نشریه مصالح و سازه های بتنی
سال پنجم شماره 1 (پیاپی 9، بهار و تابستان 1399)

Concrete columns were previously only reinforced with steel reinforcements. Nowadays, with the introduction of FRP rebar, these reinforcements are used in concrete elements as a proper replacement for steel reinforcements, especially in corrosive environments such as marine environments. But the use of this type of reinforcement in columns of concrete structures faces uncertainties, so that the various international codes do not take into account the effect of this type of rebar, or they do not allow them. Due to the elastic behavior of FRP reinforcements and their high ultimate strain as compared to the ultimate strain of concrete, these rebar are generally not contributed to concrete in concrete columns. In this study, using mathematical equations and parametric study as well as finite element software, the contribution of FRP reinforcements has been investigated and it has been shown that neglecting FRP reinforcement in some cases can lead to very conservative results in terms of capacity. The type of FRP reinforcement and the percentage of longitudinal reinforcement have the greatest impact on the contribution of these reinforcement to the compressive strength of the column so that this increase can form up to one quarter of the compressive capacity of the column.

The discontinuities are formed in different levels of concrete as a result of various curing processes. There are only few cases where cause and location of failure of a concrete structure are limited to a single discontinuity. Usually several discontinuities of limited size interact and eventually form a combined shear plane where failure takes place. So, besides the discontinuities themselves, the regions between adjacent discontinuities, which consist of strong concrete and are called concrete bridges, are of utmost importance for the shear strength of the compound failure plane. Also, the coalescence of non-persistent joints is important factors in controlling the mechanical behavior of brittle rocks and can be caused concrete failure in slopes, foundations and tunnels. Therefore, a comprehensive study on the shear behavior of non-persistent joint can provide a good understanding of both local and general concrete instabilities, leading to an improved design for concrete engineering projects. From last decade, direct shear test have been used to study shear behavior of echelon joint. Whereas, only one horizontal shear failure surface can be formed within the shear box therefore, it’s not possible to perform shear test on the echelon non-persistent joint. This paper introduces the modified shear box so the shear test can be performed on the both of the overlapped and non-overlapped echelon joint.

Fiber Reinforced Polymer (FRP) bars with significant resistance against the corrosion lead to an improvement in the performance of concrete structures and a significant reduction in costs. High ratio of tensile strength to weight, being non-conductive, and non-magnetic are other features of them. Recent international design standards, such as ACI 440.1R-15 do not recommend including FRP reinforcement in compression and replace them by concrete in calculations. In this study, due to the prediction of the effect of the GFRP compression bars on the flexural strength and ductility of GFRP reinforced concrete beams, the thirteen concrete specimens were modeled using finite element software, ABAQUS. Concrete elastoplastic behavior after the peak was defined using the concrete damaged plasticity model in software. Experimental data from previous studies were used as a criterion for numerical investigations and the model results were validated using numerical modeling. The results demonstrated that the displacement-force graphs, obtained from numerical analysis, were in good agreement with the respective curves obtained from the laboratory analysis. According to the numerical evaluation, GFRP reinforced concrete beams included higher flexural strength, i.e., the average flexural strength of steel-reinforced concrete beam was about 90% of the GFRP reinforced concrete beam. Also, the ductility of GFRP concrete beam specimens was greater than that for the steel beam specimen. Increasing the percentage of GFRP compression reinforcement resulted in higher energy absorption and ultimately higher ductility of the GFRP concrete beams. The numerical results indicated that GFRP compression reinforcement does not significantly increase the flexural strength of beams.

Various tests are carried out in order to control the concrete quality. One of the most important of these is the concrete compressive strength test. So as to do this test, concrete samples are taken by the quality-control laboratories of the concrete production companies. Different metal, composite and plastic molds exist for sampling concrete that each, of which has unique advantages and disadvantages. In this study, we investigate the effect of concrete sampling molds’ quality and material on the compressive strength and distortion of concrete samples. Finally, based on the accomplished studies, it is found that samples with metal molds compared with other samples have highest compressive strength and lowest distortion. It also observed that the lowest value of compressive strength and the highest value of distortion are related to the samples with composite molds.

