per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
1
9
article
Assessment of AE and DRA Methods for In-situ Stress Measuring and Study of Delay Time in both Methods
Ali Arianfar
1
Morteza Ahmadi
2
3
Graduate student in M.s.
There are several direct and indirect methods to estimate in-situ stress. Generally in all methods rock breaking is required for in-situ stress determination in which broken rock response is due to displacement/strain or hydraulic pressure. Hydraulic fracture, Relief method, Jacking method, Strain Recovery method and borehole breakout method are known as direct methods. On other hand, the indirect methods estimation is based on changing of some physical or other properties of rock which represent from applying stress. Even though, these methods are also laboratory methods, however, indirect techniques are non destructive, low cost and simple for estimation of in-situ stress. This is the reason which has motivated rock mechanics researchers to use Acoustic Emission (AE) and Deformation Rate Analysis (DRA) methods. Results aaccuracy of the methods are affected by rock texture, cracks type and delay time. The delay time means that time between coring in field and test time for stress measuring. The capability of AE and DRA methods in stress estimation have been assessed in this research and the effect of delay time on estimated stress are worked out. AE and DRA tests were carried out on the samples for estimation of in-situ stress. Stress has a nature tensor with 9 components, in which six of them are independent components and the rest (3 components) are dependent components. Each component of tensor need to be determined with a total of six tensors which required six tests in six different orientations. Six series of samples with different delay times (4 series with 20 days as delay time and 2 series with 5 years as delay time) were obtained from abutments of Seyamreh dam (South-West of Iran). AE and DRA tests were carried out. The values obtain from these AE and DRA tests were compared with result of Hydraulic Fracturing (HF) method which carried out at the same locations. The comparison shows a good conformity between the result of AE and DRA methods with those of HF method for horizontal stresses where as there are variations noticed for vertical stress values. This may be due to this fact that in the HF method assumes the vertical stress is equal to overburden weight which is not correct assumption. The other result of this assumption is that the others two principal stresses are horizontal. It is obvious if one of principal stresses would be vertical the two other have to be horizontal. Furthermore, this investigation infers that delay time is very important parameter on the results obtained by AE & DRA methods. Thus better accuracy can be computed when the delay time is minimized.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-2179&slc_lang=en&sid=16
Acoustic emission
Deformation Rate Analysis
Stress Measurement
Delay Time
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
11
25
article
Application of artificial neural networks in interpretation of pressuremeter test results
Mohammad Emami
1
S.Shahabodin Yasrebi
2
Student
In-situ tests play important role in any geotechnical investigation. Pressuremeter test can be considered one of the most important in situ tests.This test can be considered one of the most important in situ tests in Geotechnical Engineering. This test is capable to properly estimate deflection parameters of soil. Three types of pressuremeters exist based on their placement in the boreholes: Predrilled pressuremeters (P.D.P), Self-boring pressuremeters (S.B.P) and Push-in pressuremeters (P.I.P). The Predrilled pressuremeters (P.D.P) have been used in this project. Based on expansion of a cylinder that is placed inside the borehole the pressure-volume variation during testing is recorded. In this research, the results of approximately 500 conducted Pressuremeter tests on the soils by Pajohesh Omran Rahvar Ltd (2006-2007) are employed. The number of tests decreased to 400 due to lack of accuracy and also high changes in the range of Pressuremeter modules. The tests have been carried out on the soils of Northwest Iran (Tabriz), South Iran (Kharg Island) and Northeast Iran (Mashhad). The Pressuremeter instrument used is menard pre-boring. Conducted tests in accordance with ASTM-D4719 represented acceptable accuracy. In the current paper, three types of Artificial Neural Network (ANN) are employed in interpretation of pressuremeter test results. First, multi layer perceptron neural network, one of the most applicable neural networks, is used. Then, neuro-fuzzy network, combination of neural-phase network is employed and finally radial basis function, a successful network in solving nonlinear problems, is applied. Neural network models showed prosperity to interpret Pressuremeter test. Soil physical and compaction properties are used in all these models. The applied models own 5 input parameters and 1 output parameters. Hidden layers with different number of neurons are tested in both one and two layers networks so as to select the most proper network architecture. It has been shown that a three-layer perceptron with differential transfer functions and sufficient number of neurons in hidden layer can approximate any nonlinear relationship. Consequently, one hidden layer is used in the present study. The neural network toolbox of MATLAB7.4, a popular numerical computation and visualization software, is used for training and testing of the MLPs. Transfer functions of networks are selected by trial and error. A large complex of carried out tests on the extensive range of fine and course grained soils is used as database. In order to determine the most exact network in the perceptron neural network, some networks with different architecture are employed. Of all neural network models, multi-layer perceptron neural network proved to be the most effective. However, other applied networks have shown favorable performance. Finally, different models have been compared and network with the most outstanding performance is determined. In order to evaluate the capability of model generalization, the performance of mentioned network against inexperienced data has been compared with empirical results. Contrary to conventional behavioral models, models based neural network do not demonstrate the effect of input parameters on output parameters. This research is response to this need through conducting sensitivity analysis on the optimal structure of proposed models. Also, derivation of governing equation for neural network model give more assurance to user to employ such models and consequently this facilitates the application of models in the engineering practices.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-3911&slc_lang=en&sid=16
