جستجوی مقالات مرتبط با کلیدواژه « reinforced concrete » در نشریات گروه « عمران »

This study aims to assess reinforced concrete moment frames designed at varying ductility levels within a typical reinforced concrete structure, from a reliability perspective. The article explores the probabilistic methods for designing different ductility levels in the current Iranian Concrete Code, focusing on reliability. Specifically, a three-story concrete moment frame structure, designed to low, medium, and special ductility levels as per the Iranian code, is studied. The reliability analysis encompasses uncertainties in loading, dimensional parameters, and evaluating structural performance functions such as floor drift and acceleration. The study utilizes horizontal earthquake components specified by the FEMA P-695 standard to analyze earthquake record uncertainties. Furthermore, a comparison of the reliability index and probability of failure for each performance function is used to assess failure uniformity. The findings reveal a maximum probability of failure in collapse damage state of approximately 9%, 5%, and 2% for low, medium, and special ductility frames, respectively.

Nowadays, the significance of structural design is increasingly considered especially in the structure of important buildings against blast loads due to the growing number of military attacks on structures and advancements in armament technologies. In this order, some research has been always conducted to analyze structures confronting blast loads and achieve methods for reducing the related damages. In the present research, a novel method is also presented for the reinforcement of concrete slabs and consequently, the improvement of slabs’ performance under blast loads. Instead of using steel rebars, perforated steel plates are utilized for reinforcing the concrete slabs in this method. In order to investigate this system of reinforcing the concrete slabs under blast loads, models of concrete slabs reinforced by perforated plates and by rebars with an equal volumetric percentage of steel were simulated and evaluated in the ABAQUS software under two blasting scenarios. The findings illustrated that the center of slabs has had less displacement in concrete slabs reinforced with perforated plates under blast loading caused in the air. However, some damages have been seen on the backside of those slabs as local punches in the center of the slab under the blast loading. These slabs are more prone to concrete scaling compared to the slabs reinforced by rebar. In this regard, there was an attempt to use corrugated perforated plates or utilize perforated steel ribs as stiffeners so that the interaction between concrete and the reinforcing system of the slab increases. The results also demonstrated that utilizing perforated plates with some perforated ribs can passably reduce the displacement of the slab’s center and also the damage in the slab tremendously improves.

Composite members consisting of steel beam and CFT concrete column have been of great interest in the last few decades. Tubular columns are highly desirable in bending frames due to their high bending and twisting resistance and stiffness. Composite columns have considerable capabilities and efficiency due to the simultaneous benefit of the beneficial properties of steel and concrete materials. Also, the presence of concrete core in the CFT column causes the local buckling in the steel wall of these columns to be delayed. Therefore, proposing a suitable connection between the steel beam and the composite column makes it possible to take advantage of the potential benefits of these sections. Concrete in steel columns was initially used as a protective layer against impact and especially fire. This is because steel sections in extreme heat, very vulnerable and exposed to fire quickly lose their mechanical properties, as an example of the destruction of the two famous World Trade Towers 11 (WTC), September in America, which is one of the reasons The main effect of fire was to reduce and lower the mechanical properties of the steel used.

One of the challenges of using reinforced concrete structures is the corrosion of reinforcements in aggressive and corrosive environments such as offshore structures, stairs, etc., which will eventually lead to the destruction of concrete structures. To solve the corrosion problem in this category of structures, experts turned to the use of rebars with epoxy coating as a suitable alternative to conventional rebars. Most FRP rebars on the market today are made of high-performance continuous fibers such as glass, carbon and aramid, which are embedded in a polymer substrate by various composite production methods. FRP amplifiers are commonly used in various forms in the form of networks, rebars, textiles or cables. In this research, the numerical behavior of FRP hybrid reinforced concrete compression members and its modeling under concentric loading is investigated. All modeling is performed in ABAQUS finite element software and is evaluated using nonlinear analysis.

It is essential to properly understand the seismic behavior of reinforced concrete (RC) columns confined by stirrups that experience different corrosion rates. The current study investigated the effect of seismic performance indicators such as strength loss, energy dissipation rate, ductility and hysteresis damping on specimens and models for different stirrup corrosion rates. Analysis revealed the adverse effects of corrosion on the bond performance between the concrete and steel bars which affected the seismic performance of the columns. It was observed that severe corrosion of the stirrups undermined confinement of the concrete core and caused the seismic response to degrade. This changed the failure mode from a ductile to a brittle state. As the corrosion rate of the stirrups increased, their ductility and energy dissipation capacity decreased such that the amount of decrease depended on the corrosion rate. An attenuation relationship is proposed for the corrosion rate of the stirrups for different stirrup yield strengths, concrete compressive strengths, concrete covers and stirrup spacing. The values estimated by the proposed relationship were shown to be in acceptable agreement with the analytical results.

