نشریه مصالح و سازه های بتنی
سال چهارم شماره 2 (پیاپی 8، پاییز و زمستان 1398)

The presence of openings in concrete structure has destructive effect on the lifetime. In this paper, the interaction between two openings has been investigated using particle flow code. For this purpose, after calibration of model, one small opening has been situated in various distances and various angularities from big pore opening. The radius of smaller opening is 0.2 of radios of big opening.  This complex is situated in a concrete slab with uniaxial strength of 7 MPa. This slab is under principal stress of 2MPa and 6 MPa. The results show that spacing and angularity of small opening has important effect on the stress distribution and failure pattern around the big opening. The critical position for small opening is when it situated at 0.0 degree. Also the spacing between two openings is less, the failure volume is more.

One of the challenges that threaten buildings today is the discussion of the progressive devastation caused by earthquakes and fires. In most seismic and explosive events, most of the casualties have been caused by the demolition of buildings compared to any other direct impact; therefore, ensuring the sustainability and non-demolition of buildings is of primary importance. However, even if properly designed ductile buildings are exposed to certain undesirable features, they will suffer extensive damage. Therefore, it is necessary to apply the principles of earthquake and explosion resistant design in three different levels of structural forms, building plans and ductility for all buildings. This can cause problems for structures designed on the basis of current regulations during severe earthquakes and even lead to total demolition. In other words, any weaknesses in the design or implementation of the components may lead to the progressive failure of structures during the loading of an explosion or earthquake. Pop-up shear walls in concrete buildings are designed due to architectural limitations. These walls are less resistant than conventional shear walls, but they increase the structural ductility. Although the design of such walls is based on valid regulations and regulations, it is not considered progressive failure and in cases where the structure does not have the necessary resistance to progressive damage, reinforcement is required. The Progressive Damage Issue in Concrete Shear Wall Structures, which form the basis of the present study, examines the effect of reinforcement percentage (ρ) on the progressive failure. Progressive failure has not been investigated so far, considering the importance of this issue in this study, we investigate the effect of parametric change of reinforcement percentage (ρ) on the behavior of concrete structures under progressive failure. At the end of the study, the results showed that the effect of increasing the percentage of reinforcement (ρ) on reinforced concrete structures under an explosive load and progressive failure would improve the performance of the structures.

 In this research, in order to evaluate the effect of parameters such as geometry, stored material, concrete strength, silo wall thickness and FE mesh size on seismic response modification factor, finite element modeling is generated in three conditions: full, half-filled and empty. In this way finite element Abaqus is used for modeling and static nonlinear pushover analysis. As a sample, two types of models are created: the clinker silo (without basis) and by pass clinker silo (legged). Then, the mentioned models are subjected to nonlinear finite element method and the base shear-displacement diagrams are extracted. All of the mentioned graphs are evaluated by Young method to be bilinear. The response modification factor and the connected parameters such as plasticity, added resistance and plasticity ratio have been calculated. The calculated response factors are more than that of the design regulation of seismic buildings code (standard of 2800) and also the Code of IBC (Asce-7-16) and it can be said that regulations are conservative. The results show that the parameters of the geometry (diameter to height) and filled or emptiness of the silos are not very effective in the amount of response modification factor. However, the response behavior factor does not change significantly by increasing the strength of the concrete and it can be concluded that the response factor is not related to the concrete strength. Increasing the thickness of the silos due to increased plastic capacity increases the R Value and increasing the mesh size due to the reduction of the accuracy of the calculations, reduces R and it indicates that the change of the response factor obtained from the initial value is small and does not affect the behavior much.

Today, high-rise buildings are more welcomed due to the lack of space and the increasing population in large cities. The effect of wind on tall structures in the direction of the wind and its fluctuations are vulnerable. To design a structure against lateral loads such as wind load, the main design criterion should be provided. The importance of the impact of the lateral force increases with the height of the building. Thus, in this type of structures, mainly by wind power, design considerations with height, becomes more complicated. At a certain height, the lateral displacement of the longitudinal structures increases so that the controller's considerations are raised. The characteristics of the wind pressure on the structure are a function of the wind characteristics, structural geometry, and the characteristics of the adjacent region. Typically, standards for structures and buildings that have unusual shapes or positions are not used. The purpose of this study was to investigate the proposed design methods for calculating the wind load in international and domestic standards for the study of long and stable structures in Tehran. In this study, American, European, Japanese and Australian standards have been used for two types of structures, and their results have been compared to those derived from the National Building Regulations of Iran. The results of this study indicate that Iran's national regulations for proposed structures that are considered in Tehran are more conservative than the results of other standards.

Curing is an important parameter on the strength and durability development of concrete floors. Appropriate curing leads to the concrete strength gain, decrease in surface scaling and increasing the surface abrasion resistance of concrete. In this paper, the effects of a curing agent based on lithium polysilicates were investigated in an experimental program to verify their mechanical and durability properties. To this end, the compressive strength, water absorption, permeability under water pressure and abrasion resistance tests were carried out on the reference and cured specimens with curing agent. Based on the presented results, the compressive strength of air-cured and lab-condition specimens decreased more than 60% and 20% respectively. However, the specimens cured with Lithium Polysilicates agent lead up to 10% decrease in concrete strength. Moreover, the water absorption of specimens cured in air increased more that 3 times. The results showed that by application of such curing agents, the abrasion resistance increased by 8% in comparison with the standard curing system.

