Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Suggested Estimating Method for Hydrodynamic Pressure to Seismic Design of Hydraulic Structure Gates in Adjacent To Dam Reservoir
1
15
FA
M.T.
Ahmadi
Tarbiat Modares University
M.
Haghani
Tarbiat Modares University
Abstract:
No dam could be safely designed without functionality dependence on reliable performance of a number of appurtenant structures.
Gates are the main appurtenant structures responsible for controlling water flow from the reservoir. Earthquakes induce acoustic and surface waves in the reservoir and cause hydrodynamic pressure on the adjacent gates. Hydrodynamic pressures might surpass hydrostatic pressure on some locations of the dam upstream face. Some engineers use the hydrodynamic pressure solution concerning to axi-symmetric offshore and coastal structures for the design of such hydro-mechanical gates. Flexibility of these gates may magnify the hydrodynamic pressure due to severe generation of vibrations separate from the dam body itself even for those installed within the dam bodies. This statement reflects the design philosophy of secondary structures. Fundamental frequency of such gates are usually reduced due to the presence of infinite fluid in their vicinity. Therefore the study of their behavior is somehow complicated during the earthquake. Design regulations of hydraulic structures, demand the hydrodynamic pressure as a design action and usually admits its simple calculation from the Westergaard formula. In this article, by using floor response spectrum in gate level which is used to design the secondary systems and also the spectral acceleration parameter in gate level which is used based on predominant frequency of gate-reservoir, the common relation of gate design against hydrodynamic pressure has been corrected. Then a new non-dimension factor is suggested for sliding rectangular gates in different levels of dam body that is related to the performed analyses and log-normal distribution of data..
In general for various conditions the dimensionless coefficient of Westergaard formula changes from 0.875 to widely varying values between 0.25 to 2.5 when using the base acceleration. However when the spectral acceleration of the floor response spectrum is used for the fundamental frequency of gate-reservoir, this coefficient is more precisely determined for vertical rectangular gates.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
The influence of masonry infill panels on the progressive collapse response of reinforced concrete structures
11
11
FA
Masoud
Soltani Mohammadi
Tarbiat Modares Univ.
Sepideh
Rahimi
Ali Akbar
Aghakouchak
Reinforced concrete structures are considered as bare frames in analysis and design process, including the main structural members such as beams, columns and shear walls. However, in the urban areas, structural frames are filled with masonry walls as acoustic and thermal insulation in the middle or peripheral areas of the buildings therefore they have not the same behavior as the empty frames. This research aims at investigating the effect of unreinforced masonry infill panels on the response of RC frames against the progressive collapse. For this purpose a micro based modeling approach is adopted for numerical simulation of the masonry infill panels and through a parametric study, the effect of influencing parameters is numerically investigated. Also an equivalent compressive strut model is proposed for macro modeling of masonry infill panels. The comparison between numerical and available experimental results confirms the reliability of the developed model. Finally, the developed macro model is used to investigate the influence of masonry infill panels on the progressive collapse resistance of reinforced concrete frames with different ductility capacity. It is shown that, under the progressive collapse phenomenon, the ductility of RC frame is the main effective parameter and masonry infill panel play an important and non-ignorable role in structural response
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
experimental investigation of hydraulic fracturing propagation in multi-layer formations
11
11
FA
mahmoud
behnia
kamran
goshtasbi
ali akbar
golshani
mohammad
fatehi
Hydraulic fracturing as a method for reservoir stimulation depends on the properties of the media that fracture propagates in it. Discontinuities in the media and their mechanical properties greatly affect the geometry and propagation of hydraulic fractures. In this research, the interaction between the hydraulic fractures with the media layers interface, fracture propagation pattern and termination in multi-layered media were investigated. The true tri-axial cell was utilized to conduct experimental tests on cube multi-layered samples with discontinuities. The tests were aimed to investigate propagation of fractures from soft to stiff, stiff to soft media and also the effect of elastic properties of rocks in hydraulic fracturing. Results showed that the condition of discontinuities (healed, open or filled) and elastic properties of the layers influences the geometry and propagation pattern of hydraulic fractures. In the block with the bounded interfaces, the fracture propagates and interacts with the interfaces, then penetrates in the adjacent layers. However, for the block with unbounded interfaces the fracture propagates from the borehole up to the interface, then after filling the interface with the fluid the new fracture will propagate in the adjacent blocks. In sample where the interface was filled, the fracture propagation was terminated and then the fluid started to leak off in the interface. The results also show when the fracture reaches the interface, the pressure increased immediately and more pressure is needed for fracture propagation across the interface. In comparison between the length and width of fractures in soft and stiff layers, the study displays that the fracture width and its penetration length in soft layers are greater than those in stiff layers.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Lead Removal from Wastewater by Adsorption
using Ash and Sawdust
17
26
FA
H.R.
