Flexural Capacity Of Beams Research Articles

Effectiveness of Grouting and GFRP Reinforcement for Repairing Spalled Reinforced Concrete Beams

Corrosion of steel reinforcement from chloride exposure can compromise the strength of reinforced concrete structures. Rust formation expands, applying pressure on concrete, resulting in cracks and spalling. Prompt repair is crucial for severe cases of spalling. This research assessed the efficacy of repair strategies for reinforced concrete beams post-spalling, including grouting and different techniques involving Glass Fiber Reinforced Polymer (GFRP) reinforcement. The research examined four variations of reinforced concrete beams, each sized at 150 mm × 200 mm × 3300 mm. Results showed that the standard beam (BK) had an average maximum load capacity of 29.74 kN. In contrast, the grouted beam (BGR) demonstrated a reduced maximum load of 14.39 kN, along with decreased steel and concrete strain compared to BK. This suggests that the grouting repair did not fully restore the beam's flexural capacity after spalling. Incorporating GFRP strips (BGRS) led to a marginal increase in the beam's maximum load, albeit remaining below BK, with lower steel and concrete strain than BK. However, the steel and concrete approached their yield points, indicating enhanced flexural performance. The full-wrap GFRP beam (BGRSF) experienced an 8.08% increase in maximum load compared to BK, with concrete strain surpassing BK, suggesting an enhancement in flexural stiffness. Doi: 10.28991/CEJ-2024-010-07-05 Full Text: PDF

Improvements in lightweight concrete T beams CFRP strengthened and anchored with U‐wraps

AbstractThis research provides a study for an experimental program using sand‐perlite‐lightweight reinforced concrete (RC) beams strengthened and anchored with carbon fiber reinforced polymer (CFRP) materials. The main objective of this work is to showcase the efficiency of using U‐wrap anchors to secure the externally applied CFRP sheets on lightweight RC beams. A series of six full‐scale T‐beams with an increasing number of CFRP U‐wraps per shear span was prepared and tested. The use of U‐wrap anchorage enhanced the flexural performance of the sand‐lightweight concrete beams by progressively delaying the premature debonding of CFRP sheets as a direct function of the number of U‐wraps used per shear span. The beam flexural capacity gradually improved from 116 kN without the use of U‐wrap anchors to 182 kN when using six U‐wraps per shear span, which reflects a significant enhancement. Similarly, the ultimate deflection gradually improved from 56 mm for the beam without U‐wrap anchors to 94 mm when applying six U‐wraps per shear span. A design model established earlier, for normal weight concrete, has been successfully qualified to yield accurate findings against the experimental results. Also, the outcome of this study interestingly showed that the ultimate strength results of the anchored beams were close to their counterparts of normal weight concrete conducted on identical beams. This finding shows that U‐wrap anchors performed efficiently despite the lack of coarse aggregate interlock in the concrete mix.

Retrofitting RC beam-column joint subassemblies using UHPC jackets reinforced with high-strength steel mesh

Outdated building codes in seismic zones often did not require seismic detailing on beam-column joints, leaving many existing structures vulnerable to earthquakes. To address this issue, three different ultra-high-performance concrete (UHPC) jackets were proposed for retrofitting seismically-deficient exterior beam-column joints, with variables including construction method (cast-in-place or precast) and inclusion of high-strength steel bar meshes. The effectiveness of these jackets was investigated using cyclic loading tests on beam-column joint subassemblages. The results demonstrated that all three UHPC jackets considerably improved the strength, stiffness, and energy dissipation of the beam-column joint subassemblage, as well as both repairable and collapse drifts. However, the cast-in-place UHPC jacket, when not reinforced with steel meshes, failed to effectively improve the ultimate drift capacity of the original beam-column joint subassemblage. Moreover, retrofitting with precast UHPC jackets using chemical anchors failed to generate sufficient composite action. Only the cast-in-place UHPC jacket, when reinforced with high-strength steel meshes, successfully delayed localized joint shear damage and allowed for effective utilization of beam flexural capacity. It improved the joint shear strength by 66%, initial stiffness by approximately 35%, and total energy dissipation by 140%. Finally, strength models were suggested for evaluating the joint shear strength and beam flexural capacity of UHPC-retrofitted beam-column joints.