IKey words: Interpretation
Pressuremeter test
Artificial Neural Network
Multi-layer perceptron
Neurofuzzy
Radial Basis Function
Sensitivity analysis
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
27
36
article
Determination of Bearing Capacity for Driven Piles in Sandy Soils by Using Artificial Neural Network Method
1 1
1
2
3
1
Determining the bearing capacity of piles is an important issue that always Geotechnical engineers focus on. Effect of factors such as environmental dissonance of soil which contains a pile, pile implementation, pile gender and its shape make correct estimation of bearing capacity difficult. Pile load testing as a reliable method could be used in various stages of analysis, design and implementation of piles to determine theaxial bearing capacity of piles. On the other hand, pile load testing, despite high accuracy, imposes high cost and long duration for development projects and it causes limitations in this experiment. Thus acceptance of numerical analysis at geotechnical studies is increasing. The modeling using artificial neural networks is the method that is based on previous data and don’t need to simplify and improve the high reliability coefficient. In this study serious models of multi-layer perceptron neural network, one of the most commonly used neural networks, was used. Network design and factors influencing its behavior in this issue has been studied as a summary. In this study, artificial neural networks are used for prediction of bearing capacity of driven steel piles in sandy soil, in all models four parameters are used as input data which are length and diameter of the pile, the coefficient of elasticity and internal friction angle of soil and the bearing capacity of piles is used as output data. Models have reasonable success in predicting the bearing capacity of piles. In order to evaluation of networks, the different indices such as RMSE, MAE, MAXAE and SDAE were used. To increase the accuracy of predicting bearing capacity, for the network training stage the real tests that has been done at the geotechnical studies of dry dock area hormozgan by POR Consulting Engineers were used.Acording to (Because we) need of more data for training and testing network, several tests on pile bearing capacity, in smaller dimensions were performed in the laboratory. The sixty tests have been performed on piles with various length (35, 40, 45 and 50 cm), various diameters (20, 25 and 32 mm) and different relative compacted sandy beds (50, 60, 70, 75 and 80%). To perform these tests the device of pile bearing capacity, made in university of TarbiatModarres, was used. Models based on neural networks, unlike traditional models of behavior don’t explain effect of input parameters on output parameters. In this study, by the sensitivity analysis on the optimal structure of introduced models in each stage it has been somewhat trying to response this question. .
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-7079&slc_lang=en&sid=16
pile load testing
device of determining pile bearing capacity
artificial neural networks
Multi-layer perceptron
Sensitivity analysis
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
37
47
article
Numerical Study of Performance of Baffle Blocks in Submerged Hydraulic Jumps
Fatemeh Jafari
1
S. Ali Akbar Salehi Neyshabouri
2
Student
Prof., Hydraulic Structures Eng. Dept., Faculty of Civil and Environmantal Eng., Tarbiat Modares University
Hydraulic jumps occur in natural systems like streams and rivers as well as manufactured systems. Samples of the latter occurance are jumps in water distribution and irrigation networks formed downstream of hydraulic structures such as spillways, sluice gates, and drops. These structures are usually designed for a specific tailwater depth. Stilling basins with baffle blocks are frequently used as energy dissipators downstream of hydraulic structures. Baffle blocks are often used to stabilize the jump, decrease its length and increase the energy dissipation. If the flow rates become more than the design discharge, the tail water depth will be greater than the one required for a free jump. These situations are common in low head hydraulic structures including low diversion dam spillways and gates. Under such conditions the hydraulic jump will be submerged. The performance of the blocks in submerged jump (SJ) condition differs from the free jump (FJ) case. According to some factors such as Froude number, block shape and location and submergence factor, flow regimes on baffle blocks in condition of submerged hydraulic jumps which occurs in stilling basins, are classified into two regimes, the deflected surface jet (DSJ) and reattaching wall jet (RWJ). In this article a numerical study was conducted to investigate flow pattern, vortexes and the magnitude of vorticity in submerged hydraulic jumps with baffle blocks downstream of a sluice gate. The results were compared to ones in same conditions without blocks. 3D RANS simulations have been applied by Fluent software. RSM turbulence model were used which illustrated much precise results in verification. Three numerical models have been created; Submerged wall jet without blocks, submerged hydraulic jumps with baffle blocks in the condition of deflected surface jet flow regime and submerged hydraulic jumps with baffle blocks in the condition of reattaching wall jet flow regime. Flow pattern has been exhibited for each model and results were compared with each other. Vortexes formed in such situations classified into three groups according to axis which they whirl around. It was observed that deflected surface jet regime has more vortexes in comparison to the two other conditions. In addition, by measuring the average magnitude of vorticity in cross-sections it has been concluded that z-vortexes –vortexes which rotate around z axis– much more powerful than x- and y-vortexes as they determine the kind of flow regime. Furthermore, this magnitude is about two times larger in deflected surface regime than two other situations. This fact leads to more turbulence in the flow that makes deflected surface jet regime the desirable condition in which baffle blocks perform more efficiently as energy dissipators in comparison to two other investigated models. In order that, from energy vantage point, conditions should be provided in a way to form submerged hydraulic jump as deflected surface jet regime.
