یعقوب محمدی

The research on tall buildings has been increased due to the demands of suitable spaces. The use of pyramidal architecture in tall structures has several benefits including the ability to lighten the adjacent buildings and prevention from the closure of the view in urban spaces. However, the seismic behavior of pyramidal tube structures requires a closer examination of their design and probable behavior under lateral loads. One of the most important parameters in the pyramidal tapered buildings is the calculation of natural frequency of the vibrating structures (ω). In this study we have proposed new equations and methods for the mentioned calculations which has been compared with software calculations. Many researchers have calculated the free vibration of structures using different methods. One formula to obtain the natural frequency of tube structures is obtained from the fourth-order differential equation (Wang, 1996). An approximate solution in order to analyze the free vibration of tall tube-in-tube buildings have been proposed by different researchers (Lee, 2007; Lee and Bang, 2008; Lee and Tovar, 2014). The modeling of tall building using a beam with varying stiffness and mass subject to the variable axial force caused by simple weight was presented by Mohammadnejad (2015). Free vibration analysis using differential equation has been evaluated by Bozdogan (2009) and Bozdogan (2013). The first natural frequency of tall buildings with a system combined of framed tube, shear core, and belt truss has been calculated under axial force (Kamgar and Rahgozar, 2014; 2015; 2018). A new and simple method of determining the natural frequency of tube structures with tube-in-tube wall has been presented. The novelty of this method refers to the mathematical computation process which is much simpler and shorter. The effect of structure’s weight on the natural frequency of structure has been considered by variable axial force. Tall building is modeled by a beam with variable stiffness and mass along the height of the building. Therefore, the partial differential equation with variable coefficients is used which have been presented by Mohammadnejad and Haji-Kazemi (2018). Furthermore, there is no regular research on the vibrational frequency calculation of pyramidal tube systems, especially by mathematical methods, or a small number of studies have been done most of which have been done on 90-degree structures with tube systems.

This paper aims at investigating the content of qualitative-based research on sport management published in scientific research journals indexed in the Islamic World Citation Database. 166 qualitative articles published in scientific research journals approved by the Ministry of Science during the years 1390 to 1399 were analyzed. We use a coding checklist whose validity is confirmed by sports management experts. Also, the reliability of the checklist was obtained using the agreement coefficient between the coders of 88.50%. findings of this work demonstrate that majority of the articles employ the grounded theory(66/8%). furthermore, semi-structured interviews(56/6%) appear to be the most popular data collection method., purposive sampling(29/5%) open, axial, and selective coding(82/5%) seem to be the most popular ones. Also, in many of articles(41%), no data triangulation is reported. In addition, only in ten percent of cases, present suggestions and recommendation for future researchers. In recent years, an increasing trend for qualitative-based research in the sport management literature has been observed. Therefore, by highlighting the weaknesses and limitations of qualitative studies, solutions to improve future studies have been proposed.

The use of fiber-reinforced concrete in various industries is developing due to the desired mechanical properties, light weight of the structure, good energy absorption capacity and high initial strength under impact loads. a new generation of fiber-reinforced concrete with excellent ductility and exceptional crack control capability. Although fibre concrete is suitable for structures exposed to impacts and other extreme loads, In this study, the energy absorption and initial strength of reinforced concrete with Forta, basalt and barchip fibers under penetration impact loading were investigated. To investigate the effect of fiber percentage on impact properties, 8 specimens were subjected to experimental tests hybrid groups. Also, the fracture surface and the adhesion of fibers to fiber-reinforced concrete with degradation modes were evaluated. The results showed that the initial strength and energy absorption in hybrid-fiber reinforced concrete increased by 292.8% and 212.3%, respectively, compared to Net conceret. Also, by examining the fracture surface of the specimens, it was found that the adhesion between the two basalt and forta fibers to the base concrete is very desirable. However, the separation between barchip fibers and concrete is high and reduces the efficiency of these fibers in reinforcing concrete.