Babaei Zarch
Tarbiat Modares University
H. Ganjidoust
Ganjidoust
Tarbiat Modares University
B.
Ayati
Tarbiat Modares University
Abstract:
Water pollution due to toxic heavy metals has been a main cause of concern for the environmental engineers. Heavy metals are individual metals that negatively affect people's health. In very small amounts, many of these metals are necessary to support life. However, in larger amounts, they become toxic. Lead is one the important heavy metals that is applied in different industries such as manufacture of batteries, metal products and ammunition. Its standard limits in drinking water are 0.05 mg/L, because it affects all organs and functions of the body to varying degrees. The frequency and severity of symptoms among exposed individuals depends upon the amount of exposure. Lead entering the respiratory and digestive systems is released to the blood and distributed throughout the body. It is stored and may be released into the blood, re-exposing organ systems long after the original exposure. This is why the wastewater includes lead should be treated before discharging to the environment. Different kinds of physical, chemical and biological methods are used to remove lead. The main techniques are including precipitation, ion exchange, adsorption, membrane processing and electrolyte methods. Adsorption with many advantages is a proper method that is applied to treat heavy metal removal. In recent years, use of low cost materials as adsorbent for metal ion removal has been highlighted.
Since natural absorbents are inexpensive and may be achieved without any cost and they are usually in abundance in nature, absorption of solute ions by these materials are a proper method to eliminate heavy metals from polluted waters and industrial wastewaters.
In this study, following continuous column method, sawdust and ash, as two absorbents were used for removing lead. The experiments were carried out with the initial pH of 5 and different densities (50 and 100 ppm). In order to optimize the process of adsorption, three combined absorbents were also used which made from the above two absorbents with the ratios of 1:3, 1:4 and 1:6. Batch experiments were carried out in order to determine the parameters of adsorption. The results of sorption with sawdust have shown that Langmuir adsorption isotherm were suitable. Based on the results of the column experiments study, lead removal efficiency was more than 98 percent when combined absorbents were used. In batch experiments, the percent efficiency was 76 and 98 percent with sawdust and ash, respectively.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Measured Shear Strength and Hardness of Asphalt Mixtures Using Shear Devices Designed and Built
27
37
FA
M.
Dindar
TarbiatModares University
A.
Hasani
TarbiatModares University
A.
Kavoosi
TarbiatModares University
H.
Mohsenzadegan
TarbiatModares University
Abstract: From examining the pavement failures and itscauses, these results are obtained, improving and increasing resistance of asphalt mixtures against incoming stresses (vertical, shear and torsion stresses), causing delay and reduce failures created on pavement and thus their productivity and life will be increased.Costs that each year spent in the country to improve and repair of pavements withfailures, illustrate theImportance of improving the resistance of pavements against the incoming stresses.This study introduced two types of shear device has been developed in order to measure shear strength and shear stiffness of asphalt mixtures.Shear strength and shear stiffness of asphalt mixtures has a close relationship with the adhesion (c) and friction angle between the materials of asphalt aggregate mixtures. Increasing each of these parameters, the shear strength of asphalt mixtures will be increased. Identifying and evaluating effective parameters that increased asphalt mixtures resistance, including gradated aggregate materials used or the effect of compaction, type and amount of binder, asphalt mixtures with the appropriate shear resistance can be produced. This requires the evaluating of effective factors in shear strength of the constructed samples.The failure or destruction in asphalt mixtures in states of pure shear, pure tension, shear with pressure, and shear with traction can occur.In this study, to evaluate the shear resistance of asphalt mixtures made with two different penetration grade bitumen, two types of shear device was designed and built and Marshall samples made with two types of bitumen, under force of pressure - shear and pure shear were disjointed and the maximum shear strength and shear stiffness of them were calculated.Using any one of these two units, different parameters in the effective shear strength and hardness of the samples can be investigated and asphalt more shear resistance against shear forces produced. Testing and evaluation, this result is achieved that Because the effect of consumption of bitumen type on asphalt mixtures properties (increasing adhesion coefficient), shear strength and shear stiffness of asphalt mixtures containing bitumen 60/70 in comparison with asphalt mixtures containing bitumen 85/100 is more
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Oil Contamination Propagation Patterns in Soils
39
51
FA
M.
