مجله مهندسی عمران شریف
سال سی و چهارم شماره 3 (پاییز 1397)

Nowadays, ring footings are used widely in the civil engineering projects especially in structures with centric geometry. Among them, Telecommunication towers, water or oil tanks, bridge piers, and on shore structures are some examples. In addition to vertical or gravitational loadings, ring footings are implied by moments imposed by lateral loadings and hence, the ring footings are loaded by eccentric loads. In the literature review of bearing capacity of ring footings, there are many researches in which the vertical bearing capacity of such footings is studied and investigated in numerical, analytical and experimental categories. However, few researches exist for eccentric load of such footings. In the present paper, the Ngamma factor, which is one of the bearing capacity factors is determined by using numerical simulations for the ring footings rested on granular soils. Due to the essence of the problem, threedimensional analysis is applied using nite dierence method. Since a bearing capacity problem was only a function of plastic parameters of the soil including internal soil friction angle and cohesion, the so-called linear elastic- perfectly plastic Mohr-Coulomb model was used in the simulations. Associated ow rule was assumed in the simulations because the variation of soil dilatancy angle was aimed to be ignored and that a rule could be found among the results. These Interface elements were considered in the simulations because the partial uplift of the footing was aimed to be modeled under eccentric loads. At the start of modeling, the numerical modeling was veri ed by the virtue of numerical simulation of a centrifugal modeling experiment. The comparison of results expresses good agreements between the simulations and experiment. In the following steps, a number of numerical models was analyzed by changing soil friction angle as well as the load eccentricity. Finally, attempts were made to nd a mathematical expression for the determination of Ngamma factor de ned as a function of the ratio of load eccentricity to the footing diameter, ring radii ratio and soil friction angle.

Determination of particulate matter (PM) levels, as one of the most important pollutants, requires dense monitoring stations network in megacities. Extending monitoring network, especially in regions with sparse monitoring sites, needs a signi cant economic source and may be rejected due to feasibility considerations. During the last decade, remotely sensed atmospheric data are known as a cost- eective way with appropriate and comprehensive spatial and temporal coverage to estimate ground-based PM concentrations. In this regard, aerosol optical depth (AOD), which represents the amount of aerosol in the column of atmosphere, was used as an independent satellite derived product to predict PM values in monitoring stations. Also, meteorological variables can be used as auxiliary parameters to improve model performance during validation period. In this study, a statistical model was developed using AOD along with eective meteorological parameters to estimate ground level of PM10 (particulate matters with aerodynamic diameter less than 10m). AOD was extracted from 6 collections 6 of Moderate Resolution Imaging Spectroradiometer (MODIS) by 3 km spatial resolution over Tehran during Marchof 2009. Meteorological variables can specify vertical distributions in atmospheric November column and optical properties of PM, and they are capable to improve AOD and PMs relationship. So, to improve the model performance, model it is developed by meteorological parameters. The meteorological parameters were collected from synoptic stations in Tehran, every 3 hours, during the study period. The linear mixed eect model was tted into all independent variables to examine their in uence on PM10 concentrations. The results showed that the proposed model could explain concentration accurately with relative high correlation coecient of the variation of daily PM10 ( R2 = 0.77 ). Statistical model performance was acceptable during cross validation with 0.88 (R2 = 0.61 ). The model had the best performance during correlation coe cient of 0.78 autumn with root mean square error (RMSE) of 15:4g/m3, while the worst one occurred in summer with RMSE of 19:3g/m3.

Today, developed and developing countries try to plan the economic, industrial, and urban developments based on environmental protection due to air pollution and its consequences as a global issue. Air pollution as a potential and permanent risk has gradually threatened human health, especially in large cities. Environmental requirements depend highly on management parameters and play a very important role in the quality of life of citizens. In this study, a series of dose-response functions were applied to analyze the adult mortality due to chronic diseases, the reduced life expectancy as a result of acute and chronic diseases, and the resulting risks for ozone emissions in the city of Mashhad. There are a total of 12 stations in Mashhad which carry out monitoring, measuring, and indexing of the 5 types of pollutants, including CO, NO2, O3, PM2:5, and SO2. Information monitored with minimal error, which owned by the year 1393, has been analyzed in this study. One of the main objectives in the eld of analysis and monitoring of air pollution is the determination of dominant or responsible pollutant as in uential factors. The prioritizing and comparison of air pollutants can oer important contributions as well as create a management view in the allocation of funds in a speci ed time period. The major air pollutants were prioritized from the point of view of risk using AHP and ELECTRE methods. The results show a maximum amount of 20.8% in adult mortality and a maximum amount of 8.22 years for men and 8.51 years for women in reduced life expectancy due to chronic diseases which are on the verge of a crisis situation. Statistical investigation conducted over a period of one year (1393) in the city of Mashhad suggests that the main cause of air pollution is particulate matter less than 2.5 microns (PM2:5). The results of this research can be used to control pollutants and impose special regulations and restrictions on each contaminant.