The behavior of a suggested concrete precast beam-column connection with two different plain and high performance fiber HPFRCC concretes under increasing cyclic loading and constant axial loading are analyzed and investigated in this paper. The internal precast concrete beam-column connection was initially designed based on ACI 318 design code and modeled with finite element method and the analytical results was verified with experimental results and then there was appropriate collaboration between both results.  The numerical models with congested and non-congested stirrups in the critical zone were created and the behavior of connection under cyclic reversal loading were compared with considering two different concrete as regular and HPFRCC.  The results from non-linear finite element analysis indicated that with increasing concrete strength, the stiffness and ultimate strength of connections increased up to 10% and the ductility of connection cast with HPFRCC concrete was significantly increased up to 35%  with congested stirrups.

In recent years, geopolymers, as a new class of green cement binders, have gained significant attention as an environmental-friendly alternative to ordinary Portland cement. In this paper, the effect of 2-element hybrid fibers and nano-silica particles on compressive, tensile and flexural strengths of metakaolin-based geopolymer concrete, were studied. First, Preliminary tests were conducted to reach the optimum mixture designs. Then, fibers were added in various ratios with nano silica particles to the concrete mixtures and geopolymer specimens were prepared to study the behavior of geopolymer fibers reinforced metakaolin-based concrete. After curing, specimens were subjected to the indirect tensile and 3-pointflexural strengths tests. The test results showed that using 2-element hybrid fibers and nano-silica particles increases the compressive, tensile and flexural strengths of geopolymer concrete.

When concrete loses its moisture, it shrinks and results in cracking. In addition to undesirable effects on the appearance of concrete, cracks reduce its strength and durability. Fibers are used in concrete in order to control shrinkage cracks. The goal of this study is to evaluate the effects of micro and macro synthetic fiber in reducing the drying shrinkage and cracking under restrained conditions. For this purpose, in the first phase of the study, the effects of two types of microfibers, polypropylene and double-part, were selected. The results of the first phase of the study showed that polypropylene fibers have a better performance in improving initial cracking time and reducing the maximum crack width. The second phase of the study investigated the effect of macro synthetic fibers as well as the micro and macro synthetic fibers, hybrid mixes, in reducing the drying shrinkage of restrained conditions. The experimental results obtained in the second phase showed that the presence of macro synthetic fibers, due to the high modulus of elasticity, had a significant effect on drying shrinkage. The results also showed that the hybrid mixes had the best performance

One of the main reasons of surface texturing in concrete pavements is to provide a safe surface by supplying adequate surface friction which it could be furnished by different methods on fresh poured concrete. In this way, the hydroplaning and skidding on wet surface would be minimized. However, some other considerations such as safety, quality of driving, bumping noises and economical factor should be noticed. Required specifications should be controlled via width, depth and distance between grooves, amount of noises and grooves direction. In this paper, in order to monitor the surface texturing different classifications, texturing methods, surface properties and measuring methods have been discussed in accordance with American concrete pavement association (ACPA). Finally, different methods of surface texturing in Tehran-North highway are introduced and the results of English pendulum test on each method would be presented. The results indicate that texturing by TCM machine has better English pendulum value even in compare to asphalt overlay.

The performance of binary and ternary self-consolidating concrete (SCC) samples immersed in Persian Gulf simulated water including compressive strength, electrical resistance, bulk water absorption, total voids and chloride ions penetration were investigated. Portland cement was partially replaced with 8, 20, and 50% (by mass) of silica fume, metakaolin and slag, respectively. In addition, ternary blends containing the mentioned percentages of metakaolin and silica fume as well as slag and metakaolin were cast. The water to binder ratio was considered 0.45. The results indicated the improvement in the performance of immersed binary and ternary SCC samples compared with control samples. SCC containing the studied supplementary cementing materials showed better performance compared to the plain SCC when immersed in sea water from the view point of resistance against chloride ions attack. The best performance was arrived to the ternary SCC containing metakaolin and silica fume. The samples containing slag did not perform well in the Persian Gulf exposure which can be related to the poor quality of the studied slag.

The bonding of steel bars to concrete in a various environments is one of the most significant problems in the durability of concrete structures. There are several different factors such as concrete ages and properties, steel rebars characteristics and environmental condition which affect the bond strength between concrete and embedded steel rebars. Accordingly, in the present study, the bond strength between embedded steel rebars and self-compacting concrete which contain different values of granite and limestone powder as a filer is investigated under accelerated corrosion condition. Besides, the specimens were also preloaded up to 50% of concrete compressive strength to investigate the effect of induced cracks caused by external loading on the chloride ions penetration and corrosion process. According to obtained results from the experiments, the utilization of 15% granite powder has increased the bond strength and decreased corrosion level of concrete specimens. Also, the loading of the specimens has exacerbated corrosion and reduced bond strength considerably.

Predicting the shear capacity of reinforced concrete beams with a suitable accuracy is an essential issue for engineering applications, especially for the rehabilitation and design of such structures. It was found that there is a significant difference between experimental and existing code recommendations for shear capacity predictions. Shear capacity assessment of slender reinforced concrete beams in reason of several assumptions to equation developing is one of the most important issues. An artificial neural network has been developed as a reliable method to simulate and determine the shear capacity of slender concrete beams. For this purpose, the effects of several parameters on the shear strength of concrete beams were evaluated. Finally, an empirical formula with suitable accuracy was obtained to determine the shear strength of slender concrete beams. Experimental, code recommendations and model suggested by artificial neural networks for shear strength of concrete beams show that the model suggested by artificial neural networks gives more exact predictions.