Mechanical Properties and Flexural Response of Palm Shell Aggregate Lightweight Reinforced Concrete Beam

This work focuses on examining the mechanical characteristics and flexural response of reinforced concrete (RC) beams by incorporating oil palm shell (OPS) lightweight aggregate from oil palm shell waste. The OPS aggregates are replaced in various percentages, such as 0 to 50% of natural coarse aggregate (NCA). Mechanical properties of OPS concrete were conducted, and these properties were used to quantify the flexural performance of RC beams. Five RC beams with several gradations of OPS aggregates were cast and tested for this investigation. The first cracking, ultimate strength, load-deflection behavior, ductility index, and failure patterns of OPS aggregate beams were investigated as the corresponding behaviors to the NCA concrete beam. The fresh properties analysis demonstrated lessening the slump test by varied concentrations of OPS concrete. Furthermore, compressive strength was reduced by 44.73%, 50.83%, 53.33%, and 57.22% compared to 10%, 15%, 20%, and 50% OPC substitution at 28 days. Increasing OPS content in concrete mixes decreased splitting tensile strength, comparable to the compressive strength test. Modulus of rupture and modulus of elasticity experiments exhibited a similar trend toward reduction over the whole range of OPS concentrations (0–50%) in concrete. It was revealed that the flexural capacity of beams tends to decrease the strength with the increased proportion of OPS aggregate. Moreover, crack patterns and failure modes of beams are also emphasized in this paper for the variation of OPS replacement in the NCA. The OPS aggregate RC beam’s test results have great potential to be implemented in low-cost civil infrastructures.

Study of mechanical properties of H-shaped beam-column joints considering panel zone

In order to clarify the influence of panel zone (PZ) strength on the mechanical properties of each component (column, beam and PZ) of H-shaped steel beam-column joint, the equations of mathematical physics for the mechanical relationship of framing member end considering panel zone were established, and five groups of T-shaped beam-column joint specimens with different strength are tested to study the influence of panel zone to beam strength ratio (PBSR) on the deformation performance, bearing capacity and stiffness of the specimens. Through the finite element analysis, the effect of PBSR and weld access hole on the deformation of joints, the shear and flexural capacity of beams is discussed. Finally, based on the analysis of deformation and bearing capacity of the specimens and models, the reasonable value of PBSR is proposed.

Enhancing shear behaviour of the exterior beam-column joint using sufficient reinforcement details or ultra-high-performance fiber-reinforced concrete

This study aims to improve the low shear strength of an exterior beam-column joint (BCJ) by using a different reinforcement pattern or ultra-high performance fiber-reinforced concrete (UHPFRC) in the beam-column joint. The main studied parameters were the transverse reinforcement ratio, anchorage of the longitudinal beam reinforcement, beam-column depth ratio, and utilizing UHPFRC. Five specimens with a one-third scale were experimentally tested under one-direction cyclic loading. All the samples were compared to the control sample in terms of crack pattern, mode of failure, hysteresis and envelope behavior, ductility factor, energy dissipation, normalized shear strength, percentage of beam flexural capacity, and stiffness degradation. Compared to the control specimen, the joint shear strength increases by 13%, 25%, 9%, and 38% for specimens that were made better by increasing the transverse reinforcement ratio, increasing the beam anchorage bar length in the joint, lowering the beam-column depth ratio to 0.80, and using UHPFRC instead of normal concrete in the beam-column joint. The UHPFRC in BCJ can be used instead of increasing the anchorage of the beam bars or the transverse reinforcement within the joint to get the same or better shear strength performance.

