Failure Mode Of Reinforced Concrete Beams Research Articles

Strengthening of flexural behavior of reinforced concrete beams by using hybrid fibers: experimental and analytical study

The research investigates the flexural behavior of reinforced concrete (RC) beams by incorporating hybrid fibers (a combination of glass and steel fibers). Ten specimens measuring 150 mm x 200 mm x 1500 mm were cast and tested under two-point loading. The specimens were divided into three groups, each containing three specimens. Additionally, a control specimen was examined. Comparing the strength performance of each group to the control specimen revealed that the hybrid fiber-reinforced beams exhibited increased strength. The optimal hybrid fiber composition was 0.4% steel and 0.2% glass fiber. Similarly, the optimal steel and glass fiber percentages were both 0.4%. Experimental results showed that the load-carrying capacity improved significantly: 28.80% with glass fiber, 63.74% with steel fiber, and 79.23% with hybrid fiber compared to conventional RC beams. The study evaluated load-carrying capacity, load deflection, ductility, stiffness, and failure modes of RC beams. An analytical study using finite element modelling was conducted, and the analytical results were compared to experimental findings. Fundamental statistical values included mean, standard deviation, and coefficient of variation for load and deflection. Finite element analysis (FEA) was employed to predict experimental outcomes, and the analytical results closely correlated with experimental data. The load mean, standard deviation and coefficient of variation were 0.98, 0.01, and 0.56, respectively. The deflection exhibited corresponding values of 0.97, 0.01, and 1.41. The graphical abstract of the present study is displayed in Figure 1.

Numerical study on the torsional behavior of CFRP-strengthened RC beams

The present paper offers a numerical study on the behavior of reinforced concrete (RC) beams strengthened with carbon fiber reinforced polymer (CFRP) under pure torsional loading. The failure mode of RC beams significantly changed in accordance with torsional loading. Therefore, the effect of strengthening RC beams by CFRP under torsion is a vital area of study. This paper attempted to fill the gap by conducting a numerical (Abaqus) study, whereby the numerical investigation was in line with the parametric for a previous study of an experimental program. The numerical model achieved agreement with the results of the experimental program, then, this model was used by applying CFRP, instead of GFRP. Additionally, the numerical study was completely in line with the parametric study in terms of sample dimensions, steel reinforcement, number of FRP layers, and width of FRP strips, for the aim of comparing results. The comparative evaluation in this study aims to contrast the behavior of RC beams strengthened by CFRP with the behavior of those strengthened by GFRP under pure torsion. Parameters such as ultimate torsional moment, and the maximum angle of twist were studied. The study revealed that strengthening with CFRP improved the ultimate strength and post-cracking stiffness, in addition to localizing the damage.

Behavior evolution and deformation prediction of RC beams with double openings under fatigue loading

In the design of complex high-speed railway platforms, bridges, and other transport hub structures, openings need to be made in the reinforced concrete (RC) beam web due to the laying of pipeline lines. The performance degradation caused by the openings is a concern for the RC beam under fatigue load. To study the fatigue performance of RC beams with double openings, six RC beams with double openings were designed, with the load level ratio, location of loading points, and number of fatigue cycles as changing parameters. Fatigue tests were carried out under repeated loads. The stress state and failure mode of RC beams with double openings under fatigue load were studied, and the influence of various parameters on the fatigue performance of beams with double openings was discussed. The deformation compatibility model of opening and mid-span deformation was proposed, and the deformation evolution law of double-opening RC beam is analyzed based on the model. The results indicate that under cyclic loading, the fatigue failure modes of double opening RC beams are inclined cracks in the upper and lower beams of the opening and cracks in the corner of the opening. The specimen with a maximum load limit of 0.7Pu and a load position acting on the middle of the opening undergoes fatigue failure. The double opening RC beam has a fatigue life of at least 410000 cycles under a load level of 0.5Pu. After the fatigue test, the remaining ultimate bearing capacity, flexural stiffness, and ductility of the RC beams deteriorate with the increase of load level. The residual performance of the specimen after fatigue is even worse when the load is located in the middle of the opening. Increasing the fatigue cycle to 410000 cycles has an impact on the remaining ultimate bending moment of about 7% and the remaining flexural stiffness and ductility degrade by about 25%. Based on existing research results, a fatigue deformation prediction method for RC beams with double openings was proposed, with an error of less than 7%.