During the recent past decade, semi-supported steel shearwalls (SSSW) have been introduced as an alternative tothe traditional type of steel plate shear walls (SPSW).In this system, the shear wall does not connect directlyto the main columns of the building frame, instead, itis connected to a pair of secondary columns that do notcarry gravity loads. However, a SSSW system, comparedto the corresponding SPSW system in which thein ll plate is connected to the main frame columns, has alower span width (or lower in ll plate width) and, thus,lower strength, stiness,energy dissipation capability.To oset these eects, one eective,practical approachis the use of ber-reinforced-polymers (GFRPs)for strengthening the steel in ll plate. GFRP laminatescan be easily attached to one or both sides of the in llplates by the use of adhesive. In this paper, the behaviorof semi-supported steel shear walls reinforced byglass- ber-reinforced-polymers (GFRPs) is studied usingthe nite-element method,compared with thecorresponding systems without the reinforcement. Anumber of semi-supported steel shear walls with differentplate aspect ratios, plate thicknesses, secondarycolumn pro les,with,without opening of varioussizes is considered for this research. Both pushoverand cyclic analyses are performed. The adequacy ofthe nite-element modeling approach for representingthe pushover,cyclic responses of SPSWs is veri edthrough comparisons with experimental results. Resultsshow that the use of GFRP laminates, especially for thesystem with thinner in ll plate thickness, can signi -cantly increase the system strength, initial stiness, andenergy dissipation, while it partially decreases the systemductility. In turn, the improvement of the systemstrength,energy dissipation capability is mainly dueto the improvement of the SSSW in ll plate behavior. Infact, the use of GFRP laminates does not aect much thehysteresis,pushover behavior of the SSSW frames.

Concrete-faced rock ll dams (CFRDs) have been widely used for multi-purposes over the world. The construction of CFRD involves placing the rock ll in nite thickness layers as a dam body material, and compacting them to reach desired height. A reinforced concrete slab is then constructed at the upstream face of the dam. The concrete face will transfer the water pressure imposed by reservoir to the rock ll and nally to the dam foundation. During impounding of CFRDs reservoir, the upstream concrete face undergoes deformations, resulting in the development of compressive and tensile stresses in the impermeable face. Where, generated stresses exceed allowable values, some cracks would develop in the face and cause de ciencies in the performance of CFRD as a water barrier structure. Regarding the fact that the dam body deformation as a result of reservoir imposed pressure, has a direct eect on concrete face deformation, adopting a suitable constitutive model to simulate rock ll material behaviour, is of particular concern in predicting deformation and developed stresses in the concrete-face of CFRDs. With regard to the previous works on the behavior of rock ll material using large scale test equipments, the behavior of rock ll is found to be non-linear, inelastic and pressure dependent which clari es the signi cance of adoption of a convenient model as dam body material. In this paper, to evaluate the capability of dierent models to predict the deformation of dam body material and subsequence eect on upstream face, two elasto-plastic constitutive models have been selected and calibrated using triaxial test results. After selection of more proper model based on comparison by measured data in Da'ao dam, the performance assessment of concrete-face in terms of maximum deformation and developed in-slope direction strains, under dierent conditions was continued. Two-dimensional analyses wereconducted employing Finite Element Analysis (FEA) software, ABAQUS. This software has the ability of simulating multi-step analysis as applied for modeling of dam body in multi layers, placing the concrete face and applying water pressure of reservoir during impoundment, in this study. The analyses results, revealed the importance of rock ll material behavior in the performance of concrete-face, in addition to the remarkable role of dam height and the friction properties of face-rock ll interface.