http://journals.modares.ac.ir/browse.php?a_code=A-16-14172-1&slc_lang=en&sid=16
Energy Dissipation
submerged hydraulic jumps
baffle blocks
numerical simulations
Stilling basin
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
49
63
article
Probability distribution of relative displacement of two adjacent single degree of freedom systems
Masoud Soltani Mohammadi
1
Sepideh Rahimi
2
Tarbiat Modares Univ.
Seismic pounding between adjacent buildings is an undesirable phenomenon. Depending on the characteristics of the colliding buildings, pounding might cause severe structural damage in some cases, and even collapse is possible in some extreme situations. In order to mitigate the risk of seismic pounding between new buildings, current seismic design codes prescribe a minimum separation distance between adjacent structures. The value of the minimum separation distance is assumed equal to the peak relative displacement computed at the most likely pounding location and corresponding to a site-specific seismic intensity. Examining the collision possibility of adjacent structures as a result of earthquake is the basis of formulating regulations for determining minimum dimensions of separation distances. This distance can be calculated in different ways. In previous studies, double difference combination has been generally used to determine this distance and their only difference is in determining correlation coefficient of seismic response in two adjacent systems. This coefficient which depends on period and damping of the two systems has been obtained in previous works with the assumption of a linear behavior of structures. In the nonlinear range, the same correlation coefficient obtained from the linear mode is used by making structure behavior equivalent to linear mode and introducing values of effective damping and period. Modified values of period and damping depend on the requirement of system ductility under the applied record, which has been obtained for a specific behavioral model and from numerous numerical studies. In this study, the correlation coefficient of the two systems was presented using random vibration equations for the systems by Bouc - Wen different hysteresis behavior model. Moreover, the proposed relation could be applied for different input stimulation with specific spectral density and is more comprehensive than previous relations. Ductility demand of the system corresponding to the input spectral density was determined by random vibration relations and the probability distribution of relative displacement between the two systems which was obtained from the presented relations was compared with the existing ones. This study evaluates the accuracy of two different criteria to calculate the separation necessary to prevent seismic pounding between nonlinear hysteretic structural systems. All of the criteria considered in this paper make use of the same basic equation of the Double Difference Combination rule, but they adopt different procedures to estimate the correlation between displacement responses of nonlinear hysteretic systems. Monte Carlo analysis used to verify the relations presented for two adjacent nonlinear systems under the applied record which were simulated by a specified spectral density in stationary and non-stationary forms. Results obtained through Monte Carlo simulations indicate that the relation presented in this study is completely satisfactory and none of the two criteria evaluated in this study is exact.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-4097&slc_lang=en&sid=16
Adjacent structures
Probability equations
Bouc-Wen Model
random vibration
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
65
79
article
Mass Damper and Buoyancy Functioning of a Submerged Tank on the Response of Fixed offshore Platforms
M. Shafieefar
1
A.A. Aghakouchak
2
M.R. Moharrami
3
By increasing demand for oil in recent years, explorations from deep offshore fields are feasible. In such deep waters, even fixed offshore structures may have considerable movements under design loads, while having less displacements of the platform is often requested. Many innovative concepts have been proposed to minimize responses of structures under environmental loads in recent decades. In a tension leg platform, the buoyancy force causes tension in the tendons, which is changed by platform movement and produces a lateral stiffness to reverse the platform into its initial position. The amount of generated additional stiffness depends on the platform displacement and buoyancy forces. Fixed submerged tanks may be used in design of a compliant platform in deep water to reduce transfer weight of the structure to the support and to decrease the effects of legs buckling. However, the tanks should be located in an appropriate water depth to minimize the effect of wave forces.
In order to decrease the response of fixed offshore platforms in deep waters, an innovation concept is presented. In this concept, a submerged tank is tied up to the platform in an appropriate location acting a buoyancy force to the system. This force adds tension force to the legs which may reduce the required chord diameters and/or eliminate some braces. However, the added mass of the tank due to wave action has considerable effect on dynamic behavior of the system. In addition, the vertical buoyancy force of the tank generates a resistance moment in the system when the tank oscillates. This resistant moment depends on the location of the tank and time. In this paper, considering the effects of the tank on the platform responses, solutions for reducing platform displacement are investigated. Analyses have been carried out by taking into account the large deflection and nonlinear geometry effects for which a MATLAB program has been developed featuring the following capabilities:
Calculation of wave forces based on the Morison equation for jacket members and the Froude-Krylov method for the tank.
