AMIRKABIR JOURNAL OF CIVIL ENGINEERING (AMIRKABIR)
Year:2017 | Volume:49 | Issue:3 |Papers Count:19

Since the nonlinear static procedure (NSP) is one of the most prevalent and useful methods for the Performance-Based-Design (PBD) of buildings, it is considered by several researchers during past decades, so that the capability assessment of NSP in comparison with the nonlinear dynamic procedure (NDP) and improving the NSP accuracy are the basic subject of previous studies. Therefore, in this paper several load patterns used in conventional and advanced NSP such as displacement-based adaptive NSP (DAP) and multi-mode interaction adaptive NSP (APAM) are evaluated and the results are compared with NDP responses. Based on modeling assumptions the results demonstrate that the CPA with elastic load patterns cannot predict displacement and story drift for high-rise models. The maximum differences between CPA and APA is almost 7.9%. In addition, the DAP adaptive method presents an almost accurate prediction of seismic demands and it can consider the effect of higher modes on inelastic responses. However, although the APAM adaptive method considers the interaction between modes, but it cannot predict the interstory drift angle at lower stories accurately. This behavior is intensified while the height of buildings increases.

Despite many advantages of steel plate shear wall (SPSW) system, such as lightness, high stiffness, ductility, and fast implementation, this system is not as pervasive as other lateral load resisting systems such as bracing or reinforced concrete shear walls. To solve this problem, numerical parametric studies of system with consideration of seismic uncertainties which needs accurate non-linear models including behavioral deterioration of system is necessary. So, in this paper, besides studying existing macroscopic modeling of steel plate shear walls, a new model is introduced which is modified version of Strip model’s application with focusing on stress-strain curve proposed by one of researchers. After suggesting essential adjustments in this model and showing their necessities with emphasizing on experimental and finite element results, correctness of new model by doing several finite element analysis in different models with various plate thickness and length to height ratio is verified and proper values for parameters is proposed.

One aspect of Performance Based Earthquake Engineering (PBEE) is to allow comparison between different designs and retrofit solutions using estimation of collapse probability. To investigate this process, case study was performed on the weak RC frame that has been retrofitted with two different methods, e.g., brace and cylindrical friction damper. Models of case studies were defined in OpenSees software. Then 15 ground motions were selected and Incremental Dynamic Analysis (IDA) was conducted on models. The performances of buildings were evaluated by using a probabilistic analysis. The results show that the retrofit methods reduce the probability of exceeding of the limit states 1IO and 2CP. However, considering site-specific seismic hazard curve in which the reduction of structure period was included, the different results were obtained. In this study, although the damage probabilities for a specific hazard level for both retrofitting schemes were reduced, the collapse probability of the structure retrofitted with braces increased in comparison with the initial structure.

Frictional dampers are widely used in civil engineering structures as means of passive controler in order to dissipate the energy created by earthquake. One of the frictional dampers that have been recently introduced is called Cylindrical Frictional Damper (CFD). Several researches in the area of the energy absorption capacity of the CFD, meaning hysteretic behavior, have been performed by the authors.In this research, response modification factor of steel moment resisting frames equipped with Cylindrical Frictional Dampers is evaluated. Utilizing this factor, the standard seismic design code procedure can be applied to the frames equipped with CFDs. In order to achieve this task, Static pushover analysis, nonlinear incremental dynamic analysis and linear dynamic analysis of various structures have been performed.The results show that the response modification factor of steel frames equipped with frictional dampers is greater than that of conventional steel frames which in turns reduce the seismic forces and leads to a lighter structure. Finally, values of 11 and 16 have been suggested for ultimate limit state and allowable stress design methods respectively.

In the present study, the hydraulic capability of piano key weir (PKW) was investigated utilizing the physical model. Because of decrease in water surface at dry seasons, these structure increases upstream head water. In addition, they have an appropriate discharge coefficient at the flood. To achieve the purposes of this research, two models of PKW were built with the ratio of height to a cycle width (P/Wu) equal to 1.33 (model 1) and 0.5 (model 2). The positive and negative slopes of parapet walls were considered with slopes 3, 5.5 and 8o rather than direction of flow. The results showed that model 2 has a more capability at the increased water surface in the low discharges. Moreover, model 1 has a suitable discharge coefficient at the higher discharge. Results obtained from analysis showed that H/R parameters have a significantly influence on the discharge coefficient when this weir is not submersible or there is a low head after fully submergence. The correlation of discharge coefficient equation after and before fully submergence of weir was 0.976 and 0.973, respectively.

