جستجوی مقالات مرتبط با کلیدواژه "reinforced concrete beams" در نشریات گروه "عمران"

In this research paper about Investigation The Effect of Rebars and Joint Using Glass Fiber Reinforced Polymer (GFRP) on The Reinforced Concrete Beams, (RCB) Beams are one of the important members of reinforced concrete which needs new materials due to several reasons. One of the significant measures to improve the bearing resistance (BR) is to substitute material used with novel one. Polymer reinforced fiber Rebars(PRFR) is one of the new material that has lower weight and high resistance than conventional steel rebars can reduce the fulfillment prices as well as enhance their performance of them against shear cracks. In this study, concrete beams with the dimension 200×300 mm and a length of 2000 mm were made using the FRP rebars with glass fiber (GFRP). The results showed that the use of GFRP joints increases the shear strength and reduces the ductility of concrete beams.Keywords: Conceret, Rebars, Joint, Reinforced concrete beams, Glass fiber reinforced polymer.

During the progressive collapse of structures, reinforced concrete (RC) beams must sustain large displacements which are not considered in usual design procedures. Regarding the extensive studies during the recent years, compressive arching and catenary actions are introduced as the main resistance mechanisms against progressive collapse. Despite the extensive studies, there is still a running debate on reliable estimation of the capacities and ultimate resistance of RC members against progressive collapse. Thus, in the present study, a simple and practical analytical method is developed to estimate the ultimate compressive arching capacity of RC beams under large displacements due to progressive collapse. The proposed method is developed based on the membrane action in RC slabs and analytical calculation of lateral stiffness of the structural system. Despite the available methods in the literature, the ultimate arching capacity of RC beams is obtained based on a single-stage procedure. The capability of the introduced method is evaluated utilizing a comprehensive laboratory database, including 99 experimental studies in the technical literature. According to the performed evaluations, the proposed method provides a reliable framework to estimate the arching capacity of reinforced concrete beams in large displacements. Any change in failure mode from flexural action to shear mechanism and increasing the rigidity of the connections leading to an improvement in lateral stiffness could reduce the accuracy of the proposed method.

Optimization and economization of processes and structures have been considered from time immemorial and many things have been done to achieve this goal. Protecting the environment and reducing the amount of waste material in nature is very important. Today, the problem of using recycled materials resulting from the destruction of buildings and the reuse of these materials in the construction of concrete has been considered. In this research, the shear behaviour of concrete beams manufactured with recycled coarse aggregate was studied. 9 concrete beams with a cross-section 150 mm wide and 200 mm high and a length of 1500 mm manufactured and tested. Recycled aggregate from building demolition was used at 0%, 50% and 100% mass replacement of natural aggregate. Specimens underwent a four-point bending test. In this test, the shear capacity, maximum deflection at the mid-span of the specimens and tension strain were measured. The determination of the shear behaviour of recycled aggregates concrete beams according to transverse reinforcement spacing was the aim of this study. The results were also compared with ACI, CSA and Eurocode 2 requirements. According to the test results, it was found that there is a significant difference in the shear behaviour of recycled and natural aggregate concrete beams

The shear strength of reinforced concrete beams changes depending on the mechanical and geometrical parameters of the beam. Accurate estimation of shear strength in reinforced concrete beams is a fundamental issue in engineering design. However, the prediction of shear strength in these beams does not have very high accuracy. One of the strategies proposed in recent years to provide a suitable model for predicting shear strength of reinforced concrete beams is the use of artificial intelligence (AI) algorithms. In this investigation, the application of adaptive neural fuzzy inference system (ANFIS) and support vector regression (SVR) algorithms for predicting shear strength of reinforced concrete beams was studied and the results were compared with existing regulation. For this purpose, shear span, effective beam length, effective depth, cross-section width, 28-day compressive strength of concrete, yield stress of longitudinal reinforcements, yield stress of transverse reinforcements, percentage of longitudinal reinforcement and shear reinforcement percentage were selected as input parameters and shear strength of concrete beam as output. Using the k fold validation method, educational and test data were defined and based on these data, predictions were made. The results obtained from the prediction show that the mean square root error (RMSE) for ANFIS and SVR methods is 0.1514 and 0.0994, respectively. In general, it can be seen that both ANFIS and SVR algorithms predict the shear strength of reinforced concrete beams with great accuracy. Therefore, they can be a good alternative to time-consuming algorithms such as ANN and expensive laboratory methods.

