@article{
author = {Abbasi, Ehsan and ayati, esmaeel},
title = {Application of Zero -Inflated Regression Models for Modeling Accidents on Urban Highways},
abstract ={we handle in this paper, the research that have been performed to recognize the factors that affect crash frequency and severity in urban highways and use crash data of mashhad urban highways as a case study. Statistical models that have been used in this research include Poisson, Negative binomial, Zero-inflated poisson and Zero-inflated negative binomial regression models. Traffic flow related and road geometric related variables have been used as independent variables of models. Special task that have been done in this research ,is separation of total traffic volume into passenger cars, heavy vehicles and light non-passenger car vehicles volume to have an especial and thorough look at the role of traffic volume in crash occurrence , whether crashes with property loss only or more severe crashes, and see ,precisely which part of traffic have an effective role or more effective role in crash occurrence. In this research, the efficiency of Zero-inflated models is investigated against Poisson and Negative binomial regression models in modeling accidents on urban highways. Results of the research show that the number of access roads and horizontal curves on highway segments and the volume of light non-passenger car vehicles have increasing role in likelihood of accidents. Furthermore, Zero-inflated negative binomial regression model is the best and fittest model for modeling accidents, whether with property loss only or more severe and consequently the efficiency of Zero-inflated models in modeling accidents on urban highways of Mashhad is approved.},
Keywords = {accidents,Accidents with Property loss only,Severe Accidents,Urban Highways,Modeling Accidents,Ziro-Inflated regression models},
volume = {11},
Number = {4},
pages = {1-1},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-10685-en.html},
eprint = {},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {Ayati, A and Abbasi, A},
title = {Application of Zero-Inflated Regression Models in
Modeling Accidents on Urban Highways},
abstract ={We handle in this paper, the research that have been performed to recognize the factors that affect crash frequency and severity in urban highways and use crash data of Mashhad urban highways as a case study. Statistical models that have been used in this research include Poisson, Negative binomial, Zero-inflated poisson and Zero-inflated negative binomial regression models. Traffic flow related variables and road geometric related variables have been used as independent variables of models. We are interested in this study, to inspect the efficiency of Zero-inflated models against simple Poisson and Negative binomial regression models in modeling accidents on urban highways. Special task that have been done in this research, is separation of total traffic volume into passenger cars, heavy vehicles and light non-passenger vehicles volume. Through this special, Researcher intend to have an especial look at the role of traffic volume in accident occurrence to see precisely, which part of traffic have effective role or more effective role in crash occurrence. Accident data are two-level data, the first level is road segments i.e. highway is divided into several segments. The segmentation is based on total traffic volume i.e. each segment has a constant volume. The second level is daily hours; peak hour traffic considered as the first sublevel, day non-peak hour traffic the second and night non-peak hour traffic as the third sublevel. SAS 9.1 software has been used to fulfill statistical computations. It turns up, after statistical analyses, which factors affect crash occurrence and which do not have much effect. Comparisons between obtained results and other researchers’ results have been made then. The main object of researcher is to assess the efficiency of Zero-inflated models against Poisson and Negative binomial regression models in modeling urban highways crashes. This aim is followed by, with evaluating goodness of fit and making comparison between models. The Results of study show that the presence and number of access roads and horizontal curves on highway segments increase the likelihood of accidents, both no injury and more severe. Also increment of speed and number of lanes increase the likelihood of no injury accidents, but not more severity ones. The conclusions also demonstrate that the volume of passenger cars and light nonpassenger car vehicles increase the likelihood of no injury accidents, but heavy vehicles volume does not have much effect on occurrence of no injury accidents, also light vehicles increase the likelihood of more severe accidents, but passenger cars and heavy vehicles volume does not have much effect on occurrence of severe accidents. Finally, the results of research indicate that Zero-inflated negative binomial regression model is best fitting the modeling of accidents, whether no injury or more severe and consequently, the efficiency of zero-inflated models in modeling accidents on urban highways is approved.},
