Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Soil Cohesion Spatial Variability effects on the Bearing Capacity of Nonhomogeneous Clays
1
13
FA
Abdolhosein
Haddad
Davod
Azan
Faculty of Civil Engineering, Semnan University
The soil formation consists of complex and longtime processes in which many different chemical and physical changes occur in soil deposit, or in its original source rock. This processes cause the soil to show nonhomogeneous characteristics and to have spatial variation in its mechanical properties. The spatial variation of soil properties lead to many uncertainties in prediction of soil mechanical behavior; subsequently the design of structure which depend on soil deposits becomes troublesome. For dealing with such problem the probabilistic and statistical tools are proposed as convenient methods for choosing appropriate design soil parameters and estimating the uncertainties in design. The coupled utilization of random field theory and Monte Carlo simulation technique yield probability distribution functions for geotechnical problems in which different cases of soil distribution is assumed for analyses. In such problems the soil properties are distributed into the field according to the assumptions of random field theory by consideration of a probability distribution (with the given mean and standard deviation) and scale of fluctuations. This distribution of soil properties with the use of random field theory is performed repeatedly until a desired statistical distribution for the results is obtained. This distribution can be used as a basis for extracting the statistical characteristics for the problem in hand. In this paper the effect of spatial variability parameters on the bearing capacity of strip foundations on clayey soils were investigated. The soil un-drained shear strength (Cu) was assumed as spatial variable parameter with the use of logarithmic distribution and the so-called coupled random field theory; the Monte Carlo simulation technique was used for obtaining probability distribution of bearing capacity of foundation on nonhomogeneous clayey soil. The Mohr Coloumb elastic perfectly plastic constitutive model and the Finite Difference Method (FDM) were used for modelling soil behavior and calculating the bearing capacity of foundation. The spatial variability of un-drained shear strength was investigated using three parameters: coefficient of variation of un-drained shear strength (Cov(Cu((, and the scale of fluctuation of shear strength in horizontal and vertical directions (x, and y directions). The range of these parameters were chosen such that the results of current research can be generalized to any field problem. The results obtained from this study, were investigated by average and coefficient of variation of NC parameter which is the cohesion factor in classic bearing capacity equations (i.e. as Terzaghi, Meyerhof, Hansen and Vesic bearing capacity equations). It can be interpreted from the results that by increasing the coefficient of variation of soil un-drained shear strength the average bearing capacity decreases and the coefficient of variation of bearing capacity increases; also the average bearing capacity of foundation has an approximately increasing trend with increasing the scale of fluctuations in both horizontal and vertical directions. Finally at the end of this paper two practical simplified equations were suggested using multiple regression method for estimation of average and coefficient of variation of bearing capacity factor NC, given the spatial variation parameters of soil un-drained shear strength. These equations can be implemented by geotechnical experts for applying the variability of cohesion in the design of foundations on nonhomogeneous clayey soil formations.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Estimation of Diagrid Structures Response Factor
15
24
FA
Omid
Elhami
M.Sc. Student, Structure engineering dept, Faculty of civil eng, Yazd university, Yazd, Iran
Nader
Abdoli
Assistant Prof,Structure Engineering Dept, Faculty of Civil Eng, Yazd university, Yazd, Iran
Nowadays, with rapid grows of population and need of space for living, work or other activities in one hand and the limitation of natural resources in the other hand, make researchers and engineers introduce high rise building as a solution to respond for human needs. High rise building become a concept for future cities. At first the structural performance of tall building was very important, but the dimension and the size of these buildings have spirit and vision effects on humans, so the facade aspect of these buildings become more important than past. In recent decades, because of rising the attention to the facade of the tall building addition of structural performance, systems with both structural performance and façade were introduced and diagrid structural system is the most recent kind of these systems. Diagrid structure system is containing of an interior core that usually carries gravity loads and has no need to have shear rigidity and exterior diagrid configuration that carries gravity and lateral loads with diagonal members. This system brings good structural performance, flexible architectural design in form and plan, decrees in material consumption, and etc. because of these benefits, diagrid structures become more useful for tall building instead of common tubular structures. In studying structures seismic performance, one of the important factors for relate linear to nonlinear analysis and show structure energy absorption ability is Response factor. In this paper, five 3d diagrid structure model that are studied, contain of one 36 story model with 50.2-degree diagrid member’s angel, one 36 story model with 67.4-degree diagrid member’s angel and one 36 story model with 74.5-degree diagrid member’s angel for comparing the member’s angle change on diagrid system Response, one 50 story with 67.4-degree diagrid member’s angel and one 60 story with 67.4-degree diagrid member’s angel, to compare with 36 model story with 67.4-degree diagrid member’s angle to see the height or number of stories effect on the diagrid system Response. 67.4-degree diagrid members was selected for the optimum angle according to the articles about this issue that introduced 65 to 75 degree for the optimum angle range. First, linear analysis and designed carried out for the models by using Iran building codes to select the member’s sections, then by using FEMA-356, nonlinear static analysis (Pushover) was done for all models. At last at the final target displacement, under critical load pattern, the pushover curve was obtained. From the pushover curve the over strength factor, ductility factor and Response factor were calculated. In addition to estimating Response factor of diagrid structures, effects of changing diagrid members angle and number of stories on Response factor of this kind of structure are also studied. From the result, the suggested over strength factor is 1.5, ductility factor is 2.15 and Response factor is 3.22 for the optimum diagrid members angle (67.4 degree) of diagrid structures up to 50 story of 180-meter height and conclude that the Response factor increases with increasing of story numbers as well as with increasing of diagrid member’s angel increases.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
experimental investigation of normral hydrograph characteristics effect on scour around spur dike
25
36
FA
Ali
Babakhani
PHD student
Anton
Schleiss
Estimation of maximum possible scour depth around spur dike is an important step in the design of spur dike foundations To determine the maximum scour depth in the design of spur dike foundations, the equilibrium scour depth, which is commonly estimated using peak-flow conditions for engineering design of spur dike foundations, are used.. In fluvial rivers, significant transport of bed materials often takes place during peak-flow discharge in a flood event. For large rivers, the duration of a flood event may last for a few months, but for others the unsteadiness of a flood can be pronounced. The general practice of employing peak-flow discharge to evaluate the maximum scour depth for design may be questioned because the maximum scour depth occurring under a flood hydrograph can be much smaller than the calculated value using peak-flow discharge. In other words, using the peak-flow discharge for design can greatly overestimate the maximum scour depth in comparison to the actual conditions under the flood hydrograph. Therefore, when the flow unsteadiness is pronounced, investigation of temporal variation of clear water scour at spur dike is important to estimate the possible extension of the scour hole. This would provide useful information for safe design of footing and the selection of scour counter-measure to be implemented. The degree of severity of the problem is dictated by the magnitude of this scour hole. In this experimental study, the scour around the single spur dike was investigated under unsteady flow. These tests have been done in terms of clear water and non cohesive sediments. In order to investigating the scour around the spur dike, experiments have been done by changing the properties of normal hydrograph such as peak discharge and durability time. In order to producing the hydrograph, we used a device for adjusting the speed of pump motor and generating the variable discharge according to actual discharge time series. In the inlet pipe of pump, a magnetic flow meter is located that Measures the discharge in per one tenth of a second. Thus, the system verifies of requested discharge at any time. The results show that one of the influential parameters that affect the scour around the spur dike is the durability time of hydrograph. We concluded that when the durability time increases 6-times, scour depth will increase 40 percent, because with increasing durability time, the time that spur dike exposes tensions increases. Also, the depth of scour has increased 35 percent, by increasing 25 percent of peak discharge of hydrograph that is caused by increasing stresses imposed on the bed. Finally, the resulted scour under unsteady flow was compared with the resulted scour under steady flow (With flood peak discharge), with a significant difference between the scour under steady and unsteady flow. Then, an imperial equation was proposed for calculating the scour depth under hydrograph. This equation was obtained by adding the unsteady coefficient of flow in the equation of equilibrium scour depth under steady flow. This unsteady coefficient of flow includes effective parameters of hydrograph such as peak flow of hydrograph, peak time, durability time of hydrograph and equilibrium time of scour.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Numerical study on the effect of roughness of shallow foundations on bearing capacity factor Nγ using lower bound finite element analysis
37
45
FA
1
1
1
Somaye
Safiyari
Department of Civil Engineering, Malayer University, Malayer, Iran