Flexural capacity prediction of steel fiber reinforced concrete beam with recycled fine and coarse aggregate

In this study, the flexural performance of the steel fiber reinforced concrete beams with recycled fine and coarse aggregates was investigated through the experiments. The effects of steel fiber volume fraction, recycled fine and coarse aggregate replacement ratio, and concrete compressive strength grade on the flexural performance of steel fiber reinforced recycled aggregate concrete (SFRAC) beams were systematically studied in terms of failure mode, flexural capacity, cracking patterns, load-deflection response, and load-tensile reinforcement strain response. The results showed that the flexural capacity and deflection of beams increased and decreased with the increase of steel fiber volume fraction, respectively. The beam with 100% replacement ratio of recycled fine aggregate and 0.5% volume fraction of steel fiber presented the similar or even better flexural performance than that of the ordinary concrete beam. By adding 1.0% volume fraction of steel fiber, the flexural capacity of beam with both 100% replacement ratio of recycled fine and coarse aggregates was higher than that of the ordinary concrete beam. Based on the experimental results of SFRAC beams in this study and other literature, the effects of steel fiber volume fraction and recycled aggregate replacement ratio on the flexural capacity of beams were quantitatively analyzed. Lastly, a model for the prediction of SFRAC beam flexural capacity was proposed and verified.

Failure Mode Analysis of Reinforced Concrete Beams Using GFRP Sheet as Shear Strengthening

Corrosion is an electrochemical reaction that can cause deterioration to the reinforcing steel which has implications for the decrease in the flexural capacity of the beam. The use of corrosion resistant GFRP bar as a substitute for conventional reinforcement and GFRP sheets as a substitute for shear reinforcement without a concrete cover can increase the flexural capacity of RC beams. This study aims to analyze the flexural capacity and failure mode of reinforced concrete beams with GFRP bar and GFRP sheet, with variations in width of 50 mm (BFGS50) and 100 mm (BFGS100). Conventional RC beams (BK) and beams with GFRP bars as tensile reinforcement and conventional shear reinforcement (BFSB) were made as control beams. The beam is given a static-monotonic load until failure. The results showed that the flexural capacity of the BFGS50 and BFGS100 beams was higher than the control beam (BK and BFSB). From the failure mode analysis, the control beam experienced compression failure, while BFGS50 and BFGS100 experienced shear failure.

Effect of Using ECC Layer on the Flexural Performance of RC Beams Previously Strengthened with EB CFRP Laminates

This paper studies the efficiency of applying an engineered cementitious composite (ECC) layer to the tensile surface of (RC) beams that were previously strengthened using externally bonded (EB) carbon fiber-reinforced polymer (CFRP) laminates. One control and ten strengthened RC beams were produced and tested utilizing a four-point loading regime. For strengthened beams, two beams were kept strengthened using only CFRP, and additional ECC layers were added to the rest of the strengthened beams. The CFRP width and overlap length and position were among the test factors. Experimental results revealed that strengthening RC beams with CFRP laminates enhanced both the stiffness and flexural capacity of beams. Additional enhancements were obtained through the application of the additional ECC layers. The existence of the ECC layer alongside the CFRP laminate improved the flexural capacity by 102% and 125% when using CFRP widths of 50 mm and 100 mm, respectively, and the stiffness was improved by an average value of 318%. Three-dimensional (3D) finite element models (FEMs) were developed using ABAQUS software and verified against the experimental results to model the response of the tested beams. The verified model was used to conduct a parametric study to consider the effect of the ECC layer thickness and the reinforcement ratio on the strengthened beam behavior. The numerical results revealed that the effect of the reinforcement ratio was more significant than the ECC layer thickness in enhancing the load-displacement response, especially after the cracking stage.