Keywords = {More severe accidents,Urban Highways,Modeling Accidents,Zeroinflated
regression models,No injury accidents},
volume = {11},
Number = {4},
pages = {1-15},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-11439-en.html},
eprint = {http://journals.modares.ac.ir/article-16-11439-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {JamshidiChenari1, R and OloomiDodaran, R.},
title = {Estimation of the Scale of Fluctuation of Geotechnical
Properties in Natural Deposits Using
Random Field Theory},
abstract ={One of the main distinctions between geomaterials and other engineering materials is the spatial variation of their properties in different directions inside them. This characteristic of geomaterials (so- called as heterogeneity) is studied herewith. Almost all natural soils are highly variable in their properties and rarely homogeneous. Soil heterogeneity can be classified into two main categories. The first is lithological heterogeneity, which can be manifested in the form of thin soft/stiff layers embedded in a stiffer/softer media or the inclusion of pockets of different lithology within a more uniform soil mass. The second source of heterogeneity can be attributed to inherent spatial soil variability, which is the variation of soil properties from one point to another in space due to different deposition conditions and different loading histories. Inherent spatial variability of geomaterials is itself devided into the random component, which is attributed to different depositioaln conditions, and the deterministic trends, which are attributed to the variation in soil properties, such as increase in soil strength with depth due to increase in confining pressure. Different elements of soil inherent spatial variability such as mean, variance, and spatial correlation characteristics were introduced with the main focus on the importance of spatial correlation distane and the way to handle it. Several spatial distributions introduced to describe the probabilistic variation of geotechnical properties of soils. Among all, absolute normal distribution was adopted as appropriate distribution, which best presents these properties in horizontal direction. Variation of geotechnical parameters in vertical direction is, however, conceived to follow a deterministic trend. Using random field theory, local average subdivisions (LAS) formulation and MATLAB Mathworks, virtual data with different correlations was produced, and by employing autocorrelation function, a trend for this function was invoked for different predetermined values of the scale of fluctuations. It was found that autocorrelation function has a deterministic trend as far as the scale of fluctuation has not been exceeded. It is clearly concluded that, for distances farther than the specific scale of fluctuation, the behavior is chaotic and this can be an index to calculate the scale of fluctuation of the experimental data.},
Keywords = {Local average subdivisions,Random field theory,Scale of
fluctuation,Spatial variation,Heterogeneity},
volume = {11},
Number = {4},
pages = {17-27},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-2295-en.html},
eprint = {http://journals.modares.ac.ir/article-16-2295-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {Heydari, N and Ahmadi, M.T},
title = {Advanced Analysis of Ambient and Cement Hydration
Thermal Effects on a RCC Dam Considering Construction
Schedule},
abstract ={Mass concretes including roller-compact concrete are materials with poor tensile behavior. When subjected to shrinkage or heat in their very early ages such concretes may easily crack. Thus for controlling and minimizing the risk of thermal cracks, it is crucial to study the effects of such parameters as the rate of concrete pouring in construction layers, seasons of start, pause of construction, and the extent of pre-cooling of concrete materials. Therefore, thermal stresses and probable cracks should be controlled based on a sound construction schedule. In practice, most cases are dealt with using a simple one-dimensional analysis pertaining only internal concrete evolution and thus disregarding the surface concrete story. At the same time, the induced surface stresses are not accounted for in such analyses. However, as a minimum requirement, a two dimensional model of the dam body across its vertical section is needed to account for the main effects mentioned above. Despite that many analyses have been carried out by others so far, in this research, concrete thermal conductivity coefficient is considered as a function of concrete temperature throughout a transient heat conduction analysis. The material is assumed as isotropic in both thermal and mechanical senses. The topology of model as well its top boundaries are continuously updated according to the construction schedule. Furthermore, accounting for the dam construction schedule, heat generation due to both ambient and cement hydration phenomena, as well as inclusion of convection and radiation boundary conditions due to solar effects are considered. In addition, when dealing