AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2017 | Volume:49 | Issue:1|Papers Count:20

This article intends to discuss and assess the weaknesses of Iran seismic design code (No. 2800, 4th version) including spectral ordinates at the constant maximum acceleration and velocity ranges, starting point at response spectra. The dependency of corner period (Ts) on the strength of strong motion rather than the spectral ordinates at constant maximum acceleration as it is in the existing forms is discussed. A simple methodology for predicting the period dependent forward directivity effects parameter, N(T) is proposed. The real spectral ordinates data at 120 near source sites on the four types of soil types from the two cities in the United State are used to develop the proposed forward directivity factor N(T). The average values of the obtained design response spectra are compared with those of the 2800’s third and fourth versions and the differences are assessed. It is concluded that modifying the currently used design response spectra seems to be inevitable due. Further, the parameter (S) in the existing spectral shape form (S+1)B1(T) seems to be the cause of ambiguity to the users and needs to be changed in current status. Finally, four new forms of design response spectra are proposed meanwhile a conscious solution for the forward directivity effects parameter representative N(T) is recommended.

The Karun River receives large quantities of domestic wastewater, industrial effluents and agricultural drainage water during its course. Since every river has a certain capacity for accepting incoming pollutants and for self-purification, knowledge of the trend of changes in self-purification capacity is of great importance. This research studied changes in the self-purification capacity of the Karun River in the 42-kilometer distance between the Zergan and Kot Amir stations Such as 2008-2009 and 2013-2014. Changes in the parameters of pH, electrical conductivity (EC) and biochemical oxygen demand (BOD) in mentioned two years were first simulated for the two months of August and January using the calibrated Qual2Kw model. The observed data was then compared with the calculated data using the square of the correlation coefficient (R2) and the mean absolute error (MAE). Results showed that the Karun River could not purify itself with respect to the EC parameter in 2008-2009 and BOD parameter in 2013-2014. Moreover, the best simulation of the model was achieved for the pH parameter and the simulations for the BOD and EC parameters were the second and third, respectively.

The most important characteristics of building frames can be abbreviated in stiffness, strength and ductility. Moment frames have ductile behavior and low stiffness; Therefore, the main reason in using the lateral bracing systems is their considerable stiffness. Eccentric bracing systems are considered as ductile frames, while satisfying the required stiffness. The lateral stiffness of conventional eccentric configurations have been calculated previously. In this research, the lateral relative stiffness of eccentrically braced frame with dual vertical links (EBF-DVL) is calculated analytically. EBF-DVL has two parallel vertical links which are welded to the floor beam at the top and to one horizontal link at the bottom. In order to provide the required equations for obtaining the stiffness, the slope-deflection equations are used by considering the effects of shear deformations. The results show that EBF-DVL has a high relative stiffness and by adjusting the lengths of vertical and horizontal links, it is possible to achieve the stiffness even more than the stiffness of eccentric bracing with horizontal link between two diagonal braces. Although an increase in either the moment of inertia or shear area of the vertical link leads to an increase in the lateral stiffness of the system, the effective interval for increasing the moment of inertia of the vertical links is to be limited to approximately half of the column moment of inertia and the corresponding value for increasing the shear area is approximately 60% of the shear area of the column.

Bearing Concrete Wall (BCW) is one of the most applicable structural systems. In this paper, with the aim of evaluating bearing wall performance, nonlinear static analysis based on several assumptions drawing upon experimental research is used. To validate the nonlinear analysis method, the analytical and experimental results are compared. To evaluate the reduction factor and ductility level of BCW systems, a vast study on several models with different stories and several nonlinear analysis are performed. The results indicated that, the components of the boundary element have a limit effect on the models' ductility factor. Also, the reduction factors show acceptable values for building height up to 50 meters and the decreasing rate of this coefficient is increased in the higher elevations.