Steel shear wall can be reinforced with concrete layer or steel stieners. Steel shear wall without stieners is named special steel shear wall. Capacity of special steel shear walls before buckling is insigni cant because of thin plate or being unreinforced. Several studies have been done on steel shear walls, but because of the confusion that exists in most design codes such as our country code, it is not provided. To eliminate some of the confusion, in this paper focused on the behavior of special steel shear walls. This study, a 10-storey building was designed with special steel shear wall. The upper story of the structure was examined. The models are one span and one story whose length of span (inside into columns) and a height of story (the inside of the beams) are 3 m. Beams and columns are IPB280 and thickness of web plate is 2 mm. Finite-element modeling, boundary conditions, and loading procedures were validated by comparing published test results with the corresponding analysis results. Two single stories tested by Sabouri-Ghomi et al. and Valizadeh et al. were modeled using the nite-element program. The material properties reported by the original researchers were used in analyses of nite element models. The results show that there is little dierence between the experimental and nite element results. One of the problems of steel wall with opening is causing stress concentration at the corners. Corners are the rst place for cracking. One of the solutions that has been studied in this paper is creating a curvature in corner. In addition, eect of opening position on the period and buckling force and wall resistance is studied. The results indicated that opening on the wall increase time period. Corner opening increases period more than central opening does. Not only opening on the wall decrease buckling force, but also decrease wall resistance. If opening is closer to the wall center, the resistance of steel shear wall will be reduced further.

In the past decades, the use of steel plate shear wallsystems is on the rise in new,existing buildings toresist against lateral forces. Dual steel shear wall system,has many advantages in comparison with the conventionallateral load systems. A four story frame is selectedin 4-storey building with a height of 3.5 meters peroor. This building loading is according to 2800 standardand seismic design by AISC360-10 cod,AISCDesign Guide 20. To achieve the full range of structuralresponse under earthquake in incremental dynamic analysis,Record intensity is applied to the structure to increasestep by step. For this purpose, it is necessary toselect the parameters as seismic intensity measure (IM)that can be linked by a scaling factor to the originalrecords. Three four story frame models with dierentdynamic characteristics are subjected to an ensemble of20 far- eld earthquake ground motion records with amagnitude of 6 to 5.7 on the soil type II. This articleis studied based on 25 candidate intensity measures formodels in dierent dynamic characteristics. Accordinglytwo characteristics of eciency,suciency were determinedusing regression analysis. Engineering demandparameters, which appropriately characterize the seismicresponse of the dual steel shear wall system,itsrelated damage, are selected. Dierent proposed IMsare investigated,classi ed based on their eciencyand suciency in predicting engineering demand parameters.The optimal IMs for estimating dual steel shearwall system response due to seismic excitation are identi- ed based on both eciency,suciency. The resultsshow that the appropriate intensity measure is dependenton the dynamic characteristics of structures. Forselecting the models with short period, peak ground velocityis the optimal IMs based on both eciency andsuciency, for models with average,big period, theoptimal IM is PGV,PGA.

The skirted foundations can be considered to be as new foundation options of shallow foundations including oil and gas storage tanks, wind turbines, oil drilling platforms, and also pier and deep foundations. Skirted foundations are steel or concrete foundations, which have a top raft and a relatively thin plate beneath the periphery, the so-called skirt. The skirts penetrate into the soil beneath foundation and form an enclosure in which soil is extremely con ned. The skirts and con ned soil behave as a unit to shift loads to the soil at the level of skirt tip. The bene t of skirted foundations over conventional foundations lies in their ease and short time of installations. To study the skirted foundations behavior and comparison with common shallow foundations in terms of the bearing capacity and settlement, laboratory tests were carried out on circular skirted foundation resting on sand layer using physical modeling. In this study, parameters such as ratio of skirt depth to foundation diameter, foundation size, the relative density of sand, and roughness of skirt surface were investigated. The test results showed the overall improvement of skirted foundations performance compared to surface foundations. The enhancement in the bearing capacity as well as reduction in the settlement of shallow foundation increases with increasing skirt depth and decreasing relative density of sand. Bearing capacity ratio of skirted foundations to surface foundations increased about 2.3 to 5 times. In addition, the settlement value of skirted foundation decreased up to 8% of that a surface foundation. In this paper, based on the obtained results, charts are presented to estimate bearing capacity enhancement and settlement reduction in terms of sand relative density, skirt depth to foundation diameter ratio and roughness. Skirted foundations resting on loose sand are more bene cial than those resting on medium and dense sand.