Taking into account waves and structure interaction.
Non-linear analysis of the structure considering large deformations effects.
Dynamic analyses results showed that the tank acts as a weight damper under wave actions. In this case, the added mass has also contribution on the inertia force. So, there is an optimum stiffness for each mass. For dual mass damper and buoyancy functioning of the tank, the stiffness should be defined in such a way that the performance of the tank would be appropriated in both consequences. Results of analyses on a case study platform show that the performance of the tank on reducing the platform responses is much better for the dual mass damper and buoyancy functioning comparing to only the mass damper functioning.
http://journals.modares.ac.ir/browse.php?a_code=A-10-1000-7347&slc_lang=en&sid=16
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
77
85
article
evaluation of lime fillers effects on reduction of moisture and freeze damage by indirect tensile strength and compressive strength tests
Reza Alinasab
1
2
3
Pavement performance in Iran is not compatible with expectations and demands of contemporary society. The poor performance of pavement results in shortening country roadways lifetime and paying heavy cost. One of the pavement major problems particularly in wet conditions is stripping of aggregates. Stripping is a major distress occurring in hot mix asphalt (HMA) pavements in Iran and in various parts of the world The stripping of aggregates in hot mix asphalt not only is considered as an independent problem but also it may cause damages like cracking, rutting, raveling, fatigue cracking. The moisture first inflicts damage on the HMA mix by destroying the bond between the aggregate and the asphalt binder or by destroying the internal cohesive strength of the binder. This loss of adhesion causes the asphalt concrete to ravel under traffic loads. Stripping occurs in the presence of water, so it is often referred to as moisture damage. In this paper, the effective parameters causing stripping have been identified and the methods of increasing asphalt mixture durability have been investigated, focusing on the recognition of how stripping can be made. In this regard, limestone fillers and hydrated lime have been used in different amounts as antistripping agents (which can be found widely in the country) and the optimum resistant mixture against stripping have been prepared. In this thesis two kinds of aggregate from the east and west of Tehran and two kinds of bitumen (60/70) from Tehran and Isfahan refineries have been collected and the required experiment (on aggregates, bitumen and hot mix asphalt) have been carried out. Then according to marshal method and based on ASTM D6926 and ASTM D6927 standards, marshal specimen have been made and the optimum bitumen has been determined, using the required parameters by marshal method. Using indirect tensile strength and compressive strength tests over saturated and dry specimen, according to AASHTO T283 and ASTM D1075 standards, asphalt mixture stripping potential has been investigated. Since the resistance of asphalt mixture again moisture was not satisfactory, two kinds of limestone filler and hydrated lime were used for improving asphalt mixture resistance and their effect was investigated on asphalt mixture. Hydrated lime and limestone filler, when added to the asphalt prior to preparation of the mixtures, dramatically improved mixture resistance to moisture damage for both aggregates. The results obtained from indirect tensile strength and compressive strength tests over saturated and dry specimen, according to AASHTO T283 and ASTM D1075 standards show that using 1.5% hydrated lime or 4% limestone filler (by weight of aggregates) in asphalt concrete, significantly increased the asphalt mixture resistance against stripping. Also in this study the results obtained from two experiments methods (tensile strength and compressive strength tests) are compared.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-7466&slc_lang=en&sid=16
Stripping
Hydrated lime
Indirect Tensile Strength
limestone filler
compressive strength
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
87
99
article
1-Numerical Study of Behavior of Simply Supported RC Deep Beams with Openings
1
2
Generally reinforced concrete deep beams are used as transfer girders, pile caps, coupling beams and foundation walls. Openings are frequently provided in RC deep beams to facilitate essential services, such as ventilating ducts, water supply and drainage pipes, network access, or even movement from one room to another. Existence of opening leads to disturbance of compressive force path from the loading point to the support. Due to the lack of experiment on deep beam with opening, code provisions do not give any explicit guidance to designing these elements with opening. So this research studies the behavior of reinforced concrete deep beams with opening using finite element methods. To this end the commercial software ABAQUS/standard was used. The accuracy of model was verified with available experimental data. in two separate parts the behavior of these members was studied. First, 68 beams with opening were modeled to study the effect of size and position of opening, arrangement of web reinforcement, ratio of clear span to depth and ratio of shear span to depth. In all of these beams depth and thickness was 750 and 100 millimeter respectively. The most effective parameter on behavior and ultimate load capacity was arrangement of web reinforcement. Also the size effect on the behavior of these members was studied. So 8 beams were modeled and result indicates that by increasing size of the beams the normalized shear strength decreases. Generally reinforced concrete deep beams are used as transfer girders, pile caps, coupling beams and foundation walls. Openings are frequently provided in RC deep beams to facilitate essential services, such as ventilating ducts, water supply and drainage pipes, network access, or even movement from one room to another. Existence of opening leads to disturbance of compressive force path from the loading point to the support. Due to the lack of experiment on deep beam with opening, code provisions do not give any explicit guidance to designing these elements with opening. So this research studies the behavior of reinforced concrete deep beams with opening using finite element methods. To this end the commercial software ABAQUS/standard was used. The accuracy of model was verified with available experimental data. in two separate parts the behavior of these members was studied. First, 68 beams with opening were modeled to study the effect of size and position of opening, arrangement of web reinforcement, ratio of clear span to depth and ratio of shear span to depth. In all of these beams depth and thickness was 750 and 100 millimeter respectively. The most effective parameter on behavior and ultimate load capacity was arrangement of web reinforcement. Also the size effect on the behavior of these members was studied. So 8 beams were modeled and result indicates that by increasing size of the beams the normalized shear strength decreases.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-695&slc_lang=en&sid=16
Finite Element
ultimate load
Size effect
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
101
113
article
Optimal Control of Structures Equipped with MR Dampers Using ANFIS
Amir Fayezi
1
Hamid Moharrami
2
Tehran, Khaghani Junc., Chaychi sq., Sefidkuh st., Shavakh st., Eskandarzadeh alley, no. 8.