Heidarpoor
Tarbiat Modares University
M.
Oliaei
Tarbiat Modares University
In recent decades attention to contamination propagation into soils and underground water has been increased which has led to increasing the studies on soil contamination problems and methods of in-situ remediation. Also, soil contamination with petroleum compounds has been one of the most challenging issues. In many countries with petroleum industries, mines of oil exploration, refineries and etc, by reasons, such as leakage from tanks or pipelines of oil transmission due to corrosion and damage, soil will be contaminated by oil pollution. Hence, contaminant propagation in soils and also remediation of the contaminated soils has been considered as a sensitive, complex and critical environmental issue. According to recent studies, it is clear that further study on petroleum contamination propagation pattern in soils and underground water is needed. Therefore, the study about this pattern is main purpose of this research which has been done by means of numerical Finite Element Method (FEM). Following, the theory of pollution propagation and the mechanisms and formulation of this process are expressed. Then, the explanation of modeling has been carried out in terms of geometry, boundary conditions, method of analysis, material parameters and etc. Verification and analysis results have been presented, respectively. Finally, conclusion is given and discussed. In this research, effective parameters on oil contamination propagation in soils and underground water have been investigated. These parameters are soil permeability, relative density of contamination, dispersivity coefficients, diffusion coefficient and ground water table depth. The results show there are different propagation patterns in coarse and fine grain soils. Furthermore, the efficiency of pumping method as an in-situ remediation approach for contaminated soils is studding by authors. The most important conclusions are as following: -In coarse grain soils, downward propagation pattern and in fine grain soils lateral propagation pattern are dominant. -By increasing the longitudinal dispersivity coefficient, contamination patterns will be extended. It is more evident in coarse soils which is due to more void ratios in these types of soils. The results are more sensitive to longitudinal dispersivity coefficients variations with respect to transverse dispersivity coefficients. -The effect of diffusion coefficient has a direct relation with the perimeter of contamination domain
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Evaluation of Canyon Site Effects on Seismic Waves
53
66
FA
Naser
Khaji
Tarbiat Modares University
It is well known that ground surface with irregular topographic features causes complicated seismic responses. The complex seismic response is mainly caused by wave scattering. In this study, for a homogeneous, isotropic, linearly elastic half-space, the formulation of a two-dimensional SH-wave field based on the direct boundary element method and Neumann series expansion is developed. By discretizing the ground surface to boundary elements, the boundary integral equation is formulated into a general matrix form. This general matrix form is then reduced to a more efficient form, which considerably reduces the size of the computational matrices using Neumann series expansion. For this purpose, a Fortran computer program is developed, whose accuracy and feasibility in the frequency domain is shown by some numerical analyses conducted for grounds with semicircular convex and concave, and symmetrical V-shaped canyon topographical configurations. Comparing the results of the present study with those available in the literature shows the accuracy of the present study by just considering two first terms of Neumann series expansion. The minor differences of the results of the present research with other reseach results may be assigned to the number of terms of Neumann series expansion and the order of used boundary elements. In other words, if the number of terms of Neumann series expansion and the order of used boundary elements incease, the accuracy of the numerical results may enhance. Based on the results of the present research for various parameters of different two-dimensional canyons, the following conclusions may be obtained: When the exciting frequency increases, the wave-length decreases. As a result, the violence effects of incident wave due to canyon effects may be significant for a given canyon. Moreover, the displacement field of various canyon points follows more complicated pattern. On the other hand, for smaller exciting frequencies with larger wave-lengths, the canyon effects as the main cause of disturbation source are not so remarkable, and the displacement field of various canyon points are smoother. The effects of incident wave angle is also remarkable on the disturbation patterns of displacement field of different canyon points. When the angle increases, the triangle canyons experience more complicated patterns compared to semicircular canyons. Analyses'''' results show important effects of shape and depth of various canyons. These effects are more considerable when depth''''s variations are remarkable in comparison with the wave-length of incident wave. Furthermore, the mentioned effects are functions of frequency and angle of incident wave.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Evaluation of Canyon Site Effects on Seismic Waves
53
66
FA
N.
