AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2019 | Volume:51 | Issue:1 |Papers Count:18

Nowdays, for the designing of underground structures in addition to common loads such as earthquakes, explosives loading is considered. Most of these structures around the world are constructed in a safe depth in the soil. The depth of earth where underground structure under explosive forces does not receive damage, called “ safe” . The depth in design and construction of underground structures for use more of the anchor properties of the soil around the structure and minimize the structural weight and also using the damping properties of the soil to reduce the shock wave caused by the explosion of the exact penetrating weapons. Usually explosive loading of these structures is based on the relations and procedures from theoretical and experimental research. Also the numerical methods and using finite element softwares to calculate the explosion load of these structures has been prevalent. In this study the effects of buried explosion on a reinforced concrete underground structure is investigated numerically and analytically. The numerical simulation was carried out using finite element software AUTODYN. In order to analyze the how to explosive loading and underground structure response, the effect of weight of explosive and buried depth of structures was investigated. Additionally, numerical results with relations that presented in reliable scientific resources and US instructions for designing this type of structures were compared. Finally, according to the results of research, in order to improve the designing of these structures under explosion loading in soil, it’ s suggested that the incremental factor doesn’ t apply to such loads.

In order to study geometry of topographies on the seismic site response and evaluate essential parameters used for generalizing seismic results to the topographic irregularities, several numerical finite element studies have been performed by ABAQUS program, the results are presented in the form of the time history and dimensionless graphs. In this paper rectangular, trapezoidal and triangular topographies are studied with different heights (20-100 m) and different angles (15-75 degrees) to evaluate effect of shape ratio, height, length and angle of slope on the seismic response. Applied Seismic motion is the record of Manjil earthquake in horizontal direction. Besides, models are two-dimensional and flexible. ABAQUS infinite elements can be used to define infinite boundaries in the dynamic problems. These elements have elastic behavior and absorb the wave energy so that they act as absorbent boundaries. Researchers such as Nielsen, Preisig and Jeremic have examined the performance of these elements. Actually, if slope angle of topographic irregularities is increased in how slope length of topographies is decreased, seismic response will be weakened even though shape ratio is boosted. Also slope height of topographic irregularities is increased in how slope length of topographies is boosted too; seismic response will be amplified even though shape ratio is constant.

The most important part in pavement management systems is data collection. The modern technologies which are used for this purpose, such as point-based lasers and laser scanners, are too expensive to purchase, operate, and maintain. Thus, it is rarely feasible for city officials in developing countries to conduct data collection using these devices. This paper aims to introduce a cost-effective technology which can be used for pavement distress data collection and 3D pavement surface reconstruction. The applied technology in this research is the Kinect sensor which is not only cost-effective but also sufficiently precise. The Kinect sensor can register both depth and color images simultaneously. An apparatus is designed and developed to hold an array of Kinect sensors. The cameras are calibrated and the slopes of collected images from surfaces are corrected via the Singular Value Decomposition (SVD) algorithm. Then, a procedure is proposed for stitching the RGB_D (Red Green Blue– Depth) images using SURF (Speeded-up Robust Features) and MSAC (M-estimator SAmple Consensus) algorithms in order to create a 3D-structure of the pavement surface. Finally, transverse profiles are extracted and some field experiments are conducted to evaluate the validity of proposed approach for detecting pavement surface defects.

Collapse soils have a stable loose honeycomb-type structure in a low degree of saturation which is susceptible to a large reduction in total volume or collapse upon wetting. The aim of this study is to evaluate the collapse potential and shear strength parameters due to saturation of soil caused by the infiltration of contaminants including leachate wastewater and chemicals into the soil. Since the separation of leachate components is difficult, especially with change of ingredients and pH in long time, the two factors sulfuric acid and sodium hydroxide were used as representatives of the leachate in the pH of 1 to 14. Furthermore, collapse tests and direct shear tests were performed on soil samples which were saturated by leachate. Experimental results show that leachate with a low pH or acidic solutions increase the soil collapse potential; on the other hand, leachate with a high pH or alkaline solutions cause less soil collapse. Variation range of soil collapse in acidic solution was much more than alkaline solution. Direct shear test results demonstrate that acidic leachate increase the soil cohesion and reduce the internal friction angle of soils; however, alkaline leachate reduce the soil cohesion and increase the friction angle of soils.