Tehran, Tarbiat Modares University, Faculty of Civil and Environmental Engineering, Department of Structural Engineering
Due to high capacity and low energy consumption of Magneto-Rheological (MR) dampers, they are vastly being utilized to control seismic responses of structures. Presenting more precise methods for control algorithm, and including more realistic physical characteristics of MR dampers (e.g. nonlinearities, uncertainties and …) will help engineers to employ this kind of damper more efficiently. In order to achieve a controller that quickly and accurately determines the input voltages to the MR dampers, in this paper, a new strategy is proposed. The proposed strategy utilizes Adaptive Network based Fuzzy Inference System, (ANFIS) for optimal control of structures that are equipped with MR dampers. To obtain optimal time histories of demanded voltages, a new objective functional (J) that is a combination of some control criteria including reduction of relative drifts, absolute accelerations and absorbed energy is suggested. The optimization problem is such formulated that the set of equations of motions and equations representing the nonlinear model of MR dampers (here Bouc-Wen) are solved simultaneously. The optimization problem is solved by the enhanced method of steepest descend algorithm by Moharrami and Fayezi [3]. In this way, for a 15-storey building frame subjected to two deterministic earthquakes, the time histories of optimal input voltages of dampers are numerically computed. Next, the optimal voltages associated with the data on drifts, velocities and accelerations of stories are used as desired input- output data pairs to train the ANFIS as a quick and accurate controller. Three ANFISs were trained by different weights for drift (q1) and absolute acceleration (q2) data versus voltages. The weights of q1 and q2 controlling data were assumed to be (1,0), (0,1) and (1, 0.42) for ANFIS1, ANFIS2 and ANFIS3, respectively. Finally, to establish a context for assessment of the effectiveness of the proposed strategy in comparison with other conventional methods and to analyze the effects of weights in the objective functional, two numerical cases are presented. In the first case, the aforementioned 15-storey building frame is controlled against some earthquakes which were not applied for training process of ANFIS. Results show that ANFIS1 has decreased maximum and time-averaged relative drifts more than other control methods. In addition, this controller has somehow attenuated base shear similar to passive-on but has not been successful in reduction of absolute acceleration values. The ANFIS2 has controlled absolute accelerations better than other controllers whereas drifts have been reduced fairly well. By the ANFIS3, one can achieve reasonable decrease in all controlling criteria. Their values are between ANFIS1 and ANFIS2. It can be concluded that depending on the relative importance of control on drifts or accelerations of stories, one can chose proper weights for q1 and q2. In the second example, a benchmark six-storey building that is equipped with 2 dampers in the first, and 2 dampers in the second storey, has been controlled by the three proposed controllers. The results are compared with several conventional methods. The proposed strategy show more flexibility in reduction of the structural control criteria in comparison with some other conventional methods.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-3270&slc_lang=en&sid=16
ANFIS
Optimal Control
MR damper
ANFIS
objective function
shear frame
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
127
135
article
Investigation of effect of the liquefiable layer geometry in behavior of pile Foundations
Ali Komak panah
1
Komeil Khakpour
2
Mohammad norooz Olyaei
3
Lateral ground displacement due to liquefaction causing damages to major infrastructures like buildings, bridges, pipe, shore line utilities etc. When the surface slope is mild, a common mode of failure is lateral spreading with surface displacements that can exceed several meters. Considering the widespread use of pile foundations, their safety in the occurrence of earthquake has a special importance. Studies after the earthquake have shown that both the force due to structure and the Kinematics interaction between the pile foundations and the soil play an important role in mechanical behavior of piles. Since the effect of the superstructure on the pile-soil interaction analysis is significant; the analysis should be done based on the interaction axis of pile-soil-structure. In this study, finite difference method (FDM) has been used to investigate the effect of the thickness of liquefied layer, slope of liquefied layers and the underground water level on behavior of pile foundations. Results indicate that with an increase in the slope of liquefied layers, the maximum bending moment raises but the slope of this graph for low underground water level (near the surface) is higher. This type of behavior also is observed in the shear force created in the pile foundation.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-3438&slc_lang=en&sid=16
Pile
Liquefied soil
Finite Difference
Dynamic Analysis
Pile and soil interaction
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
137
146
article
UV-TiO2 Photocatalytic Degradation of Compost Leachate
Nader Mokhtarani
1
Saeid Khodabakhshi
2
Bita Ayati
3
Assistant Professor, Civil & Environmental Engineering faculty, Tarbiat Modares University
