Structural Performance Of Reinforced Concrete Beams Research Articles

Structural performance of RC beams strengthened with hybrid bonded CFRP

Debonding at the interface between externally-bonded (EB) carbon fiber-reinforced polymer (CFRP) composites and the concrete limits the performance of CFRP-strengthened reinforced concrete (RC) beams. To mitigate the interface debonding and improve the material utilizing efficiency of CFRP, a hybrid-bonding (HB) technique was developed. HB CFRP system combines the adhesive bonding and mechanical fastening (i.e., anchoring the CFRP plate through bolted cover steel plate bonded on the surface of the CFRP plate). When interfacial debonding occurs, the friction between the steel cover plate and the CFRP plate and the reacted normal stress at the interface enhanced d the concrete aggregates interlocking and the bond strength of CFRP-to-concrete interface. Additionally, the normal stresses can be also activated through pre-tightening the anchors. Five HB CFRP-strengthened RC beams, two conventional EB CFRP-strengthened RC beams, and two un-strengthened RC beams were tested. Two different steel cover plates lengths and three different pre-tightening torques were adopted. The test results demonstrated that the HB technique improved the local bond behavior in the anchored regions, resulting in higher strength utilization efficiency of CFRP and increased load-carrying capacity of the strengthened beams. Such improvement was more significant when longer steel cover plates and higher pre-tightening torques were deployed.

Strengthening of RC beams with inadequate lap splice length using cast-in-situ and anchored precast ECC ferrocement layers mitigating construction failure risk

Design standards necessitate the use of a sufficient lap splice length when dealing with longer spans of Reinforced Concrete (RC) members. An inadequate lap splice length results in a reduction of both the flexural strength and ductility of reinforced concrete beams. The failure risk of these beams is considered a potential threat which is experimentally identified, numerically analyzed, and carefully mitigated in this research to increase building safety and sustainability to avoid risk of construction failure. The ongoing experimental and numerical research focuses on examining the structural performance of RC beams with insufficient lap splice length, which have been fortified through various applications of Engineered Cementitious Composite (ECC) ferrocement layers. A total of eleven beams, divided into four groups, were purposefully designed and tested under bending loads until they reached the point of collapse. The investigated parameters included the casting technique, installation strategy, and anchorage length (La) for such layers. Cast in situation and pre-casting scenarios were utilized in order to cast the strengthening ECC layers. The La for all layers was designed to be the main studied variable beside type of casting and installation technique. Three La values were studied: 30D, 40D, and 50D where D is the bar diameter of main reinforcement steel in tension side. It was found that, the application of chemical anchor bolts in cast in situation ECC ferrocement layers credited the higher enhancement in both cracking and ultimate stages by about 92–137% and 114–164% for cracking and ultimate levels, respectively. Then, the experimentally measured outcomes were employed for developing nonlinear Finite Element Models (FEMs) to simulate the performance of such ECC ferrocement layers that employed. The variance between numerical results and experimental counterparts ranged in between 6% and 9%, achieving an acceptable variance.

Structural performance of RC beams with openings shear strengthened by hybrid techniques (EBR/EBRIG)