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 use of reinforced concrete wall of the coupling causes better control of lateral displacement and also more energy dissipation due to the earthquake. This paper examines the types of energy demands in coupling walls in which two reinforced concrete walls are coupled by reinforced concrete beams. First, the structures are designed using the spectral analysis method according to valid regulations and then by preparing a nonlinear model of the wall with fiber elements in PERFORM-3D software and performing time history analysis due to near and near earthquakes faults, input energy, kinetic energy, energy Damping and inelastic energy are investigated and the contribution of reinforced concrete beam and wall to energy dissipation is studied. Two approaches, single plastic hinge (SPH) and extended plastic hinge (EPH), are considered for reinforced concrete walls. In the SPH approach, the plastic joint is traditionally allowed only at the foot of the reinforced concrete wall, and the rest of the wall is modeled elastically. In the EPH approach, the entire wall has the ability to expand plasticity. The results showed that in all structures, the share of coupling beams in inelastic energy dissipation is higher than the share of reinforced concrete walls. On average, in the EPH approach, the share of beam beams is about 60% and the share of reinforced concrete walls is about 40% of inelastic energy, and these numbers in the SPH approach are about 77% and 23%, respectively. The reason for the increase in the share of coupling beams from inelastic energy in the SPH model is that the wall is elastic at 90% of its height and the share of the wall decreases, and therefore the share of coupling beams in inelastic energy will increase.

The use of post tensioned flat slabs is common in structures that require the construction of long span. The main advantages of using this type of slabs are increasing the span to thickness ratio, deflection control and reducing the thickness of the floor. Post tension slabs are usually designed to withstand gravitational loads in the building. However, slab column connections in these systems must be able to withstand the deformations created by lateral loads and have sufficient ductility. In this research, an exterior unbonded post tensioned slab column connection is validated in ABAQUS finite element software. After ensuring the accuracy of the numerical model results, the effect of concrete compressive strength, the amount of effective prestressing levels and the tendon bonding influence in the seismic behavior of post tension slab joints are investigated. The results showed that the compressive strength of concrete and the prestressing level of concrete have a significant effect on the load-bearing capacity and ductility of the joints, while the bonding condition does not have much effect on the behavior of the joints.

Deep beams are members considered to have span to depth ratio less than 4. These beams are widely used in different sorts of structures including dams, reservoirs, silos, caissons and high-rise buildings. The cracking mode of deep beams is mainly dependent on their boundary conditions. Due to the rule of shear failure, deep beams are designed against shear. So, strengthening and repairing these beams has always been important to improve shear resistance. One of the applied methods is the use of CFRP fibers for repairing and strengthening deep beams. These fibers can be fabricated in the form of strips, sheets and rebars. Due to the constructional limitations, CFRP strips are frequently installed on the external surface of beams. For this reason, the failure of strengthened beams coincides with debonding of CFRP strips. The former experiments indicate that strengthening deep beams with CFRP strips is useful for improving their behavior. These experiments also indicated that parameters including strengthening angle, shear span to depth ratio and the method of CFRP installation can affect the strength increment due to CFRP. One of the other remarkable parameters that affects the behavior of reinforced concrete beams is size effect. This parameter matters when the geometry of struts and nodal zones remains slender in deep beams. To assess the intensity of size effect in deep beams, the force strength of beam must be normalized based on the compressive strength of concrete and the beams sections area. This study was conducted to investigate the effect of CFRP strengthening on the size effect on deep beams. It was aimed to use explicit dynamic analysis method in Abaqus software so as to model and analyze 53 CFRP-strengthened deep beams with evaluation of previous experiments. In this method, due to the absence of excessive iterations within each analysis step, the number of analysis steps is increased. The so-called method is also appropriate for simulating quasi static models. To reach the purpose of study, the specimens of three different experiments were modeled and analyzed to evaluate the assumptions of numerical modeling. After the evaluation conditions were satisfied, 53 deep beams were modeled in Abaqus software. The specimens were subjected to two incremental point loads and were divided into four-member groups with depths of 400 mm, 600 mm, 800 mm and 1000 mm. The beams shear span to effective depth ratios are 0.5, 1 and 1.5; The compressive strength of concrete also varied from 24.8 MPa to 35 MPa. Since changing the width of deep beams does not affect the intensity of size effect, the beams width was considered constant and equal to 80 mm.The results of the study indicate that strengthening deep beams with CFRP strip or sheet is suitable for reducing the size effect; In addition, increasing compressive strength of concrete and keeping the loading plate constant can amplify size effect of deep beam. Increasing shear span to effective depth ratio of beam caused the size effect to be decreased. Strengthening deep beams with both angles of 45 and 90 degrees was appropriate for decreasing deep beams size effect.