Khaji
Tarbiat Modares University
M.
Amini
Tarbiat Modares University
It is well known that ground surface with irregular topographic features causes complicated seismic responses. The complex seismic response is mainly caused by wave scattering. In this study, for a homogeneous, isotropic, linearly elastic half-space, the formulation of a two-dimensional SH-wave field based on the direct boundary element method and Neumann series expansion is developed. By discretizing the ground surface to boundary elements, the boundary integral equation is formulated into a general matrix form. This general matrix form is then reduced to a more efficient form, which considerably reduces the size of the computational matrices using Neumann series expansion. For this purpose, a Fortran computer program is developed, whose accuracy and feasibility in the frequency domain is shown by some numerical analyses conducted for grounds with semicircular convex and concave, and symmetrical V-shaped canyon topographical configurations. Comparing the results of the present study with those available in the literature shows the accuracy of the present study by just considering two first terms of Neumann series expansion. The minor differences of the results of the present research with other reseach results may be assigned to the number of terms of Neumann series expansion and the order of used boundary elements. In other words, if the number of terms of Neumann series expansion and the order of used boundary elements incease, the accuracy of the numerical results may enhance. Based on the results of the present research for various parameters of different two-dimensional canyons, the following conclusions may be obtained:
When the exciting frequency increases, the wave-length decreases. As a result, the violence effects of incident wave due to canyon effects may be significant for a given canyon. Moreover, the displacement field of various canyon points follows more complicated pattern. On the other hand, for smaller exciting frequencies with larger wave-lengths, the canyon effects as the main cause of disturbation source are not so remarkable, and the displacement field of various canyon points are smoother.
The effects of incident wave angle is also remarkable on the disturbation patterns of displacement field of different canyon points. When the angle increases, the triangle canyons experience more complicated patterns compared to semicircular canyons.
Analyses' results show important effects of shape and depth of various canyons. These effects are more considerable when depth's variations are remarkable in comparison with the wave-length of incident wave. Furthermore, the mentioned effects are functions of frequency and angle of incident wave.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Amplification Factor for Estimation of Maximum Inelastic Lateral Displacement of Reinforced Concrete Moment Resisting Frames
67
78
FA
M.
Zaker Salehi
Tarbiat Modares University
A.A.
Tasnimi
Tarbiat Modares University
Abstract: In seismic design of structures, estimating maximum inelastic lateral displacement of the structure occurring in the sever earthquake is of grate importance. Although by conducting nonlinear time history analysis good estimates of inelastic displacements can be obtained, but this method is relatively expensive and needs high expert in this field and its use is impractical in most of the design offices. So in most seismic design provisions, maximum inelastic displacement of the structure is estimated by amplifying the lateral displacement computed from an elastic analysis with a displacement amplification factor (Cd). Reviewing several seismic design provisions indicates that in most of them Cd is only dependent on the earthquake force resisting system. In this paper in addition to the earthquake force resisting system, the effect of some important parameters such as number of stories of the structure, story number, characteristic of the earthquake ground motion and number of bays on Cd is investigated. For this research 32 reinforced concrete moment resisting frames with high and moderate ductility which have 3 or 5 bays and 2, 3, 4, 5, 6, 8, 10 and 12 stories are considered. For determination of real displacements occurring in major earthquake (inelastic displacements), nonlinear time history analysis using IDARC program is performed. In nonlinear analyses, 7 earthquake ground motions consistent with soil type II of Standard no. 2800 are used. These records are scaled according to Standard no. 2800 directions. For linear analyses, equivalent static procedure is employed using ETABS program. The inelastic displacements which are computed by averaging the results of 7 ground motions, are then divided by elastic displacements and so Cd for each story of 32 frames is determined. In this research, like most researches and provisions, Cd is considered as a function of R (structural behavior factor) and for simplicity Cd/R is shown by DF and the following results are presented for DF. The first important result is that DF in high ductility frames are more than corresponding ones in moderate ductility frames especially in low frames and lower stories of tall frames. Furthermore in more than 97% cases, this factor decreases by increasing story number showing that inelastic deformations and damages are mostly concentrated in lower stories. Also it was observed that in low frames and lower stories of tall frames, the response of structure is more sensitive to the characteristic of the earthquake ground motion. Another conclusion is that in all frames, DF is almost independent of the number of bays. Then by recognizing the most affecting parameters and conducting nonlinear regression, an equation for computing displacement amplification factor in special and intermediate reinforced concrete moment frames is suggested. In the proposed equation, DF has been recognized as a function of lateral load resisting system, story number and height of frame (natural period of frame). Finally, results are compared with Standard no. 2800 formula (DF=0.7) for estimating inelastic displacements. It is concluded that inelastic lateral displacement of frames obtained from nonlinear time history analysis are largely different from those calculated by Standard no. 2800 formula especially at upper stories. This difference is originated from the fact that considering a unique DF (0.7) for all stories results in a deformed shape in nonlinear domain similar to that in linear domain which is true only if damages and inelastic deformations occur monotonous in height of structure; but this assumption is not consistent with real response of structures during the sever earthquake.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Optimization of Geometric Parameters of Submerged Vane in Straight Alluvial Channel With Taguchi Method and GRA.
