moosa mazloom

In this paper, the fracture parameters of lightweight geopolymer concrete based on the C - class fly ash (LWFCGC) are presented. The experiments include three-point bending tests on 36 beams with different activator to binder ratios. Compressive and tensile strength tests were also performed on hardened concrete after 24 hours of curing at 80 ° C. In this research, three mix designs with activator to binder ratios of 0.4, 0.5 and 0.6 were considered. The samples showed relatively decent compressive strengths. In each mixture, the fracture parameters were analyzed using size effect method. The results showed that by increasing the activator to binder ratio fracture toughness and fracture energy decreased. Moreover, the ductility, measured by means of the effective length of fracture process zone, increased.The samples showed relatively decent compressive strengths. In each mixture, the fracture parameters were analyzed using size effect method. The results showed that by increasing the activator to binder ratio fracture toughness and fracture energy decreased. Moreover, the ductility, measured by means of the effective length of fracture process zone, increased.

Self-compacting lightweight concrete (SCLC) is one type of concrete that its usage has widely increased. The use of some additives in the production of SCLC can both reduce its costs and improve its properties. The effects of different cement replacement materials have been studied by several researchers. Jalal et al. (2012) claimed that the use of silica fume could improve the electrical resistance and mechanical properties of self-compacting concrete, and reduce its water absorption. Moreover, the use of silica fume in normal concrete improves the bond between aggregate and paste surfaces, and it has positive effects on fracture toughness, compressive strength and tensile strength (Lam et al., 1998). To simulate the fracture behavior of concrete in numerical models of concrete, depending on the model, some parameters such as fracture energy, fracture toughness and critical effective crack-tip opening displacement ( or δc), which generally are known as fracture parameters, must be determined. In this regard, Peterson (1980) showed that the fracture parameters are significantly affected by water to cement ratio (w/c) and the quality of aggregate. In other words, by reducing w/c or using stronger aggregate, the fracture energy of concrete increases. In this study, the effect of w/c and silica fume on the fracture toughness and fracture energy of SCLC has been investigated. Therefore, by making six mix designs and 126 concrete specimens, fracture parameters, mechanical properties and the workability of fresh concrete were carefully studied. Initially, four mix designs with the w/c of 0.37, 0.42, 0.47 and 0.52 were made. Afterwards, by replacing 0, 5% and 10% of the weight of cement with silica fume, the effects of changing this parameter on the fracture parameters of SCLC were studied.

Due to the increasing development of fiber-reinforced cementitious composites, studying their fracture behavior is necessary for the possibility of widespread use in the construction industry. In the present study, a new cementitious composite with strain hardening behavior has been fabricated. To reduce the adverse environmental problems, part of the cement has been replaced with pozzolanic materials such as blast furnace slag. Due to the fact that composites with high pozzolanic materials have lower strength at early ages than composites produced with ordinary cement, nano-silica has been used to solve this problem. Therefore, in this study, the effect of adding nano-silica on the fracture behavior of cementitious composites has been discovered. The double-k fracture method (DKFM) has been used to analyze the fracture behavior at different stages of specimen failure, i.e., crack initiation and stable and unstable crack propagation. In addition, the digital image correlation technique has been used to find the initial crack load and the crack opening displacement at different loading stages. The results show that the addition of 3% nano-silica positively affects compressive and flexural strength. In addition, it increases the toughness of the fiber bridging and reduces the brittleness of the composite.

Due to the widespread usage of self-compacting concrete and the need to reduce the level of cement and increase the strength of concrete, this study investigates the effects of silica fume, nano-silica and polypropylene fibers on self-compacting concrete. For this purpose, 23 mixes were made. In order to study the self-compacting properties of concrete, J-ring, V-funnel, slump flow and T50 tests were performed. Compressive, tensile and flexural strength tests were also performed on the hardened concrete at the age of 28 days. The experimental results showed that silica fume and nano-silica, in addition to reducing the workability of self-compacting concrete, increased its compressive, tensile and flexural strengths. Polypropylene fibers increased mechanical properties, especially tensile and flexural strengths. Also, with the simultaneous addition of silica fume, nano-silica and fibers, the mechanical properties of self-compacting concrete were doubled. In the mix with the highest compressive strength, the sample had 5% silica fume, 0.75% nano-silica and 1.5% fibers. The compressive strength of this mix design increased by 40% compared to the control mix. Also, the best mix in tensile and flexural strengths had 5% silica fume, 0.75% nano-silica and 1% fibers. tensile and flexural strengths of this mix design increased by 26% and 28% compared to the control mix, respectively.