with stress analyses and safety evaluation against cracks, the dependencies of concrete elasticity modulus on time and temperature, and concrete compressive as well as tensile strengths on time (i.e., the ages of layers) are all considered. Indeed, the thermal analyses are carried out after performing each single layer. Also after every 10 layers are performed, a full stress analysis is conducted under the current thermal and gravity loads. Safety factors are calculated considering the material properties and strength available at the same instance in each layer. To study the effect of these parameters on heat generation, and the subsequent thermal stresses in the body of RCC dam, "THA-DAN" dam in Thailand was chosen as a benchmark introduced by ICOLD. This dam has been built of 160 layers of 30 centimeter thickness. Program ANSYS-6.1 was employed in a special manner to allow such a coupled transient Abstracts 140 analysis for both thermal and stress parts. Initially, a basic verification of calculated temperatures versus the measured ones (as provided by ICOLD) was done for the layered construction at the dam site. The results of this study showed that maximum hydration temperature occurs at the layers poured in the hottest season. The efficiency of pre-cooling techniques is rather low, because by each 5˚C pre-cooling, only 1˚C drop in the temperature of internal concrete and 0.3 MPa drop in tensile stresses are gained. Tensile stresses are concentrated on the free surfaces of the concrete as well as on the ground interface due to constraints. This happens at a 3-4 meter thick layer there due to the high thermal gradients. Inclusion of gravity load in the stress analyses helps reducing the tensile stresses, particularly near the ground. Furthermore, if the frost of concrete materials could be avoided, winter would be the most efficient season for starting the construction. The most critical case is to start the construction in summer. Elongated construction pause in hot seasons is very effective for controlling the thermal cracks, although it has only negligible effect in cold season on the final distribution of heat and the maximum temperatures induced in the dam body. It is interesting to notice that the lower is the speed of concrete pouring, the cooler the core concrete becomes. At lowest speeds the warm core approaches to the ground surface. Although the above observations were found through a single dam being investigated, but they could also be mostly true for most of the gravity type RCC dams.},
Keywords = {Finite Element,Heat conduction,Environmental Condition,Tensile
stress,Thermal cracks,Cement hydration,RCC Dam},
volume = {11},
Number = {4},
pages = {29-41},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-1090-en.html},
eprint = {http://journals.modares.ac.ir/article-16-1090-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {Khaffaf, A and Arbabi, F},
title = {Confined Masonry Walls Retrofitted with FRP},
abstract ={Masonry buildings with confined walls have performed well during the past earthquakes. The same cannot be said for unreinforced masonry walls. In the former buildings, even when damage occurs, falling roofs and losses of life do not usually follow. This is because confined masonry walls have higher strength ductility and are more stable. The Iranian Seismic Code (Standard 2800) makes the use of horizontal and vertical ties mandatory for masonry buildings. In spite of this, such confined walls have not been studied sufficiently. In this study, the nonlinear behavior of masonry walls is examined using finite element discretization. From the two types of modeling that are commonly used for the study of masonry material, namely macro- and micro- modelings, the latter are employed here. This is because such a model can provide more detailed information. Micro- models are the best tools available for understanding the behavior of masonry structures. They can depict all the failure mechanisms of the system. The behavior of mortar joints and masonry unit-mortar interface is lumped into a set of discontinuous elements. In this way, each joint, consisting of mortar and two unit-mortar interfaces, is modeled by a zero-thickness interface element. In other words, the masonry structure is modeled by a set of elastic blocks bonded together with potential fracture/slip lines at the joints. The composite interface model includes a tension cut-off for mode I failure, a coulomb friction envelope for mode II failure and a cap mode for compressive failure. For modeling the behavior of concrete, a model suggested by Thorenfeldt and Hordijk is used. For the longitudinal reinforcing bars, the failure criterion is that of Von Mises. The hardening of steel is also considered. The interface between the reinforced concrete members and the masonry units panel is modeled by the coulomb friction model including a tension cut-off mode. A parametric study is conducted for confined masonry walls by changing with different dimensions, boundary conditions and loading patterns. The results indicate that failure has one of the two failure modes: diagonal tension