79
93
FA
M.
Rostamabadi
Tarbiat Modares University
A.A.
Salehi Neyshabouri
Tarbiat Modares University
A.R.
Zarrati
Amirkabir University
Submerged vanes are plane structures mounted vertically on river bed with an angle to the approach flow. These structures are usually used in group. The operation of the submerged vanes is production of secondary flow around their length axis that changes the flow pattern and bed topography. The performance of a submerged vane is related to its geometric parameters such as length, height and the angle of attack of the approach flow. In this study the optimization of geometric parameters of a submerged vane in a straight alluvial flume is done numerically to achieve the best condition for increasing the scour depth of channel in front of lateral intake and deviation of sediment from lateral intakes. The SSIIM software is applied for simulating the flow and sediment pattern around a submerged vane. Verification of numerical model with experimental results is done. The effect of geometric parameters of the vane on the performance of the submerged vane is studied. Length, height and the angle of a vane are investigated in four levels and four responses including minimum scour depth near the leading edge of the vane, minimum scour depth near the trailing edge of the vane, maximum scour volume at the downstream of the vane and maximum sedimentation depth at the downstream of the vane are calculated numerically. In previous studies the scour depth at the leading and the trailing edges of the vane were not included in optimization and this is one of the innovation of this paper. The other two last responses are normalized with appropriate parameters. The maximum scour volume at the downstream of the vane is normalized with the volume of the vane and the maximum sedimentation depth at the downstream of the vane is normalized with the length of the vane. Taguchi method is used to design studies in order to minimize the number of cases without affecting the results. 16 tests are investigated instead of 64 tests. Grey Relational Analysis is used for analyzing the responses. The results of this study show that the angle of a vane has more effect on the performance of the vane than the height and the height is more effective than the length. The ratio of 0.25 for the height of the vane to the depth of flow and 15 degree for the angle of attack are proposed to obtain the optimum performance of the submerged vane. Changing the ratio of the length to the height of the vane has a little effect on the responses. So the smaller length of the submerged vanes (in this paper the ratio of 1.25 among 1.25 to 3 for the length to the height of the vane) is economical.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Effects of Bed Roughness on Turbulent Characteristics of a Three-Dimensional Wall Jets
95
104
FA
A.
Shojaeizadeh
Tarbiat Modares University
M.
Ghodsian
Tarbiat Modares University
A.A.
Salehi Neyshaboori
Tarbiat Modares University
A.
Safarzadeh
University of Mohaghegh Ardabili
Abstract:
In this paper the experimental study of the flow pattern around a round wall jet has been carried out to investigate the effect of the bed roughness on the turbulence characteristics, including Reynolds stress and turbulence intensities. Measurements were conducted using the three-dimensional velocimeter, ADV and time series of the velocity components are used to investigate the variation of the turbulent flow parameters along the measuring domain. The results showed that by increasing the bed roughness, the streamwise and vertical turbulence intensities increase by downstream distance and for a specific bed roughness the streamwise turbulence intensity is higher than the vertical one. Furthermore, by going downstream from the jet entrance the bed shear stress reduces and by increasing the bed roughness, the bed shear stress has an increasing trend along the jet centerline. Location of the maximum bed shear stress does not change by changing the bed roughness.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Numerical Modeling of Cone Penetration Test
105
117
FA
A.A.
Golshani
Tarbiat Modares University
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 the axial 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.
In this study serious models of multi-layer perception neural network, one of the most commonly used neural networks, was used.