Creating the openings in the existing reinforced concrete (RC) beams causes sudden deterioration, especially in the shear zone. This study investigates the effectiveness of a novel strengthening technology using externally reinforced fibre-reinforced polymer (FRP) strips in groves (EBRIG) on the shear behaviour of RC beams, compares it to that of externally reinforced (EBR) strips, and uses hybridisation between them to address the weakness brought on by the presence of an opening in the shear zone. Also, an innovative anchorage mechanism is suggested and studied to postpone the beginning of the strengthening system’s debonding. The strengthening material used in this research is glass fibre-reinforced polymers (GFRPs). For this study, 11 RC beams with an opening and a control beam without an opening, each measuring 120 × 300 × 2600 mm in size, were cast and subjected to the four-point loading test. All test beams had the same geometry and reinforcement details. The effect of the following parameters was investigated in this study: the dimension of the opening (square ‘150 × 150’ or rectangle ‘100 × 300’ mm), the strengthening technique used (externally bonded reinforcement [EBR], EBRIG and hybrid technique ‘EBRIG + EBR’) and the wrapping configuration of the strengthening (fully warped strips or U-shaped sheets with anchors). All techniques used raised the efficiency of shear resistance to approximate the fading effect of the opening, especially the technique of hybridising EBRIG and EBR. All strengthened beams showed an increase in the ultimate shear capacity ranging from 74% to 142% compared with the reference beams with the opening. The EBRIG technique shows numerous advantages over the EB system and can employ the strength of FRP materials. It also deals with the problems of weather factors that were facing EBR, and this is because of the covering that protects in the EBRIG technique. The technique to hybridize EBRIG and EBR was more effective at withstanding shear.

Numerical study on the behavior and strength of concrete beam strengthening with fiber reinforced concrete jackets

The recent experimental results for slender reinforced concrete beams with a thin steel fiber reinforced concrete (SFRC) jacket have demonstrated their feasibility in enhancing the performance in terms of serviceability and ultimate limit states and strongly suggested the need for a comprehensive analysis to show the effect of important parameters. Within this context, the bond between reinforced concrete (RC) beams and SFRC jacket is an essential parameter to avoid any slippage failure before the beam achieves its shear capacity. The behavior of the bonded element is affected by slip at the interface between the old and new concrete. However, it is common in design to ignore slip and consider the bonded element monolithic. The values of slip and shear stress relation of the strengthened element are reviewed in this paper. In addition, an analytical procedure for predicting the distribution of slip along the interface between the initial beam and the new layer of concrete is presented. The research paper aims to develop a detailed three-dimensional (3D) finite element (FE) model for evaluating the structural performance of RC beams strengthened with SFRC jackets taking into accountthe effect of the bond between the beam and the jacket. It also aims to investigate the effect of significant parameters on the response of strengthened RC beams in shear. These parameters are as follows: jacket compressive strength (30, 60, and 85 MPa), fiber volume fraction (0.5, 1.0, 1.5, and 3.0%), jacket thickness (30, 40, 50, and 60 mm), and spacing between shear connectors (100, 200, and 500 mm). The proposed model's results were compared to those of previous experimental research. The analysis result showsgood agreement with the correlating experimental measurement. The parametric study results proved that increasing the volume fraction of fiber, jacket thickness, and compressive strength of the jacketincreases ductility and shear capacity. Increasing the spacing between shear connectors has no noticeable effect on shear capacity but prevents debonding. Finally, reference equations were made to study the behavior of RC beams strengthened with SFRC jackets, taking into accountthe effect of the bond between the beam and the jacket.