An experimental study on RC beams shear-strengthened with Intraply Hybrid U-Jackets Composites monitored by digital image correlation (DIC)

Reinforced concrete (RC) beams are commonly strengthened using steel stirrups, but these materials have limitations such as added weight and susceptibility to corrosion. Fiber-reinforced polymers (FRPs) offer a promising alternative to steel stirrups with high mechanical performance, low density, and resistance to corrosion and chemicals. In particular, Intraply Hybrid Composites (IRCs), which comprise multiple fibers oriented in different directions within a single matrix, have recently gained attention in the construction industry. Cakir et al. [1] investigated the use of three types of IRCs (Aramid-Carbon (AC), Glass-Aramid (GA), and Carbon-Glass (CG)) for strengthening 2-meter-long RC beams (the ratio of shear span (a) to effective depth (d) equals 3 (a/d = 3)) against shear fractures. In this study, the effects of these IRCs on the shear strength of 1.5-meter-long RC beams (a/d = 2) without transverse reinforcement were examined. In this scope, four-point bending tests were conducted on the beams after U-shaped IRC strengthening, and the impact of IRCs on shear strength was evaluated using both digital image correlation and classical measurement equipment such as strain gauges and linear variable differential transducers. The maximum load measured in RC1.5 was 194.50 kN, while the ultimate load capacity reached 265 kN in AC1.5, 246 kN in GA1.5, and 229 kN in CG1.5 after strengthening, representing increases of 36%, 26%, and 18%, respectively, compared to RC1.5. Additionally, the maximum mid-span deflections were determined as 30.40 mm, 16.10 mm, 22.20 mm, and 36.40 mm for RC1.5, AC1.5, GA1.5, and CG1.5, respectively. Moreover, the experimental results were compared with the predictions obtained from the international codes. It should be noted that the failure modes of RC beams are directly affected by the type of IRCs used, highlighting the significant contribution these materials can make to the structural behavior of RC beams.

Fatigue response of RC beam strengthened by BFRP laminate

Strengthening RC structures become more essential due to its deterioration, updating in new design codes, lack of quality control, and changes in the use of the structure. The technique of external bonding fiber reinforced polymer is recognized as a convenient method for repairing existing reinforced concrete structures and provides immediate shelter rather than replacement of the whole existing structure. Basalt Fiber Reinforced Polymer gaining more demand in recent research due to its eco-friendly properties. In this regard, this research investigates the efficaciousness of externally bonded Basalt Fiber Reinforced Polymer (BFRP) laminates in the reinforced concrete beam under repeated load. BFRP is externally bonded at the soffit of reinforced concrete (RC) beams to enhance its fatigue resistance. The load-deflection relationship, stiffness, crack pattern, and energy dissipation capacity of the BFRP-reinforced concrete beams are experimentally investigated and validated with the ANSYS simulated results. The experimental results exhibits that the BFRP reinforced concrete beams enhances the fatigue response, load carrying capacity and prevention of premature failure. The numerical results are validated with the experimental results which are found to be correlated with negligible deviation. Also, both investigations reveal the failure mode of RC beams, which helps fatigue life prediction in its application.

Time-Variation of Shear Forces Affecting the Impact Resistance of Reinforced Concrete Beams

One of the most hazardous scenarios for reinforced concrete (RC) members is due to the actuation of impact loads. Such impacts may be either accidental or induced events. Experimental research has demonstrated that the failure mode of RC beams is strongly governed by shear, due either to the formation of a shear plug close to the impact point or to the full development of inclined shear-bending cracks along the shear span. In order to analyze the shear strength under impact conditions, it is essential to understand how the development of inertia forces leads to a time-dependent distribution of shear forces and bending moments which differs significantly to those produced by quasi-static loads. In the paper, an experimentally-based determination of shear forces and follow-up of crack pattern is presented for RC beams tested under impact loads. A Digital Image Correlation technique supported by a high-speed camera is used to understand the evolution of shear forces at critical sections and to discuss the ultimate shear strength provided by M-V interaction diagrams.