The purpose of the present study was to develop and validate a scale to measure internal branding in sport federations. Therefore, the methodology of the present study, from the point of view of purpose, is applied and in terms of data gathering, it is a correlation type that is specifically based on structural equation modeling using Smart PLS 3 software. The population of this study consisted of all employees, managers of Iranian Sport Federations (1062 persons). And based on the Barclays index, the sample size(195) required for the research was considered. The instrument used in the study was a researcher-made questionnaire whose construct validity was confirmed by confirmatory factor analysis as well as its content and face validity by experts (n = 7) in the field of brand marketing and sports marketing management. The validity of the questionnaire was also assessed by the Composite reliability(0/97) and Cronbach's alpha(/0973). The findings of the present study suggest that training activities, group meetings, briefings, internal communications, and leadership and management activities are factors that influence the internal branding of sports federations, and it is recommended that appropriate oversight be exercised. Ensure that all stages of establishing an internal branding system are carried out continuously and effectively through the managers and heads of federations. Also, the main components of this tool can be used by sports managers to develop internal branding.

The need for adequate and appropriate living and working spaces and population density and the increasing cost of land and use of high-rise buildings requires growing research on these structures. The tube system is one of the most suitable structural systems for high-rise buildings. The purpose of this study was to obtain one of the most important dynamic properties, namely the natural frequency (ω) for a number of tall buildings with a pyramidal tube system. A tube-in-tube approximate method for analyzing and calculating the natural frequency of a combined pyramidal tube system with shear wall pyramid is presented. The size of the pyramid angle of the tube frame varies with the length (height) of the structure. The proposed method enables us to calculate the natural frequency of vertical and curved tall buildings with the help of computer programming. The models were analyzed using finite element form and mathematical analytical method. The results show that the investigated method correctly calculates the natural frequency and is in good agreement with the finite element results and has better compatibility with pyramidal angle structures with higher altitude, and the resulting computational error is much lower. The results of the proposed mathematical model provide an easy-to-use method for understanding the dynamic properties of structures and the effects of angle-frequency variations. Furthermore, this analytical method has the least error for tube systems with tube-in-tube and the highest error for shear wall pyramidal systems.

In the present study, the use of buckling-restrained braces (BRBs) has been evaluated as a research innovation aimed at reducing the potential of progressive collapse in steel braced frames. These braces prevent the overall buckling of brace and provide much more energy absorption than conventional convertible bracing systems. For this purpose, three-dimensional finite element models of 4, 8, and 12-story buildings were simulated in two modes using ordinary and buckling braces and their response against progressive collapse was evaluated. The progressive collapse analysis was carried out using an alternative load path method and the response of the structures to column removal was investigated. Simulation of models was done using ABAQUS software. Also, the accuracy of the finite element method used in simulating the models was evaluated and a suitable agreement between the results was observed. The most significant results show that in steel frames that have BRBs, less stresses have been created compared with conventional steel braces. In all cases, BRBs with internal energy absorption of the structure have caused lower stresses to other structure member, thereby reducing the potential of progressive collapse. Also, the use of BRBs has reduced the rotation of the beam to column connection, compared to conventional bracing. This effect is especially noticeable in buildings with higher altitudes; the maximum amount of joint rotation corresponding to the 12-story building with BRBs has been reduced by 21% compared with the conventional braces. The reason for this is that, in buckling-restrained braces, the members are able to withstand a pressure above the tensile yield strength, and, unlike ordinary systems, the inherent ductility is due to the occurrence of yield in pressure before it begins to buckle.

Roller Compacted Concrete is defined as a concrete with zero slump. It will support a roller while being compacted in its unhardened state. RCC is used in two general areas of engineered constructions: dams and pavements. In this study, RCC will be discussed only in the context of its use in pavements. In this regard, Some material savings may be possible due to the lower cement content normally needed in RCC pavement mixtures to achieve strengths equivalent to those of conventional concretes. The other advantages of using RCC include cost savings as a result of the construction method and the increased placement speed of the pavement.Unreinforced concrete has a low tensile strength and a low strain capacity at fracture. It was reported in many studies that NS significantly improved the mechanical properties and durability of cement-based materials. In this study we carried out a comprehensive investigation of the results caused by the addition of steel fibers and nano silica particles in mechanical properties of RCCP. Therefore, with varying amounts of steel fibers (0.00%, 0.33%, 0.67% and 1.00% by the volume of concrete) and nano silica particles (0.0%, 0.5%, 1.0% and 1.5% by the weight of cement), RCCP was prepared and consistency and mechanical properties (compression strength, tension strength, flexural strength, and thoughness) were investigated. The results indicated that the addition of steel fibers and nano silica leads to positive mechanical properties of RCCP.