Nonlinear Finite Element Analysis of Corroded Reinforced Concrete Beams

Corrosion in reinforcing bars is a major cause of concern for sustainability of Reinforced Concrete (RC) structures exposed to extreme environmental conditions. Various RC structures, such as bridges and buildings are adversely affected due to the rebar corrosion, reducing its global load carrying capacity and ductility. In order to ensure an earthquake resistant design of any structure, the ductility of structural members is of chief concern. However, corrosion of reinforcing steel in RC members reduces its seismic performance. Thus, for safety and economic viability of any RC structure, an effective maintenance and repair work strategy is necessary. Based on the strong column - weak beam design concept of RC frames, the beams are the first structural members to absorb damage due to earthquake. Thus, to carry out maintenance and repair work, structural health assessment of RC beams considering the effect of reinforcement corrosion is of utmost importance. The present study aims at establishing a relation between the amount of corrosion induced and its effect on the ductility of an RC beam. A 3D Finite Element (FE) model of an RC beam including the effects of corrosion for nonlinear performance assessment has been modelled in ABAQUS. The FE model is validated with past experimental study including the effects of corrosion. Modelling of uniform corrosion in reinforcement bars involves defining the loss of bond between rebars and concrete, inducing spalling stresses on concrete and reduction in the cross-section area of the rebars. Bond-slip model between surface of concrete and reinforcement has been incorporated through cohesive surface. Spalling stress for uniform corrosion is applied in form of outward uniform pressure on the reinforcement and concrete interface. The cracking of cover concrete due to corrosion along with the flexural cracking in concrete due to incremental loading are implemented together in the present study. A comprehensive FE model is developed in order to obtain correct assessment of corroded beams. As observed from the FE model, the failure mechanism of the considered corroded RC beam is observed to be mostly shear failure as the corrosion level increases. Concrete crushing at the center of the RC beam is identified at the failure point of the beam due to corrosion induced damage. Evolution of displacement ductility index with respect to corrosion is determined for an RC beam based on the numerical study. It has been observed that the displacement ductility index of the beam is reduced significantly after considering a corrosion level of about 12%. Hence, the present study is an effort to establish a relation between structural performance of RC beams and level of reinforcement corrosion, which will be useful in proactive maintenance and repair work for corroded RC beams.

Flexural Performance of RC Beams Strengthened with Pre-Stressed Iron-Based Shape Memory Alloy (Fe-SMA) Bars: Numerical Study

The iron-based shape memory alloy (Fe-SMA) has promising applications in strengthening and repairing aged steel-reinforced concrete structural elements. Fe-SMA bars can produce pre-stressing forces on reinforced concrete members by activating their shape memory phenomenon upon heating. This study aims to numerically evaluate the impact of pre-stressed Fe-SMA bars on the structural behavior of reinforced concrete (RC) beams at the serviceability and ultimate stages. Nonlinear finite element (FE) models were developed to predict the response of RC beams externally strengthened with Fe-SMAs. The model shows to correlate well with published experimental results. A parametric investigation was also carried out to examine the effect of various concrete grades, pre-stressing levels, and Fe-SMA bars’ diameter on load-deflection behavior. In light of the innovative nature of the Fe-SMA strengthening technique, a comparison investigation was established between RC beams strengthened with Fe-SMA bars against different pre-stressing systems, such as carbon fiber reinforced polymer (CFRP) bars, glass fiber reinforced polymer (GFRP) bars, and steel strands. The numerical findings showed a significant increase in the beams’ load-carrying capacity with larger Fe-SMA bars’ diameter. Specifically, using 12 mm Fe-SMA bars instead of 6 mm increased the beam’s strength by 73%. However, a 14% reduction in ductility was recorded for that case. Moreover, the pre-stressing level of Fe-SMA bars and concrete grade showed a negligible effect on the ultimate strength of the examined beams. Moreover, increasing the pre-stressing level and concrete strength significantly enhanced the load-deflection response in the serviceability stage. Furthermore, using 2T22 mm of Fe-SMA bars resulted in a better structural performance of RC beams compared to other techniques with 2T12 mm, with a comparable cost. Thus, it can be concluded that using Fe-SMA bars embedded in a shotcrete layer attached to the beam’s soffit is a viable and promising strengthening strategy. Nevertheless, further experimental investigations are recommended to further ascertain the reported findings of this numerical investigation.

Effect of External Tendon Profile on Improving Structural Performance of RC Beams