Because of lightweight concrete has less mechanical properties than normal concrete, one of the objectives of engineering society is to design light weight concrete with a structural mechanical characteristic suitable for optimum resistance. Therefore, in this paper, using the Taguchi method to studied the parameters influencing of the compressive strength of Self-Compacting Light Weight Structural Concrete containing Nano-Silica. According to the Taguchi data, a total of 9 mixed designs were considered, taking into account the effects of the whole content, which included the ratio of water to cement materials, the ratio of Nano-silica to cement materials, the ratio of superplasticizer to cement materials, and the ratio of aggregate to total concrete weight. The results show that the maximum effect on the compressive strength is related to the change in water-to-cement ratio, which is about 56.5% of the impact on the pressure resistance. The percentage of Nano-silica to cement was 36.1. The third degree of impact on the compressive strength of the concrete is related to the effect of the superplasticizer ratio on the cement, which is about 7%, and finally the weight ratio of aggregates to the total concrete volume with an impact of about 0.4% in the fourth grade is important. Finally, the quality criterion was considered for lightweight concrete so that the optimal state for achieving Self-Compacting Light Weight Structural Concrete containing Nano-Silica with water to cement ratio was 0.35, the percentage of Nano-silica to cement was 4%, the superplasticizer percentage was 0.8%, the ratio of aggregate to total concrete volume was 0.48 obtained.

In this study, the mechanical properties of self-compacting lightweight green concrete were investigated by replacing copper slag as part of cement. Due to the positive effect of microsilica in this concrete, in order to reduce the grade of cement in self-compacting lightweight green concrete, a basic design without copper and microsilica slag and 7 mixed designs with 0, 5, 10, 15, 20, 25 and 30% copper slag It was provided with 10% microsilica. In order to study the properties of fresh concrete, experiments were performed on slump flow, T50, V funnel and J-ring. Also, compressive, tensile and bending strength tests were performed on hardened concrete at different ages of 7, 28 and 90 days. . Finally, microsilica has been shown to reduce concrete performance and improve compressive, tensile and flexural strengths. Copper slag also increases the performance of concrete and improves its self-compacting properties, but with increasing copper slag, the specific gravity of concrete increases. Also, the optimal percentage of copper slag replacement was 15%. The optimal mix design, with its self-compacting and lightweight properties, weighed 1871 kg / m3. Also, the 28-day compressive, tensile and flexural strengths of this mix increased by about 17%, 18% and 11% compared to the control mix.

In the present study, the effects of glass and basalt fibers (GF and BF) and temperature on the properties of self-compacting lightweight concrete (SCLC) has been investigated. For this aim, the fresh and hardened properties of 12 SCLC mixes have been investigated that contained monotype and hybrid fibers. The volume of the monotype fibers were 0.25%, 0.5%, 0.75% and 1% of the concrete volume. The hybrid fibers had volume fractions of BF/GF= 0.25%/0.75%, 0.5%/0.5%, and 0.75%/0.25%. The self-compacting properties of SCLC was assessed by means of slump flow, T500, V-funnel and J-ring. After 28 days of curing, the compressive, splitting tensile and flexural strengths tests were performed to characterize the mechanical properties of SCLC at room temperature of 20 °C and high temperatures of 100 and 300 °C. The test results of fresh concrete showed that all the mixes could be defined as SCLC with good flowability, viscosity and passing ability. Hardened test results indicated that the addition of the fibers reduced the compressive strength and increased the tensile strength, flexural strength and fracture energy. Moreover, compared to monotype fibers, the hybrid ones formed effectively enhanced mechanical behaviors of SCLC. The mixes containing 0.75% GF and 0.25% BF was the optimum one and determined acceptable fresh and hardened properties as well as high temperature resistance.