Due to the complexities associated with the determination of bearing capacity coefficient Nγ, researchers have proposed different values for this coefficient. As the roughness of foundation influences the value of this parameter, it is essential to consider its effect on Nγ. In the present research, the values of bearing capacity factor Nγ, has been determined by lower bound finite element method. The problem has been solved for a two-dimensional domain of the soil beneath a strip foundation. The domain was discretized into a three-nodded linear triangular element. In this method, in contrast to the conventional finite element analyses, the primary variables are three components of two-dimensional stress matrix. Differential equations of stress equilibrium in horizontal and vertical directions are the governing equations of problem. The bearing capacity is defined as the maximum load which can be applied to the foundation while not violating the stress constraints. The constraints include stress discontinuity and yield condition constraints. The stress components at a node common in adjacent elements are not essentially equal. The stress at adjacent element can be discontinuous. The condition of stress discontinuity means that the stress components should be such that the tangential and normal forces at common border lines of adjacent elements are in equilibrium. Moreover, the stress components should be such that they do not violate the Mohr-Coulomb failure criterion. The failure criterion was linearized into definite linear segments. The aforementioned equality and non-equality conditions construct a set of linear equations. The maximum load can be applied to the foundation was determined by linear programming as an optimization technique. The Nγ factor was calculated at two conditions of rough and smooth conditions. For the smooth foundation, an additional constraint was applied. The horizontal at the soil-foundation interface was imposed zero. The values of Nγ were compared at different values of soil friction angles. The values of the factor obtained from the current research were compared with the results of other relevant researchers including the results obtained from limit equilibrium, slip line method, upper bound solutions and lower bound solutions. The results indicate that the roughness of foundation affects the value of Nγ factor and consequently affect the bearing capacity. Therefore, in order to calculate the precise and reliable bearing capacity of a foundation, it is essential to take the effect of foundation roughness into account. The results of comparisons with the relevant studies indicate that the results of different methods do not differ substantially for the friction angles less than 30 degrees. On the other hand, the values of factors obtained from different methods differ substantially from each other for the friction angles higher than 30 degrees. This divergence increases by increasing the friction angle. The factors obtained from upper bound solutions are essentially higher than those obtained from the present research which is a lower bound solution. As the exact solution is higher than what obtained from lower bound solution, it could be stated that the reliability index of the factors obtained from the current study is higher than other methods. It could be concluded that the proposed factors can be regarded as a safe estimate for Nγ factor.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Empirical Modeling of Compressional Wave Velocity of ّFine Grained Unsaturated Soils Subject to Drying
47
56
FA
Mahnoosh
Biglari
Civil Eng. Dept., School of Engineering, Razi University.
Iman
Ashayeri
Civil Eng. Dept., School of Engineering, Razi University
Mokhtar
Elyasi
MSc. Graduated student, Civil Engineering Department, School of Engineering, Razi University
Seismic wave propagation in surficial stratified soil and deep rock is studied in many engineering fields like Geotechnical earthquake engineering, Geophysics and seismology. Seismic waves might be generated by a significant seismic event, volume collapse in earth’s mantle, chemical or nuclear explosions and surface impact sources. Although the seismic waves’ path in soil layers may be shorter than their path in bedrock, they are influenced significantly by the mechanical properties of surficial soil layers. Soil layers may be saturated or not fully-saturated by a single fluid, which is known as unsaturated soil. Seismic waves generated at the source are known to be body waves of two categories (a) compressional wave (P-wave), (b) shear wave (S-wave).In spite of the abundance and deepness of theoretical analyses, experimental results on measuring the compressional waves in unsaturated soils and rocks are inadequate and mainly have focused on the relation between first compressional wave velocity and degree of saturation instead of suction. Furthermore, the experiments focus on the specimens of sandy soils and rocks with a series of repeated experiments in various degree of saturation conditions. This paper presents the results of three series of ultrasonic tests carried out on fine grained soils.The soils chosen for experimental study are three commercial kaolin named ZK1, ZK2, and ZK3, from Zenoz mine in northwest Iran. These materials have plasticity index (IP) of 9%, 15%, and 19%, and classified as lean clay (CL), silt (ML), and elastic silt (MH) respectively according to Unified Soil Classification System. 15 specimens were compacted at different initial water contents and void ratios and subsequently allowed to dry gradually until air-dry. cylindrical samples, 50 mm in diameter and 100 mm high, were prepared in a mold by compacting a soil – distilled water mixture at proctor optimum dry density and another four points of standard proctor compaction curves; two at 0.5 kN/m3 less than optimum dry density in both dry and wet side of optimum water content point and two at 1 kN/m3 less than optimum dry density in dry and wet side of optimum water content point. All samples were compacted in seven layers using the under-compaction technique to ensure specimen homogeneity along the height. Measurements of compressional wave velocity (Vp) (using ultrasonic) and matrix suction (using the filter paper technique), together with water content, were made at various stages during the drying process (4 times for each specimens; at the time of making the sample and after 4, 8, and 16 hours). The results of the tests suggest that, as a soil dries, its compressional wave velocity increases with increasing in suction. The results imply that in prediction of compressional wave velocity the effectiveness of void ratio must be considered as well as the suction effects. Both compressional wave velocity (Vp) and the corresponding suction (s), have been shown to vary in consist and predictable manner as a function of the initial void ratio at compaction state (ecomp), the suction and the soil’s plasticity index (PI). Thus, an empirical expression was developed which permits estimation of the value of compressional wave velocity, Vp of compacted fine grained soils subject to drying at the suction and material properties expected in prototype conditions.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Analytical study of steel-FRP bridges vibration subjected to moving mass
57
70
FA
hamed
khezrzadeh
Hamed
Jafari
Faculty of Civil and Environmental Engineering, Tarbiat Modares Uniersity
Given the key importance of the bridges in transportation system lifelines and due to their high initial cost, there is a constant need for the study and monitoring of such structures. The FRP composites, due to their special characteristics including high specific modulus, high specific strength, corrosion resistance, low mass density, and modular construction, can be a good alternative for common bridge deck systems. Too much effort is devoted to implement FRP materials as a whole or in part in bridge construction. There have been several different methods of using FRP materials in bridges, including FRP stay-in-place forms for concrete decks and whole FRP bridge decks. Bridges constantly bear moving mass loads while due to technological progress the moving speeds are approaching higher and higher thresholds, so in this study, effects of moving mass on the dynamic response of steel-FRP and steel-concrete bridges are studied and compared. The deck and moving mass inertia substantially affect the dynamic response of the bridge system. To compare the effect of moving mass on both bridge types, at first, the multi layered beam method (MLB) for determining the FRP beam characteristics is reviewed and its applicability on determining the mechanical properties of laminated beams is investigated through comparison of this method results with numerical and experimental data. It is shown that by using the MLB method very good estimates of the mechanical properties of FRP composite can be achieved. Consequently, the problem of moving mass and its governing differential equations is reviewed and the numerical procedure for solving the set of governing PDEs of the moving mass problem is verified against experimental data. Comparing the theoretical results with the experimental data reveals that the presented methodology correctly estimates the dynamic response of beams subjected to moving masses. After setting up the theoretical framework for the moving mass problem on steel-FRP bridges, the effect of moving mass loading on the dynamic response of steel-FRP and steel-concrete bridge systems is investigated. The results indicate that the mass per length and the stiffness of the deck significantly affect the response of the bridge subjected to moving mass. These effects are captured through two different main parameters which characterize the dynamic behavior of beams subjected to moving masses. The first parameter is the Critical Influential Speed (CIS) at which the maximum deflection of deck at certain location happens. The calculated CIS through the aforementioned methodology indicate that the CIS for steel-FRP system is significantly higher than steel-concrete system. The second important parameter which is determined is the Dynamic Amplification Factor (DAF) which is defined as the ratio of maximum dynamics deflection at the midspan of the beam to its static value. The corresponding results of the DAF indicate that the steel-FRP bridges are less influenced by the moving masses than steel-concrete bridges of the same stiffness. It is shown that the values of DAF are lower in the case of steel-FRP bridge. It can be concluded that this will result in lower vibration amplitudes, which will contribute to higher fatigue life of the bridge system. Regarding these results, this system can be advised in the cases of high and ordinary speed transportation.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Seismic Vulnerability Assessment of Simple Steel Buildings with RC Shear Wall
71
83
FA
ali
hajipour
Department of Civil Engineering, University of Hormozgan
Mohammad Reza
Mohammadizadeh
Department of Civil Engineering, University of Hormozgan