Rubber dams are flexible cylindrical structures, attached to a rigid base, and are inflated with air and/or water. Most of the rubber dams are permanently inflated, however, they have the advantages of deflating and being flat, when they are not needed, and then inflated in a short period of time when they are required. Large deformation of the membrane due to the internal and external loads, makes the governing equations of such problem to be non-linear and complicated. In the present study, three-dimensional behavior of the rubber dams with respect to the boundary conditions of dam and flow was simulated numerically. Dam geometry and flow hydraulics were modeled, using ANSYS software, CFX and transient structural in workbench environment, simultaneously. Flow hydraulic characteristics and deformation of the dam are obtained, considering fluid-structure interaction. Water free-surface was obtained, applying two-phase air-water flow interface. SST turbulence model in CFX was employed for modelling the separation of flow, downstream of the inflatable dams. Due to the flexibility of the structure, large deformation theory was used in the transient structural solution. Consequently, different features of the flow field, including flow streamlines, velocity and pressure profiles are obtained and compared with those of the rigid circular-crested weirs. Results indicated that the flow hydraulic characteristics over the equilibrium shape of the rubber dams is analogous to those of the rigid circular-crested weirs.

Every year, many structures are being constructed on fined-grained soils. Drainage of these soils is necessary for constructing new or maintaining existing structures. Considering low drainage capacity of these soils, it is required to use appropriate methods. Electrokinetic is one of these methods, which can be used for increasing drainage in fine-grained soils effectively. In this method, two electrodes are placed in the soil and then electrical current is established in the electrodes using a power source. As a result, charged particles move to the electrodes with opposite charge. This mechanism causes rapidly drainage of the soil. In this research, soil’s drainage investigated using electrokinetic method. The charged particles moving, was investigated within the soil using mathematical equations and soil drainage was tested in a laboratory reservoir with dimension of 180×60×60 cm3 serving electrokinetic method. This was made by applying different voltage levels in the soil and acidic environment. Results showed that soil bearing capacity, drainage and consolidation were increased in the Saturated fine soil by applying electrokinetic method.

Ground response curve is a component of convergence-confinement method in rock support interaction analysis which is used for determining the displacement around tunnels excavated by New Austrian Tunneling Method. Analytical solution of the ground response curve is based on the assumption of isotropic in-situ stress field and is applicable for deep tunnels. Today, urban tunnels mainly excavated in shallow levels and often under anisotropic in-situ stress field. In this paper, for 2D models with geometry and specific environmental characteristics, the response curves for different depths and different in-situ stress ratios, are determined in two ways: 1) By analytical solution and using anisotropic stress field equivalent to an isotropic stress field. 2) Numerical solution. The results of these analyzes were compared with together and range of application of analytical solution of the ground response curve is determined. Based on the results, tunnel wall displacement is mainly influenced by the ratio of the initial in-situ stresses in comparison of tunnel depth. The results showed that crown and floor numerical displacements deviate more from analytical solution than the wall displacement. The only displacement that can be accurately obtained from the analytical solution for the shallow tunnel is the displacement of the tunnel wall under isotropic stress. In the case of isotropic stress field, the results given by the analytical solution agree with the numerical ones at depths higher than 14 times radius of the tunnel. The difference between numerical and analytical solutions becomes higher while increasing the initial in-situ stress ratio, even for deep tunnels.

Dispersive soils are vulnerable to erosion by water. In soil layers where clays are saturated with sodium ions soil can disintegrate into fine particles and wash away. In such soils, the clay particles lose adhesion in the presence of water and consequently, soil’s colloidal particles easily move away from each other. In order to deal with the adverse effects of this kind of soils, three major options are available: avoiding construction on such soils, replacing dispersive soil and using various additives to improve and stabilize the soil. In most cases, application of the first two methods is infeasible and cost effective but adding various additives is beneficial to overcome the encountered problems. In this study, the effect of nanoclays on dispersive soils of the Minab wastewater treatment plant has been investigated by using special tests for the determination of the soil dispersion. The results of the experiments indicated that, adding a low percent of nanoclays to the soil can improve the level of dispersion a little but adding excessive amounts of nanoclay increases the dispersivity potential.