UV-TiO2 Photocatalytic Degradation of Compost Leachate Abstract The growing rate in solid wastes production leads to considerable generation of leachate. Leachate is defined as the aqueous effluent generated as a consequence of precipitation percolation through wastes, biochemical processes in wastes body and the inherent water content of wastes themselves. Since the leachate contains significant amount of organic and inorganic compounds, it is not allowed to be directly discharge to the environment. Conventional treatment techniques to remove organic matters from leachate include physical, chemical and biological processes. Most of these techniques are non-destructive and do not solve the environmental problems because the wastes are simply transferred from water to another phase creating secondary wastes pollution. Biological method was regarded as the most efficient and cheapest process to eliminate organic materials from leachate. However, biological process cannot usually remove refractory substances. Therefore, the effluent values of the organic content do not meet the standards of the treated wastewater with respect to persistent contaminants. Due to limited biodegradability, the treatment of leachate, apart from biological methods necessitates the application of other methods, which complement and support the main process. Advanced oxidation process has been intensively studied in the past decade to improve the removal of these large refractory organic molecules or to transform them into more easily biodegradable substances. Among them photocatalytic process is one of the appropriate methods for final treatment of these kinds of waste. In this study, application of photocatalytic process via UV light and TiO2 Nano particles immobilized on concrete surface in post-treatment of composting leachate was investigated. This investigation was conducted in laboratory scale and batch mode. A biological pre-treated leachates sample which contains some macromolecular organic substances that were resistant to biological degradation were collected from the effluent of leachate treatment facility, of Gorgan composting plant (Golestan, Iran). UV-C lamps with different power in the range of 8-107 W at a constant distance of 10 cm from the surface of the leachate were used as the source of irradiation. Pervious concrete was constructed using LECA lightweight aggregates with the dimension of 30*10*10 cm. Immobilization of TiO2 on concrete surface was done by using concrete sealer. In order to investigate the effect of each parameter individually, some experiments were carried out. The results showed that the presence of nanoparticles and UV radiation alone did not significantly affect on the COD removal. According to the conducted experiments the maximum COD removal of 62% was achieved after 20 hr radiation with 7.5 mW.Cm-2 intensity in pH value of 5 and in presence of 60 g.m-2 of TiO2 coated on concrete. According to Iranian environmental standards and with regard to organic loading of leachate, removal efficiency of this process was in such a way that it could be directly discharged into the environment. Keyword: Leachate treatment, Photo Catalysis reaction, TiO2, light intensity, Color, COD
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-707&slc_lang=en&sid=16
COD
Leachate treatment
Photo Catalysis reaction
TiO2
Color
COD
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
147
158
article
Optimized Linear Programming for Ramp Metering, Case Study
Amirreza Mamdoohi
1
Mahmood Saffarzadeh
2
A bazargany
3
Tarbiat Modares university
Tarbiat modares University
Freeways have a particular role in urban transportation networks due to their high capacity compared to other facilities of lower hierarchical classification. Although these facilities do not have any at-grade junctions and are of the highest mobility and least access classification, their flow control can help general urban traffic condition. Traffic control strategies are thus of particular importance to urban transportation. Ramp metering of urban freeways and highways is one of the efficient traffic control policies that can alleviate traffic congestion by restricting on-ramp flows to the main stream. A main challenge of this policy is the determination of optimal flow rates of the on-ramps leading to optimal flow rate of the main stream. In this paper, a linear programming model is developed considering the capacity constraint of the main stream and the constraints of queue length of ramps. Although the queue length of the on-ramps increase due to the ramp metering strategy by holding up vehicles on these ramps, the travel time of the main stream as the main body of traffic whose traffic condition is of higher importance, decreases due to the increase in the speed of this stream caused by the drop in vehicle density. The main objective of this paper is the implementation of a mathematical programming model developed for a rather congested case study in Tehran; and the analysis of its challenges and impacts. This model takes into account the maximization of flow in the transportation network while flow conservation and capacity constraints are not violated. In the field survey, flow rate data of about 15000 vehicles west-bound of Shahid Hemmat highway segment from Modares freeway to Shahid Chamran off-ramp were gathered for three hours. This segment includes five on-ramps and four off-ramps whose flow rate data along with that of the main stream was collected on a Tuesday in summer 2011. The data was collected through video recording and then obtaining the necessary variables like flow rate data by re-watching the films carefully and counting the vehicles. Although very time and budget consuming, but this survey method made possible the data collection phase to be valid and reliable. Flow rates for 5 minute time intervals for all the ramps and the main stream were obtained to comprise part of the research data base. Capacity, as a model parameter, was predicted for the segment under study. Results of the mathematical programming optimization model indicate that level of service of the segment under study increases from F to E and that the speed in the main stream increases between 18 and 24 kilometers per hour and that travel time in this segment has a decrease of nine minutes. Results of the optimization model indicate that freeway traffic performance can be optimized by careful management of on-ramp monitoring and control realized through ramp metering strategy, emphasizing quantitatively and scientifically the importance and necessity of detailed traffic data and its analysis for the betterment of traffic conditions through merely management techniques which do not require much time or budget to use the existing facilities more efficiently. .