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. 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. According 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. To perform these tests the device of pile bearing capacity, made in university of Tarbiat Modarres, 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 answer this question.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Foundation design using topology optimization
111
111
FA
fatemeh
zahedi tajrishi
civil department of university of technology/ph.d student
hamid
moharami
tarbiat modares university
In this paper a methodology for design optimization of foundation of structures has been proposed. The structural model comprises three different finite elements, i.e. plate elements for mat foundation, solid elements for soil and some compression-only members for connection of foundation to soil. To facilitate the optimization algorithm, a 3D analysis is performed in the elastic range under one design loading. Due to numerous finite elements and accordingly considerable number of design variables, the classical topology optimization algorithms become inefficient for solution of the problem. Therefore in this paper an innovative topology optimization algorithm, which does work based on efficiency of foundation elements, is proposed. This new algorithm cuts out the foundation elements that do not bear (or bear low value) compression under design load(s). The overall optimization methodology consists of two phase optimization: namely topology optimization and size optimization. After every topology optimization, an analysis is done and a size optimization algorithm is used to proportion the thickness of the foundation and corresponding reinforcement. The consequent topology and size optimization processes are repeated until no enhancement is obtained in the design. The capabilities of the proposed method have been shown by four design example.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Numerical and Experimental Simulation of Dowel Action across RC Cracks under Cyclic Loading
133
148
FA
A.R.
Moradi
Tarbiat Modares University
M.
Soltani Mohammadi
Tarbiat Modares University
A. A.
Tasnimi
Tarbiat Modares University
Abstract: Evaluation and analysis of RC structures performance without using proper constitutive models doesn't have acceptable accuracy due to the complicated nature of shear transfer mechanism across cracks. Cracks and interfaces have been recognized as important planes in global behavior of RC structures. In fact, response of structures, failure modes and even the capacity of RC elements can be affected by stress transfer mechanism across cracks. On the other hand, understanding and expressing the different kinds of stress transfer mechanisms in finite element-based analyses is important. Aggregate interlock and dowel action are the two main shear transfer mechanisms across RC cracks and stress-induced interfaces. Cyclic nature of earthquake excitation increases cracks opening and causes major reduction in the contribution of aggregate interlock mechanism. This makes dowel action as the main mechanism resisting against applied deformation hence it is important to assess the behavior of crossing bars under cyclic loading. During the past years, extensive experimental and analytical investigations have been carried out. Many researchers have predicted the load-carrying capacity of a dowel within a limit-analysis method considering the simultaneous formation of plastic hinge in the embedded bar and a localized crushed zone in subgrade concrete. Some results showed that a localized plastic hinge is just a rough approximation. Therefore, beam on elastic foundation analogy (BEF) has been known as the most common approach to simulate dowel action mechanism. In spite of its shortcomings, the BEF analogy has been recognized as a suitable approach to simulate concrete and reinforcement interaction across cracks and different types of connections in RC structures. In this paper, dowel action mechanism has been examined analytically and experimentally and in order to simulate the shear transfer by dowel bar under different loading conditions, the beam on elastic foundation analogy has been generalized by proposing the elasto-plastic relation for foundation springs. The subgrade stiffness is the most relevant parameter to capture the global behavior of embedded dowel bars hence by adopting the proper formulation, the final loading stage as well as the initial stage can be described. Local crushing and high inelasticity of surrounding concrete near the interface is simulated by gradual changes in the spring stiffness due to increasing bar shear displacements. On the other hand, the BEF is developed to beam on inelastic foundation (BIF) by proposing an appropriate relation for spring stiffness. The suggested equation can specify the stiffness changes in consistent and simple manner during loading path. In order to have a better insight into cyclic response of crossing bars and to determine the relative parameters, some beam-type specimens under pure cyclic and repeating shear loading have been tested. Dowel action mechanism has a considerable nonlinear response under reversed cyclic loading path. The source of nonlinearity should be sought in the plasticity of dowel bars and fracturing of the surrounding concrete. The amount of applied shear displacements as well as the direction of loading and also the number of loading cycles can lead to nonlinear response. To extend the formula to unloading and reloading cases, spring deformation is divided into two components, the elastic and the residual plastic deformations. Some efforts have been devoted to assume direct proportionality between the maximum and the plastic deformation and kept constant regardless of loading history. Experimental results show thatthe maximum deformation changes due to increasing deformation of bar and cannot be assumed a constant value for it. It seems that determining the plastic bar displacement can improve the stiffness of unloading and reloading diagrams. So, the results of the experimental program and the available experimental results has been categorized for cyclic and repeating loading in order to obtain a reasonable relation between the maximum and the plastic deformation. The plastic displacement of dowel bar in each loading step is suggested by statistical analysis of collected experimental data. The effect of cyclic loading is thought to be a degradation of surrounding concrete represe-nted by inelastic springs. Therefore, improving the spring stiffness-deformation relation can capture the global behavior properly. Stiffness-deformation relation for cyclic loading has been suggested based on the available experimental results. A systematic experimental verification has been carried out to examine the reliability of the proposed model. The closed form equations lead to the considerable reduction in computational efforts. The results confirmed the accuracy of the new approach.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Artificial Neural Network Model for Telecommuting Demand: A Technique to Decrease Urban Traffic
149
159
FA
A.R.