Study on the residual performance of RC beams exposed to processed temperatures and fire

PurposeThe Reinforced Concrete(RC) elements are known to perform well during exposure to elevated temperatures. Hence, RC elements are widely used to resist the extreme heat developing from accidental fires and other industrial processes. In both of the scenarios, the RC element is exposed to elevated temperatures. However, the primary differences between the fire and processed temperatures are the rate of temperature increase, mode of exposure and exposure durations. In order to determine the effect of two heating modalities, RC beams were exposed to processed temperatures with slow heating rates and fire with fast heating rates.Design/methodology/approachIn the present study, RC beam specimens were exposed to 200 °C, to 800 °C temperature at 200 °C intervals for 2 h' duration by adopting two heating modes; Fire and processed temperatures. An electrical furnace with low-temperature increment and a fire furnace with standard time-temperature increment is adapted to expose the RC elements to elevated temperatures.FindingsIt is observed from test results that, the reduction in load-carrying capacity, first crack load, and thermal crack widths of RC beams exposed to 200 °C, and 600 °C temperature at fire is significantly high from the RC beams exposed to the processed temperature having the same maximum temperature. As the exposure temperature increases to 800 °C, the performance of RC beams at all heating modes becomes approximately equal.Originality/valueIn this work, residual performance, and failure modes of RC beams exposed to elevated temperatures were achieved through two different heating modes are presented.

Impact resistance of ultra-high performance concrete strengthened reinforced concrete beams

To improve the impact resisting performance of reinforced concrete (RC) components, three strengthening designs based on ultra-high performance concrete (UHPC) are proposed in this study. Drop hammer impact test was conducted to evaluate the dynamic response and failure modes of RC beams and UHPC strengthened RC-UHPC beams. Test specimens included two control RC beams, a RC beam with UHPC layer retrofitted on the tension surface, a RC beam with UHPC layers retrofitted on both the compression and tension sides, two RC beams with UHPC layer that was not directly attached to the tension surface, but with 5 mm gap between the interfaces. Test results showed UHPC strengthened beams had a good impact resistance. Under the impact from 641 kg weight dropping from 0.5 m, with a 15 mm UHPC layer directly attached to the tension surface of the RC beam, the crack pattern shifted from concrete spalling to diagonal shear failure, and the maximum and residual displacements decreased by 9.1% and 25.3%, respectively. RC-UHPC beams with non-attached interfaces exhibited even better impact resistance, the UHPC layer was able to develop multiple energy dissipating tensile cracks prior to failure, and the gap ensured a larger moment resistance leading to reduced beam deflections. The repeated impacts were performed on RC-UHPC beams. With the same total impact energy, the single impact was found to be more hazardous than the repeated impacts. Nonlinear finite element modelling was developed to further interpret the experimental results. With the validated numerical model, energy absorption curves, dynamic shear force and bending moment distribution diagrams were derived. Based on the experimental and numerical data, the shear mechanisms of RC beams and RC-UHPC beams were studied. The effects of non-attached spacing length, spacing depth and UHPC layer thickness were investigated in the parametric study.

Investigation of support type effect on plastic hinges in RC beam under impact load

AbstractThis study investigates the effect of support types on plastic hinges in reinforced concrete (RC) beam under the influence of impact loading. In previous studies, the assumption of the linear distribution of inertia force under impact loading was examined and verified according to experimental, analytical, and numerical results. Furthermore, it was emphasized that the most important parameters affecting the behavior of RC beams under impact loading were plastic hinges. A three‐stage study was planned to investigate this subject. The first stage was an experimental study. In this part, four RC beams with simple and fixed supports were tested under the low‐velocity impact load with two different impact energy levels by using a free‐weight test setup with advanced measurement techniques. The time histories of the accelerations, the displacements, and the impact loads acting on RC beams were recorded, and the cracks from impact loading were observed. The dynamic responses obtained from experiments have been interpreted in detail. The most important issue about plastic hinges was that the hinges do not reach the supports and remain on the beam. This is valid for both hinge support and fixed support. In the second stage of the study, an explicit numerical analysis model, which was verified with experimental results, was developed. The clear agreement between the experimental and numerical results was demonstrated. It has been concluded that proposed finite element procedures can be used for evaluation of the dynamic responses and failure modes of RC beams under low‐velocity impact loading. The last part was an analytical study. In this part, the proposed analytical procedure in the previous studies considering the plastic joint formed in a simple support beam under impact loading was confirmed, and a new coefficient for fixed support was proposed. A good agreement has been achieved between analytical and experimental work.

