition to the effect of low and high temperatures on the adhesion between the CFRP sheet and substrate concrete, the materials properties involved in this systems are also seriously affected by the extreme temperatures. Examination of the ultimate strength of the strengthened beams also indicates that as the temperature reaches the glass transition temperature of the glue, the reduction in the ultimate strength becomes noticeable. Comparison of the experimental results with the related results of the analytical method, is also presented in this paper.

Control of boundary layer is a common problem in river engineering to reduce the scouring around bridge piers. There are different approaches for controlling the boundary layer such as: motion of the solid wall, accelerating flow by blowing and suction, elimination of flow separation using streamlined profiles and continuous suction. There is not any information about the solution of boundary layer equations coupled with continuous suction around elliptical sections. The present work is to study the laminar boundary layer developed by 2-D incompressible flow around circular and elliptical sections. The boundary layer equations and its control using continuous suction are surveyed analytically. Compariosion between the present results and those of other investigations indicates that the present analytical model is a good tool to predict the velocity profiles around an elliptical cylinder. The velocity and shear stress distribution, the boundary layer thickness, drag force and the friction coefficient distribution are determined and presented with and without control. The control procedure presented here could be applied for different speeds of flow suction.

In this study the theoretical framework of a thermohydromechanical damage model (THHMD model) for non-isothermal unsaturated porous media is presented. The framework of this model is based on the use of independent state variables (net stress, suction and thermal stress). The damage behavior law stems from phenomenological and micro-mechanical concepts. The stress-strain thermodynamic conjugation relations are derived from the free energy, which is written as the sum of damaged elastic deformation energies and of residual strain potentials. The damaged mechanical rigidities are computed by applying the Principal of Equivalent Elastic Energy (PEEE) for each stress state variable. The influence of damage on liquid water and vapor transfers is accounted for by introducing damage-induced intrinsic conductivities. In this paper after the review of the mentioned model, a parametric study is performed to assess the influence of the Excavated Damage Zone (EDZ) on the response of the nuclear waste repository during the heating phase. The trends meet the theoretical expectations.

Density is one of the effective parameters in the particles flotation. For heavier particles, gravity force is more than bubble- particle cohesion force and it increase the probability of separation of particle from bubble. In this research the effect of particles density on flotation were investigated by using sample a-quartz and amorphous silica with density of 2.67 and 2.2 g/m3 respectively. The result of flotation studies showed that in the size range of -250+212 mm with increasing of density the recovery of flotation decreases from 97.74% to 93.42%, whereas in the size range of -150+125 mm this decrease of recovery is not noticeable. In the size range of -75+53 mm with increasing of the density recovery increased from 88.49% to 92.42%. The probability of detachment increases with an increase in particle size and density.

Hollow core reinforced concrete columns are usually used to decrease the cost and weight/stiffness ratio of members. These columns usually carry axial forces together with bending moment.Fiber- reinforced polymer FRP wrapping provides a confinement to the concrete. In this study, concrete columns were analyzed with and without external confinement; and interaction diagrams were compared with those obtained from experimental results. Based on the results it was realized that external confinement with FRP composite could increase the strength of concrete column. However, the influence of the number of layers of FRP on the specimens after five Layers under loading is not so pronounced. Wrapping three layers of FRP increases columns axial strength about 30% to 40%, while it can reach up to 50% for pure bending. Strength increase with seven and nine layers is about 5% more than retrofitting with five layers. Also, increasing hole dimensions reduces columns ultimate strength. Comparing columns with circular and square hole shows that columns with circular hole have better function.

The main purpose of this paper is presentation of proper finite element formulation for dynamic analysis of concrete gravity dams under nonuniform translational and rotational components of earthquake considering dam- reservoir interaction. Time delay of travelling waves is considered to generate the nonuniform ground motion and the rocking component of earthquake has been obtained using the corresponding translational components based on classical elasticity and elastic wave propagation theories in term of wave frequency functions. The translation and rocking components of ground motion are applied to support points of dam-reservoir bottom and analyses are done using finite element method based on Lagrangian-Lagrangian approach. Results show that the rocking component and time delay of travelling translation waves can considerably affect linear dynamic response of concrete gravity dams in some cases.

Value engineering has been used for more than 50 year as a successful technique in the upstream authorities and documents of Iran. Although it has been used in the role of an effective method to improve the constructive projects and plans, value engineering has not reached its real position yet. This can be attributed to many reasons such as optimistic view of managers towards the results of a project, improper understanding of the technique, and insufficient culture and motivation among project components as well.This study aims to codify motivation authorities of the value engineering in addition to evaluate necessities of motivating the value engineering parameters in Construction and Development of Transportation Infrastructure Company (CDTICO) as one of the most important firms with many huge projects in Iran. Thereby, value engineering can enable the company and many other governmental organizations to utilize this advantageous technique more than any time before. This research has been conducted by using advices from value engineering experts through interviews and questionnaires since they were sufficiently familiar with CDTICO.

Tall buildings classify as interior and exterior systems regarding to structural system. Important forms of exterior systems are tube, tube-in-tube w/o interior core, tube-in-tube with outrigger, braced tube and bundled tube. In order to evaluate pros and cons of each system, full 3D model implemented by using SAP2000 and seismic performance assessment defined as a major aim of this research. Shear absorption, story drift, inter story drift, shear lag factor (SLF), fundamental period and maximum along-wind displacement and acceleration are evaluated parameters.The qualitative results showed that using aforementioned led to improve seismic response of building compared with tube system. However, a considerable effect on response reduction observed by using braced system. On the other hand, variation rate of SLF on columns located at tension flange was much uniform. In addition, SLF became one on the upper floors in all cases. Finally, by using braced tube, and maximum along-wind displacement and acceleration calculated with ASCE7-10 meet the comfort criterion of occupants.

The advantages of treated wastewater such as decrease of water resource limitation and environmental pollution reduction caused to be considered as a valuable source in irrigation. However, the probable pollutants in the treated wastewater cause some restriction on its reuse. Risk assessment is an important tools in understanding the potential risks of a project and its potential consequences. In this study, the risk assessment of wastewater reuse is done using the technique of Bayesian networks. In this method, a network of cause and effect is created and two indexes of hazards and impacts are defined. Hazards are due to treated wastewater pollutants and impacts referred to the effects of hazards on human and plant as the main receptors in this analysis. The present survey is applied for the risk analysis of wastewater reuse of Alborz industrial park treatment plant located in suburb of Ghazvin city for irrigation of adjacent farmland. Results showed a 46% risk for human and 38% for the plant which the cadmium, detergent and nitrate have the highest share in the total assessed risk. Mitigations measures for risk reduction includes construction of pretreatment, precise supervision and improve the operation and continuous monitoring.