or rocking. In cantilever walls with rather large heights compared to their length, the failure mode is rocking. In the other cases, diagonal tension failure mode occurs. The use of tie also affects the capacity of the wall. This can be considered in the design of masonry structures. The results of nonlinear analyses show that deboning does not occur between the ties and the body of masonry walls. Therefore, in analytical studies, the adjoining nodes for the two parts can be merged. Upon determination of failure modes, different patterns of FRP were investigated for the dominant mode in order to select the most suitable pattern. The FRP configuration patterns considered for strengthening the wall were: 1. FRP in vertical direction; 2. FRP at both ends in vertical direction; 3. FRP in diagonal direction; 4. FRP covering the whole surface of the wall. The last pattern was considered only for reference as it cannot be justified because of the increased cost. In confined masonry walls with diagonal tension or rocking mode, the best strengthening configuration is diagonal. The increase in the capacity of strengthened walls with rocking and diagonal tension failure modes depends directly on the amount of FRP. In fact, the capacity increases from 1.2 to 2 for the walls with rocking mode. For the walls with diagonal tension mode, this increase is from 1.5 to 3.},
Keywords = {FRP,tie,Retrofit,masonry wall},
volume = {11},
Number = {4},
pages = {43-56},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-10806-en.html},
eprint = {http://journals.modares.ac.ir/article-16-10806-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {ZabihiTari, M and Saffarzadeh, M and SharifiYazdi, M and Abdi, A},
title = {An Optimum Model for Hub-and-Spoke Network
Based on the Current Demand
(Case Study: Iran Airport Network)},
abstract ={Air transportation has an important position among the other modes of transportation due to its significant impact in the economy and welfare of a society. Within the several components of air transportation market, flight network plays a fundamental role and considerably affects the airlines revenue. Improvement of the network system requires an accurate plan and programming. Hub-and-spokes are of further interest; as such networks reduce the operational costs, create proper ground for flight network development and extension, and help in competition. However, several models have been introduced for hub-and-spokes design purposes based on the diversity of the effective factors, decision-making variables and different forms of the network. Generally speaking, hub-and-spokes are categorized into two principal sectors: single allocation and dual or multiple allocations. Within a single allocation, traffic is accumulated in a single hub and then distributed to the destinations, while within a dual-allocation network, the gathered traffic at the first hub is again distributed to another hub before directing it to the final destination. This research presents a linear model for hub-and-spokes evaluation and planning, determining optimum flight routes and fleet assignment. The model considers both direct flights and hub connections, and outputs an optimum network based on the mixture of these two options. Sets of airport connections are so designed to well cover all the necessary inter-airport trips. This particular is done by utilizing hub-and-spoke system as the airport networks. To fulfill the requirements of the study location (Iran), in this paper, single allocation was selected to develop the models, meaning that just one hub has been considered in the modeling process. Inter-airport demands of the passengers were inputted in the network and the model works only for passenger transportation. The objective was to design the hubs so as to obtain an optimum network. In other words, the model is to suggest the best option with which the demand is handled cost-effectively. Trips are planned to be either direct or meeting a one-hub maximum. As the model is to minimize the cost, such variables as demand for variety of routes and type and quantity of the available aircrafts were included. The model was developed in two stages to ease the process. The first stage dealt with the target function and the fleet was assigned to the Abstracts 136 outputs of the stage one. Iran's internal flight network was chosen as the case of study to develop the model based on the country's geographical situation and available data. 59 airports were chosen as the total set of airports and trip origins. The number of hub candidates and destination airports were eight including Isfahan, Ahwaz, Bandar Abbas, Tabriz, Tehran, Shiraz, Kerman and Mashhad airports. Based on the availability, the data of five types of aircrafts were used in the model development. Lingo Version 8 has run the model using branchand- bound method to obtain accurate and reliable outputs. Up to eight hub networks were considered by the model and the model confirmed that with increase in the number of hubs, operational cost decreased. However, cost reduction had lower rate for the systems with six hubs and