One of the most important weakness points of concrete is its drawback in tension and cracking. The use of fibers in concrete greatly reduces this disadvantage. Fiber reinforced cementitious composite (FRCC) is a type of fiber reinforced concrete (FRC) that does not contain coarse aggregate and has only fine aggregate. In fact, the high level of cement in FRCC is a problem for the environment. This problem can be solved with using different cement replacement materials as a part of cement. In this study, the effect of copper slag on the mechanical properties and fracture energy of fiber reinforced cementitious composite (FRCC) containing polypropylene fiber is investigated. Silica fume and copper slag were replaced as a part of cement. For this purpose, a control mix without silica fume and copper slag, 4 mixes containing 5%, 7%, 10% and 15 % silica fume, and 4 mixtures with 5%, 10%, 20% and 30 % copper slag were casted. In specimens containing silica fume, the ones with 15% of it had the highest quantity of fracture energy, compressive, tensile, and flexural strengths. Among the samples having copper slag, the ones containing 10% and 20% of it had the highest values above. It is worth noting that some binary mixtures containing both copper slag and silica fume were prepared too. Comparing the results of all the mentioned mixtures, it is concluded that the best results belong to the binary mixture containing both 15 % copper slag and 15 % of silica fume.

The purpose of this study is to investigate the effects of adding nanosilica and microsilica on the mechanical properties of cementitious composites containing polypropylene fibers. For this purpose, 13 composite mixes with the water to cement ratio of 0.28 were considered. One mix without microsilica and nanosilica, 4 mixtures with 0.5%, 1%, 3% and 5% nanosilica replacement levels, 4 mixes with 5%, 7%, 10%, 15% of microsilica, and 4 mixtures with the combination of microsilica and nanosilica were investigated. According to the results of the experiments, the composite samples containing microsilica and nanosilica had better results than the samples containing only one of these particles. In fact, the results of 28-day tests showed that the combination of 10% microsilica and 1% nanosilica produced the best cementitious composite according to compressive, tensile and flexural tests.The compressive strength was 61.32 MPa, which was 44.69 percent higher than the control mix, the tensile strength was 4.319 MPa with 34.88 percent improvement, and the flexural strength was 6.971 MPa with 30.37 percent improvement from the control mix. Using more than 3 percent of microsilica had negative effects in all circumstances comparing to the control mix. For example, the ones containing 5 percent of nanosilica and without microsilica had the compressive strength of 37.41 MPa, which was 11.72 percent lower than the control mix.

The use of fiber reinforced polymers, FRP, is one of the methods for strengthening and retrofitting concrete structures. In this research, the strengthening of reinforced self-compacting concrete beams against shear, torsion and bending has been investigated using GFRP. For reinforcing the beams against shear, bending and torsion, the strips of GFRP were used in the forms of U-shape, straight on the bottom surface and screwed around the beams respectively. In this study, the experimental results were compared with the results of the numerical models and their accuracies were confirmed. Then reinforcement sheets were applied in one and two layers on concrete beam models. By studying the numerical results obtained from Abaqus software, it was observed that with the increase of cracks in the concrete beams, their stiffness decreased and then the stresses were tolerated by the adhesive layers and the GFRP sheets, which has led to an increase in the bearing capacity of the beams. The results of numerical finite elements modeling show that by reinforcing the concrete beams with one layer of GFRP, the load bearing capacities of the beams improved in shear and torsion about 32% and 47% respectively. Moreover, if two layers of reinforcement sheets were used, the shear and torsion capacities of the beams increased about 45% and 61% respectively. The bending capacities of the concrete beams strengthened with one and two layers of GFRP increased up to 32% and 48% respectively.

In this numerical investigation, rectangular spiral reinforcement behavior have been examined. This article presents the finite element models of the experimental tests of 27 reinforced concrete beams that have rectangular spiral reinforcement with the distance of different vertical and horizontal leg angles. The explicit analyses have been verified the condition of confinement by changing in stress-strain curve of the reinforced concrete beams. According to the results of modeling, increasing the transverse reinforcement and improving in confinement advances the maximum torsion and more ductility of the concrete beams. Using continues rectangular spiral reinforcement in comparison with commonly used stirrups, with the same percentage of transverse reinforcement, improved the maximum torsion capacity from 5 to35%. In rectangular spiral reinforcement with various top angles, and the same percentage of the transverse reinforcement, increasing the top and side angles improves the maximum torsion. This improvement in torsion capacity is for the top angle of up to 20 degree. Exploring the results of rectangular spiral reinforcement that their top angles are not zero indicates that for the angles less than 14 degree, the results of maximum torsion have little deference with the ones having no top angle. Therefore, using rectangular spiral reinforcement with zero top angle is recommended. Its simple manufacturing and decreasing the cost of producing is considerable too.