Mamdoohi
Tarbiat Modares University
A.
Ardeshiri
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Abstract:
Heavy transport costs have lead researchers in the field towards more efficient techniques to reduce peak period congestion. One such technique is telecommuting which is planned to, in line with the most travel demand management techniques, to decrease motorized trips during commuting hours. By allowing employees to work from home or a center near home equipped with telecommunication technologies, telecommuting causes an increase in efficiency of the urban transport system and a decrease in fuel consumption costs, air pollution costs and the need to invest infrastructures. Identification of the actual demand for telecommuting is a prime to analyzing the potential consequences of telecommuting in mobility improvement, congestion reduction, and energy conservation. Considering the vast socio-economic dimensions of this technique, the present paper intends to model telecommuting demand for the metropolitan of Tehran, Iran, by employing the artificial neural network (ANN) approach. ANNs are applied as a modeling tool for the complex systems of recognition and prediction, inspired by the interconnectivity of the human nervous system. ANN simulates adaptive interaction between processing elements in parallel architecture. A multi-layer perceptron model using error back propagation is deployed to predict the suitable number of weekdays telecommuting for each employment category. Using the data from an interview-filled questionnaire, designed for this purpose, various structures of ANN models were calibrated based on 80 percent of a 676 size sample. The remaining 20 percent of the preference data was preserved to assess the prediction strength of the model as it encounters unforeseen cases. Four endogenous inputs that inferred from organizational characteristics of employees arrayed the neural network model. Due to unordered nominal values of independent variables, ANN was determined to be an appropriate approach to recognize the telecommuting suitability pattern. The proposed neural network is composed of 21 neurons in 3 layers with tan-sigmoid, log-sigmoid, and linear transfer functions in the corresponding hidden and output layers. Results of the proposed model with 171 unknown parameters, converging after 1800 iterations, indicated a fair capability to replicate observations, such that mean square error, coefficient of determination, and percent correct criteria for the test set equaled, respectively, 1.177, 0.19 and 39 percent. The ANN model successfully estimated the stated quantities of telecommuting days per week, within a range of one day error, to 86 percent and 84 percent correct for the train and test sets, respectively. The evaluation results of train and test subsets are relatively close, which indicates a low generalization error, meanwhile demonstrates the reliability of ANNs to forecast the telecommuting demand.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Experimental Study on the Effect of Aggregate Fineness Modulus on Physical and Mechanical Properties of Concrete
161
172
FA
M.
Yazdandoust
Tarbiat Modarres University
M.
Yazdani
Tarbiat Modarres University
Abstract:
Concrete is one of moderately new materials, which is used widely because of its appropriate properties. Many Scientifics and researchers have tried to develop and utilize the beneficial properties of this new material and as a result its ingredients have been investigated extensively. Concrete properties are dependent on many parameters such as ingredients, production and technology, construction methods and curing conditions that have made concrete 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 desirable properties.
As it was discussed previously, ingredients are of those important parameters that play an essential role. Therefore investigating ingredients, their interactions and effects of their properties on properties of concrete are seriously important. Of the most important of concrete ingredients are aggregates, which are usually deemed unimportant despite their momentous contribution to concrete production. As about three forth of concrete's volume is its aggregates, studying aggregates' properties including the effect of grain size distribution on physical and mechanical properties of concrete is pivotal, although few comprehensive and acceptable investigations have been carried so far. Shape, particle size distribution, dimensions, surface characteristics, and minerals are parameters which are effective in making a homogenous and united medium. In fact there are various parameters (criteria) which determine an ideal material. In this study, the effect of fineness module of fines aggregate on mechanical and physical parameters of concrete has been investigated among other parameters. Fineness module is defined as total accumulated percentage of remained material on standard sieves in fines range.