Retrofitting of RC beams using FRP techniques: a review

In structural and civil engineering, reinforced concrete structures are susceptible to inordinate loadings such as earthquake disasters, terrorist attacks and accidental impacts. This prompts an increasing desire to strengthen as well as enhance the fatigue performance and extend the ability of fatigue life of reinforced concrete structural components especially beams. Since 2003, Iraq has suffered major damage to the structural buildings, so it has become an important issue to study the existing concrete structures. Among the different techniques of rehabilitation of existing structures, fibre reinforced polymer (FRP) as an external bonding has been considered as a popular one. This paper reviews several features of Reinforced concrete (RC) beams strengthened with FRP. Also this paper aims to impart a comprehensive insight on adhesive curing, surface arrangement, and failure modes of RC beams modified with FRP. This effect of FRP for enhancing the techniques of rehabilitation is a three-fold task, to strengthen and retrofit of concrete structures, to extend the fatigue life of the structural element, and eliminates the crack growth rate.

Impact resistance of RC beams under different combinations of mass and velocity: mesoscale numerical analysis

The concrete structures under impact loading duress may be destroyed within an extremely short period of time. The importance and complexity of exploration on the impact resistance of concrete members make this area still open for discussion. In the present study, a 3-D mesoscale numerical model was established to investigate the effect of the combination of impact mass and velocity on the mechanical behavior of reinforced concrete (RC) beams subjected to impact loadings. Heterogeneity of concrete and strain rate effects of concrete and steel bars were taken into account. Furthermore, nonlinear interaction between the concrete and steel bars was considered herein. Results from macroscale and mesoscale simulation were compared with the available physical tests, indicating that the mesoscale numerical model can better represent the influence of heterogeneity of concrete on the mechanical behavior of RC beams. Five different impact energy levels were involved to study the effect of the combination of impact mass and velocity on the impact resistance of RC beams. At last, the residual bearing capacity and natural frequency of impacted RC beams were numerically calculated and their relationship was discussed. It is indicated that the deformation of RC beams is influenced strongly by the impulse, which increases with the increasing impact mass at identical impact energy. Besides, the failure mode of RC beams turns from shear-dominant failure mode to bending shear failure mode with the increase of impact mass, accompanied by the increase of energy dissipation of steel bars and the whole member. Despite this, in the present work, the combination of the impact mass and velocity had little influence on the damage extent (based on the performance) of the RC beams. Moreover, an empirical relationship between the residual bearing capacity and the natural frequency of the impacted RC beams was established as a rough reference for damage evaluation in engineering practice.

Shear Capacity of RC Beams Strengthened with Flax Fiber Sheets Grafted with Nano-TiO2.

Flax fiber sheets provide the advantages of high specific strength, a short growth cycle, environmental friendliness, wide availability, and low cost. Therefore, in this study, the shear capacities of reinforced concrete (RC) beams strengthened with ordinary flax fiber sheets, flax fiber sheets grafted with nano-TiO2, and unidirectional basalt fiber sheets were compared. The bearing characteristics and failure modes of RC beams strengthened with flax fiber sheets were investigated. The results showed that after reinforcement with flax fiber sheets, the bearing capacity and mid-span deflection of the RC beams are considerably improved, and the reinforcing effect of flax fiber sheets grafted with nano-TiO2 is greater than that of unmodified flax fiber sheets. After reinforcement with flax fiber sheets grafted with nano-TiO2, the shear capacity of the RC beams is considerably improved to 653 kN, which is 72.8% higher than that of the unreinforced RC beams. Meanwhile, the mid-range deflection of the beam reached 14.6 mm, which is 75.9% higher than that of the unreinforced RC beams.