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-2861&slc_lang=en&sid=16
"Ramp metering"
"Optimization"
"Linear Programming"
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
159
170
article
A Numerical Study on Uniaxial Behavior of Aluminum Replicated Foams with Regular Microstuctures
1
sh sh
2
1
It is a decade that replication process has gained lots of interests in the production of open-cell metallic foams. Replication process usually involves the steps of preparing porous preform, filling the free spaces by foaming material, and removing the space-holders (usually by dissolution). Independent control of pore size, pore shape, and relative density, the possibility of producing foams with pores of few microns, nearly fault free and uniform structures critical in conducting reproducible mechanical tests, applicability to various metal and alloys, and the simplicity of producing functionally graded structures are some of the benefits making replication process quite appealing for researchers involved in the field of cellular solids. This study assumes that the space-holders are initially monomodal spheres packed in regular simple cubic (sc), body-centered cubic (bcc), and face-centered cubic (fcc) configurations. However, the primary shapes and structures of these assemblies undergo considerable changes in the process of compaction. Thus, the realistic numerical simulation of replicated foams is required to address this compressing stage. Accordingly, the physical processes of cold isostatic pressing and preform removal (dissolution) is simulated using nonlinear finite element method and voxel element method, respectively. A code is written to take the deformed shape of a preform (as a set of finite elements), efficiently invert the geometry, and create the FE model of replicated structure as a set of voxel elements. Three pore sizes of 0.1, 1, and 10 mm are assumed. The corresponding unit cells are compressed to reach the desired void volume fractions of around 5 to 25%. Assuming an aluminum alloy as the foaming material, uniaxial compressive load is applied to the samples and their elastic moduli, Poisson’s ratios, and yield stresses are extracted. In the range of preforms and pore sizes simulated, no cell size dependency of the results has been observed. The fcc structure, owing to its oblique beam-like elements, shows the most flexible behavior. On the other hand, the sc structure is found the stiffest in the group. The dependencies of elastic and yield properties to relative density increase by migrating from the sc to the bcc and next to the fcc structures. More in-depth study of the results reveals that the bcc samples of higher relative densities have inherent elastic behaviors near those of the sc specimens. From yield stress point of view, the bcc and fcc foams are found superior and inferior, respectively. The computed yield stresses are also compared to some previously reported analytical estimations from which the strength level of each structure is identified. The power law exponents of numerically calculated yield points are shown to be less than their empirical counterparts. This is attributed to the random structure of actual foams and their imperfect struts. Finally, it needs to note that, the extended application of the developed computational procedure to the random assemblies of spherical preforms is already under investigation.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-7169&slc_lang=en&sid=16
replicated foam
Numerical simulation
uniaxial compression
finite element method
voxel element
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
171
181
article
Amelioration of the nonlinear seismic responses of RC structures based on the yield displacement
(On the Comparison of CSA and YPS analysis methods)
1
2
Abstract Seismic performance evaluation of different structures requires nonlinear analysis utilizing static or dynamic methods. Among the dynamic nonlinear methods is the time history (TH) method can be noted. Performing dynamic nonlinear methods is not decree because of these methods has complex process and need long time to perform so often engineers do evaluations of seismic performance of different structures by using static nonlinear methods. In static nonlinear methods, capacity spectrum analysis using the concept of nonlinear spectra with constant ductility (CSA) and yield point spectrum analysis (YPSA) can be pointed. Both of these methods determine maximum displacement of structure by comparison capacity spectrum and demand spectrum but YPS method is easier than CSA and need lesser attempts. In additional of this advantage YPSA can be used in design. In order to Performing any of these Methods seven records is needed as history of the sever ground motions. These records are proportionate with the soil of type II. To allow comparison and homogenization of results of these methods scaling of the records is necessary. Also in scaling process the effect of vertical component of ground motion is neglected. In this paper the accuracy of CSA and YPS methods in determining the structural responses, has been assessed by their comparison with the TH method as the witness and accurate method of analysis. In this comparison is used the average of the results. Results include of Displacement of roof of the structures and Inter-story drifts. For this purpose, three 3D structural models of 8, 12 and 15 stories of moderate ductility were selected. These structures consist of a dual system (wall-frame) in one direction and moment resistant system in