Many structures, such as dams, bridges and hydraulic structures suffer deterioration induced by alkali- aggregate reaction (AAR) which impairs the durability and safety of installations. Alkali-silica reaction (ASR) is an internal chemical reaction that appears in concrete between certain forms of siliceous aggregates and the alkaline pore solution in concrete. The result is a more or less crystallized silica- alkaline product which can exert pressures on the surrounding matrix. ASR induces concrete expansion and generally leads to loss of strength and cracking. The structural behavior of concrete which has been affected by ASR is difficult to model due to various random parameters that govern this chemical process. The aim of this paper is to investigate the effect of ASR on behavior of reinforced concrete beams using three methods. For this purpose, 100x150x1100-mm concrete beams were built in the laboratory and reinforced with different ratio of compression and tension bars. Then ASR and creep strains were modeled by reducing the elastic modulus of concrete and applying equivalent tension force. For the purposes of verifying the numerical methods involved, fourteen beams were conditioned in a suitable environment using similar dimensions and loading system. Experimental results on reactive concrete samples were simulated so as to test whether the model was capable of describing the behavior of affected reinforced concrete beams under service loads. The comparison reveals that finite element model had good compatibility with acquired test results.

As the volume of renewable water resources has been significantly decreased and developing new water resources are faced with serious limitations, there has been a change of emphasis in management practices from supply-sided to demand-sided approaches in most regions of the world. Water consumption management strategies seek to reduce water consumption and establish a reasonable and sustainable balance between water supply and demand. In this paper, a multi-attribute decision-making method and an algorithm is developed for selecting water consumption management strategies for water distribution networks. To demonstrate the applicability of suggested method, a case study is conducted in Tehran in which different water consumption management strategies are prioritized using Fuzzy Analytic Hierarchy Process (FAHP) and based on water and wastewater experts' judgments. Applied strategies are performing educational programs among water users, non-revenue water reduction, increasing water price and using water-saving appliances. Furthermore, decision criteria used in this study are costs, time of implementation, water user's satisfaction, the volume of non-revenue water and water-saving efficacy. To evaluate the impact of uncertainties lied in the model on final results, a sensitivity analysis is performed in terms of changes in the weight of decision-makers’ judgments and the shape of fuzzy membership functions. Finally, the non-revenue water reduction is gained the first rank among all water consumption management strategies. The results of this study show that in case of high degree of fuzzy uncertainties and dearth of sufficient quantitative data, the presented method can be employed as a robust decision-making tool by urban water managers.

In this paper, a finite element model is developed for the fully hydro-mechanical analysis of hydraulic fracturing in saturated porous media. The model is derived within the framework of generalized Biot theory. The fracture propagation is governed by a cohesive fracture model. The flow within the fracture zone is modeled considering the lubrication equation. In order to describe the fracture in the saturated porous media, momentum equation and mass balance equation with Darcy law are employed. The standard Galerkin method and Newmark scheme are used for discretization in space and time, respectively. Finally, the effects of permeability and rate of injection on the hydraulic fracture propagation are studied. It is observed that an increase in permeability leads to slower crack propagation. In addition, increasing flow rate leads to a faster crack propagation. When permeability increases by 3.3 times, CMOD and crack length decreases by 43.8% and 20%, respectively after 1 second and decreases by 29.4% and 15.9%, respectively after 6 seconds. In addition, when flow rate increases by 2, 3, and 4 times, the crack length increases by 30.5%, 55.9%, and 76.3% after one second.

The estimation of soil parameters in geotechnical practice is always an important step for design of geostructures. In order to control the stability and to perform a stress-deformation analysis of a geotechnical system, it is essential to know the in-situ stress state of the ground. The in-situ vertical stress can be calculated easily if the depth and the soil density are known. However, determination of the in-situ horizontal stress is a complicated task because it depends on several other soil characteristics, such as stress history and over consolidation ratio (OCR). This has always been one of the most challenging geotechnical problems. In the past, attempts have been made to find reliable methods to determine the coefficient of at-rest earth pressure by means of in-situ or laboratory tests. This is especially true for cohesionless soils, using in-situ test results such as pressuremeter test, blade test and cone penetration test (CPT) to name a few. In this study, the calibration chamber data on CPT tests performed at universities worldwide or well known institutes were gathered. Then using these series of reliable CPT calibration chamber test data and a system consisting of three types of neural networks, the coefficient of at rest pressure (K0) is predicted while it has good agreement with measured data. In this proposed system, a series of neural networks perform some tasks and finally by strategically combining the networks, the system will be able to predict parameter (K0) with reasonable accuracy. The proposed system uses self organizing map (SOM) for clustering data into training, testing and validating sets and probabilistic neural networks for classifying the sands and back propagation neural networks for conclusive function approximation. Details on the development of such a system are described in the present paper and finally results obtained by this system are compared to the available relations suggested by other researchers.