Near surface mounting technology with glass fibre reinforced polymer and sisal rope fibre for flexural strengthening of reinforced concrete beams

Using the near-surface mounted (NSM) technique, the purpose of this work is to investigate effectiveness of the flexural strengthening of the reinforced concrete (RC) beam. Extruded Glass Fibre Reinforced Polymer (GFRP) bars and sisal rope fibres are both being used as part of the research project in order to enhance the material. Following that, the purpose of this research is to evaluate the impact that embedment length has on the flexural behaviour of the beams. In order to accomplish this goal, the NSM reinforcements were either placed throughout the length of the beam or in the flexure zone (max bending moment area). In all, ten beams were put through the two-point load testing procedure. The results of the tests showed that beams strengthened with GFRP bars performed better than those that had been mended with sisal ropes. The GFRP strengthened beams showed increase of 28% in flexural capacity of the beam whereas the sisal rope strengthened beams showed 16% increase in the flexural capacity of the RC beam. In addition, beams that were retrofitted with NSM reinforcements over the whole length of the beam exhibited enhancement 8% in flexural capacities than beams that were just modified in the flexure zone (maximum bending moment region).

Orthogonal Analysis of Flexural Capacity of Beams Reinforced by High Strength Reinforcement and Ultra High Performance Concrete with Coarse Aggregate

In order to study the influencing factors of the flexural capacity of ultra high performance concrete with coarse aggregate (UHPC-CA) beams with high strength reinforcement, the orthogonal test method was used to analyze the influence of reinforcement grade, reinforcement diameter, section effective height and concrete strength grade on the flexural capacity of UHPC-CA beams with high strength reinforcement. The results show that the diameter of reinforcement is an important significant factor affecting the flexural capacity of UHPC-CA beams with high-strength reinforcement, and the grade of reinforcement and the effective height of section are general significant factors. With the increase of the three factors, the flexural capacity of the beam is gradually improved. The influence of concrete strength grade on the flexural capacity of UHPC-CA beams with high-strength reinforcement is small. With the increase of concrete strength grade, the flexural capacity first decreases slightly and then increases slightly. The effect of reinforcement ratio on flexural capacity of UHPC-CA beams with ordinary strength reinforcement is greater than that of UHPC-CA beams with high strength reinforcement.

Flexural Behaviour of Different Stiffener Section Area on Full Height Rectangular Opening Castellated Steel Beam

Vierendeel is one of failure mechanisms in a castellated steel beam. Vierendeel mechanism is the main failure that occurs in a full high rectangular opening castellated beam. Vierendeel decrease castellated flexural capacity compare to the original wide flange section beam. One solution to prevent the vierendeel mechanism is by installing a diagonal stiffener in form of a steel bar on a castellated beam. The research’s purpose is finding the effect of different size of steel bar diameter on the flexural capacity. Four different sizes of steel bar diameter used in this research: 10 mm, 12mm, 16 mm, and 19 mm. Castellated beam flexural capacity is analysed with the method of truss analysis and pushover analysis. This study shows it can be infer that the bigger size of steel bar diameter does not always determine the higher flexural capacity of the castellated beam. Optimum value of the beam’s flexural capacity is affected by the strength of the flange section. The largest increment of flexural capacity between original wide flange compare to the castellated beam is 139.4% by using 16 mm diameter of the diagonal stiffener.

Effects of Axial Restraints on Beam Flexural and Joint Shear Behaviors in Reinforced Concrete Frames under Seismic Loading

ABSTRACT The elongation of beams in reinforced concrete frames due to flexural cracking and yielding is restrained by the surrounding structural components, thereby leading to axial force in the beams. To study the effects of beam axial restraint on the beam flexural and joint shear behaviors, cyclic lateral loading experiments were conducted on four beam-column substructures, two of which were restrained from beam elongation. The experiments indicated that the passively developed axial force significantly increases the beam flexural capacity. Moreover, the beam axial restraint increased shear demand on beam-column joints; as a result, joint shear failure occurred in one test specimen.