The objective of the research is to improve the structural behavior of reinforced concrete (RC) T–beams by applying various techniques of external pre-stressing tendons, thus enhancing the load-carrying capacities and raising the resistance to applied forces. Seven identical RC T–beams were subjected to four-point loading to study the influence of the deviator number, tension mechanism, and tendon profile on flexural behavior. Of these, one beam was an original specimen without any tendons. The other six beams were strengthened with external tendons: two identical specimens with straight–line tendons but with a different number of inner deviators; two identical specimens with V–shaped tendons but with a different tension direction; and finally, two identical specimens with U–shaped tendons but with a different tension direction. The results and discussion were achieved using finite element (FE) software, ANSYS WORKBENCH. The results from all specimens were listed and analyzed for the failure mechanism, load-carrying capacity, deflection, and ductility. According to the FE results, external tendons greatly enhance the load-carrying and stiffness of RC beams. In addition, strengthening beams with external pre-stressing techniques can delay the early cracking load, yield load, and ultimate load by approximately 250%, 570%, and 30%, respectively, when compared to an unstrengthened beam. Moreover, the straight-line tendon with inner deviators was obtained to be the most effective technique for simple beams.

A review on the behaviour of reinforced concrete beams with fibre-reinforced polymer-strengthened web openings

Web openings often need to be created in reinforced concrete (RC) beams for the passages of utility ducts and/or pipes. Such web openings reduce the cross-section area of the beam in the affected region, leading to decrease in its load-carrying capacity and stiffness. Therefore, a fibre-reinforced polymer (FRP)-strengthening system generally needs to be applied around the web opening to ensure the safety of the weakened beam. A number of studies have been conducted by researchers all over the world to examine the behaviour of RC beams with FRP-strengthened web opening/web openings, and plenty of useful findings have been generated. This article presents a critical literature review of existing relevant research from three aspects: experimental studies, numerical studies and theoretical studies. The effect of main factors, including the size, shape, location and number of the web opening, the shape and shear span ratio of the beam, the concrete strength, the loading scheme and the FRP-strengthening scheme, on the structural performance of RC beams with FRP-strengthened web opening/web openings have been thoroughly analysed and discussed. Finally, directions for future research based on the gaps which exist in existing studies are pointed out.

Structural performance of RC beams containing high-volume ground granulated blast furnace slag and recycled coarse aggregate with lime

In this paper, the structural performance of reinforced concrete (RC) beams containing high volume ground granulated blast furnace slag (GGBFS) and recycled coarse aggregate (RCA) in replacement of Ordinary Portland cement (OPC) and natural coarse aggregate (NCA), respectively, with lime activator is studied. Nine beams of different combinations of RCA and GGBFS with/without lime and superplasticiser are designed as per IS: 456 (2000). The beams are subjected to two-point loading under universal testing machine. Various structural parameters like cracking, load bearing capacity, load vs. deflection, stiffness and energy absorption are studied. All the beams except two beams have failed in shear. These two beams, which are prepared using RCA, GGBFS, lime and superplasticiser, fail in flexure and show better structural performance than the control beam. It may be due to the reason that the above combination enhances the compressive strength of the concrete significantly, i.e. up to 16% more than that of the control mix, and consequently the shear strength. The enhanced shear strength changes the failure mode from shear failure (brittle) to flexural failure (ductile) showing better structural performance. Moreover, these two beams have shown up to 7.14%, 8.18%, 18.3%, 45% and 53.3% enhancements in cracking load, load bearing capacity, stiffness, deflection and energy absorption, respectively, as compared to those of the control beam. A comparison between the results obtained experimentally in the present investigation and predicted from different standard codes and model shows that the experimental results are in a conservative side due to which these codes/guidelines can be used safely for the GGBFS based RAC. This study clearly reveals that the concrete containing high volume GGBFS and RCA with addition of lime and superplasticiser having better structural performance in comparison to the normal can be used safely in structural applications by utilising high volume of wastes, preserving huge natural resources, reducing cement consumption and enhancing the environmental soundness due to which it can achieve sustainability in the construction industry.