The rock materials surrounding the underground excavations typically demonstrate nonlinear mechanical response under high stress states. The dominant causes of irreversible behavior are plastic flow and damage process. The plastic flow is controlled by the presence of local shear stresses which cause dislocation to some preferential elements due to existing defects. During this process, the net number of bonds remains practically unchanged. The main cause of irreversible changes in quasi-brittle materials such as rock is the damage process occurring within the material.In this paper, a coupled logarithmic damage and plastic model was used to simulate irreversible deformations and stiffness degradation of rock materials under loading. In this model, damage evolution and plastic flow rules were formulated in the framework of irreversible thermodynamics principles. To take into account the stiffness degradation and softening in post-peak region, logarithmic damage variable was implemented. Also, a plastic model with Drucker-Pruger yield function was used to model plastic strains. Then, an algorithm was proposed to calculate the numerical steps based on the proposed coupled plastic and damage constitutive model. The developed model was programmed in VC++ environment. Then, it was used as a separate and new constitutive model in DEM environment code (UDEC). Finally, the experimental oolitic limestone rock behavior was simulated based on the developed model. The irreversible strains, softening and stiffness degradation were reproduced in the numerical results. Furthermore, the confinement pressure dependency of rock behavior was simulated in according to experimental observations.

Drying of soils and shrinkage cracks is a crucial issue in geotechnical and geo-environmental engineering. Better understanding of the soil cracking process is essential in analyzing desiccation effects on buildings integrity. In this study, cracking behavior of the clay due to desiccation investigated experimentally at different temperatures on thin clay layer. Experimental tests carried out on the clay slurry saturated with water content about 60%, (1.5 times of its liquid limit). In this study, the clay supplied from clay mine in Abadeh, a city in Fars province in Iran.Experimental results showed that the critical water content, which corresponds to the initiation of desiccation crack increases when the temperature rises. In addition, the number of produced cracks decreases by increasing the temperature. This phenomenon can be attributed to the reduction of water surface tension force or voids central tendency in soil mass. Also, the width of crack opening decreases by increasing the temperature.

In the current study, the response surface methodology has been used for designing of the experiments. Considering the conventional soil-compaction method, the main factors investigated include cement and w/c contents. The upper and lower levels of the factors of cement and w/c content were 308-392 kg/m3 and 0.34-0.39, respectively. The dry specific weighs, compressive strengths, permeable voids, and capillary absorption coefficients were determined according to the ASTM D 1557, ASTM C39, ASTM C642 and ASTM C1585 at ages up to 180 days, respectively.Using the statistical analyses, the prediction models and contours of the durability characteristic and 28 day compressive strength were derived. The analysis of variance (ANOVA) was also performed on the results to estimate the significance of the factors. It could be concluded that the terms of the cement content, w/c and their interaction significantly influenced the responses of the compressive strength, dry specific weight, water absorption and permeable voids. The results also indicated that by obtaining an optimum level of dry density one could reach the lowest level of permeable voids and water absorption into the concrete. This is achieved by adjusting the interaction of cement content and w/c content. However, no meaningful correlation was found between the dry density and capillary absorption coefficient. This indicates that the tortuously and continuously of microstructure may be independent from the dry density. However, similar contour trends were obtained for the dry density and capillary absorption coefficient.

This article intends to investigate the effects of site-to-fault distance on the earthquake intensity measure (basic design acceleration, A, and response spectra, Sa) where is not taken into account in Iran standard No. 2800. Regarding that the relation between site-to-fault distance and the design-base acceleration (A) parameter (or Sa) in currently used attenuation relations is highly non-linear, thus assigning the same value of such parameters to different site-distances in big cities, particularly at near fault sites, seems to be quite challengeable. In order to make this problem clear, forty series of site specific seismic hazard analysis in the two cities, Ahwaz and Kerman, are performed over ten sites having four different site-soil conditions and the “A” parameters are calculated and discussed. The results of this study showed that the site-to-fault distance can significantly influence upon the site’s intensity measure (A) parameter (about several times as distance become smaller) and have significant differences with those of the Standard No. 2800. This problem also highly affects the effectiveness of “N” parameter presented in thee 2800 standard as the representative of near fault directivity parameter.