Reinforced concrete structures are strengthened in differentways. Near surface method (NSM),FRP con- nements are some of these ways. Studies show thatthe use of FRP for the con nement of columns increasesboth the load carrying capacity,ductility.Former studies in the eld of using FRP bars by applyingNSM method show that these bars increase thecolumns exural capacity. Despite increasing bendingcapacity by NSM-FRP bars, this method of strengtheningleads to decreasing ductility,energy dissipationcapacity of the columns. Besides the aforementionedshortcomings of this method, the lack of completeusage of load-carrying capacity of FRP bar is anotherde ciency of the aforementioned method in whichthis de ciency is removed by compounding this methodwith CFRP con nement. In the experimental part ofthe study, ve specimens of square reinforced concretecolumn strengthened by the methods of NSM-GFRPand NSM-GFRP in combination with CFRP con nement,the eect of concrete covering on the load-bearingcapacity, initial stiness, ductility,energy dissipationcapacity were assessed. Also, hysteresis curves andLoad-versus-drift ratio envelope curves were comparedwith each other. The specimens, under cyclic uniaxialexure with constant axial load, were tested untilfailure. The results show that the use of both strengtheningmethods increases the columns carrying capacity.However, the NSM-GFRP method decreases energy dissipationcapacity,ductility of the columns. Contraryto this method, the CFRP con nements in combinationwith the NSM-GFRP would increase the ductility andenergy dissipation capacity, indicating that this is oneof the useful methods for strengthening of the structure.Also, the results show that with the increase of the concretecover from 20 to 40 mm, load-bearing capacity,ductility,energy dissipation capacity would be reducedin both strengthening methods. With the increaseof concrete cover from 20 mm to 40 mm, carrying capacity,ductility,energy dissipation capacities of 10,3,18% for specimens strengthened by NSM-GFRPmethod,of 25, 40, 33 % for specimens strengthenedwith the combination method of NSM-GFRP,CFRPcon nement would reduce, respectively. Thus, the eectof concrete cover on combinatory reinforcing method ishigher.

Due to a huge increase in world energy consumption, the limited traditional fossil energy resources, and increased environmental concerns, a requirement for alternative energy sources has been paid great attention in recent years. Biodiesel is known as a nontoxic, renewable and environmental-friendly biodegradable fuel that is free from sulfur and aromatic compounds. The biodiesel production by transesteri cation of vegetable oils has the potential to solve the above problems and concerns. Nanocatalysts are considered as important material in chemical processes, energy production and energy savings, and prevent environmental pollution. In this study, the characteristics and performance of TiO2 nanoparticles (TNPs) and one commonly used catalyst for alkaline-catalyzed transesteri cation, i.e., sodium hydroxide, were evaluated using waste olive oil. The present method aords nontoxic and non-corrosive medium, high yield of biodiesel, clean reaction and simple experimental and isolation procedures. The catalyst can be recycled by simple ltration and reused without any signi cant reduction in its activity. The process variables that in- uence the transesteri cation of triglycerides, such as volume ratio of methanol to waste olive oil, type and loading of catalyst, reaction time and reaction temperature, were investigated. High catalysis activity and a much more speci c surface TNPs were found to be more superior to sodium hydroxide under the same conditions. The results showed that TNPs as catalyst can improve the biodiesel production up to 87.8% in the same condition in which the eciency is 76.4% for sodium hydroxide as a homogeneous catalyst. The eect of biodiesel/diesel blend fuels on engine exhaust emissions in a Robin engine was evaluated. The testing results show that the B20 blend fuel (including 20% and 80% v/v biodiesel and diesel fuel, respectively) reduced (HC) and carbon monoxide (CO) emissions to 28.9 and 20.6% compared to the petroleum diesel fuel, respectively. In addition, in this study, the eective use of biodiesel to reduce air pollutant emissions was approved, although a slight increase in nitrogen oxides emissions than pure diesel fuel was observed that quite what was expected due to increasing combustion temperature.

Use of steel plate shear walls (SPSW) as an eective structural system for resisting lateral force in low- to mid-rise buildings increased in recent years. The SPSWs control the lateral force response of the building and the building's natural period of vibration. The SPSW with coupling beam (SPSW-WC) system consists of a pair of planes SPSWs linked together with coupling beam at the oor level. The degree of coupling (DC), which represents the level of interaction between the two piers, is a key parameter in understanding behavior and developing design for the system. Determining the DC is dicult, but necessary. Therefore, this study investigates the relationship between DC and building's natural period of vibration in SPSW-WC structural system. Some analytical 3-, 6-, and 9-story structures with dierent lengths of link beams were analyzed for determining rst two natural periods and evaluating DC of SPSWWCs. This study applied a new design technique using orthotropic membrane model proposed in design codes. In this method, after preliminary design of the system, in order to distribute correctly the forces between the wall members, an orthotropic membrane model was developed using ETABS program. Natural period estimations using this method were compared with the niteelement solution, and good agreement is demonstrated. Based on outcomes, an increase in stiness of coupling beam results in increasing in coupled steel plate shear wall's degree of coupling. On the other hand, an increase in stiness of coupling beam results in a decrease in structure's rst natural periods of vibration. However, if degree of coupling tends to one, then rst natural period of structure does not aect stiness of coupling beam. This paper also presents a model for estimating the DC of SPSW-WC from the rst two natural periods of vibration.