One of the most important issues that is of great importance in self-compacting concrete is the rheological properties of self-compacting concrete, however mechanical properties and durability also riquire significarlt considerations. The objective is to determine the maximum amount of fiber, where the workability of concrete is maintined. In this research 10 mix designs have been studied, in which one mix is considered as control and the rest contain 0.1, 0.15, 0.2 fiber percentages of steel, glass and polypropylene. The results on rheology behavior shows, when the percentage of fibers increase, the concrete efficiency decrease, and the yield stresses dynamic and static, plastic viscosity and Thixotropy increase and as a result it will reduce the rheological properties. In mixes with 0.2% polypropylene and glass fibers the minimum standard values for self-compacting concrete is reached whereas for more of fiber peruntage the self-compacting state is violated.

With regard to the adverse environmental impacts of cement production, the use of geopolymer concrete (GPC) can be considered as a more environmentally friendly approach for concreting. This study deals with an experimental investigation on the effects of partial replacement of the GGBS (replaced with 5, 10, 15, 20, 25, and 30%) used in GPC with natural zeolite (NZ) and silica fume (SF) simultaneously with different concentration (4, 6 and 8 M) of sodium hydroxide (NaOH) together with sodium silicate (water glass) solution on the compressive strength. Results indicate that increasing concentration of NaOH yields decreases the compressive strength of the concrete. In contrast, adding NZ and SF into concrete results in increasing the compressive strength. In addition, gene expression programming (GEP) was employed to develop mathematical models for predicting the compressive strength of GPC based on GGBS. Using the experimental results, an extensive and reliable database of compressive strength of GGBS-based GPC was obtained. The database comprises the compressive strength results of 351 specimens produced from 117 different mixtures. The five most influential parameters i.e., age of specimens, NaOH solution concentration, NZ, SF and GGBS content of GPC, were considered as the input parameters for modeling. The results reflected that the proposed models are accurate and possess a high prediction capability. The findings of this study can enhance the re-use of GGBS for the development of GPC leading to environmental protection and monetary benefits.
1- Ground Granulated Blast- Furnance Slag

Polymer modified concrete (PMC) have been called by various names, such as latex modified concrete (LMC). LMC is defined as hydraulic cement combined at the time of mixing with organic polymers that are dispersed in water with aggregates. The improvements from adding polymer modifiers to concrete include increased bond strength, freezing-and-thawing resistance, abrasion resistance, flexural and tensile strengths, and reduced permeability and elastic modulus. A reduced elastic modulus might be useful considering the application of LMC as a bridge-deck overlay or repair surface. Concrete overlays have higher durability and life time compare to asphalt overlays. In this article the applications of concrete pavements and LMC overlays are discussed. Due to the fact that LMC overlays have not been used in any road construction projects in Iran, research needed to be done in order to produce the styrene butadiene latex used in LMC. The research and development group at Chimisazeh Armani successfully produced the SBR latex and placed a sample in Tehran-North High way project by following the guidelines given by ACI and FHWA. The result proved that LMC is a great choice as an bridge deck overlay.

In this paper, a detailed analytic solution of the 1-D heat equation is presented to determine the distribution of temperature within a steel section integrated into a concrete slab, known as composite slim-floor beams (CoSFB). At first, the previous studies about the thermo-mechanical behavior of the slim-floor beams in the scale of experimental campaigns and numerical modeling have been investigated. Then, an analytical method, function of space and time, is suggested to determine the temperature distribution within the SFB section. Therefore, a steel section integrated into a concrete slab which is subjected to a time-dependent heat flux according to the standard fire curve will be examined. The proposed method is an analytical solution of the general form of the heat equation for transient conduction that simplified in order to calculate the load bearing resistance of SFB. This non-homogeneous differential equation is solved by applying the method of variation of parameters, setting up a homogenous problem and applying the separation of variables to get the homogeneous system. Hence, according to the results of FE modeling, the method has been based on assumptions to retain the accuracy of the calculations as well as to reduce the complications in the analytical method. At last, the results of the simplified analytical solution are compared with the numerical simulation, which confirms the logical process. Contrary to numerical methods, the newly proposed method can pragmatically be solved the heat equation with the moving boundary.