Newmark's sliding block method is commonly used for estimating earthquake-induced permanent displacement of earth slopes and embankments. Since this method is a simplified dynamic analysis procedure with acceptable accuracy, it has received considerable attention among the geotechnical practitioners. However, it has some shortcomings such as neglecting system response and sliding mass rotation. Hence, researchers have proposed modified procedure to enhance the realistic features of this method. The effect of sliding mass rotation, which sets the block in a gentler condition, was previously considered by continuous increment of yield acceleration. Since the sliding mass is three dimensional in reality, smaller permanent displacement is expected when the width of block is accounted for. In this paper, width of the rotating-sliding mass is taken into account in the coupled and decoupled solution of sliding block equations. The results show that the width of the slip zone is effective on the resulting displacements. With a constant slip length, whatever slip width is reduced, yield acceleration increases and consequently difference between the modified decoupled (or modified coupled) and decoupled (or coupled) increases.

Carbonate sands have being known as problematic soils in civil engineering and their strength is different from those of quartz sands. In this paper Triaxial consolidated-drained shear strength of a carbonate sand obtained from north beach of Oman sea is compared with Firoozkooh quartz sand. Energy concept is used for the analysis. Tests were performed in the same conditions such as particle size distribution, relative density and confining pressure on sands with different particles shapes. Tests results and analysis showed considerable differences between two sands regarding the shear strength and its components, soil volume changes, particle breakage potential and its effects on the shear strength, consumed energy for the particle crushing, dilation and particle crushing portion from the total internal friction angle of soils. At the end, it was found that there is a linear relation between the consumed energy for particle crushing from total applied energy to the soil specimen and particle breakage portion from the soil total internal friction angle. In the carbonate sand with high particle breakage ability a value of %14-31 and in the quartz sand maximum %10 of applied energy is consumed for particle breakage.

There are many structures subjected to impact and projectile penetration loading due to accidental, military and/or sabotage threats. Thus, assessment of behavior and vulnerability of materials, structural members and non-structural members is important to provide suitable materials having minimal vulnerability and better behavior. Ultra-high performance concrete reinforced by steel fibers has much better performance against these loads than ordinary concrete. The fiber specifications are the main parameters influencing the performance. This study mainly aims to find the effects of steel fiber density on impact behavior of ultra-high performance steel fiber reinforced concrete (UHPSFRC), which also considers economic aspects. Here, low velocity impact is studied by experiments, while high velocity impact is studied by numerical simulations. The simulations are verified by experimental results. Also, some tests are conducted to determine mechanical properties of concrete for the simulations. The effects of projectile diameter and specifications of steel fibers are investigated, too.

Study on single degree of freedom (SDOF) structures provided information on seismic demand for elastic and inelastic systems. But this information needs to be modified to become of direct use for design of real structures, which are mostly multi-degree of freedom (MDOF) systems, governed by several modes. According to the near fault ground motions have cause much damage in the vicinity of seismic sources, this paper evaluate the modification that must applied to strength reduction factors derived from simplified SDOF models in order to account for MDOF structures in near fault zones. This proposed by estimation the ratio of strength in MDOF systems that result by limiting maximum story ductility ratio to the strength corresponding to the same ground motion and same level of ductility in an equivalent SDOF system having a period equal to the fundamental period of the MDOF structures. Nonlinear dynamic time history analysis were carried out on four steel moment resisting frames with two distinct behavior of yield mechanism, undergoing five level of ductility ratio when subjected to 15 near fault ground motions with forward directivity effects. Modification factors spectra were computed as a function of period and number of stories and were compared to those of corresponding spectra for far fault ground motions. The required modification factor for inelastic MDOF systems, for near fault motions was shown to be dependent on target ductility ratio and the type of yield mechanism and to a lesser degree, period of vibration and number of stories. The result demonstrate that in the low level of ductility ratio, during the short period range, the modification factor given from near the fault ground motions is less than those from the far fault ground motions, and this is true during all period range as the level of ductility is increased. Finally, since the equivalent pulse of near fault ground motions have significant effect on structural response, modification factors were proposed as a function of the ratio of structural period to equivalent pulse period and ductility ratios.

In this study, a three-step screening process is presented for selection of consistent earthquake records in which number of suitable earthquakes is quickly screened and reduced from a few thousands to a handful number for practical use in the time history analysis. Records that remain at the end of this screening process are the most appropriate for the studied structures meaning that they considerably reduce the dispersion of structural responses.