ABSTRACT: Construction industry has been one of the most energy and material consuming industries in recent years. Environmental assessment of construction methods that includes energy consumption and emission release are important for implementation of improvement option to life cycle of construction. Despite the significant effect of selecting appropriate method on reducing amount of material, energy and emission, the studies often do not consider or incompletely model the environmental impact. The research has studied the energy consumption and carbon emission of two conventional and industrial methods of construction for concrete buildings: in-situ concrete and pre-cast concrete structural methods. This study has figured out how implementing precast concrete structure affects on environmental sustainability of the construction process. In addition the features of construction methods that can help the designer to achieve more sustainability have been assessed. The model developed to use the life cycle assessment (LCA) as a comprehensive sustainability methodology to quantify the environmental impact of several phases of building construction from extraction of raw materials to end of construction phase (cradle to gate). To investigate the environmental impact of each construction method two designed concrete structures with in-situ and precast elements modeled in building information modeling (BIM) and linked to the designed spread sheet.Extracted results indicated using the high strength concrete for precast concrete structure, just in construction periods, is an effective way that reduces energy consumption of process and decreases carbon dioxide but in manufacturing process precast concrete consumes more energy and emits more carbon to environment. In Recognition of different features of energy consumption, material use and emission release of proposed method of construction, assist the project team in better decision making from environmental impact point of view and enable designers to provide recommendations toward achieving sustainable construction methods.

High electrical conductivity of metals such as gold, silver and platinum extensively increased the use of these metals in electronics. In addition to the platinum group metals, large amounts of copper, tin and lead are present in E-Waste. For an effective recovery of precious metals, and also from an economic perspective, it is essential to recover the mentioned metals. In this paper, separation of copper from tin and lead by solvent extraction was studied. Fluoroboric acid and LIX984N was used as leachant and organic solvent, respectively. Effective factors such as the concentration of organic solvent, pH, temperature and concentration of copper on the extraction of copper were investigated. The treatment of leach liquor for solvent extraction of copper with LIX984N showed that 20% LIX984N in kerosene, a 30 min period of equilibrium, and a pH of 3 were sufficient for the extraction of Cu (II) and 99.99% copper can be recovered from the leached solution.

ABSTRACT: Modal split models, as the third step in the four-step transportation modeling framework, determine the share of different travel modes. Choice models as probability models have been used in recent decades and have faced significant progress. The mixed logit model has been known for many years, but has only become fully applicable since the advent of computer and simulation technology. This model can approximate various random utility models according to the accuracy required, through adopting appropriate distributions for attributes coefficients in the utility function. The purpose of this research is to present a mixed logit model structure for mode choice, in order to describe the taste variation among individuals and the source of the variation in response to the various attributes that influence the mode choice. The required data is from Mashhad O-D survey in 1387 and model calibration is executed in Biogeme software. Results of mixed logit model indicates among passengers a taste variation in choosing between a personal car and motorcycle, based on car and motorcycle ownership. The source of this taste variation is modeled and captured through random coefficient analysis. Finally, it is shown that mixed logit models are superior to multinomial logit model with a confidence level of 99 percent. The superiority is however small, partly due to the inadequacy of the aggregate data.

Nowadays; cycling is considered as a solution to address traffic congestion problem and its consequences, especially air pollution. However, this mode requires suitable facilities including bicycle paths. This paper discusses prioritizing of five bicycle paths in district 1 of the city of Shiraz, Iran, regarding “Safety”, “Appeal” and “Mobility” criteria. The safety criterion is subcategorized into five factors as follows: number of street crossed by the path (i.e., intersections), slope of the path, heavy vehicles in the path, speed limit of the path and number of direction offsets along the path. The criterion of appeal of the path is subcategorized into two factors as follows: attractiveness of the path sides and the diversity of land uses along the path and at last, the mobility of path is subcategorized into number of public transit stations along the path, residents alongside the path and educational centers along the path. Based on the Analytical Hierarchy Process (AHP), the weights of criteria and factors demonstrate that according to transportation experts’ opinions, the most important factors were slope and speed limit of a path. Furthermore, the application of the method in one of the districts of the city of Shiraz has been conducted.

Considering the population growth and rapidly housing demands, it is inevitable to adopt industrial building systems for the purpose of raising the quality of industrialized building construction. Construction industrialization is an important factor in increasing production and striking the right balance between supply and demand in the market. There are multiple methods for industrialized building construction, the most common of which is the prefabrication concrete industry. An attempt has been made in this study to put forward the appropriate method for understanding the current status of this industry in developing countries and adapting it with economic, social and environmental criteria of sustainable development and to present suitable management methods for choosing and piloting the route toward sustainable development. The results suggested that when compared to the cast in place concrete, prefabricated concrete is of higher quality according to the sustainable development criteria. The results indicated that the order of desirability of prefabricated concrete in terms of different aspects of sustainable development is as follows: environmentally, socially and economically. According to the sustainable development criteria, prefabricated concrete could provide more opportunities to communication development. Moreover, there are more opportunities than threats in the industry of prefabricated construction. In this article, appropriate strategies were formulated by means of SWOT analysis for the purpose of developing and improving and expanding the prefabricated concrete industry.