Alkali-Aggregate Reaction (AAR) is a type of destructive and time-dependent chemical process in concrete that occurs between alkali ions in the cement and reactive minerals in certain types of aggregates. First recognized in 1930s, AAR is divided into two major categories of Alkali-Silica Reaction (ASR) and Alkali-Carbonate Reaction (ACR), both of which produce an expansive gel in the concrete which expands as a result of water absorption. The expansion of the AAR gel exerts significant internal pressure in the concrete, which may lead to internal and external cracks. With the occurrence of such cracks, many parameters affecting the stiffness and strength of the structure, such as compressive strength, tensile strength, and modulus of elasticity are diminished. As a result, the safety and serviceability of the structure may be seriously impacted. While advances in concrete materials science have led to means to prevent AAR in new construction, numerous existing structures worldwide, such as dams, power plants, and bridges, are affected by these reactions, the replacement of which may be impractical, or in some cases, impossible. As a result, it is crucial to simulate the behavior of such structures for reliable estimation of their safety and providing rehabilitation measures as necessary. One of the major indicators of AAR is the anisotropic expansion it generates inside the concrete member, which changes drastically based on the boundary conditions and internal and external restraint imposed on the expansions. As a result, the prediction of the anisotropic expansions is of utmost importance in successful simulation of AAR-affected reinforced concrete structures. This paper presents a practical simulation methodology for estimating the directional distribution of AAR expansions. The methodology makes use of the user subroutine capability in the finite element software Abaqus. A mathematical model is used to simulation AAR-related expansion based on the stress tensor, whereas concrete damage is simulated using the concrete damage plasticity model. The model is used to simulate a variety of AAR-affected reinforced and plain concrete cube and beam specimens for which the directional expansion data have been reported in the literature. Comparison between numerical and experimental results shows that the proposed methodology is capable of reliably simulating the AAR-induced expansions and the interaction between AAR expansions and the ensuing damage for a variety of reinforcement configurations. The model showed that the yield strength of reinforcing bars plays a major role in the directional distribution of expansion. However, changes in the mechanical properties of concrete were found to be inconsequential in the distribution of the expansions. Moreover, changes in distance between reinforcing bars and the reinforcement ratio in each direction were observed to affect the accuracy of the model. However, the model was found to be successful in reasonably capturing the trends in all case studies investigated. The results of this study are of great value to the simulation of AAR-affected reinforced concrete structures.

Evaluating the vulnerability of bridges to flooding is essential for risk-informed planning of their maintenance. This paper aims to develop a systematic model for investigating the behavior of bridges at the time of flooding, in which structural, geotechnical, and hydraulic parameters are considered. A three-dimensional finite element model of reinforced concrete bridge piers was developed, in which the material nonlinearity and the interactions between the pier and the surrounding soil and the flood water were considered. The parameters used in the model were validated based on experimental data from a single pile and a reinforced concrete column under axial and lateral loading. The validated modeling approach was then used to simulate an existing bridge pier, for which the structural, geotechnical, and hydraulic parameters were varied to evaluate the effective parameters. The results showed that the presented modeling approach is capable of providing reliable predictions of the performance of bridge piers at the time of flooding, which makes it suitable for practical vulnerability assessment of bridges. Moreover, it was observed that the behavior of the bridge piers against floods was more sensitive to geotechnical and hydraulic parameters than structural parameters, to the level that by changing the soil type from medium sand to loose sand, the lateral displacement of the structure is 1.87 times. Also, by increasing the longitudinal slope from 0.004 to 0.005 and decreasing the roughness coefficient from 0.025 to 0.021, the lateral displacement of the structure will change to 2.57 and 6.55 times its initial value, respectively.