Landfill leachate usually contains high concentrations of pollutions that are seriously harmful to the environment and human health. The main purpose of this study was removing organic pollution, ammonia, nitrate and total nitrogen in Isfahan composting facility leachate by horizontal constructed wetland systems. A pilot-scale study was conducted on subsurface flow constructed wetland systems operated in horizontal mode (HFCWs). Two horizontal systems with different plants were constructed, one planted with Vetiver and the other one without plant as a control. They were operated identically at a flow rate of 27 L/day with a 5 day hydraulic retention time. The average removal efficiencies for control and experiment were BOD5, 9% and 30%; COD, 19 and 34%; TN, 37 and 50%; Ammonium, 8 and 26%; nitrate 33 and 40% respectively. Due to high concentration of pollutants (the mean leachate concentrations of COD, BOD5, TSS, NH4+ -N, NO3- -N, TN were 104514.9, 69200.0, 8478.3, 317.5, 4633.2 and 1500 mg/L, respectively) the subsurface flow constructed wetland systems with Vetiver plant is a suitable solution for leachate treatment.

One of the tunneling methods is cut and cover method, in which the excavation starts from the ground surface and deep in the ground, then a concrete box is made as a tunnel. Thus in this method, the cross section of the tunnel is not circular but rectangular. The aim of this paper is seismic analysis of rectangular tunnels. For a special accelerogram, tunnel geometry, depth of overburden and ground conditions are the three main factors affecting the dynamic behavior of the tunnels. By numerical methods and by assuming the plane strain condition, models of this type of tunnels were analyzed. According to the results, the maximum internal forces that are generated in the tunnel lining and the stress concentration are at the corners of the cross section of rectangular tunnel. In seismic mode, the internal forces of concrete lining are several times of static mode. In this situation, the ground surface settlement profiles are asymmetric and the settlement is greater than the static mode. In tunnels with large width, in 2D cases, if a column is placed in the middle of span, the ground settlement, bending moment and shear forces is decreased in comparison with 1 span tunnel with the same dimension.

In this study, to prevent pavement destruction and enhance the quality level, restoration and improvement of roads are carried out. The operational costs include fuel consumption, travel time, accidents, tires' wear and tear and so on. In the economic evaluation, reduction of such costs due to the improvement of the quality level of roads is considered as the project's benefits. In this paper, the benefits gained through roads’ improvement (i.e. costs reduction) are compared with another one and then the priority of each one in the economic evaluation is determined using the results found from the B/C and Net Present Value (NPV) methods. For this purpose, the required model has been prepared using software written with the Visual Basic Programming Language and its output has been presented as the results of a case study carried out in Fasa-Zahedshahr main road. The evaluation of each element in the economic viability of roads' improvement projects is one of the specific features of the model presented in this paper.

In transportation literature, in order to relate supply (street network) and demand (traffic zone) sides, definition of centroids and connectors is essential. Centroids and their connector(s), despite their importance, are usually selected based on the engineering judgment and experience of experts. The main purpose of this paper is to investigate the effect of centroid connection pattern on static traffic assignment. Applying user equilibrium approach, different scenarios of connector patterns (from centroids to all possible connector nodes) are implemented and evaluated for the real-size city of Qazvin with a population of about 0.4 million and 113 traffic zones. Results of 6 different scenarios show that different patterns and number of connectors can result in about 10 percent change in average link volumes and about 20 percent change in total vehicle-kilometer. Results also indicate that due to the high number of connection patterns, it is difficult to specify the optimum pattern; this difficulty indicates the effects of connector pattern on traffic assignment results.

The construction industry is the largest industry in the world. It is more of a service than a manufacturing industry. The success of construction projects is a fundamental issue for most governments, users and communities. Multi criteria decision making is an approach that can be used to deal complex problems. In this paper, to treat multi criteria decision making problems in uncertain condition a model based on grey theory-including grey relational analysis and grey numbers is proposed. The scope of research about gray theory and multiple criteria decision making is relatively new field, so in this study we used the integration of Taguchi and Taxonomy with gray theory to forecasting the success of construction projects. Using Taguchi method and gray theory, weight of each criterion was determined. Finally, using Taxonomy and gray theory the success of thirteen construction projects was forecasted. Findings of this study provide clear understanding of construction project and could potentially enhance existing knowledge of construction project success.