Nowadays with development of urbanity, request for dwelling has increased extremely. In all the cases the steel structures as for the high speed of construction have a special status. Among the defect of steel buildings than concrete type is higher cost of construction. Hence, occasionally the fabricators with a view to imparting of advantage of both the construction speed and some deal decreasing providing cost of steel lateral bracing, use the steel buildings with reinforced concrete shear wall as lateral bearing system. Hence, study in the field of analysis and design of this structure system seems necessary. At present, one of the most important goals of earthquake engineers is predicting of the structures behavior versus future earthquakes. Today, it has become evident that structures designed on the basis of the existing regulations sustain extensive damages in under intense earthquakes. Thus, performance-oriented design as a method based on acceptance of expected displacement and ductility has been considered. In earthquake engineering, it is imperative to determine the capacity and the seismic demand of the structure in terms of performance. The performance assessment of nonlinear systems is a complex task requiring appropriate analytical methods suitable for modeling the behavior of the structure against the earthquake. The incremental dynamic analysis is an analytical tool which can be used to assess performance in earthquake engineering. This method is able to estimate the seismic demand and limit states of the capacity of a structure under seismic loading using suitable records scales to several levels. Utilizing this method, one can attain better understanding of the behavior of a structure from elastic to destruction conditions. In the present research, dynamic analysis of the time history and the robust software OpenSees have been employed considering the geometric nonlinear effects of materials for seven buildings having 3, 6, 9, and 12 stories and two plans. The structures under consideration are analyzed using incremental dynamic analysis and the robust Opensees software subsequent to the design phase and considering the designed sections, gravity loading characteristics and specifications and seismic parameters. Then, graphing the cluster curves and IDA quantiles the buildings under consideration are assessed. Although the results of this study indicate better performance of the moderate structures in comparison to the short and rise structures, it seems that the proper height of a structure with respect to the characteristics of the soil of its construction site and the parameters of the resonance and damping between the structure and the soil (the effect of soil and structure interaction) and the frequency content of the acceleration records of the first mode in the region. The seismic intensity estimation parameter (which is considered in this study, the first-mode spectral acceleration) is a determinant factor in reflecting the behavior of the earthquake acceleration record applied to the structure. In order to conduct a detailed study with the IDA analysis, it is necessary to select the severity criterion in a way that best describes the content of the selected accelerogram.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
A new approach for vibration analysis of crack in reinforced concrete beams with composite sheets
85
99
FA
javad
razzaghi
Assistant Professor, Faculty of Engineering, University of Guilan
Morteza
Khomami Abadi
Civil group, Faculty of Engineering., University of Guilan, rasht, Iran
Ali
Alijani
Assistant Professor, Department of Mechanical Engineering, Bandar Anzali Branch, Islamic Azad University, Bandar Anzali, Iran
In this paper, cracking in the first mode (opening) is modelled for reinforced concrete beams with FRP sheets based on presenting a new method by using the principles and relations of fracture mechanics and finite element method. In this method, for modelling the relationships of determining the stress intensity factor is developed for reinforcement sheet. In the proposed method, elements of the beam are divided into two categories, including elements with and without the crack. In the elements without the crack, the relationships, equation, stiffness and mass matrices of the beam are established with considering the changes in the moment of inertia due to the reinforced FRP sheet. In the elements with the crack, a change in the cross-section of the reinforced concrete due to the crack and a discontinuity in the crack point leads to an improvement in the standard governing relationships. So that the reduction of the stiffness of the cracked element is equivalent to the change in the size of the discontinuity. Here, the variation of the stiffness of the cracked element is calculated and presented as a function of the stress intensity factor. In this approach, the simulation of the crack is done by dividing the element to two sub-elements into the two sides of the rotational spring. In which, The stiffness and mass matrices of the two sub-elements and the improved stiffness and mass matrix of the element are derived by satisfying the continuity equation at the crack point. This method is developed from a vibrating analysis. The effects of crack depth and location and the effect of crack expansion on the static and vibrational behaviour of a concrete beam are investigated. To ensure the accuracy of the proposed method, all analysis performed in Abacus software is implemented. Comparing the results of the proposed model with the results of comprehensive modelling in Abacus software is applied to verify. The comparison of the results shows that the proposed methods are suitable for the analysis of reinforced concrete structures resistant to cracking. So that it can be generalised and optimally desirable for other models. In this paper, cracking in the first mode (opening) is modelled for reinforced concrete beams with FRP sheets based on presenting a new method by using the principles and relations of fracture mechanics and finite element method. In this method, for modelling the relationships of determining the stress intensity factor is developed for reinforcement sheet. In the proposed method, elements of the beam are divided into two categories, including elements with and without the crack. In the elements without the crack, the relationships, equation, stiffness and mass matrices of the beam are established with considering the changes in the moment of inertia due to the reinforced FRP sheet. In the elements with the crack, a change in the cross-section of the reinforced concrete due to the crack and a discontinuity in the crack point leads to an improvement in the standard governing relationships. So that the reduction of the stiffness of the cracked element is equivalent to the change in the size of the discontinuity. Here, the variation of the stiffness of the cracked element is calculated and presented as a function of the stress intensity factor. In this approach, the simulation of the crack is done by dividing the element to two sub-elements into the two sides of the rotational spring.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
The influence of ethylene vinyl acetate and vinyl acetate polymers on mechanical properties, shrinkage and durability of Calcium Aluminate Cement based mixtures
101
114
FA
Ali
saeedikia
Graduate Student, Department of Civil and Surveying, Graduate University of Advanced Technology, Kerman, Iran
Hesam
Madani
Department of civil engineering, Kerman Graduate University of Advanced Technology, Kerman, Iran
Nowadays, the utilization of polymer modified cement base materials in waterproofing coatings and mortars is spreading. However, the influence of polymers on some types of special cements has not been investigates appropriately. In the current study due to the characteristics of calcium aluminate cement such as fast hardening and accelerating, the effects of some types of polymer materials on the properties of polymeric modified mixtures have been investigated. To this purpose the incorporation levels were 5, 15 and 25 percent by weight of cement. The water to cement ratio in all the mixtures was also 0.38. In order to keep the water content of the mixtures in a constant level, the water content of superplasticizer and the latexes (vinyl acetate and ethylene vinyl acetate) was considered as a part of the mix water. It should be mentioned that the polymers were replaced with sand. In this experimental study, a combination of dry and wet curing conditions was utilized. For this aim, after demolding of the specimens, they were cured in water for 6days, and after this period the specimens were cured in dry conditions at temperature of 25 degree of Celsius. The mechanical properties which studied in this research were compressive strength, flexural strength and flexural toughness. The shrinkage of the specimens has also been measured. It should be noted that in this study, the rapid chloride migration test was used to evaluate the durability properties of the cement base mixtures against diffusion of chloride ions. The results indicate that use of the polymers could improve the mechanical characteristics such as flexural strength and durability in regards of chloride ion diffusion as well as length change due to shrinkage. The polymer materials in calcium aluminate cement based mixtures have deceleration effect on cement hydration which results in lower compressive strengths compared to the plain mixture, which this effect is more evident at higher replacement levels. Despite the considerable reduction in compressive strength results at early ages especially for the mixtures with high contents of polymers, the differences at later ages were significantly lower. For instance, at 5% incorporation level, similar results with the plain mixture were obtained. In contrast to the compressive strength test results, high levels of polymer materials increased the flexural as well as flexural toughness in comparison with the plain mortar. It is noteworthy that incorporation of ethylene vinyl acetate in the mixtures could provide improved characteristics compared to the mixes with vinyl acetate at replacement levels of 5% and 25%. However, at 15% replacement level, similar results were obtained for the aforementioned polymers. The rapid chloride migration coefficient in the plain mix increased with age. However, using the polymers compensated for this effect and lower permeability values were obtained at later ages. It should be mentioned that the Rapid Chloride Migration Test coefficients were so low that the mixtures could be considered as relatively impermeable mortars. The shrinkage was also influenced by content of the polymer materials and those with higher contents have reduced length change.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Short-term prediction of passenger demand in bus stations, case study: Karimkhan bridge- Jomhoori square
115
129
FA
Seyedehsan
Seyedabrishami
Assistant Professor of Transportation Engineering
Ali
Mohades Deylami
PhD Candidate in computer Engineering, Electrical and Computer Engineering Dept.,Tarbiat Modares University
vajihe
amini
Master graduated in Transportation Planning, Tarbiat Modares University, Tehran, Iran
Maryam
Iranmanesh
Master Graduated in Transportation Planning,Tarbiat Modares University