over. The results also suggested that the probability of stop in a hub rises for longer trips. Flights longer than 1.5 hours had to stop at one hub in three-, four-, five-, six- and eighthub networks. Four-hub network was found to be the optimum one due to having the shortest stop slot where fixed cost has been allocated for selecting an airport as the hub. The hubs of the optimum fourhub network are Tehran, Shiraz, Kerman and Isfahan airports. The results showed that demand is not the only effective factor in the selection of the hub; it means that another key factor, geographical positions, has effect and the airport with higher demand is not necessarily selected as the hub. Therefore, hub-and-spokes can enhance the efficiency of the airports with lower demands. As an example out of the results, passengers intended to use Isfahan and Kerman airport as their hubs in a four-hub network were more than the ones targeting Isfahan and Kerman airports as destinations. Analysis of the four-hub network cleared that, according to the current demand and operational costs of different aircrafts, large planes (e.g. Airbus 300) and small lpanes (e.g. Foker 50) will perform more flights in comparison the with other types. Using the model developed in this research, airlines will be able to forecast and plan their required fleet combination based on the demands.},
Keywords = {Hub and Spoke,Air transpetation,Airport,optimization},
volume = {11},
Number = {4},
pages = {57-68},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-6364-en.html},
eprint = {http://journals.modares.ac.ir/article-16-6364-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {Farshchi, H.R and Moghadam, A.S and Jazany, R},
title = {Experimental and Analytical Study of Connection
Strength Effects in X-Type Braced Frames},
abstract ={SCBF (Special Concentrically Braced Frame) is a common structural system for steel construction in Iran. This system could be used where increasing of strength and stiffness is the main concern for a structural system over the ductility. In SCBF, it is assumed that most of stiffness and strength are provided by the brace element. The contribution of gusset plates in total stiffness and strength values is even overlooked in the structural analysis and design. Ignoring these effects is conservative for controlling of seismic responses and is on the safe side. But, in practice, this hypothesis is not valid since this extra portion of stiffness and strength values is not included in the design of gusset plates and the connections. The importance of this phenomenon will be more noticeable when the brace element material behavior significantly enters the nonlinear phase. Based on previous descriptions, experimental and analytical study of this kind of structural system under seismic loading seems necessary in order to evaluate the contribution of stiffness and strength of each mentioned element i.e. gusset plates and double- seat angle connections. Three test specimens were built in half scale and designed regarding the AISC seismic provisions (2005); the first test specimen consisted of one-by-one story frame with simple connection, i.e. double seat angle connections, known as simple frames. The second specimen was simple frame with gusset plate connections without brace elements. The third specimen was braced frame; the specimens were tested cyclically and companion Finite Element (FE) analysis was then conducted. Verification of FE models in ANSYS finite element program using “Solid 45” element with proper mesh dimensions, obtained by sensitivity analysis, showed good agreement between the analytical and experimental responses. The experimental results showed that the stiffness value of simple frame and simple frame with gusset plates reached 60% to 65% and 86% to 98% of stiffness values of the braced frame, respectively. Also energy absorption values of simple frame and simple frame with gusset plate reached 4 % and 10% of the energy absorption value of braced frame, respectively. Moreover, ultimate strength value for simple frame and simple frame with gusset plate reached 11% and 25% of the ultimate strength values of braced frame. As a result, it could be mentioned that gusset plates and double seat angle connections have significant contribution in the total stiffness values of a braced frame whereas their contributions in strength value of a braced frame are insignificant. The results of FE analysis also confirmed the above-mentioned results with a definite low tolerance.},
Keywords = {Connections,Braced frames,Steel frames,Gusset plates},
volume = {11},
Number = {4},
pages = {69-82},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-397-en.html},
eprint = {http://journals.modares.ac.ir/article-16-397-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {MahinRoosta, R. and Farrokh, H.},
title = {Prediction of stress- strain behavior in gravelly material
based on Artificial Neural Networks},