Deep beam have large depth/thickness ratio compared to conventional beams. In deep beams, the bending strain distribution through the depth of transverse sections of beam considerably deviates from the linear distribution. So their behavior is different with ordinary beams and are designed based on shear strength. The design of deep beams, due to their widespread use, is a crucial issue in structural engineering. So far, numerous studies have been done to determine the shear strength relations or models for deep beams. One widely used approach to determine shear strength of is the strut-and-tie method, which is employed by the American Concrete Association (ACI). However, It has been a long time since the Iranian Concrete Code (ICC), regardless of this research, uses a direct relation for the design of deep beams. In this research, methods and relations provided by other researchers along with the ICC method for deep beam design have been evaluated based on 240 experimental specimens. Moreover, a new equation for predicting the shear strength of RC deep beams using the genetic programming (GP) method is presented. Some input and output data should be used for feeding GP and equations producing. This equation was only based on primary specifications of RC deep beams and compared with other methods presented in the literature. In addition, the effect of different parameters on shear strength of RC deep beams were investigated. The results of this study showed that the proposed equation had acceptable accuracy compared to the experimental results and other equations presented in the literature. The proposed equation predicts the experimental results with an average error of 6%. Comparison of the results of the of ICC method in the design of deep beams with ACI method results showed that design in accordance with the ACI method resulted in a 27% lower error.

The foundation is usually assumed to be rigid, in the design of buildings and the impact of soil type on the flexibility of the foundation is not directly applied in simulations. However, considering the interaction between soil and structure can affect the structure's response. On the other hand, shear walls are widely used in concrete buildings today. When these walls are affected by severe earthquakes, elevation and oscillating movements can be seen at the base of these systems. As a result, the foundations of these systems are lifted from the ground under certain conditions. In this study, the support conditions of columns and shear walls in concrete RC buildings with dual shear wall-frame were investigated. For this purpose, at first, an 8-storey concrete building with a dual RC shear wall-frame system was analyzed and designed in accordance with the national building regulations of Iran using SAP2000 software. In the next step, the outer frame of the structure was simulated using finite element method and ABAQUS software under two different boundary conditions. In the first case, the effect of the foundation was evaluated as rigid and in the second case, the effect of the foundation was evaluated with the possibility of lifting (creating a rocking motion). In order to consider the possibility of lifting the foundation and local-nonlinearity of the soil (creating a rocking motion) springs depending on the type of soil were defined with Bowles stiffness values. The variables include the type of boundary conditions, the strength of the concrete (C21, C40, and C60) and the type of soil (Clay, loose sand and dense sand). The results showed that considering the possibility of lifting the structure by a rocking motion depends on the characteristics of the soil under the foundation, so that the type of soil can play a role in stress, lateral displacement and base shear of the structure. Also, in frames where the boundary conditions of the column and shear walls were considered to be flexible, the change in soil type caused the maximum stress changes of the frame to reach about 60%.

In this paper, the effects of concrete compressive strength, macro synthetic fibers named MEX-200 and its percentage, and also confinement of concrete cylinders on impact due to free fall of weights to specified mass is investigated in laboratory and the level of concrete destruction is studied. The number of specimens tested is 54 cylindrical specimens classified with 20, 30 and 40 MPa strength and 1, 1.5 and 2% fibers. Specimen weights are recorded before and after impact. In the impact test, the specimens were affected by two weights of 46.7 kg and 66.8 kg with 1.6 meters height. One layer of GFRP with a 90 degree angle was used to confine the specimens. Experimental results show that specimens with 20, 30 and 40 MPa strength without GFRP wrap, with 1 and 1.5% fibers, 33%, 25% and 20% respectively, and with 2% fibers, 66%, 50% and 40% increase the number of impact compared to specimens without fibers . For specimens with 20, 30 and 40 MPa with GFRP wrap, for without fibers, 500%, 400% and 340%, and for 1% fibers, 530%, 425% and 360%, and for 1.5% fiber, 566%, 450% and 360%, and for 2% fiber, 600%, 475% and 400% increase in the number of impacts is observed.

In this research, numerical modeling and evaluation of the using new smart alloys in concrete shear wall structures is investigated via finite element method. For this purpose, two 5-story concrete shear walls, one of which is without opening and the other is with openings, are modeled in Abaqus software. In these shear walls, steel and shape memory reinforcement with different percentages were installed in these walls. Then, the results of seismic behavior analysis after installing members made of shaped-memory alloys in reinforced concrete shear wall with interface joint beams are presented. The obtained results are compared with the response of shear wall structures without these members. There are no shape memory bars in the reference shear wall and all its reinforcement is made of steel. The finite element method is a technique which widely used in this field of study. Utilizing this type of analysis and comparing the behavior between single shear wall and shear wall by using shaped-memory alloys, improving seismic behavior and dramatically reducing final and lasting deformation in shear wall structure with shape memory alloy are monitored. In static loading, similar results were observed, indicating the elimination of permanent deformation by these alloys