Nowadays, cities as a place of living and human activity are facing serious challenges in providing human needs. Increasing in population growth, vehicle ownership and communication development has led to complexity of the transportation system and its problems, including congestion, environmental pollution and the consumption of non-renewable resources. Therefore, changes in urban transport policies and efforts to develop and more use of the public transport, especially the bus, are one of the most important concerns in urban transport planning. A review of various studies suggests that planning for efficient use of bus infrastructures and enhancing the efficiency of public transportation operation in the world, require information on the infrastructure and passenger demand for lines and bus stations. Accordingly, it is necessary to carry out studies to predict passenger demand for bus stations in Tehran. Thus, this study predicts bus stations passenger demand for future short-term periods, using data gathered by AFC (Automated Fare Collection) and AVL (Automatic Vehicle Location). For this purpose, firstly AFC and AVL data was sorted according to the time for each bus line. Since passengers use their smart card while they are getting off the bus it means at the exit station thus identifying their origin station is vital, so that in second step, data of two data bases is compared and matched by writing computer code in Matlab software to determine the origin stations of passengers and then forming origin-destination demand matrix for each bus line in terms of its stations. This matrix is considered as the main data base of the study, a time series analysis, a seasonal autoregressive integrated moving average (SARIMA) and neural network as an artificial model are calibrated based on the available data. Both models’ goodness of fit indices are compared in terms of learning and generalization capabilities. For this purpose, initial data is divided into two subsets called learning and test data sets and comparison indices are computed for both aforementioned sets. The models’ results show that the multi-layer perceptron neural network model in terms of goodness of fit indices in both learning and generalization capabilities in prediction of bus station passenger demand is better than SARIMA model; however, the manner of influencing different factors such as day of week or month of year in passenger demand in each station is more clear in time series analysis. The passenger demand for each stations in first month in spring is different from the rest months in this season. Months in summer is also show different trends for passenger demand, while all months in fall and the first two months in winter have similar passenger demand in various stations. Official holidays has also significant influence on passenger demand so that reduce passenger demand by approximately 256 persons on average. All days in week have meaningful effects on passenger demand in comparison with Friday so that Monday and Thursday have the highest and the lowest effect on weekday passenger demand in bus stations in comparison with Friday, respectively. This analysis comparison show that if the precision of future prediction is important then neural network outweigh time series regression, while the identification of influential variables on passenger demand is better done by time series analysis.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Experimental-Numerical modeling of seismic behavior of dry sandy slopes reinforced by piles row
131
142
FA
Yazdan
Shams maleki
Kermanshah Razi University
Hassan
Sharafi
Assistant Prof. Razi university, Kermanshah, Iran
In this study the behavior of floating piles row with circular cross-section were installed inside the dry sandy slope by help of three-dimensional numerical analyses and physical modeling have been simultaneously studied. The three-dimensional numerical modeling was used for conducting the parametric studies about effects of directions of imposition of harmonic seismic loading on the main geotechnical parameters of floating piles row-sandy slope problem. The seismic loading of harmonic sinusoidal waves in the form of seismic motions in the in-plane and out-of-plane directions along the longitudinal and transverse directions of slope model and both of them were imposed on the slope physical and numerical models. Moreover, the physical modeling of the investigating problem was implemented for validation of numerical results by imposing the sinusoidal harmonic loading in the longitudinal and transverse horizontal directions of micro-scale slope model by help of small-scale geotechnical shaking table. Reinforcing of a dry sandy slope by a row of floating piles (similar to reinforcing of slope by end-bearing piles row) results in significant decrease (to about more than 50 percent) in slope’s vertical displacements. Out-of-plane components of seismic loading such as transverse component of earthquake, T component, (productive of horizontal shear waves, i.e., SH waves) also in the presence of site’s effects such as “directivity effects” can produce the responses as large as the in-plane motion components such as earthquake longitudinal contained component, L (productive of P and SV seismic waves). The motion of slope sliding wedge in the strong ground motions is a rigid block motion while the failure wedge displacement under weak ground motions is a negligible motion and occur in a flexible block manner. Simultaneous seismic loading along two-axes of three coordinate axes in contrast to the current slope seismic loading that the seismic loading are imposed along one axis and in the longitudinal direction of slope failures surface, have great effects on the slope displacements values and internal efforts generated in the reinforcing piles row. Studying and solving the classic problem of in-plane and out-of-plane seismic-waves propagations in the combination with the existence of slope in the ground and piles row interaction (i.e., adding the piles row-slope seismic interaction to the initial classic problem) by help of present available analytical and mathematical solutions will be a very difficult problem. By combining of the in-plane and out-of-plane seismic motions the complexity of the piles row-sandy slope dynamic interaction problem will increase and in the some cases presenting analytical and closed-form solutions can be impossilble. The alternating solutions for solving these complex problems proposed by the present paper are the simultaneous using of numerical and shaking table physical modeling for understanding the precise details and ambiguities of the problem in the complete scientific and practical-empirical frameworks. The results of present study show that installing a row of floating piles similar to the end-bearing piles row can reduce the displacements of loose dry sandy slope and through this manner the seismic stability of slope against the local and general failures increased. In the present paper despite of increasing the directions of seismic loading from one-direction to the two-directions the installed floating piles row sufficiently played their roles in the reducing seismic displacements of slope. Indeed, according to the experimental-numerical results of the present paper, decreasing of slope crest settlements by installing a row of floating piles in the seismic loading cases are more than 50 percent. The results of small-scale 2DOF geotechnical shaking table physical model were used to verification of the obtained 3D numerical results. There is a good agreement between the numerical and physical models results.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Investigation of Crack Growth in Rock-Like Brittle Material
143
155
FA
Mahtab
Alitalesh
Ph. D. Candidate, Geotechnical Engineering group, school of civil and environmental engineering, Tarbiat Modares University, Tehran, Iran
Marjan
Naeimabadi
M.Sc. Student, Geotechnical Engineering group, school of civil and environmental engineering, Tarbiat Modares University, Tehran, Iran
Mahmoud
Yazdani
Assistant Prof., School of Civil and Environmental Engineering,Tarbiat Modares University, Jalal-Al-Ahmad Highway,Tehran, Iran
Understanding initiation and growth of cracks leads to better evaluation of rock masses behavior. Investigation of crack growth and propagation is noteworthy in geotechnical engineering, petroleum engineering, geology, seismology and many other sciences which encounter with rock fracture mechanics problems. Evaluation of rock slopes stability, design of retaining structures, design of tunnels, and prediction of flow path through rock masses, are some example of application of crack growth study in geotechnical engineering. By evaluating cracks growth, propagation and coalescence, faults seismic behavior can be understood. In general faults are considered as quasi-static cracks, so study of crack propagation under various loading conditions brings important information about faults. Many researchers studied crack growth in Brazilian disk shape specimen under diametrically compression loading. Previous research focused on open crack propagation and closed crack were infrequently included. In this paper using molded gypsum, as a model material, crack growth in Brazilian disk shape specimens with pre-existing open and closed flaws are investigated. The dimension of specimens is 100 mm in diameter and 50 mm in thickness. Inserted open and closed flaws length is 30 mm. Open and closed flaws are inserted using 1 mm thickness steel shims and 0.05 mm thickness silicon tapes, respectively. In this study, the specimens engineering properties were determined by conducting uniaxial compression test and indirect tensile test on Brazilian disks. The experiments were conducted according to ISRM and ASTM standards. Uniaxial compressive strength, Poisson ratio, elastic modulus, and tensile strength of specimens are, respectively, qu=38 MPa, υ=0.25, E=8.5 GPa, and σt=7 MPa. Diametrical compressive loading was applied to the specimens in various inclination angles of flaws with respect to the loading direction. In this paper, influence of open and closed cracks on strength of the specimen is investigated. Fracture toughness of mode I, II and mixed mode I-II, are also determined using analytical solutions. Throughout the tests, slippage between closed crack surfaces is continually monitored by digital microscope. According to the curves of slip distribution along the crack length derived from laboratory data, there is a good agreement between slip distribution along closed flaws and that recorded from real faults by other researchers. Also, results of this study show that open and closed flaws reduce disks strength, significantly (i.e., more than 50%). Inclination angles of the flaw with respect to the loading direction affects crack propagation patterns. Generally, new wing cracks initiate form the flaw tips and then propagate toward the loading direction. Increase in the inclination angle leads to a reduction in the effect of open flaw on crack growth and for angles more than 27.2˚ (i.e., pure shear, mode II) new crack does not initiate from flaw tips. At inclination angle of 90˚, flaw has no effect on crack propagation pattern and the disk fails under tensile splitting condition. In disks with closed flaws, new cracks initiate from flaw tips expect for the case of 90˚ which is the same as open flaws. For the material used in the study, mode I and II fracture toughness are calculated form experimental data and found to be equal to 0.250 and 0.258, respectively. The obtained values for fracture toughness indicate that used material is brittle. Also, the values of mode I fracture toughness for angels above 27.2˚ are negative which point to the fact that flaw tips in these angles are in compression and not in tension.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
An Approach for Estimating the Rotation Capacity of Wide Flange Beams using Bayesian Regularized Artificial Neural Networks (BRANN)
157
169
FA
Seyed Alireza
Alavi
M.Sc. Graduated, Faculty of Civil Engineering, Semnan University, Semnan, Iran
Hosein
Naderpour
Associate Professor, Faculty of Civil Engineering, Semnan University, Semnan, Iran.