another direction of the plan against seismic load. All these structures were analyzed and designed according to the Iranian standard 2800 (IS-2800) for seismic analysis and Iranian concrete code of practice respectively. For 12 and 15 stories structures, all records scaled base on demand spectrum given by IS-2800. In the case of 8 story structure the records scaled base on equal maximum acceleration (0.4g). All structures analyzed utilizing all the methods of TH, CSA and YPSA. In all these analysis the flexural and axial behavior of elements and the shear behavior of the walls were considered nonlinear. Also in the both nonlinear static methods, the strength reduction in the demand spectrum of applied earthquakes was not taken into consideration. Results show that the YPSA method is not accurate enough in case of the earthquakes that cause the structure to largely enter the nonlinear state. Also this method is highly sensitive to the yield displacement for determining the response. Thus, strategies to address these deficiencies are presented. It’s also been shown that the best range for considering the yield displacement in dual system of concrete structures up to 50 meter height is 0.6% to 0.8% of the height of structures. Key Words: Capacity Spectrum Method, Yield Point Spectrum, Time History Nonlinear Analysis, Dual System, Reinforced Concrete Structures
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-6538&slc_lang=en&sid=16
Capacity Spectrum Method"
Yield Point Spectrum"
Time History Nonlinear Analysis"
Dual System"Reinforced Concrete Structures "
per
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
2476-6763
2014-09
14
20
183
195
article
Experimental Study on Combined effects of microsilica weighted ratio content, fineness modulus of aggregates and water-cement ratio on mechanical and physical properties of concrete
majid yazdandoust
1
mahmood yazdani
2
student
Teacher
Concrete properties are dependent on many parameters such as ingredients, production and technology, construction methods and curing conditions that have made concrete as a complex and unpredictable material. But these are virtually ignorable against its precious advantageous and precise studies on above parameters may help us to produce concretes with our desirable properties. Ingredients are of those important parameters that play an essential role. Therefore it is seriously important to have enough knowledge about ingredients, their combined effects and interactions and also effects of their properties on concrete properties. Pozzolan materials can help us to achieve desirable characteristics of concrete and develop its mechanical and physical parameters, hence they are used widely. Improvement of mechanical parameters, permeability reduction, and durability increase are among their fabulous benefits of application. They are deemed as essential ingredients of high durable and strength concretes. Pozzolan weighted ratio is major parameters which develop a homogenous and united medium and improve the physical and mechanical parameters of concrete. The effects of pozzolan on physical and mechanical properties of concrete, moreover it’s specifications, depend on the parameters of other ingredients, such as type of aggregates, particle size distribution of aggregates, fineness modulus of fine aggregates, water-cement ratio, cement type and ect. Then study of combined effects of pozzolan specifications and parameters of other ingredients is inevitable for achieving to a concrete with ideal parameters. As we know, microsilica is the most popular pozzolan material which is used widely and it’s parameters and other ingredients parameters (such as type of aggregates, particle size distribution of aggregates, fineness modulus of fine aggregates, water-cement ratio, cement type and ect) have combined effects on the variation of concrete physical and mechanical parameters. So, in this study we selected microsilica as a pozzolan to determine the combined effects of its weighted ratio content, fineness modulus of fine aggregates and water-cement ratio on physical and mechanical properties of concrete. In this study, the combined effects of microsilica weighted ratio content, fineness modulus and water-cement ratio on physical and mechanical properties of concrete were investigated. For determination the effects of microsilica weighted ratio content on concrete parameters in different water-cement ratios and particle size distributions, 5 different microsilica weighted ratio contents, 3 water-cement ratios and 3 particle size distributions, were selected and totally 45 mix designs were prepared and subjected to slump test and compressive strength, tensile strength and modulus of elasticity tests. Obtained results show a direct relationship between microsilica weighted ratio content and physical and mechanical properties of concrete. Increase in microsilica content from 0% to 10 % in all water-cement ratios and fineness modulus, leads to slump decrease and mechanical parameters increase, while from 10 % to 20 % of microsilica content, mechanical properties fall down, but the reduction trend of slump continues. Also it can be seen that the effect of different weighted of microsilica, on physical and mechanical properties of concrete, reduces by increasing in water-cement ratio and intensifies with increment of fineness modulus of fine aggregates.
http://journals.modares.ac.ir/browse.php?a_code=A-16-1000-9170&slc_lang=en&sid=16
microsilica
fineness modulus
water-cement ratio
concrete mechanical and physical properties