abstract ={Prediction of stress-strain behavior of geotechnical material is one of the major efforts of engineers and researchers in the field of geomechanics. Experimental tests like tri-axial shear strength tests are the most effective apparatus to prepare the mechanical characteristics of gravelly material; but due to difficulties in preparing test samples and costs of the tests, only several tests will be done in a new project. Artificial neural network is a kind of method, in which engineer could judge the results based on numerous data from other similar projects, which enable the engineer to have a good judgment on the material properties. In this research, the behavior of gravelly material was simulated by use of multi-layer perceptron neural network, which is the most useful kind of artificial neural networks in the field of geotechnical engineering. For instance, first exact information was provided from laboratory tests of various barrow areas of embankment dams in the country and effective parameters on shear strength of coarse-grained material were studied. After omitting incorrect or weak data, 95, 20 and 23 sets of data were used for learning, testing and evaluating data, respectively. Input parameters for the model were as follows: particle-size distribution curve, dry density, relative density, Los-angles abrasion percent, confining pressure, axial strain; and outputs were selected as deviator stress. In order to reach a steady state in the model and force the model to behave homogenous to the all inputs, data was normalized to the value between .05 and 0.95. In the simulation, back-propagation algorithm was used for learning or error reduction. The aim of the simulations was defined to reduce error between real data and predicted values; for instance root mean square error (RMS) was used to be minimized through simulation and predicted versus real graphs were used to observe the global error of the model. After modeling the data based on some criteria, it was shown that curves of stress-strain from simulation tests were in good agreement with those from laboratory. These close coherencies were observed in all training, testing and evaluation data, in which the RMS errors were 0.038, 0.037 and 0.026, respectively. To reach this ultimate step, a 10*19*1 multilayer perceptron was used via trial and error. In order to determine quality and quantity of the effect of inputs on outputs, and prove that the results were in good agreement with soil mechanic principles, sensitivity analyses were done on the average data of the inputs. Results show that confine pressure, uniformity coefficient and relative density of the material were the most effective parameters on the stress-strain curves; thus the model has enough capability to predict the stress-strain behavior of gravelly soils.},
Keywords = {Gravelly soil,stress-strain curve,artificial neural network,Multi-layer perceptron,Sensitivity Analysis},
volume = {11},
Number = {4},
pages = {83-95},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-8168-en.html},
eprint = {http://journals.modares.ac.ir/article-16-8168-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {Peykanu, M. and Zeinodini, M. and Daghigh, M.},
title = {Local Buckling of Corroded Tubular under Cyclic
Compression & Tension Loadings},
abstract ={Abstract: Plastic axial strain, local buckling, wrinkling and plastic buckling of pipeline are caused by cyclic compression and tension loadings. This kind of local buckling is amplified by initial defect, heat affected zone and circular welding. Progressive plastic failure or ratcheting is caused by frequent periods of cyclic loading. On the other hand, life time of the offshore pipelines is decreased by the corrosion effect caused by fluids inside the pipeline and the sea Environment. This kind of corrosion can be found with variable size and depth in the inner or/and the outer surface of the pipeline. Corrosion can effect on the strength of pipeline. In the current study, an advanced finite element program has been used to simulate the ratcheting response of carbon steel tubes. The numerical model has been applied to reproduce a series of laboratory tests on small-scale tubes. These tests were carried out by the authors on intact and defected tubes, in which wrinkling and ratcheting behaviour of tubes under axial monotonic and cyclic loads were studied. A nonlinear isotropic/kinematic hardening model has been employed to represent the cyclic behaviour of the material. The verified model has then been used for a parametric study on ratcheting behaviour of the defected tubes under cyclic axial loading. Several stabilized cycles of specimens that are tested experimentally under symmetric strain cycles are used to obtain stress-strain data and hardening parameters of the material. The numerical model has then been used to investigate the effect of mean stress, stress amplitude and geometrical defects on the ratcheting response of steel tubes. It has been noticed that: a) The ratcheting strain rate was governed by (a) the initial non-linear strain in the tube, (b) by the stress amplitude and (3) by the mean stress, respectively. b) The ratcheting strains in the defected tubes had significantly higher rates in comparison to those in the intact tubes and very rapidly turned exponential. c) In defected tubes the local wrinkling first initiated from the damaged part. This local buckling then gradually proceeded to the entire circumference. The ratcheting strains in the defected area very rapidly turned exponential, while the ratcheting strains in the perfect zone still remained linear trajectory. d) It showed that surface corrosion imperfections had a very pronounced effect on the ratcheting response of the defected tubes, as compared to their monotonic response. e) The wrinkles in the defected tubes were non-axisymmetric and initiated from the damaged part of the tube},