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.

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.

In this research, the effect of recycled aggregates obtained from the demolition of the old building on the preparation of concrete mixtures has been studied. The purpose of this study was to determine flexural behavior, flexural strength in reinforced concrete beams made of recycled aggregate. In the production of samples, recycled aggregates are used with 0%, 50% and 100% natural aggregates, respectively. The samples were tested for static quadrilateral bending and tested after 28 days of experiment. Therefore, by examining the results of laboratory studies, the flexural behavior of RC beams with the expansion of the recycling has been investigated. In addition, the results are compared with the relationships provided by ACI318, CSA and EuroCode2. The results obtained from this review show that by adding the ratio to the recycled aggregate substitute, the amount of net bending size at the criterial level increases and, with the expansion of the crack extending to the place of loading, the load is released flexibly. In addition, the use of 100% recycled aggregate increases the shape and flexural strength of RC concrete beams.

The rehabilitation of existing reinforced concrete structures and infrastructures becomes necessary due to ageing, corrosion of steel reinforcement, defects in construction/design, demand in the increased service loads, and damage in case of seismic events and improvement in the design guidelines. Fiber-reinforced polymers (FRP) have emerged as promising material for rehabilitation of existing reinforced concrete structures. The use of externally bonded Fiber Reinforced Polymer (FRP) sheets is an effective technique for strengthening and retrofitting of reinforced concrete beams especially under flexural loads. The use of FRP has been on the rise, mainly due to composite materials’ high strength and stiffness, non-corrosive nature and ease of installation. The purpose of retrofitting is to structurally treat the member with an aim to restore the structure to its original strength. Few investigations have performed to investigate the characteristics of retrofitted reinforced concrete flexural members. In the present study, a method for analyzing of the reinforced concrete beams retrofitted by FRP is proposed. The equilibrium equations and associated strain boundary conditions are used to determine the deflection and moment at each point along beam. As it is demonstrate in the numerical example, the proposed procedure can yield in efficient way, accurate result for FRP concrete beams.

In this paper, cracking in the first mode (opening) is modelled for reinforced concrete beams with FRP sheets based on presenting a new method by using the principles and relations of fracture mechanics and finite element method. In this method, for modelling the relationships of determining the stress intensity factor is developed for reinforcement sheet. In the proposed method, elements of the beam are divided into two categories, including elements with and without the crack. In the elements without the crack, the relationships, equation, stiffness and mass matrices of the beam are established with considering the changes in the moment of inertia due to the reinforced FRP sheet. In the elements with the crack, a change in the cross-section of the reinforced concrete due to the crack and a discontinuity in the crack point leads to an improvement in the standard governing relationships. So that the reduction of the stiffness of the cracked element is equivalent to the change in the size of the discontinuity. Here, the variation of the stiffness of the cracked element is calculated and presented as a function of the stress intensity factor. In this approach, the simulation of the crack is done by dividing the element to two sub-elements into the two sides of the rotational spring. In which, The stiffness and mass matrices of the two sub-elements and the improved stiffness and mass matrix of the element are derived by satisfying the continuity equation at the crack point. This method is developed from a vibrating analysis. The effects of crack depth and location and the effect of crack expansion on the static and vibrational behaviour of a concrete beam are investigated. To ensure the accuracy of the proposed method, all analysis performed in Abacus software is implemented. Comparing the results of the proposed model with the results of comprehensive modelling in Abacus software is applied to verify. The comparison of the results shows that the proposed methods are suitable for the analysis of reinforced concrete structures resistant to cracking. So that it can be generalised and optimally desirable for other models. In this paper, cracking in the first mode (opening) is modelled for reinforced concrete beams with FRP sheets based on presenting a new method by using the principles and relations of fracture mechanics and finite element method. In this method, for modelling the relationships of determining the stress intensity factor is developed for reinforcement sheet. In the proposed method, elements of the beam are divided into two categories, including elements with and without the crack. In the elements without the crack, the relationships, equation, stiffness and mass matrices of the beam are established with considering the changes in the moment of inertia due to the reinforced FRP sheet. In the elements with the crack, a change in the cross-section of the reinforced concrete due to the crack and a discontinuity in the crack point leads to an improvement in the standard governing relationships. So that the reduction of the stiffness of the cracked element is equivalent to the change in the size of the discontinuity. Here, the variation of the stiffness of the cracked element is calculated and presented as a function of the stress intensity factor. In this approach, the simulation of the crack is done by dividing the element to two sub-elements into the two sides of the rotational spring.