Pouyan
Fakharian
Ph.D. Candidate, Faculty of Civil Engineering, Semnan University, Semnan, Iran
In this paper, for the first time using of Bayesian regularized artificial neural network (BRANN) model, which is a novel method of among soft computing (SC) methods (such as fuzzy logic, genetic programming, neural network) to predict the rotational capacity of wide-flange steel beams. Steel is one of the most commonly used materials in construction industries, mainly in steel structures. There are many researches and studies on the behavior of a structural member of steel structure such as beams under different types of loading. The accurate estimation of rotation capacity (plastic rotation capacity) is of significant importance issue for plastic and seismic analysis and design of steel structures especially for high rise building (nonlinear behavior). Similarly, the moment redistribution in a steel structure also depends on the rotation capacity of the section. So the determination and accurate prediction of rotation capacity of steel structures members such as wide flange beams become an important task. Using different methods such as finite element, regression and statistical methods in previous studies has been used in recent years. Therefore, in order to estimate the more accurate value of the rotational capacity of wide flange beams, Artificial neural networks are used with the Bayesian learning process. The Bayesian regularized network assigns a probabilistic nature to the network weights, allowing the network to automatically and optimally penalize excessively complex models. The proposed technique (BRANN) reduces the potential for overfitting and overtraining, improving the prediction quality and generalization of the network. The proposed model (BRANN) is based on experimental data that collected from previous studies. After a comprehensive review of existing literature, 77 data of wide flange beam were selected which had experienced to determined rotation capacity. For this purpose, Half-length of flange, height of web, thickness of flange, thickness of web, length of beam, yield strength of flange and yield strength of web were consider as input parameters (six inputs) while rotation capacity is treated as target of the Bayesian regularized artificial neural network model. The Bayesian regularized artificial neural network is modeled in MATLAB software and applied to predict the rotation capacity. The results of this model were compared with experimental results and other models and equations that presented in the past (including Genetic programming (GP), Li equation and Kemp Equation. An analysis is carried out to check the performance of the proposed BRANN model based on the common criteria such as Mean Absolute Percentage Error (MAPE). The optimal and best model should have the lowest values of MAPE, this parameter is 20.32% for BRANN, 23.49% for a Genetic Programming model that proposed by Cevik, 47/20% for Li’s Equation and 56.98% for Kemp’s equations. The results of Bayesian regularized artificial neural network approach indicate a good agreement between the predicted and measured data. Furthermore, the Bayesian regularized artificial neural network model shows the most optimized results compared to all the previous model and equations. The result indicated that the Bayesian regularized artificial neural network could be used as a powerful tool for engineers and researcher to solve this kind of problems.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Effects Of Deep Excavation on Seismic Vulnerability of Existing Steel Framed Structures
171
185
FA
MEHDI
FARAJMOHAMMADIEH
فارغ التحصیل
Ahad
aouria
Associate Prof, Civil Engineering Dept ,University Ardabil
In this paper the effects of deep excavation on seismic vulnerability of existing buildings are investigated. It is well known that deep excavations induce significant changes both in stress and strain fields of the soil around them, causing a displacement field which can modify both the static and dynamic responses of existing buildings. A FEM model of a real case study, which takes into account geometry, non-linear soil behavior, live and dead loads, boundary conditions and soil–structure interaction, has been developed in order to estimate the soil displacements and their effects on seismic behavior of a reinforced concrete framed system close to deep excavation. Along with increasing urban activities, and developing underground facilities, subway stations, parking spaces and other underground structures, excavations made with various depths in urban areas around existing structures has been turn into an inevitable issue. The excavations cause significant changes in the stress and strain fields of the soil under the existing building foundations and finally result in horizontal and vertical displacements under the foundation as well as large changes in static and dynamic response of existing structures. The main objective in the present study is in particular to investigate the above-mentioned problems using a study performed on 4 types of soil as classified in 2800 earthquake regulations with a model of deep excavation in the vicinity of a steel framed building. In this study in order to evaluate the effect of deep excavation on seismic vulnerability of existing buildings, the required analyses has been carried out in three parts and using PLAXIS and SAP 2000. Nonlinear dynamic analysis of soil has been performed using PLAXIS software in which due to its inability to perform nonlinear dynamic structural analysis, the SAP 2000 software is used for nonlinear dynamic analysis. In the first part of the study, using PLAXIS software for conducting the static analysis horizontal and vertical displacements under the foundation subjected to dead and live load have been calculated in two stages before and after the excavation. In the second part, using PLAXIS software, dynamic analysis has been conducted for both mentioned stages with the application of ten scaled records which are chosen based on the model of each site. Afterwards, the acceleration response under the foundation is calculated. This part aims to evaluate the effect of excavation on the acceleration response and use it as an input for structural analysis in SAP 2000 software. In the third part, the structure is modeled in SAP 2000 software, the displacements resulted from the first part are applied to the foundation and using the acceleration response (output of PLAXIS), nonlinear dynamic analysis of the structure is conducted in two stages. The results indicate that the excavation made in all models causes the increased horizontal and vertical displacements. Therefore, both increasing the excavation depth and performing struts, vertical displacements and horizontal displacements increase by a smaller and bigger percentage change, respectively. The acceleration response under the foundation in soil types 1, 2, 3, and 4 increases 51%, 35%, 66% and 27%, respectively. In addition, the maximum displacement of the structure increases 1.6, 1.3, 1.9 and 2.5 times more compared to that before excavation, respectively.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Three-dimensional modeling for seismic response of pile-raft in saturated sand to investigate local site effect
187
200
FA
Mojgan
Falllahzadeh
Semnan University
Yaser
Jafarian
Abdolhosein
Haddad
Semnan university
Saturated loose soils have constituted superficial layers of the ground in vast regions of the country. For instance, geotechnical site investigations have revealed that shoreline of the Mazandaran Sea involves thick layers of uniform sand mixtures. Presence of such soil deposits in the northern and southern Iran, which are prone to seismic activity, may produce severe damages due to liquefaction occurrence. To prevent earthquake damages to the structures relied on liquefiable soils two strategies might be preferred: (1) improvement of liquefiable soil and ceasing liquefaction, and (2) bypassing the liquefiable layer via deep foundations. The latter strategy aims to transfer the superstructure load to the underlying stiff layer by end-bearing piles while raft foundation is also required because the superficial liquefiable soil may be unable to provide sufficient bearing capacity due to seismic pore pressure generation. In pile-raft systems passing through the liquefiable layer it seems that the liquefiable layer has less influence to the response of the system. However, several interactions in the environment such as pile-liquefiable soil, pile-pile, pile-raft, and raft-liquefiable soil could result in a sophisticated problem; affecting the amplification of the upward propagating seismic waves. Amplification of seismic wave denotes variations of amplitude and frequency content of upward propagating wave passing through the reinforced liquefiable soil layer. It is expected that the pile-raft system in conjunction with the liquefiable layer considerably change seismic response of the ground compared with the free-field liquefiable ground in the absence of pile-raft system. In the design of routine projects for which the national seismic building code is employed, there is no clear recommendation to account for the influence of pile-raft on the site amplification factors. The currently used building codes have poorly addressed the problem; and thus, considerable researches might be required. The aim of this paper is to study the characterization of seismic wave amplification by considering the presence of piled raft. To achieve this goal three-dimensional numerical modeling of piled raft and free-field in both liquefied and dry sand deposit is used. Results of some centrifuge experiments of a piled raft structure on liquefied sand are used to evaluate the predictive capabilities of the numerical model constructed in OpenSees, as a state-of-the-art numerical tool. Fully-coupled solid-fluid 3D nonlinear numerical simulations were performed in OpenSees, in combination with the pressure-dependent-multiyield soil constitutive model that enables dynamic effective-stress modeling of soil liquefaction in addition to embedded pile and superstructure elements. The numerical simulation results demonstrated reduction of seismic wave amplification in liquefied sand versus dry sand due to reduction of soil strength and increase damping. In both liquefied and dry state, the presence of piled-raft increases the soil stiffness and seismic wave amplification. The level of site amplification depends on many factors such as lateral stiffness of the pile-raft system and characteristics of input motion. Parametric study was then carried out to address these factors. Results of this study indicate that amplification factor decreases due to the presence of liquefied soils. However, the decrease of amplification factor at the free-field is larger than pile-raft foundation. Furthermore, amplification factor increases due to increase of pile stiffness, amplitude and period of input motion. Therefore, the site-specific analysis might be necessary to account for the presence of piled-raft system in the sites involving thick sand layers.