Keywords = {wrinkling,Cyclic loading,Ratcheting,corroded pipe,Circular tubes},
volume = {11},
Number = {4},
pages = {97-104},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-8699-en.html},
eprint = {http://journals.modares.ac.ir/article-16-8699-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {KhanMohammadi, L. and VaseghiAmiri, J. and Navayi-nia, B.},
title = {Evaluation of Eulerian and Lagrangian Methods in the
Analysis of Concrete Gravity Dam Including Dam Water
Foundation Interaction under Earthquake},
abstract ={Hydrodynamic pressure on the upstream face of the concrete dams under the effect of earthquake is one of the most important parameters, in planning dams' structure in earthquake zone. Because of the reservoir effect, dynamic analysis of concrete dams is more involved than other common structures. This problem is mostly sourced by the differences between reservoir water, dam body and foundation material behaviors. As a result, researches in this case must be able to evaluate the response of dam with consideration of dam’s interaction with reservoir and its foundation. This problem has been studied vastly by different researchers. The first research on the analysis of concrete gravity dam has been done by Westergaard in 1930 and hydrodynamic pressure on the dam face was obtained by some simplifications. There were a lot of other researches which studied the seismic behavior of the dam-reservoir system, including nonlinear behavior of the dam under pressure and also cavitation. In each research, different modeling methods are presented which are divided into two main groups. In first method which is called Eulerian method, pressure is the main unknown variable in reservoir nodes. In the second method that its main unknown variable is displacement of nodes is called lagrangian method. Each of the methods contain some advantageous and disadvantageous. The purpose of this paper is to evaluate possible advantages and disadvantages of both methods. Specifically, application of the above methods in the analysis of dam-foundationreservoir systems is leveraged to calculate the hydrodynamic pressure on dam faces. Within the frame work of dam- foundation-reservoir systems, dam displacement under earthquake for various dimensions and characteristics are also studied. To achieve this purpose, visual C#.NET 2003 computer programming language is used in this investigation that produces possibility of dynamic analysis of concrete dams under earthquake with system modeling by both methods. Nine node elements for reservoir and eight node elements for dam and foundation are used for both methods. Also newmark average acceleration method is used for solving dynamic’s equilibrium equation. Modares Civil Engineering Journal (M.C.E.L) Vol.11, No.4, Winter 2011 131 In this paper the response of the tallest, non-overflow monolith of Pine Flat dam in California, which is 122 m high, to horizontal and vertical component of earthquake is computed. A water depth of 116 m is considered in full reservoir condition, and the water has the following properties: unit mass, 1000 kg /m3 , bulk modulus, K 2.07*109 kg/m2 , and pressure wave velocity, w c 1440m/ s . The finite element model of reservoir consists of 12 isoparametric elements and it extends upstream a distance of 366 m, three times the dam height. The dam consists of 20 isoparametric elements. The concrete of dam has the unit mass of 2500kg /m3 , young’s modulus ofE 2.275*1010kg /m3, and poisson`s ratio of 0.25. The concrete of foundation has the unit mass of , young’s modulus ofE 4.45*1010 kg / m3 f , and poisson`s ratio of 0.25 f . The peak acceleration of S69E and vertical components are 0.18g and 0.1g, respectively. The results of both Lagrangian and Eulerian methods for Pine Flat dam are quantitatively evaluated and compared in different condition and following results are achieved: 1- In Lagrangian Method, there is only one variable in equilibrium equation and mass and stiffness matrixes are symmetric. But there is not such a condition in Eulerian method. Also, the numbers of unknown parameters are different in two methods. By considering these differentiations, needed time for analysis of Pine Flat Dam under Taft earthquake ,with mentioned characteristics, by Lagrangian method is 1.17 times more than needed time for Eulerian method. 