Impact resistances of RC beams at/after high temperature: Meso-scale analysis

Impact (or blast) and fire often take place simultaneous and threaten the service life of buildings. The coupling effect of high temperature and high strain rate on the reinforced concrete (RC) structures has aroused wide concern of researchers. Based on the heterogeneity of concrete, a meso-scale numerical model was established to study the impact resistance of RC beams at/after high temperature. The strain rate effect of both concrete and steel bars and their performance degradation affected by fire and bond-slip behavior between them were taken into account. The effectiveness of numerical model was validated by comparing the results observed from the simulation and drop hammer test at room temperature. Then the impact responses of RC beams at/after high temperature was compared and analyzed. It is indicated that the proposed numerical method can effectively describe the failure mode of RC beams under the combined effect of fire and impact. RC beams at high temperature exhibit more serious damage than those specimens after cooling down at specified fire duration. The difference is widening along with the increase of fire duration.

Influence of drop weight geometry and interlayer on impact behavior of RC beams

A number of drop weight tests on reinforced concrete (RC) beams have been reported in literature. These tests conducted by different researchers used drop weight of different geometries. Some researchers also placed an interlayer between the drop weight and RC beam in the tests, while others directly dropped the weight on the beam. These different testing configurations surely affect the testing results. However, only very limited studies have been conducted to investigate their effects on the impact behavior of RC beams. In this study, the influence of drop weight geometry and interlayer on the impact behavior of RC beams is numerically investigated by using explicit finite element code LS-DYNA. The numerical models of RC beams subjected to drop weigh impact are verified by available testing data. With the calibrated model, the responses of RC beams impacted by five commonly used drop weights are analyzed and discussed. The effect of steel plate or rubber pad interlayer between drop weight and RC beam is also investigated. It is found that both the drop weight geometry and interlayer property significantly affect the impact loading profile and the failure mode of RC beams. Furthermore, although most drop-weight tests assume vertical impact, small inclination angles of drop weight impacting on beams might occur. The influence of this small testing error on testing results is also investigated.

Experimental investigations of failure modes of reinforced concrete beams without web reinforcement

This paper reported an experimental investigation into the stochastic nonlinearities inherent in reinforced concrete (RC) beam without web reinforcement. A series of specimen tests were conducted with a static monotonic four-point bending regime. Three kinds of RC beams (total of 27 specimens) without web reinforcement of three shear span-depth ratios of 5.1, 4.6 and 4.0 were designed. Each kind of beams had 9 samples. All beams were constructed in the same condition and at the same time. Specifically, the materials (both concrete and reinforcement bars) used in the beams were derived from the same batch, and the same testing program was performed during the experiments. Statistical nonlinearity responses to beams with three shear span-depth ratios, including the strain-deflection curves of longitudinal reinforcement bars, crack patterns, failure modes, and load-deflection curves were obtained from the tests. Different failure modes occurred in the beams with the same shear span-depth ratio. The probabilities of different failure modes of RC beams without shear reinforcement were statistically calculated based on the test results. It is found that the randomness of the mechanical properties of the materials results in the stochastic initial damage distribution and the subsequent stochastic nonlinear evolution of the beams. In addition, the shear span-depth ratio is an important parameter, which significantly affects the stochastic failure mode in the investigated members.

Experimental and modelling of the flexural performance degradation of corroded RC beams under fatigue load

Corrosion of reinforcing bars accelerates the fatigue damage accumulation and significantly reduces the fatigue life of aging reinforced concrete (RC) bridges. This paper experimentally investigates the effects of corrosion on the fatigue behavior of reinforced concrete beams. An accelerated corrosion test is conducted in the laboratory conditions to obtain various corroded beam specimens. The initial crack width and the crack distribution are discussed. Based on the fatigue loading test, the load-deflection, fatigue crack propagation of concrete, fatigue life and the failure modes of RC beams after different fatigue cycles are investigated. Following that, a developed flexural stiffness calculation model for the corroded beams after fatigue is proposed. This model includes the effects of fatigue, corrosion-induced cracking and fatigue modulus degradation of concrete and other influential factors. The proposed method is validated with the experimental observations from various corroded RC beams of the current paper and available in open literature.