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Short-term Prediction of Particulate Matter Related to Traffic Flow Using Support Vector Machine (Case Study: Tehran City)
201
210
FA
Mohammadreza
Kashipazan Qomi
Civil Engineering Department, Faculty of Engineering, Kharazmi University, Tehran, Iran
Behrooz
Shirgir
Civil Engineering Department, Faculty of Engineering, Kharazmi University, Tehran, Iran
In recent decades, increasing population density and economic and industrial activities in metropolitan cities has increased traffic volumes and, consequently, increased levels of air pollution. The major source of air pollution in major developing cities is the massive transport of vehicles that use more than standard fuel and energy, and heavy traffic in the streets of these cities is often rooted in problems such as there is a lack of traffic management and traffic culture. One of the important issues in cities and metropolises that face pollution problems and harmful effects is the issue of informing about the future status of air quality and the amount of urban air pollution to the people. This can be achieved through daily or even hourly forecasts of air pollution and preventing people from being exposed to contaminated areas and their irreversible consequences. Therefore, the need to predict the quality of the air and the quantitative estimates of the concentration of pollutants in the aftermath of the equipment makes it felt that in this study, the problem of the predicted hourly concentration of particulate matter (PM2.5) in the district 11 municipalities of Tehran have exceeded 80% of the contaminated days under the influence of this pollutant. The difficulty and uncertainty associated with estimating and predicting the share of road traffic volume at the general level of air quality is the most important factor that can, if properly diagnosed, be very helpful. In order to take into account the effects of varying the volume of different traffic fleets in the process of changes in the concentration of pollutants and air pollution, it is necessary to pay attention to the effects of other influential variables including hydrological variables, geographical variables, etc. To achieve this, The methods of analytic analysis seem to be able to examine all of these effects together and in an omnipresent manner. The method used to predict this study is one of the methods for analyzing neural networks called Support Vector Machine (SVM). Artificial neural networks are important tools in the field of computational intelligence. Different types of artificial neural networks have been introduced, mainly in applications such as classification, clustering, pattern recognition, modeling and approximation of functions (or regression), control, estimation and optimization of the case Are used. Support Vector Machines (SVM) are a special type of neural network that, unlike other types of neural networks (such as multi-layer perceptron MLP and radial base functions of the RBF), instead of minimizing the error, minimize the operational risk of classification or modeling. Slowly This tool is very powerful and can be used in various fields such as classification, clustering and regression. The results of this study showed that SVM models work well in predicting the contribution and time share of road traffic in propagation of particulate matter, and predictions are well-coordinated with observations. It provides the opportunity to be used as an air quality management tool. Variable significance analysis results for SVM models provide this opportunity to be used as a tool for air quality management, in which the sensitivity of models to variations in emissions can be used to evaluate the effectiveness of a The air quality management scenario will test traffic fleet technology, combine the traffic fleet or its volume.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
The Effect of Porosity and Rainfall Intensity on Performance of Urban Runoff Treatment Via Previous Concrete Pavement
211
221
FA
Nader
Mokhtarani
Assistant Professor, Civil & Environmental Engineering faculty, Tarbiat Modares University
Urban development is always associated with infrastructure surfaces icreasment such as road and building construction and other impermeable surfaces that lead to precipitations runoff. Urban runoff contains heavy contaminants such as nutrients, heavy metals and organic substances including hydrocarbons and polycyclic aromatic hydrocarbons (PAHs). This pollutants can infect water and soil resources by road surface washing and discharging into the receiving waters or infiltrating into surrounding area soils. Stormwater management has recently shifted towards a focus on site level low impact development (LID) techniques that aim to reduce the total stormwater runoff volumes in addition to attenuating peak flows and removing pollutants at or near the source of runoff. Permeable pavement systems (PPS) are a subset of LID stormwater best management practices (BMPs) of particular interest in dense urban areas because they can be installed in parking lots and low traffic roadways where the availability of land space for more traditional BMPs is not available. Such information is necessary to improve the selection of BMP/LIDs for stormwater management. Previous concrete pavement are subset of PPS and able to reduce the volume of urban runoff significantly which leads to hydraulic differentia reduction and its specific side effects urban utilities in addition to providing requirements for treatment processes and in-situ urban pollution management. In this study, porous concrete pavement performance has been surveyed in terms of quantitative and qualitative reduction of synthetic runoff. The effect of porosity and rainfall intensity were investigated. To investigate the effect of concrete porosity, four levels including 15%, 20%, 25% and 30% have studed and for evaluating rainfall intensity effect, a range of precipitation between 25 to 250 mm/h concidered according the recent studies considered. The pilot used for this study consisted of a tank made of galvanized steel that simulated PCP was replaced layer by layer at the bottom of tank. Synthetic runoff sprinkled on the previous concrete surface with specified flow rate. Effluent is collected from the orifice that embedded under the tank then effluent quality parameters were evaluated. Befor run the pilot Previous concrete mixed designs calculated and prosity, percolation rate and Compressive strength were verified. The parameters examined in this study including COD, TDS, TSS, turbidity and EC of pervious concrete pavement system was compared to synthetic runoff. According to study outcomes, the system efficiency in TSS removal was between 75.7% to 88.6%, highest COD removal detected was 15% in case the porosity was 22.9%. Effluent quality analysis demonstrated that PCPS had little ability in TDS and EC removal. However PCPS was able to remove turbidity from syntetic runoff. The maximum efficiency of turbidty removal was detected 70.3% at rainfall intensity of 37 mm/h and the porosity of 22.9%. By comparing the results of the above parameters, it was determined that porosity has almost no effect on runoff quality. Results showed the rainfall intensity dose not have significant effect on PCPS efficency although the systems overall removal efficiency was drastically deacrased due to rainfall intensity increase even in cases with low emissions gradients.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Effect of Ground Motion Scaling Methods on Inter-story drift Distribution of Steel-Moment Frames Designed Based on Performance-Based Plastic Design
223
237
FA
Behnoud
Ganjavi
Department of Civil Engineering, University of Mazandaran, Babolsar, Iran
Amir Ali
Hadinejad
Department of Civil Engineering, University of Mazandaran, Babolsar, Iran
Abolfazl
Gholamrezatabar
School of Civil Engineering, Center of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science & Technology, Narmak, Tehran, Iran
Majid
Bararnia
Department of Civil, Water & Environmental Engineering, Shahid Beheshti University, Tehran, Iran