A state of the art review on transverse web opening for reinforced concrete beams with and without strengthening method

To erect modern constructions needs many ducts and pipes to accommodate essential services such as telephone, electricity, air conditioning, and computer network. Transverse web openings throughout the Reinforced Concrete (RC) beams enable the installation of these services. In recent decades, the researchers suggested several strategies for improving the structural behavior for deep, continuous, and simply-supported beams; involving transverse web-holes underwent shear forces, bending, torsion, and cyclic loads by utilizing supplementary internal steel reinforcing bars, Fiber Reinforced Polymer (FRP) rods or plates, steel fiber, and Carbon Fiber Reinforced Polymer (CFRP) sheets. The current paper presents the previous investigations on the structural action of the RC-beams with the transverse web-openings. The effect of the shape, size, position of the opening, and type of strengthening on the structural performance of RC beams highlight and discussed in this paper. It found when the diameter of circle opening equal or greater than 40% of the depth of beam attributed by reducing in beam strength and earlier cracks occurred. Besides, the deflection of beams was rose when the openings settled below the centroid of the section. Finally, this study proves that the few previous studies discussed the RC beam’s behavior with openings under cyclic loading. However, this paper aims to develop insights for future studies about assessing and strengthening methods for the RC beams with the transverse web opening.

Effect of the correlation of steel corrosion in the transverse direction between tensile rebars on the structural performance of RC beams

Reinforcement corrosion is highly nonuniform and spatially distributed in reinforced concrete (RC) structures. Since RC members are reinforced with multiple rebars, corrosion of one rebar might affect another rebar in the transverse direction, thereby influencing the behavior of the structure. Hence, greater attention should be paid to studying the effects of the correlation of localized corrosion between adjacent rebars on the structural performance of RC members. In this paper, the effects of localized corrosion and the correlation of steel corrosion between tensile rebars on the structural performance of corroded RC beams were investigated through experiments and finite element (FE) analyses. The experimental results indicated that compared to the RC beams corroded over their entire length, the partially corroded RC beams with highly localized steel corrosion in the mid-span experienced large reductions in both loading capacity and ultimate deflection. Moreover, for beams with multiple rebars, the results showed that the beams with higher correlation coefficients of cross-sectional area loss between rebars had lower load and deflection capacities than the beams with lower correlation coefficients. The load–deflection responses of the beams with multiple rebars simulated by the 3D FE model were found to be in better agreement with the experimental results than those of the 2D FE model. Furthermore, a Monte Carlo simulation (MCS) was performed using a 3D FE model for two different cases: correlated and uncorrelated steel corrosion in the transverse direction of the RC beam. The results showed that a stronger correlation of steel cross-sectional area loss on different tensile rebars led to a larger variation in the load capacities of the corroded RC beams.

Effect of non-uniform rebar corrosion on structural performance of RC structures: A numerical and experimental investigation

The structural behavior of reinforced concrete (RC) beams subjected to non-uniform rebar corrosion is studied here by developing a simplified numerical approach using three-dimensional (3D) nonlinear finite element (FE) analysis and experimental study. In order to validate the proposed numerical model and to understand the influence of nonuniform rebar corrosion on the structural performance of RC beams, seven reinforced concrete beams with identical dimensions and reinforcement layout were tested under static loading. Out of the seven beams, six beams were subjected to a different level of corrosion using an electrochemical method, and another beam was used as a control specimen without corrosion. To further verify the accuracy of the numerical model, another experimental study from the literature was selected. Finally, to investigate the influence of non-uniform rebar corrosion on the global behavior of RC structures, a hypothetical building was modelled based on the experimental result, and non-linear structural analysis was carried out. Results from the experimental and numerical study demonstrated that non-uniform corrosion of steel bars led to a significant decrease in the ductility and load carrying capacity of the RC beams. Findings of this study will be useful in assessing the residual structural performance of the RC structures with non-uniform rebar corrosion. Therefore, this study will facilitate the optimization of the maintenance and repair strategies for the deteriorated RC structures.