Sodium hydroxide-free geopolymer binder for prestressed concrete applications

Geopolymer is a sustainable binding material which can be produced from industrial by-products, such as fly ash and ground granulated blast furnace slag. Despite having higher mechanical strengths and durability properties than conventional ordinary Portland cement (OPC) concrete, geopolymer concrete has not been widely used in structural grade concrete, so far. The safety hazards in mixing and handling of concrete due to the use of liquid sodium hydroxide in geopolymer binder is one of the barriers to the adaptation of geopolymer in the concrete industry. This study aims to use sodium hydroxide-free one-part geopolymer binder for structural concrete applications, such as prestressed concrete beams. In this study, the mechanical and serviceability properties of grade 50 MPa geopolymer concrete cured at ambient temperature are investigated and compared against same grade OPC concrete. The effects of tensile strength of concrete in load–deflection behaviours of prestressed concrete beams of different spans and sizes are investigated using finite element analysis for short-term and long-term durations. This study finds that geopolymer concrete has around 27% higher indirect-tensile and flexural strengths than OPC concrete of same strength grade which contributes to geopolymer prestressed concrete beams to withstand around 20% higher first-crack load than OPC concrete beams of same span. In addition, geopolymer prestressed concrete beams show a relatively smaller loss in prestressing stress which results in a smaller loss in flexural capacity of beams over the service life of the structure.

Flexural behavior of reinforced concrete beams with high strength material layer in compression zone

The flexural behavior of reinforced concrete beams with high strength material layers in the compression zone was observed. The compression zone of the beams was filled with high strength material to increase the ductility of the beams. Three control beams and three beams with high strength compression layer were tested until failure. The tested beams were simply supported and loaded with a four-point bending mechanism. The test variable in this study was the ratio of longitudinal reinforcement (1%, 1.5%, and 2.5%). The test results show that the ductility of beams with high strength material in the compression zone is significantly higher than the control beams. However, the flexural capacity of beams with high strength materials is almost the same as the control beam. Theoretical prediction using finite element analysis also confirms that beams with high strength material in the compression zone show higher ductility.

Flexural capacity of RC beams strengthened with near-surface mounted steel bars

An experimental study carried out to observe the flexural capacity of reinforced concrete beams strengthened with Near Surface Mounted (NSM) steel bars is presented. The test was carried out on nine concrete beams. All tested beams were subjected to two-point monotonic loads. The ratio of longitudinal reinforcement (1%, 1.4%, and 2.4%) and NSM bars (1D16 and 2D16) were used as test variables. It was found from the test result that NSM steel bars significantly increase the flexural capacity of reinforced concrete beams. However, the strengthened beams failed in brittle mode, as indicated by a sudden drop of beams capacity. An analytical study was also conducted to obtain the flexural response of the specimens through all ranges of elastic and post-peak load. The prediction of the flexural capacity of the beams compares well with the test result.

Flexural capacity of steel‐FCB bar‐reinforced coral concrete beams

AbstractSteel‐fiber composite bar (SFCB) is a new technique with steel core embedded into the fiber‐reinforced polymer (FRP) bars, which solve the shortcomings of poor ductility and low stiffness of FRP‐reinforced concrete members. Based on the experimental study, flexural behavior of a new type concrete, SFCB bars‐reinforced coral concrete beams, is investigated. The deflection, failure mode, tensile strain, and ultimate flexural capacity of this new type of concrete beam are studied in detail through a series four‐points bending tests. The results show that the failure process of SFCB‐reinforced coral concrete beam can be divided into three main stages: elastic, cracking, and failure. Because exterior layer of SFCB bar is able to continue to withstand tensile stress after its steel core yield, hence, the flexural rigidity and flexural capacity of the beams both increase. The flexural stiffness of SFCB bars‐reinforced coral concrete beams is also increased, and the load‐deflection relation is more or less nonlinear. By using SFCB bars, the stiffness of the beams can be increased by about 20%. However, under high stress state, the relative slip between the carbon fiber and the concrete as well as that between the steel core and the carbon fiber cause tensile stress loss which weakened the flexural resistance of the SFCB bar‐reinforced coral concrete beam. The bonding performance between the round surface steel core and the carbon fiber is obviously weaker than that of the threaded surface steel core, and the steel core slip is more likely to occur under the higher tensile stress. When Using ACI440.1R‐15 and GB50608‐2010 to calculate the flexural capacity of the SFCB beams, the ratios of the theoretical value and the measured value from tests are 1.07 and 1.12, respectively. By introducing two new factors k1 and k2, a formula was developed through modification of the existing ones from ACI440.1R‐15 and GB50608‐2010 to calculate the ultimate flexural capacity of SFCB bar reinforced concrete beam which agrees as high as 93–99% with the experimental results.