Due to the world rapid depletion of mineral reserves, extraction of major elements (such as magnesium, potassium, sodium and etc. ) from brines and bitterns has been a matter of discussion. Although sea salts applications in diverse branches of arts and sciences, industrial and economic factors has been limiting their production. In recent work, we represented affordable extraction method for magnesium hydroxide using sodium hydroxide (NaOH) in experimental (1000 ml) and pilot (5000 L) scale studied. The laboratory research aimed to optimization critical parameters as washing time with mixed sea and fresh water, and excellent bittern density for the dosage adding NaOH. High grade and recovery can be attained in 15 min time consumption 5 ml NaOH (12/5 M), stripping rate 180 RPM, 5 level washing combining 2 liter fresh water mixing 9 liter sea water respectively, 99/7% and 46/87%. Washing process indicated classifier had unsatisfied the cycle results, but applying 3 similar polyethylene ponds Outcomes acquired very close to laboratory scale. Furthermore, pilot assessments emphasized that design of salt work effluents for 7 days conditioning is urgent and unavoidable. Also, XRD analysis in conformity with increase concentration Kainite and schoenite during the certain time.

In this paper lateral behavior of composite shear walls is studied. The composite wall consists of a steel shear plate and a concrete cover connected together with a suitable mechanical means such as studs or bolts. The most important role for the steel plate of a composite shear wall is to increase stiffness and ductility while that of the concrete cover is to prevent buckling of the steel plate. The focal point in this study is to assess the variables affecting the lateral behavior of such walls, such as thickness of plate, thickness of concrete cover, spacing between the connectors and strength characteristics of concrete and steel. For modeling of the nonlinear behavior, material and geometric nonlinearities and large deformations are considered within the Abaqus software. According to the results of analysis, thickness of the steel plate proves to be the prime factor affecting lateral strength of the wall. On the other hand, lateral stiffness of the wall proves to be independent of the thickness of the concrete wall, spacing of the shear studs, and the compressive strength of the concrete cover. The study is distinguished from similar studies for the number of parameters studied and the extensive range of their values, detailed modeling of all components, and presenting the lateral behavior of the composite shear wall against the mentioned parameters.

In recent years, in order to have a comprehensive evaluation of structural damages, quantitative methods are developed. In this regard, several research works have been done. The damage indices are based on structural drift regarding the importance and vast application of performance-based design. In this paper, the relationship between the performance levels and damage indices are studied. Several models of RC moment resisting frames were selected and analyzed using dynamic and pushover methods. Furthermore, various damage indices i. e.; Park-Ang index, stiffness index, drift index, and maximum softening and Plastic softening index for different models were estimated. Finally, the relationship between the values of these indices and the performance levels of frames is discussed in accordance with FEMA-356.

Expanding stilling basins not only are effective energy dissipators, but also appropriate translations between hydraulic structures. Hence, the present study aims at numerical simulation of the effect of end-sill location on the energy dissipation. Doing so, Fluent software was employed and hydraulic jump under two divergence angels and four end-sill locations in the range of 4 to 8 Froude number was examined. According to the results, for larger expansion angles, the sequent depth and jump length are lower and energy dissipation is much more. Moreover, as the end-sill closes to the basin’ s entrance, the lower sequent depth, shorter jump, and less energy dissipation are observed. For very close locations more instability in the flow surface are seen. Results showed that for a given expansion angel, improving the location of the end-sill can decease 20% the conjugate depth, enhance 90% the amount of energy dissipation, and reduce 26% the jump length.

Increasing urban populations and creating traffic problems, the use of the underground spaces in the transportation is inevitable. Recent studies have shown that seismic response of ground on tunnels can differ from free field movement during earthquake and change the model of propagation of seismic waves. However, these effects have not been used in the seismic standards for the design of surface structures. In this research, using the finite difference method and FLAC 2D software, the effects of tunneling on earthquake amplification on the surface has been studied. For this purpose, the variation of the shear wave velocity of the soil under harmonic waves by different frequencies and amplitudes in both forms of the presence of a tunnel and in the free field have been investigated. The results of the studies showed that soil hardness and frequency of waves have a significant effect on the site response, and can increase the acceleration of the surface in harmonic waves to about 1. 3 and with the acceleration of the Bam earthquake to about 1. 7 times. Whereas, the presence of tunnel does not affect at longer distances of 15 times its radius. The coefficients obtained the site response can be used in seismic zoning of urban areas and for the design of seismic structures in the area affected by the tunnel.

In recent years, technology development and using various tools have led to produce environmental contaminations. Radon (Rn-222) is one of the dangerous and fatal indoor air pollution. According to Environment Protection Agency (EPA) and many other international organizations, Radon is major cause of lung cancer after smoking. In present research, Radon measurements have been done in 30 dwellings of Tehran using AEOI devices. According to research achievements, the average Radon concentration in Tehran is measured 104 Bq/m3. Maximum and minimum concentrations are 460. 2 Bq/m3 in west and 31 Bq/m3 in north respectively. Risk assessment was done using EPA method. Results showed that independent of age, the lung cancer death rates and risk were 14 times or 12 times (for males and females respectively) greater for ever smokers than never smokers. In conclusion, females are more at risk than males. It was determined people who were older than 70 and also ever smokers are more at risk that must be followed up.