2- The effect of material on reservoir's bottom in absorbing energy and `reducing system's response was considerable especially under vertical component of the earthquake. Results indicate that this case is not affected by reservoir modeling method. By applying this effect, the response will decrease about 15% under horizontal component and 60% under vertical component of the earthquake. 3- By evaluating the effect of reservoir bottom's slope, it is concluded that in the case of rigid foundation, the response by Lagarngian modeling is about 10% more than Eulerian one. With the increase of slope, the response will decrease under horizontal component of earthquake but it will decrease or increase about 13% under vertical component of the earthquake. In other words, reservoir bottom slope has little effect on response of the system under both vertical and horizontal component of earthquake. But this effect is not negligible. 4- It is included from the analyses that by decreasing the depth of reservoir the response will decease up to 50 percent under horizontal component of earthquake. This amount is 80 percent under vertical component. Also in the case of decreased depth, response of Lagarngian method is about 10% more than Eulerian method. 5-In all analysis, the assumption of rigid foundation results in greater answers than the cases of flexible foundation.},
Keywords = {Dam-Reservoir-Foundation Interaction,Concrete gravity dam,Eulerian and
Lagrangian Method,Earthquake},
volume = {11},
Number = {4},
pages = {107-116},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-6284-en.html},
eprint = {http://journals.modares.ac.ir/article-16-6284-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {YousefiKhatoni, S. and Shokati, H. and ShaikhBagloo, M.},
title = {Compared to Non-Linear Behavior of Flat and Corrugated
Sheet Steel Shear Walls},
abstract ={Steel shear walls has been noticed against wind and earthquake lateral loads about high buildings in the last three decades. This modern phenomenon is growing rapidly worldwide so that system have been employed highly in construction of new buildings and seismic upgrading of existing buildings in some countries such as USA and JAPAN. That is a very simple system from viewpoint of implementing and there isn’t particular complexity. High strength and ductility are main advantages of these systems. Current paper has investigated comparatively behavior of steel shear walls made of smooth and corrugated sheets. Also the paper has assessed push-over curves and cyclic binding. According to this result of the research, corrugated steel shear walls have lower ductility than smooth shear walls. The research also founded that despite the high strength of corrugated sheets in low displacement, behavior of flat shear walls is more stable than corrugated shear walls. On the other hand flat steel shear walls attract energy more than corrugated shear walls. Therefore using of flat shear walls is recommended in high seismic regions. In this research, 18 samples of flat steel shear walls and corrugated shear walls were modulated. In all models, panels height were 3 m and panels span were 3, 4 and 5 m. the thickness of sheets in the samples were 3, 4 and 5mm. According to results of the research: 1- Corrugated sheets are unstable and unpredictable in high thinness. In the low displacements occurs a mutation state, so it distinguishes the corrugated and flat shear walls behavior. 2- At low displacement, a corrugated sheet bears greater load than a flat sheet. 3- In a constant thickness for thinner corrugated sheets is increased the mutation rate and its behavior becomes more non-uniform. 4- Despite of the fact, pynchyng phenomenon appears in all samples, but all samples behavior is stable and significant energy attraction is observed.},
Keywords = {Finite Element Method,ductility,Corrugated steel shear walls,Push over curve,Cycliccurve},
volume = {11},
Number = {4},
pages = {117-126},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-2767-en.html},
eprint = {http://journals.modares.ac.ir/article-16-2767-en.pdf},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}
@article{
author = {Farshchi, Hami},
title = {APPLICATION OF SHEAR-FRICTION HINGE CONNECTION IN MID-STORY STAIR SLABS TO COLUMN JOINT},
abstract ={Providing mid-story stair slab to column hinge connection is practically difficult in concrete moment resisting frame structures. The problem is due to the fact that this connection is modeled as hinge connection in the modeling phase of structural analysis but in practice because of lack of proper detailing this is not fully satisfied and can lead to inappropriate column behavior and may affect the structural behavior as a whole. In this article, a simple hinge connection detailing based on shear-friction behavior has been proposed. This connection is based on the Iranian national building code and can provide the proper hinge connection in the mentioned joint.},
Keywords = {mid-story beam,concrete connection,stair,column},
volume = {11},
Number = {4},
pages = {123-123},
publisher = {Tarbiat Modares University},
url = {http://journals.modares.ac.ir/article-16-11899-en.html},
eprint = {},
journal = {Modares Civil Engineering journal},
issn = {2476-6763},
eissn = {2476-6763},
year = {2011}
}