Concrete is heterogeneous at all length scales and its microstructure evolves continuously over decades. Through the use of nanoparticles, it is possible to alter the microstructure of cementitious materials from within the first microsecond. This study is aimed to carry out a comprehensive investigation on the effects caused by the addition of nanoclays on properties of cement based composites. Therefore, a replacement of cement by with different percentages of montmorillonite nanoclay (0%, 0.5%, 1%, 1.5%, 2% and 3% by weight of cement) in cement pastes and mortars was planned and The effects of adding nanoclay on hydration process, rheological properties (adhesive properties, water demand and setting time), mechanical properties (compressive strength) and durability properties (water absorption and drying shrinkage) of mixes were investigated. As well, The cement matrix microstructure was examined using scanning electron microscopy. The results indicates that the addition of nanoclays causes positive effects on cement composites properties.

In this paper, our concern is to produce light-weight concrete with using different ingredients in the concrete mix. Specimens were satisfied the density and strength regulators of structural lightweight concretes. The final aim is to increase ultimate strength and effects of added Nano-silica and steel fiber on the mechanical behavior. Nano-silica increases tensile compression and flexural strength with improving the concrete structure (Quercia et al. 2010). In the other hand, using steel fibers reduces the crack width and parallelize their orientation by bridging between microcracks (Qing et al. 2007).

One of the methods for assessing the potential of progressive collapse occurrence is the APM method. This method done by direct removing of one or several columns. However, in this method the damage of adjacent elements of removed columns under blast conditions was ignored and this issue can lead to an incorrect prediction of progressive collapse. Therefore in this study to evaluate the potential of progressive collapse due to blast loading a 4st steel moment frame building with Abaqus/CAE 6.11 software is simulated, and two methods '' alternative load path and applied of blast load directly'' were evaluated in this study. The results indicate that in assessment of the potential of progressive collapse occurrence by considering the blast loading as the initial reason of failure, the structure response will be different compared with the common methods that used for evaluation of progressive collapse occurrence and in those methods the initial reason of progressive collapse was ignored.

Over the course of time into the 21th century, concrete has been known as one of the most high usage materials in the construction industry. As a consequence, trying to produce light concrete is an active and developing area within the new field of construction science. This technology consists of lowering the whole weight of structure by using new bulding techniques, new materials and optimizing ways of manufacture. Lowering the weight not only economizes on the expenses, time and energy but also decreases the damages of earthquakes. Furthermore, it keeps the constructions safe and minimizes the damages resulting from the overweight of the structure during different waves of shocks and aftershocks. In spite of considerable amount of compressive strength, low tensility strength and relatively high fragility of the concrete, there are limitations in using it in some parts which are partially or fully under forces of tention in different parts of structures. This fundamental defect of concrete in practice can be eliminated by reinforcing it through using steel tabs in the direction of traction forces. Having in mind that the armature just constitues a small part of the whole cross section of the structure, it will not be correct to conceive of the cross section of concrete as an isotropic and homogeneous surface. In recent decades, in order to come up with the isotopic condition and decrease the fragility, weakness and retrogression of concrete new techniques and trends of applying slender fibers running through the internal section of the bulk of concrete has become prevalent and common practice. The concrete containing nano materials compared with the normal concrete affected by nono chemical materials with cement particles and clcium hydroxide crystals which exist in cement, has a severe effect on the performance of concrete composites while such mixtures come into each others’ contact.
In this study,we examined the effect of Nano-silica and polypropylene fibres on mechanical properties and durability of normal and light weight concretes. In the design of light weight concrete, lecalight weight aggregates were used. More than 384 cubic and cylindrical samples were made based on ASTM standards and compressive strenght, indirect tensile strength, ultrasonic and electrical resistance experiments were done.
The results of the experiments showed considerable increase in mechanical characteristics and durability of normal and light weight concretes. Nano-silica contributes to the proper spread of the fibers. Compressive strength, indirect tensile strength, and the dynamic elasticity module of the ordinary concrete were higher than those of the light weight concrete, while the electrical resistance of the light weight concrete was higher compared to the corresponding samples.
Compressive strength and indirect tensile strength increased to 71 and 55 percent in normal concrete and to 43 and 47 percent in light weight concrete respectively. Considerable increase in electrical resistance indicates high durability of these kinds of concretes. Of course, economic considerations of using nano-silica and polypropylene fibers require special attention. Finally, the right amount of utilization of the polypropylene fibers and nano silica were determined in order to achieve normal concrete and light weight concrete with optimal properties.