It is well known that the behavior of concrete is extensively affected by the initiation of cracks and their propagation. Among these cracks, diagonal or shear cracks have more complicated and less known behavior. In spite of extensive research in this field, current codes of practice do not provide a uniform margin of safety against shear failure of reinforced concrete yet. To simulate the non-elastic behavior of concrete in the fracture process zone, the distribution of cohesive forces through the crack sides have been used by researchers. The aim of this study is to evaluate the effect of the crack’s tip cohesive forces on the load-deflection response of reinforced concrete beams using fracture mechanic. In the numerical analysis used in this study, the non-linear behavior of concrete in the compression field is simulated by damage-plasticity model. To simulate the non-linear behavior of concrete in the tension area and simulating the onset and evolution of cracking, non-linear fracture mechanics based on cohesive crack model is used. Using finite element software of ABAQUS, a step by step approach is used. In the presented approach, the probability of possibility of crack evolution in beams is considered. Comparing the calculated load-deflection curves for several reinforced concrete beams with the experimental ones showed a good consistency.

Corrosion of steel reinforcement has a complex process which leaded the reduction of crass section bars and degradation of concrete structure. the corroded reinforcement bars were the most important issue of the concrete permanence in the marine structures. The important effects of corrosion are in the damages made by corroded concrete structure which include all kinds of structural and non-structural damages. The first one is more important because of the reduction of the safety factor of the structure against the applied external loads. These failures include the reduction of cross-section bars and the changes in the steel mechanical behavior. Corrosion includes two processes: (1) corrosion initiation and corrosion propagation. The initiation time is when the corrosive ions receive on the surface bars and lead to activation of the steel. (2) The propagation time is when the structure loses its capability subject to the loss of the cross-sectional area of reinforcing steel bars, reduction of bond and crack initiation and propagation. The predicative models of life-service of a reinforced concrete structures should be included the two processes of corrosion. Because for new structures, the initiation time of corrosion and insurance from the long-time of corrosion initiation time, and for the existing structures, controlling the corrosion propagation is more important.
In this paper, statistical characteristics of the chloride diffusion coefficient, corrosion initiation time and corrosion rate including the best probability distribution function and its parameters are investigated based on Mont Carlo simulation of pitting corrosion data. The distribution function parameters of the corrosion variables i.e. the chloride diffusion coefficient, corrosion initiation time and corrosion rate were calculated using the Maximum likelihood method based on mathematical pitting corroded model that corrosion initiation and corrosion propagation processes are considered in this model. the probability density functions such as: Gamma, Gumbel, Lognormal, Normal, and Weibull were used in the statistical analyses of corroded pitting parameters. The best probability distribution function was selected using chi-square statistic. the Lognormal distribution function was obtained the best probability function for the threshold chloride concentration, the corrosion initiation time and the corrosion rate. The corrosion initiation time depend on four basic random variables such as: the concrete compressive resistance, the concrete cover, the threshold chloride concentration and the surface chloride concentration. Thus, their statistical effects of these random variables on corrosion initiation time are parametrically investigated using 10000 Mont Carlo simulations. It is obvious that increasing the concrete resistance leads to increasing the corrosion initiation time and standard deviation of the density function. The concrete physical and mechanical characteristics are effective variables on the corrosion initiation time but the threshold chloride concentration and the surface chloride concentration are insensitive variables on the mean of corrosion time but lead to significant changes in standard deviation of the corrosion time. Finally, Various diameters bars such as: 8, 12, 16 bars and 20 were investigated in time-depended area of the corroded steel of concrete beams. Results illustrated that and the cover depth is important variable in corroded crass section of bars. Also, increasing the bar diameter and decreasing the corrosion time period were leaded to reduce the rate of the crass section bars.