Time history analysis, which is the most important analysis tool in performance-based seismic design, has become more and more popular worldwide. In the seismic design, seismic demand is mainly governed by three factors including the peak value of ground motion, the characteristic of earthquake spectrum and duration. An earthquake intensity index of ground motions is normally used as a scaling parameter that is critical for seismic analysis and design. A number of researchers have, from their own perspective, proposed various intensity indices. However, due to the complexity and randomness of earthquake motion, it has been a difficult task to accurately evaluate the applicability of various existing intensity indices. In addition, an objective and quantitative method is lacking in the evaluation of the applicability of such indices. This has been a challenging issue in seismic engineering research and has become a fundamental problem in performance-based seismic design. Nonlinear structural response is often highly sensitive to the scaling of input ground motions. Thus, many different ground motion scaling methods have been proposed. The “severity” of an earthquake ground motion is often quantified by an intensity measure, IM, such as peak ground acceleration, PGA, or spectral acceleration at a given period. The PGA of a record was a commonly used IM in the past. More recently, spectral response values such as spectral acceleration at the fundamental period of vibration have been used as IM. Scaling of ground motions to a given spectral level at the fundamental period of vibration significantly decreases the variability in the maximum demand observed in the structural system. However, it is widely known that for records with the same spectral acceleration at the fundamental period of vibration value, spectral shape will affect the response of multi-degree of- freedom and nonlinear structures, because spectral values at other periods affect the response of higher modes of the structure as well as nonlinear response when the structure’s effective period has lengthened. Similar attention to the influence of nonlinear behavior of a structure on the period of vibration led to an IM that accounts for period softening to reduce variability at high levels of maximum inter-story drift ratio, drift demands larger than 5%, for composite structures. Previous studies have focused on evaluation of different ground motion scaling methods in single-degree-of freedom and buildings of multi-degree-of-freedom with shear-type behavior or common steel-moment frame structures. However, over the last decade, the performance-based seismic design philosophy has emerged as a promising and efficient seismic design approach. The novel Performance-based plastic design (PBPD) approach explicitly accounts for the inelastic behavior of a structural system in the design process itself. PBSD approaches based on plastic analysis and design concepts were recently developed for different lateral load resisting systems such as steel moment resisting frames, steel braced frames, etc. In these design methods a pre-selected yield/failure mechanism and a uniform target drift (based on inelastic behavior) were considered as performance objectives. The analytical validation of these methods showed that structures designed using these methods were very effective in achieving the pre-selected performance objectives. Considering a gradual shift towards PBSD for seismic design methods in general, this study is aimed at examining the effects of six different IMs on the estimation and distribution of the maximum inter-story drift for three short, moderate, and long-period steel-moment resisting frames designed with PBPD method buildings using the concepts of efficiency and sufficiency. An ensemble of 42 far-filed earthquake ground motion without pulse characteristics were used and scaled based on two target spectrum MCE and Design Response Spectrum to conduct nonlinear dynamics analyses by using OPENSEES. Results indicate that, the cod-compliant scaling method was not reliable for nonlinear dynamic analyses of structures designed by PBPD method, and cloud be very sensitive to the ground motion characteristics. Among them, depending on the number of stories, the three scaling methods including scaling ground motions to a given PGA and those that take into account for periods of higher modes generally decrease the variability in the maximum demand observed in the structural systems.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Assessing the effect of cement and nano-clay mixture on the stabilization of heavy metal contaminated soil
239
250
FA
Amir reza
Goodarzi
Mahdi
Sahabroshan
Faculty of Engineering, Hamedan Branch, Islamic Azad University, Hamedan, Iran
HamidReza
Abari
Faculty of Engineering, Hamedan Branch, Islamic Azad University, Hamedan, Iran
Stabilization/solidification (S/S) has emerged as a cost-effective method for treating a variety of wastes, particularly heavy metal (HM) contaminated soils. Among the many available fixing agents, Portland cement (PC) has been used extensively for the remediation of contaminated sites. However, there are significant environmental and technical impacts associated with PC application. Thus, the present research was conducted to address the efficacy of cement and nano-clay mixture in enhancing the S/S process. In so doing, artificially contaminated soils were first prepared by mixing kaolinite with zinc (Zn) at levels of 0 to 2%. Afterward, tow type of nano-clay (Na-Montmorillonite and Na-Cloisite), cement and cement/nano-clay (CNC) were separately added to the sample, and then, a set of macro and micro level experiments including batch equilibrium, pH, toxicity characteristic leaching procedure (TCLP), unconfined compression strength (UCS), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analyses were carried out at various curing periods (1, 7 and 28 days) to assess the effectiveness of the additives. The results obtained show that the addition of nano-clay can increase the HM retention capability of soil; however, this may be partly lost when the treated soil are subjected to acidic TCLP solution. In addition, with increasing the HM content, due to the decrease in buffering capacity of system and the restructuring of the clay particles, the soil remediation potential at presence of nano-clay is decreased considerably. It was found that the application of sole cement may significantly enhance the HM retention capacity of soil. But in this case, the physicochemical reactions of Zn ions with cement could hinder and/or reduce the generation of hydration products phases such as calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), resulting in the degradation of cementation structure-bonding of S/S matrix, as clearly confirmed by the formation of calcium zincate and the diminution in the cementitios compounds peak intensity in the XRD patterns of cement-treated soils. Therefore, the leaching characteristics and the mechanical properties of the S/S material with sole cement are adversely affected by increasing the amount of HM ions. As a result, a large quantity of cement (20 wt% per one percent of HM) and a long time of curing (≈ 28 days) should be employed to meet the full needs of HM immobilization in contaminated soil and give the EPA-acceptable UCS value (≥ 0.35 MPa). The TCLP and XRD test results indicate that the cement/nano-clay combination can expedite the S/S process and alleviate the deleterious influences of metal ions and acidic attack on the stabilized sample. The EDX analyses also support the increase in the development of hydration reactions and the formation of cementing materials in the presence of CNC, providing the enhancement of binding capacity that will lead to the greater strength (up to 50%) in comparison to cement application. Hence, the CNC binary system is more efficient in modifying the contaminated soil with a lower amount of binder (to about 40%) and shorter curing ages (by nearly 4 times) than that of the sole cement. Overall, it is concluded that the cement/nano-clay mixture can be utilized as an effective S/S amendment and CNC content of 15 wt% per 1% of HM can successfully remediate the contaminated soil after 7 days of curing.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
251
264
OTHER
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Determination of the Longitudinal Velocity Profile of Turbulent Flow over Rough Beds Using Double Averaging Method
265
276
FA
Seyed Hossein
Mohajeri
Most natural open-channel and overland flows belong to the class of hydraulically rough-bed flows. Although hydrodynamics of such flows has been studied extensively for the last two decades, there are still many unsolved problems awaiting clarification. In general, turbulent flow is modeled and studied through Reynolds averaged Navier-Stokes (RANS) equations. Despite the ability of these equations in modeling of turbulent flows, they have some deficiencies in natural flows (such as atmospheric flow or water flows in rivers and estuaries) where flow characteristics vary in multiple time and length scales. In addition, in some situations, these equations are not practicable due to the highly three-dimensional small-scale structure of the mean flow and turbulence, especially in the near bed region. Moreover, RANS equations are locally resolved the flow characteristics, which is in contrast to many hydraulics fundamental concepts such as uniformity, Manning coefficient, water discharge. To resolve this problem, the time averaging of the Navier-Stokes equations should be supplemented by spatial averaging in a plane parallel to the mean bed surface. After such an averaging a new system of equations will be obtained which are known as double averaged, or spatially averaged, Navier-Stokes equations. The double-averaging procedure gives new momentum and continuity equations for fluid, which are averaged in both time and space domains and which explicitly contain important additional terms such as