Space is considered a signi cant and eective resource and constraint in building construction projects. In order to execute project activities, other resources, such as labor, machinery, equipment, and material, require space. In other words, each activity needs dierent types of space. In case the space constraint is neglected, resources allocated to two or more activities, will be obliged to work in a common area during at least a portion of activities duration. Con ict among spatial requirement of activities, can cause serious problems in their execution. Nowadays with the considerable increase in demand for early completion of projects, in many cases the project schedule is compressed. Schedule compression is also used for the purpose of delay compensation. "Fast tracking" or the parallel execution of previously sequential activities, is among the common methods to shorten the project schedule. In case of fast tracking, more activities will be executed concurrently. Therefore, con ict among their spatial requirements will be more likely. Physical con icts among concurrently executed activities are referred to as \time-space con icts", and these con icts are among the most eective factors in labor productivity decrease in building construction projects. They can also seriously impact other performance indexes such as time, cost, quality, and safety. Thus, development of ecient methods and tools for workspace planning can have a signi cant eect on project performance. In the present research, considering the mentioned necessity, the signi cance of space as a resource and constraint in building construction projects is studied, and various types of space and space requirements in building construction projects are identi ed. Furthermore, a 4Dbased software approach is developed to identify potential time-space con icts in the schedule and assess their impact on labor productivity. This approach makes con- ict identi cation and assessment of its eects possible. Through this approach, with the use of proper solutions, the number of potential con icts will be reduced before the start of the construction phase; therefore, an optimized schedule is resulted.

The prediction of the collapse stages of a structure, caused by special explosives, used for controlled demolition, or under any extreme loadings, such as blast has been of interest to designers and structural engineers in recent decades. In this article, the collapse stages of high rise RC buildings with moment resisting frames, due to removal of certain members of the structure, destroyed intentionally or accidentally, has been simulated by the aid of a developed computer program. The computer software, to simulate the process of collapse, is able to carry out sequential analysis, assuming an elastoplastic behavior for materials. After each analysis, plastic hinges, formed in structural members, are identi ed. Structural elements which satisfy failure criterion are removed and then the geometry of the structure is updated. The deformed shape of the structure, in each stage of collapse after removing each destroyed members, is visualized. The collapse stages of three selected buildings, introduced in previously published papers, investigated and the computer software is veri ed. In a dierent case study the process of the collapse of a 20 story building has been predicted for four scenarios of controlled demolition. It is shown that the software can be used to predict progressive collapse of the structures.

Due to human activities or natural changes rivers are subject to erosion and sedimentation. One of the best ways to control erosion and sedimentation is through grade control structures. Grade control structures are, in fact, a kind of structures constructed along the river reach to decrease longitudinal bed slope and control erosion. They stabilize the riverbed by increasing resistance to ow shear stress. This research deals with developing an optimization model to design a special type of these structures with the above function, called bed sills. Bed sills are constructed transversely across a cross section with the same level as bed elevation to protect river bed from erosion. In this respect, optimization model is developed as composition of hydraulic and structure modules under objective functions of minimum construction cost and maximum structure stability. The result of model not only consists of optimized dimension of bed sill, which consists of width, height, distance and number, but also the costs of construction implementation and depth of scouring. The model is then calibrated for Dough river. Comparing the obtained results with Bed sills of Dough river shows that the optimization modeling of grade control structures is able to obtain variations of designs for the objectives of minimum construction cost and maximum structure stability. In the next step, sensitivity analysis is carried out on input variables of longitudinal slope and design discharge to understand the eect of variations of these on cost and dimensions of the structure. Further on, sensitivity analysis results are applied for validation of the model. Model's sensitivity in the longitudinal slope can be applied in the Mountain rivers. These rivers can choose equations such as Meyer-peter and Muller equation, because they reduce costs and increase stability of Bed sills. The results of this study can be used for the prediction of optimized dimensions of Bed sills.