Many structures, such as dams, bridges and hydraulic structures, suffer deterioration induced by the alkali-aggregate reaction (AAR), which impairs the durability and safety of installations. ASR is an internal chemical reaction between certain forms of siliceous aggregates and alkaline pore solution in concrete. The result is a more or less crystallised silico-alkaline product which can exert pressure on the surrounding matrix. ASR induces concrete expansion and generally leads to loss of strength and cracking. The structural behaviour of concrete which has been effected by the alkali-silica reaction (ASR) is difficult to model due to various random parameters that govern this chemical process. The aim of this paper is to investigate the effect of ASR on the behaviour of reinforced concrete beams using three an experimental model, conventional structural analysis and the finite element method. For this purpose, 100 x 150 x 1100-mm concrete beams were built in the laboratory and reinforced with different ratios of compression and tension bars. Then ASR and creep strains were modelled by reducing the elastic modulus of the concrete and applying an equivalent tension force. For the purposes of verifying the numerical methods involved, fourteen beams were conditioned in a suitable environment using similar dimensions and loading systems. Experimental results on reactive concrete samples were simulated so as to test whether the model was capable of describing the behaviour of affected reinforced concrete beams under service loads. The comparison revealed that the finite element model had good compatibility with the acquired test results.

During some deflection tests of concrete beams, the measurement instruments are damaged in the concrete failure moment. Because of this damage, load-deflection data becomes insufficient and therefore application of a better method is in need. In the load-deflection relation, the reinforced concrete beam has an elastoplastic behavior and load-deflection curve can be obtained by an analytical model. The aim of this paper is to propose an analytical model to figure out the load-deflection curve in the situation that the measurement instruments are damaged. For this purpose, an experimental model is initially built and concrete strength parameters are calculated through the 4-point test. Then an elastoplastic analytical model is proposed and the same parameters are calculated again. Comparison of the results of two models shows that the error rate of the analytical model is less than 9 percent. Hence, the proposed model has a good agreement with the experimental model and is useful when the measurement instruments are damaged during the test.

Concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars exhibit large deflections and crack widths as compared with steel reinforced concrete beams due to the low modulus of elasticity of GFRP bars. Different studies show that ACI 318 equation for the effective moment of inertia Ie does not predict deflection well for FRP reinforced concrete beams. The purpose of this paper is to propose new equations for estimating the effective moment of inertia of FRP reinforced concrete beams based on genetic algorithm and experimental results. Genetic algorithm is used for optimization of error function between experimental and analytical responses. In the experimental part of the study, nine beam specimens were manufactured and tested. The parameters of reinforcement ratio and concrete compressive strength were selected as the variables for the beam specimens. Also fifty five beam specimens tested by other researchers were used for experimental database. In this paper, the effect of elastic modulus of FRP bars, reinforcement ratio and the applied level of loading on the effective moment of inertia is taken into account. In addition, the proposed equations are compared with different code provisions and the existing models for predicting deflection of FRP reinforced concrete beams. Also, the calculated values by the proposed equations are compared with different test results. The experimental results correlated well with the values predicted by the proposed equations especially in high reinforcement ratios and high levels of loading.