form-induced stresses and, for the flow region below roughness tops, form and viscous drag terms. These type of Reynolds averaged Navier-Stokes equations have various applications in hydraulic studies. One of the main application of these equations is in heterogeneous turbulent flow above rough surfaces such as vegetated or gravel bed flow. The present study demonstrates applications of double averaged equations in study of rough bed flows. To this end, laboratory measurement were conducted in an open-channel laboratory flume. Experimental measurements cover an appropriate range of the bed roughness characteristics so that the channel aspect ratios, the ratio between the channel width and water depth (B⁄H), are 6.2 and 7.7. Bottom of the channel is roughened using two series of crushed stone which are spread randomly at the bed and then glued to the bed. Acoustic Doppler Velocimeter (ADV) is used to measure three components of velocity field. Both velocity profile and Reynolds shear stress are estimated based on the measured velocity time series. Results of these measurements show that velocity field in the near bed region shows strong spatial variation due to the rough bed elements protrusions. To properly take in to account this spatial variation in shear velocity, spatially averaged Reynolds shear stress profile can be reliably used for determination of the bed shear stress. Furthermore, a new method for determination of the vertical logarithmic profile of streamwise velocity is introduced using the bed shear velocity obtained from spatial averaging. This method is an iterative process in which parameters of logarithmic profile, i.e. zero-plane displacement (the bed origin displacement due to the rough elements presence) and constant if integration will be estimated based on the measured velocity profile. Results of experimental data analysis, using the new method, show that the logarithmic profile parameters can be efficiently determined.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Experimental Study of Contaminant Transport in Porous Media Using ANFIS-RBF Hybrid Model
277
288
FA
Shahram
Mousavi
Young Researchers and Elite Club, Miyaneh Branch, Islamic Azad University, Miyaneh, Iran
Some uncertainties in the field parameters such as dispersion and hydraulic conductivity, unknown boundary conditions and the noise of the measured data are among the main limiting factors in the groundwater flow and contaminant transport modeling. Thus, simulation of contaminant transport can be an important task in hydro-environmental researchs and consequently, it is necessary to develop the robust models which can determine the temporal and spatial forecast of contaminant. For temporal modeling contaminant concentration, several numerical methods, such as finite volume method, finite difference method, boundary element method and finite element method have been used for computional solution of governing advection-dispersion partial differential equation. In this study, a new hybrid model based on adaptive neuro-fuzzy inference system (ANFIS) as an black-box model and radial basis function (RBF) as a meshless method was developed. In fact, the proposed method employed the advantageous of both arthificial intelligence and meshless techniqus for modeling contaminant transport in porous media. In this research, an experimental was done for examining the efficiency of the proposed method. In this way, an acrylic sand tank was made with ten piezometers, one inlet with three adjustors. In order to supply contaminant a submersible pump was used. Also, constant water level was maintained using adjustor valves at both end of the tank. The thickness of acrylic sand tank 10 mm and dimensions 2.00×1.30×0.20 m3 were chosen. The sand sample porosity was measured 0.3. The grid size and time interval were considered 0.1×0.1 m×m and 3-minute, respectively. The constant-head test was employed to meaure the hydraulic conductivity of soil as a standard laboratory test. An UV Spectrophotometer (DR5000, HACH Company, USA) was used for measurement of the AO7 concentration. The maximum wavelength was measured 485 nm for AO7 concentration. Also, an electrical conductivity meter (EC600, A FLIR Company, USA) was used for measurement of the resistivity and electrical conductivity of AO7. In this study, time series of AO7 concentration observed at different piezometers of sand tank were firstly de-noised by the wavelet-based data de-noising approach. Then, the effect of noisy and de-noised data on the performance of ANFIS model was compared. For this end, time series of AO7 concentration observed in 10 different piezometers were trained and verified via ANFIS model to predict the AO7 concentration at one month ahead. Then, considering the predicted AO7 concentration of piezometers as interior conditions, the multiquadric radial basis function as a meshless method which solves partial differential equation of contaminant transport modeling in porous media, was employed to estimate AO7 concentration values at any point within the study area (in the experiment, sand tank) where there is not any piezometer. In this stage, optimal values of dispersion coefficient in advection-dispersion partial differential equation and shape coefficient of MQ-RBF were determined using cross validation approche. The cross validation method was finally applied to verify the performance of the proposed ANFIS-RBF model for two piezometers which were not considered in the calibration stage.In temporal contaminanat transport modeling, de-noised data enhanced the performance of ANFIS methods up to 5 percent in the experimental study. Results showed that the efficiency of ANFIS-RBF model is a reliable thechnique for contaminant transport modeling in porous media.
Tarbiat Modares University
Modares Civil Engineering journal
2476-6763
18
4
2018
11
1
Study of the sensitivity of seismic-isolated structures response to nonlinear behavior of superstructure and simultaneous design of superstructure and isolator based on the concept of target ductility
289
303
FA
Sayed Ahmadreza
Mirbod
Department of Civil & transportation engineering, University of Isfahan
Hossein
Tajmir Riahi
Department Of Civil Engineering, University Of Isfahan, Isfahan
Maryam
Daei
Department of Civil & transportation engineering, University of Isfahan
In the design of seismically base-isolated structures, it is expected that the isolator will experience nonlinear behavior while the superstructure still behaves linearly. Therefore for modeling these systems, a linear behavior is assumed for superstructure and different nonlinear models are used for isolator. But there are special conditions such as strong ground motions in which superstructure behave nonlinearly. In this study, the nonlinear behavior of seismically base-isolated structures is more accurately investigated. This is done using nonlinear time history analysis of structures using ground motions. Two sets of ground motions are selected which represent earthquakes with 475 and 2475 years return period. OpenSees software is used for modeling these structures. The effective parameters on the response of seismically base isolated structure which are investigated are: response modification factor of the superstructure, stiffness of the isolator, damping ratio of the isolator, stiffness of the superstructure and damping ratio of the superstructure. Studies of this paper are divided into two parts. In the first part, two-degree freedom model with viscoelastic isolator has been used to investigate the effect of superstructure nonlinearity. Also a sensitivity analysis is done to find important parameters which have more effects on the systems response. Results of this part show that, nonlinear behavior of superstructure increases system ductility demand drastically. It is concluded that the period of isolator and superstructure have the most effect on the ductility demand. In the second part, the effect of different parameters and higher mode effects on the response of seismically base-isolated structures is investigated using muti-degree of freedom models sited on isolator with bilinear behavior. Results obtained in this part also confirm the increase in the response of the system when the superstructure has low strength. Likewise in this condition, the isolator deformation decreases. Distribution of ductility demand in the height of structure is also non-uniform in this condition and lower stories are more vulnerable. Isolators with a lower fundamental period and also isolators with a lower yield force lead to the least amount of isolator deformation and ductility demand of superstructure. By increasing damping in the isolator, ductility demand of superstructure will increase. A stiffer superstructure with nonlinear behavior has a much more ductility demand rather than similar structure which is more flexible. But when the superstructure behaves linearly, the fundamental period of superstructure and isolator deformation increase or decrease together. Finally, due to the intensive increase in the ductility demand of the superstructure when it behaves nonlinearly, a solution is proposed with the aim of simultaneous optimization of the superstructure and isolator systems. This strategy uses a combination of uniform ductility theory and a modified artificial bee colony algorithm. By applying this method and using ductilities of superstructure and isolator simultaneously, it is possible to obtain the desirable ductility in the isolator, in addition to achieve a more economical choice for the superstructure. If there is no constraint around the structure for movement, by increasing the target ductility of the superstructure, the weight of the superstructure can be reduced by reducing its yield force.