For determination of the fracture parameters of self-compacting lightweight concrete (SCLC) size effect and work of fracture methods were used. For considering the behavior of concrete in different strengths, two mixes with water to cement (W/C) ratios of 0.42 and 0.47 were utilized. At first, the workability of the concrete was investigated and, after ensuring their self-compacting properties, the mechanical properties of the hardened concrete were determined. Then, by using the above-mentioned methods and conducting three-point bending tests on 30 beams, concrete fracture parameters, and crack-tip opening displacement were achieved. The results showed that with increasing W/C ratio from 0.42 to 0.47, the initial and total fracture energies, and fracture toughness decreased by 39.4%, 33.4% and 25.3%, respectively. The effect of the W/C ratio on the fracture parameters of this type of concrete was discussed. Furthermore, several empirical relations have been proposed that by the use of them and only by the determination of the compressive strength, the initial fracture energy, total fracture energy, the ratio of energies to each other, and fracture toughness can be determined. Then, by using the fracture parameters, the mechanical properties of the concrete and the extended finite-element method, the crack propagation was modeled. The results showed that this method has high accuracy in the numerical solution of the fracture problems as well as the efficiency of the obtained parameters for determining the behavior of self-compacting lightweight concrete.

Existing reinforced concrete (RC) frame buildings with non-ductile detailing represent a considerable hazard during earthquakes. These types of buildings suffered severe damages and were responsible for most of the loss of life during the major seismic events. Among seismic performance upgrading methods, several options are normally available, and one of them is to employ energy dissipation devices (Aniello, 2007). Energy input by a strong earthquake is expected to be greatly dissipated by these devices, (Ghobarah, 2001) and if they are damaged, the rehabilitation is quite easy after the earthquake since these devices are designed to be replaceable (Ramadan, 1995). In particular, this paper focuses on removable steel eccentric bracing systems (EBs).

In this research, the hysteretic behavior of 14 inverted-V braces and their gusset plate connections subjected to inelastic cyclic loading is examined through analytical simulations. It was modeled in ABAQUS software and the analysis type was static nonlinear analysis. Gusset plates with a constant thickness but with different sizes and shapes were used. To verify the correctness of the analysis, hysteretic behavior of gusset plates obtained from analysis was compared with experimental results. This comparison showed the exactness of the modeling. Then 14 samples of more important gusset plates in terms of ductility and strength were compared. The final result is that although stiffener in the gusset plates increase the strength of connections, they reduce ductility; so, numerous and indiscriminate addition of stiffeners in gusset plates are not recommended.

Nowadays, concrete is one of the most important and widely used human product. Improving concrete characteristics have always been one of the fundamental subjects for engineers. Improve the physical properties of water, as one of the main elements of concrete, is one way to improve the characteristics of the concrete. When water passes through the magnetic field, its physical quality has changed, it is called Magnetic water. This study examines the effect of the use of magnetized water (MW) with a solenoid current-carrying, on the compressive strength and workability of high performance concrete. The variables of this study were the intensity of magnetic field, the silica fume replacement level and water to cement ratio in different mixes. The results show that using MW increases the workability of concrete about 36% in average.MW in combination with superplasticizer is more effective than MW on workability and compressive strength of concrete. MW had more positive effects on the samples without silica fume. Increasing the intensity of magnetic field improved the workability, 28 and 90 days compressive strength concrete.

According to the Iranian code of practice for seismic resistant design of buildings, soft storey phenomenon happens in a storey when the lateral stiffness of the storey is lower than 70% of the stiffness of the upper storey, or if it is lower than 80% of the average stiffness of the three upper stories. In the combined structural systems containing moment frames and shear walls, it is possible that the shear walls of the lower stories crack; however, this cracking may not occur in the upper stories. The main objective of this research is to investigate the possibility of having soft storey phenomenon in the storey, which is bellow the uncracked walls. If the tension stresses of shear walls obtained from ultimate load combinations exceed the rupture modulus of concrete, the walls are assumed to be cracked. To estimate rupture modulus from compression strength, 144 compressive specimens and 144 rupture modulus specimens were constructed. For calculating the tension stresses of shear walls in different conditions, 10 concrete structures containing 15 stories were studied. Each of the structures was investigated according to the obligations of Iranian, Canadian, and American concrete building codes. Five different compressive strengths of 30, 40, 50, 60, and 70 MPa were assumed for the concrete of the structures. In other words, 150 computerized analyses were conducted in this research. In each analysis, 5 load combinations were imposed to the models. It means, the tension stresses of the shear walls in each storey, were calculated 750 times. The average wall to total stiffness ratios of the buildings were from 0.49 to 0.95, which was quite a wide range. The final conclusion was that the soft storey phenomenon did not happen in any of the structures investigated in this research.