Concrete is one of the most important structural materials which is produced from proportional mixture of cement, aggregates, water and admixtures. Compaction of the concrete is one of the factors that make it difficult to use, particularly in the structures with high reinforcement steel bars. In cases such as foundation of bridges, bottom of the columns of skyscrapers and ets, vibration of concrete for compaction is almost impossible. To solve this problem we can use self-compacting concrete which causes complete compaction and also increases casting velocity. This kind of concrete is produced with superplasticizer and other admixtures. This Article examines the effect of the addition of nanosilica on mechanical properties and Durability parameters self-compacting concrete in sulfate destructive environment. For this purpose, in laboratory studies we have used some tests such as compressive strength and permeability. The results show that the addition of nanosilica could effect on mechanical properties of self compacting concrete, also increase the durability of concrete against sulfate destructive factor that reduce the compressive strength at later stages. Nanosilica reduces the porosity in hydration cement by filling the pore space between the larger particles at the nano-scale and greatly reduced permeability.

Until very recently, there have been many studies on concrete, but in Iran there has not been a lot of research in roller compacted concrete (RCC), particularly the effect of nano-silica on RCC. To address this gap, the use of nano-silica in RCC is investigated in this research. The aim of this study is to address the effects of nano-silica on RCC, its properties and the mechanical characteristics and permeability. For this purpose, three different amounts (2, 4, and 6%) of nano-silica in concrete with water cement ratio of 0.35 by using the ASTM standards were prepared. In total, more than 90 cubic and cylindrical samples were casted. Then, the compressive strength and permeability tests were conducted on both 28 and 90 days samples. The results have shown that different ratios of nano-silica in RCC have significant effects on the mechanical properties and durability of concrete samples.

One of the major destruction of concrete in cold region is due to freeze and thaw cycles. Resistance to freeze and thaw cycles depends on high stress in concrete particularly when water in the pores of aggregates freezes. This leads to a volume change and resulting in more cracks in concrete and loss of durability. Nano-silica in the mix not only activates pozzolanic reaction but also acts as filler which in turn improves micro-structure of concrete paste. Use of glass fiber can help to bridge the gap initiated due to frost action [1]. In this study the effect of different replacement percentages of nano-silica with cement and fiber glass، and the number of freeze and thaw cycles on concrete strength was evaluated.

This study was conducted to investigate the accumulation of three heavy metals including lead، tin and zinc in the liver and muscle tissues of 60 silver carp (Hypophthalmichthys molitrix) collected from different stations of the Anzali wetland (located at the west south of Caspian sea): Pirbazar، Anzali، Khazarvila، Beshman، Sangachin and Abkenar، in April 2011. Samples were prepared according to standard method (MOOPAM، 1999) and amounts of three heavy metals were measured using atomic absorption spectrophotometer. Based on the results the concentrations of lead and tin in muscle were significantly higher than liver. In contrast، zink accumulation was significantly higher in the liver than muscle. The accumulation and distribution pattern of metals in the fish from different stations were as follow: Zn> Sn> Pb، and Abkenar ≤ Khazarvila < Sangachin ≤ Beshman ≤ Pirbazar ≤ Anzali. the Pb concentration in the liver of fish from all stations was lower than permissible limit of WHO. However، the Pb accumulation in the muscles of fish collected from all stations (except Abkenar) were higher than permissible limit of WHO. The levels of tin and zinc in both tissues of all fish were lower than permissible limit of WHO.

Anzali wetland¡ one of the most important ecosystems¡ located in the south of the Caspian Sea (lat. 37º28΄ N: lon. 49º25΄ E)¡ receives a large amount of urban¡ agronomic and industrial swages. Nonethless it is a main place to brees¡ to grow up and to take winters for waterfowls. Twelve Common Moorhen (Gallinula chloropus Linnaeus¡ 1758) have collected alive from four stations on Anzali wetland¡ during April 2010. Histopathological investigation were shown clear alterations in liver tissues withdegeneration of hepatocytes¡ pigments macrophage aggregation¡ rupture of cells with dilation of diss space¡ congestion and haemorrhage¡ hemosiderin pigments aggregation. Aggregation of leukocyte infiltration¡ capillary dilation¡ hypertrophy¡ degeneration and shrinkage of the cells¡ affected portion of the kidney¡ glomerular expansion and absence of the Bowman’s space¡ tubular epithelial cell hypertrophy¡ were also observed in kidney tissues. Results of the present stude were revealed that kidney and liver tissues of Common Moorhen can be investigated as a pollution bioindicator in Anzali wetland¡ due to their relatively long period of wintering migratory and also high polluted body of ecosystem in Anzali wetland area.