In this study and in respect to above factors, in order to study the effect of fineness modulus of aggregates on physical and mechanical properties of concrete, using 7 different grain size distributions with various fineness modulus and 11 cement-water ratios, totally 77 different mix designs were tested for slump test.
Also 462 samples were prepared using those various mix designs and were tested at 7 and 28-day life long under compressive loads. The obtained results suggest clearly the direct effect of fineness modulus of aggregates on mechanical and physical properties of concrete. In details, the decrease in fineness modulus from 3.26 to 2.66 has caused an increase in slump values and compressive strengths.
The rise in compressive strength can be addressed to more unity for aggregates with smaller fineness modulus. Furthermore, the existence of smaller aggregates (smaller fineness modulus) has led to more comfortable conditions for larger grains to travel. This in turn incited the slump values' boost while fineness modulus decreased. As a result it can be concluded that the grain size distribution can play a crucial role in dominating physical and mechanical properties of concrete.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
Modal and Nonlinear Analysis of Cracked Concrete Beams and FE Modeling for Damage Assessment
173
184
FA
A.R.
Gharighoran
University of Isfahan
F.
Daneshjoo
Tarbiat Modares University
Abstract:
For theoretical and practical investigation of damage increase on dynamic characteristics of concrete structures can use analytical model to extract dynamic characteristics such as natural frequency and mode shape. In this research, results of experimental and finite element analytical model for various specimens were compared. These specimens include RC beams and pre-stress concrete beams that constructed in laboratory. In this paper, one of the specimens was modeled for showing how modeling cracked concrete beams and specials notes related to nonlinear static analysis and modal analysis. In test case, damages are produced step-by-step applying the static load and modal characteristics of the specimen are measured via modal test immediately after loading step. However, in finite element modeling case is two complicated problems. Firstly, because concrete is a composite material, modeling of cracked concrete is very difficult. Secondly, in RC structures, both the concrete and steel have nonlinear behavior. Results of this research include peculiar notes that can be useful for other similar researches.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
13
2
2013
5
1
The Effects of Beam Characteristics on Seismic Behavior of Chevron Braced Frames with Different Configurations
185
194
FA
M.N.
Maderpour
Tarbiat Modares University
A.A.
Aghakouchak
Tarbiat Modares University
One of the most common types of steel frames is Concentrically Braced Frame (CBF). A certain type of CBF called Chevron braced frame has always been interesting to designers due to architectural advantages. When lateral earthquake-induced displacements are applied to these frames, their nonlinear behavior starts with buckling of compression brace. The buckled brace experiences a considerable reduction in resistance. On the other hand, the tension brace tends to increase its internal force. The unsymmetrical behavior of braces in tension and compression leads to application of a force known as unbalanced force to the beam. The unbalanced force can yield the chevron beam and result in failure of this kind of CBF configuration.
In this paper the seismic behavior of ordinary chevron braced frames, super-X braced frames, zipper braced frames and suspended zipper braced frames are investigated. In order to achieve this goal, six types of chevron braced structures are considered. These structures are symmetrical and are braced in one bay of the perimeter frames. The braces of the structures are selected so that that they comply with the seismic provisions of Chapter 10 of Iranian National Building Code. By changing the section properties of chevron beams, six types of chevron braced frames are obtained. Then, five types of these frames are converted to super-X frames, six of them to zipper-braced frames and one of them to suspended zipper frame. The performance of these structures is assessed by non-linear static analysis. For each structure, the pushover curves are plotted and the capacity demand ratios (DCRs) of different elements for Life Safety performance level are determined. The performance of different elements is investigated by interpreting the outputs. It is observed that in ordinary chevron frames slight strengthening of the beam is not helpful unless it is fully strengthened so that it can resist the unbalanced force linearly. Otherwise, strengthening the beam may exacerbate the global performance of the frame. It is also observed that the conversion of inverted-V configuration to super-X configuration improves the behaviors of these frames. The non-linear analyses show that adding the zipper column to the frame can improve the seismic behavior of the frame only when the structure has the characteristics of suspended-zipper frames.