Dynamic responses of reinforced concrete beams under double-end-initiated close-in explosion

Abstract The reinforced concrete (RC) structural component might suffer a great damage under close-in explosion. Different from distant explosions, blast loads generated by the close-in explosion are non-uniformly distributed on the structural component and may cause both local and structural failure. In this study, an experimental study was conducted to investigate the dynamic responses of RC beams under double-end-initiated close-in explosions. The experimental results show that the distribution of blast loads generated by the double-end-initiated explosion is much more non-uniform than those generated by single-point detonation, which is caused by the self-Mach-reflection effects. A 3D finite element model was developed and validated in LS-DYNA by employing the modified K&C model. Intensive numerical calculations were conducted to study the influences of the initiation way, scaled distance and longitudinal reinforcement ratio on the dynamic responses and failure modes of RC beams. Numerical results show that the RC beam suffers greater damage as the cylindrical explosive is detonated at its double ends than the scenario in which the cylindrical explosive is detonated at its central point. RC beams mainly suffer flexural failure and flexure-shear failure under the double-end close-in explosion, and the failure modes of RC beams change from the flexural damage to flexure-shear damage as the scaled distance or the longitudinal reinforcement ratio decreases. The direct shear failure mode is not usually observed in the double-end-initiated explosion, since the intense blast loads is basically concentrated in the mid-span of RC beam, which is due to self-Mach-reflection enhancement.

Shear strength of reinforced concrete beams strengthened in shear using externally-bonded FRP composites

A shear strength estimation model for reinforced concrete (RC) beams, the so-called dual potential capacity model (DPCM), has previously been proposed by the authors. In this study, the DPCM is extended to estimate the shear strength of RC beams strengthened in shear by using externally-bonded fiber-reinforced polymer (FRP) composites. The proposed model has been derived so as to take into account the effects of the type of FRP composite, fiber-bonding configuration, and fiber layout, and it can also determine the critical shear failure modes of RC beams strengthened by externally-bonded FRP composites. To verify the accuracy of the proposed model, shear test results of 227 RC beams strengthened by externally-bonded FRP composites were collected from previous studies, and it is shown that the analysis results estimated by the DPCM agree well with those test results.

Parametric study of RC beams under a wide range of loading rates

Over the years, numerical investigation has been presented as a viable alternative to experimental studies, as testing of structural members to assess the effect of several parameters at a time is not only cumbersome but also expensive. Thus, after validating the results from a finite-element analysis with experimental outcomes, a numerical parametric study was conducted to investigate the effects of various parameters on the dynamic increase factor (DIF) of the maximum resistance and the failure mode of reinforced-concrete beams under a wide range of loading rates. From the results, it can be concluded that the DIF of maximum resistance for beams with a small amount of longitudinal reinforcement is greater than that for beams with a large amount of longitudinal reinforcement. A change in the failure mode can be observed (mainly at high rates, 2 m/s) when the longitudinal reinforcement ratio is increased (approaching the balanced-reinforcement ratio) in an under-reinforced beam. For beams with a large amount of transverse reinforcement, the DIF would be lower than for beam with a small amount of transverse reinforcement. Furthermore, it was found that the yield strength of longitudinal reinforcement is the key parameter affecting the failure mode change from flexure at static loading to shear at high loading rates.

Parametric study of RC beams under a wide range of loading rates

Over the years, numerical investigation has been presented as a viable alternative to experimental studies, as testing of structural members to assess the effect of several parameters at a time is not only cumbersome but also expensive. Thus, after validating the results from a finite-element analysis with experimental outcomes, a numerical parametric study was conducted to investigate the effects of various parameters on the dynamic increase factor (DIF) of the maximum resistance and the failure mode of reinforced-concrete beams under a wide range of loading rates. From the results, it can be concluded that the DIF of maximum resistance for beams with a small amount of longitudinal reinforcement is greater than that for beams with a large amount of longitudinal reinforcement. A change in the failure mode can be observed (mainly at high rates, 2 m/s) when the longitudinal reinforcement ratio is increased (approaching the balanced-reinforcement ratio) in an under-reinforced beam. For beams with a large amount of transverse reinforcement, the DIF would be lower than for beam with a small amount of transverse reinforcement. Furthermore, it was found that the yield strength of longitudinal reinforcement is the key parameter affecting the failure mode change from flexure at static loading to shear at high loading rates.