Reinforced concrete structures with standard steel rebar are vulnerable to corrosion and harsh environmental conditions, hence RC structures reinforced with fiber-reinforced polymer (FRP) rebar were commonly used these days. Du to FRP rebar’s better performance such as high strength, low self-weight, electromagnetic transparency and, as mentioned, non-corrodibility nature, using them as reinforcing bar is very widespread now. Because of financial matters, between different kinds of FRPs, GFRP is a better choice. Considering GFRP’s high strength and elastic behavior until failure, Although a large amount of reinforcement ratio is needed in composite beam components, the flexural stiffness of GFRP rebar reinforced beams is relatively lower compared to steel-RC, and more deflection and cracking are allowed in the serviceability design of these beams. Recently, shear and flexural behavior of continuous concrete beams reinforced with GFRP bars has been well investigated. Because of linear elastic behavior of GFRP materials until failure, considering moment redistribution in analysis and design of these beams is not allowed in almost all of cods and guidelines. Although many experimental and numerical researches investigated the moment redistribution in FRP-RC continuous beams with rectangular section, the behavior of these beams with T-section is almost unknown. This paper is a numerical investigation of existence and variety of moment redistribution in concrete continuous T-section beams reinforced with GFRP bars using finite element method with ABAQUS software. The verification of numerical models was done with some experimental beams, so the simulation can be used for further researches. The considering variables included the longitudinal reinforcement percentage, the number of main bars with constant bar ratio, transverse reinforcement ratio, stirrup space with constant ratio and constant bar size. For investigating mentioned parameters, 35 beams were modeled in software according to Canadian design and construction of building structures with FRP code, so 5 groups of beams were made which one beam is constant in each group. T-section beams were modeled assuming which failure happens because of concrete crashing not rebar failure. Deflection and serviceability were not interested, so bond-slippage behavior of GFRP rebar with concrete is not considered in modeling. Problem is indeterminate, so the percentage of moment redistribution was determined by comparing the reactions resulted from numerical and elastic analysis. Load-deflection and load-moment redistribution curves were used to discuss. The results show, as there is in steel-RC structures, moment redistribution exist in GFRP-RC continuous beams with T-section; however the amount of it is lower. Amount of bars between 2.5 times of balance reinforcement ratio and 3.5 times of it, in top and bottom of beam, shows the highest flexibility load and moment redistribution capacity. Increasing the number of main bars with constant reinforcement ratio and increasing the stirrup space with constant transverse reinforcement ratio reduce the moment redistribution capacity. It seems that the minimum amount of transverse reinforcement considered in Canadian code is not enough for preventing shear failure in these beams. So, with considering some points, the moment redistribution can be taken to account in analysis and design of GFRP-RC continuous beams with T-section.

Although infill panels are considered as non-structural elements in analysis and design process of building frames, these members may significantly affect the seismic performance of the frames. Nowadays, tendency to design and construct the irregular buildings has increased. Behavior factor plays an important role in the seismic design of buildings. Seismic codes usually present the same Behavior factor for the regular and irregular lateral load-carrying systems. In this investigation, the influence of masonry infill walls on the behavior factor of the vertically irregular moment resisting reinforced concrete frames was evaluated. To do so, 3-, 6-, 9- and 12-story moment resisting reinforced concrete frames with various types of vertical irregularities were considered. These frames were assessed with/without considering the influence of infill walls. The capacity curves of the frames were derived using incremental dynamic analysis using 14 acceleration ground motions and then the behaviour factors were achieved. Outcomes demonstrated that infilled frames present higher response modification factors and more efficiently performance in lateral load-carrying rather than bare frames. Furthermore, it was shown that vertical irregularity affects the seismic responses and the behavior factor of moment resisting reinforced concrete frames. Eventually, two approximate relations were developed to acquire the response modification factors of bare- and infilled- vertically irregular moment resisting reinforced concrete frames.

One of the favorable structural mechanism to mitigate the progressive collapse in reinforced concrete structures and increase the load-carrying capacity is the mechanism of compressive membrane action. In the present study, for predicting the compressive membrane capacity, an analytical model for analysis of reinforced concrete beams is used. This analytical model is formulated based on a sectional analysis approach to establish equilibrium and compatibility conditions at each section along the length of the beam. Programming of the analytical model for analysis of RC beams was carried out with FORTRAN software. In order to investigate the membrane action in slender RC beams, several beam specimens with different span-depth ratio are analyzed in parametric studies. Analyzes are carried out to investigate the effect of four parameters of concrete compressive strength, reinforcement ratio, axial stiffness and rotational stiffness of the support on the membrane action in RC beams. The results show that with increasing the span-depth ratio, the effect of membrane action on beams decreases. It is also observed that the effect of all four parameters on the load-carrying capacity is greater in short beams. In evaluating the effect of support stiffnesses on the membrane action response, it was also observed that membrane action capacity increases with restraint stiffness only in the regime of weak restraints. Axial stiffness and span-depth ratio have the highest effect on axial restraint response, and also it is observed that rotational stiffness of the support and span-depth ratio have the highest effect on the maximum midspan deflection response.