Structural performance of RC beams with web openings reinforced with quadrilateral spirals

This article evaluates the structural performance of reinforced concrete (RC) beams with web openings and proposed opening reinforcement. This study proposes a new opening reinforcement that includes rectangles and rhombuses in a spiral configuration. The proposed web reinforcement is convenient for construction and effective for crack control. Seven specimens under anti-symmetric moment are designed to estimate the structural performance of the proposed web reinforcement. The test variables are the presence of web opening, the presence of web reinforcement, the position of web opening and the failure mode. The circular web openings with same size are applied in all the specimens. The experimental results showed that the shear capacity and the shear behaviour of the specimens reinforced by the proposed web reinforcement were similar with those of the specimen without web openings. In addition, the specimens with proposed web reinforcement showed an excellent crack control capacity.

Structural performance of RC beams in relation with the corroded period in chloride environment

This paper presents experimental work to investigate the influence of chloride corrosion of the reinforcing bars on the residual structural performance of reinforced concrete (RC) beams. A mechanical experiment was conducted with a three-point loading system on four corroded beams that had been exposed to a chloride environment for 14, 23, 26 and 28 years. The load and deflection at the mid-span were recorded to study the residual mechanical behaviour of the beams. The corroded tensile bars were extracted from the beams to check the cross-sectional loss of the reinforcements. Non-corroded beams, which were cast at the same time and had the same composition, were also tested to highlight the effect of corrosion on the mechanical behaviour of the beams. The results show that the corrosion of reinforcement modify the behavior of corroded element but that according to the definition of the end of service life, cracks width >1 mm, concrete spalling or residual capacity reaching the initial design load; the propagation period appears significantly longer than the initiation period. As a result, owners would be interested to include the propagation period in service life design of RC structures.

The problem of shear in RC beams strengthened with CFRP laminates

The effectiveness of externally bonded reinforcement of a strengthened Reinforced Concrete (RC) beam subjected to a shear-dominant loading regime is not well-established. The aim of this paper is to clarify the structural performance of RC beams without any internal shear reinforcement but strengthened with Carbon Fibre Reinforced Polymer (CFRP) laminates when the primary mode of failure of the un-strengthened beam is in shear. Four RC beams were specifically designed without and with an externally anchorage system, which was carefully detailed to enhance the benefits of the strengthening lamina and counteract the destructive effects of shear forces. All the four beams were identical in terms of their geometry, internal reinforcement and concrete strength but varied in their test loading regime to highlight the role of shear. All the beams were tested under four point bending and extensively instrumented to monitor strains, cracking, load capacity and failure modes. The structural response of the four beams is then critically analysed in terms of deformability, strength and failure processes under a shear loading regime. It is shown that with a carefully designed anchorage system, a predominantly brittle shear failure of a strengthened beam can be transformed to an almost ductile failure with well-defined enhancement of structural performance in terms of both deformation and strength. The results presented in this paper should enable engineers to totally avoid shear failure in strengthening beams with little or even no internal shear reinforcement.

Alternative Strategies for Temporary Support during Structural Repair of Reinforced-Concrete Beams

Repairs to reinforced concrete beams suffering from chloride-induced corrosion necessitate breaking out concrete around reinforcement. Reinforcement and concrete cannot act compositely where bars are exposed, and the pattern of strains in a beam under load is altered. The present study evaluates postrepair structural performance of reinforced-concrete beams repaired when relieved of load and when repaired under load and using a variety of alternative approaches to maintain structural stability during repair operations. Two series of four or five beams each were loaded and subjected to simulated repair in the laboratory. A reference as-new beam was also tested in each series for comparison. The ultimate strength of beams repaired under load was not reduced in comparison with as-new companion specimens, although ductility, deflection crack widths, and flexural stiffness were all affected. However, results do not suggest significant benefits in postrepair performance will be obtained through relieving a structure of load or from application of temporary longitudinal prestress while repairs are carried out. For beams repaired under load, two stage repairs (in which only half the reinforcement at a section is exposed at any one time) offered little overall improvement over single-stage repairs in which all bars were exposed simultaneously.