This paper shows the results of an experimental study on the behavior of rectangular reinforced concrete columns that strengthened in bending with NSM FRP bars and CFRP jacketing under combined compression axial load and cyclic lateral loading. Near surface mounted (NSM) fiber reinforced polymer (FRP) is one of the best retrofitting techniques for reinforced concrete (RC) structures. This technique is based on inserting fiber reinforced polymer bars into slits in the cover of reinforced concrete members. For this purpose, seven rectangular RC columns including one control specimen constructed and tested under constant axial load and lateral cyclic displacement. Experimental parameters include different ratios of NSM FRP bar, maximum lateral load capacity, and failure modes are describes based on the test results. The crack patterns in the specimens are also presented. Also, the study was designed to evaluate the necessity of anchoring the end of NSM FRP bars in the foundation. The test results show that a significant increase in the load carrying capacity, stiffness, and energy dissipation of rectangular RC columns can be achieved by using the NSM technique.

Typically, management and operation of wastewater treatment plants are based on comparison of the effluent quality with the defined standard values. Under this approach, only after the occurrence of a failure, the problem in system performance is recognized. In the present study, a new methodology is proposed to predict the wastewater treatment plant performance as well as its units, based on the inflow characteristics. For this purpose, first, the wastewater treatment plant simulation model is developed. After that, the relative importance of each inflow characteristic on the performance of the system is evaluated. Then, performance indicators are defined. In the present study, the chemical oxygen demand (COD) and suspended solids (SS) removal efficiency have been used for this purpose. This process reduces the costs and risks of the system failure. The proposed methodology in this study was implemented on a real case study. The selected indices well response to the inflow variables (such as flow and SS). As a result, it is possible to estimate and check the total and unit performance of wastewater treatment plant with acceptable accuracy. Finally, it can be used effectively to adopt preventive policies for improving the performance of wastewater treatment plants and risk management.

The most important indicator of a project’ s success is not only it should be cost-effective, but also it should be ended on the predicted time. In some projects like constructing subways, dams and so on, delay in construction causes big problems in financial, social or political levels in the countries. To reduce or eliminate delays in construction projects, time optimization should be planned. The main goal of this project is to study the time delay in construction of Karaj subway. In this regard the reasons are recognized and evaluated. In the first step, by reviewing project documents and designing a questionnaire which was completed by a set of experts, factors of delay in constructing Karaj subway were recognized. In the next step, by using multi-criteria decision-making methods, these factors were phased out, weighted and prioritized. At the end, by using Fuzzy logic and to estimate the delay of projects, a method was provided that according to it the project manager can use experts’ ideas and recognizes how much this project has progress and do necessary actions to have a more rapid exploitation.

In the present study, the effect of sill on the discharge coefficient (Cd) of radial gates in a free flow condition has been investigated. Variable geometric parameters of these sills are length, upstream slope, downstream slope and sill height. In addition, the effect of sill location on Cd was investigated so that in case 1, with an open gate, the sill was located in front of the gate. In case 2, the sill is located under the gate and not in front of it. In total, 43 physical models of different shapes of sills and different sizes of sills were used. The results showed that when the radial gate is open and sills are in front of the gates (case 1), the sill operates as a barrier and reduces Cd. But in case 2, the semicircle shape has a better performance and increases Cd by about 30%. Also, the rectangular and trapezoidal sills always increase Cd. In these sills, increases in Cd depend on the sill length to its height (L/Z). Small values of L/Z increase the discharge coefficient up to 25%. Finally, for circular and semicircular sill shapes, two regression equations were presented which can be used by designers.

Improvement of problematic soils using chemical additives has had a long history in the field of geotechnical engineering. One of the common materials used for soil stabilization is Portland cement that has had detrimental impacts on the environment thus engineers are looking for a green material with the same characteristics as an alternative. Geopolymer materials have recently drawn attentions of civil engineers since they have similar properties to cement. In current study, natural pozzolan based geopolymer has been used for improvement of sandy soil. Besides efforts have been made to use glass powder as a replacement for natural pozzolan. Two kinds of alkaline activators were used. The first type was a combination of sodium hydroxide and liquid sodium silicate and the second type had different concentrations of sodium hydroxide. Beside the unconfined compressive strength test which was the main comparison criteria, the microstructural characteristics of geopolymeric samples were investigated with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results indicated that with the increase of pozzolan and activators, the unconfined compressive strength of the samples were increased. In addition, increasing the concentration of type II activator will lead to the increase of unconfined compressive strength of the samples.