Análisis de elementos finitos de Vigas de Hormigón Armado CFRP

This study concerns with flexural behavior of RC beams strengthened by carbon fiber reinforced polymer (CFRP) using finite element method (FEM). ABAQUS program has been used in this research. The load-deflection relationship, crack pattern, strain in the concrete at mid-span section of the beam and failure modes of all tested beams are studied. After validation of FEM model, parametric studies are presented to assess the effect of the compressive strength of concrete, thickness, and length of CFRP, and the presence of CFRP on stress in steel bars. From the current results, it can be obtained that the flexural capacity of RC beams strengthened with CFRP increased by 6.6% for beam strengthed by EBR and to 108.8% for beam strengthed by near surface mounted (NSM) compared to the reference beams. According to parametric studies, it is found that by increasing the compressive strength of concrete from 30 MPa to 70 MPa, the beam capacity increase by 25.6%, while increasing the length of CFRP from 600 mm to 900 mm leads to increase the beam capacity by 12.7%. Increasing thickness of CFRP sheet from 0.11 mm to 0.5 mm leads to an increase in the stiffness and the flexural capacity of the beam by 47.9%. Also, the results of this study approved that the strengthening of RC beams by CFRP laminates using the NSM technique is more efficient than externally bonded reinforcement (EBR) techniques and this is agreed with the experimental results. Finally, it can be concluded that the finite element model provides good accuracy compared to the experimental results and ACI-440 results .

Revisiting flexural overstrength in RC beam-and-slab floor systems for seismic design and evaluation

Beam flexural overstrength is an important parameter in seismic design and evaluation of reinforced concrete (RC) moment resisting frames. It affects the column-to-beam flexural strength ratio (CBSR) which is a key parameter to avoid unfavorable column-driven mechanisms. In RC beam-and-slab floors, interaction between beam growth and slab panels is of a very complex nature which significantly alters the beam flexural overstrength. Enhancement of beam flexural capacity in slab floor systems depends on several parameters that should be considered on a case-by-case basis. To include some of the effects that were not considered in previous studies due to physical limitations of experimental works and lack of appropriate computational tools, a generic two-by-two bay archetype story model with a beam-and-slab floor system were considered for further investigations by means of numerical modelling. In order to consider the spatial effects of the floor system, several computational models were assembled by changing the span and cross section of beams in terms of depth, width and reinforcement ratio as well as the thickness of slabs to perform a parametric study on beam flexural overstrength ratio. Multilayer nonlinear shell elements were used for finite element modelling of slab panels to account for the kinematic effects of beam elongation along with the restraining effects of the floor slab. According to the results of analyses, variation of positive and negative flexural overstrength ratios of beams at different performance levels were presented for different parameters. Results demonstrate that the flexural overstrength ratio is greatly affected by the level of chord rotation (beam lateral drift or performance level) reinforcement ratio and the type of connection. However, beam-to-slab flexural stiffness ratio as well as beam length are not overly important parameters for flexural overstrength evaluation. This study reveals that, despite code prescriptions, CBSR should not be considered identical for all cases; hence, it should be revisited based on the desired performance level, type of connection and the beam reinforcement ratio.

Experimental Study and Reliability Analysis of Flexural Capacity of RC Beams Reinforced with 600 MPa Grade Steel

Flexural capacity of beams reinforced with 400 or 500 MPa grade steel can be accurately estimated by using equations provided in design codes. Recently, 600 MPa grade steel has evolved in the construction industry, and the applicability of existing equations for this grade of steel should be verified by performing experimental investigation. By conducting tests on concrete beams reinforced with 600 MPa grade high‐strength steel, this study investigates the flexural performance for different concrete strength grades and different reinforcement ratios. Flexural capacities of concrete beams reinforced with 400 MPa, 500 MPa, and 600 MPa grade steel are analyzed based on equations in various codes and based on experimental studies in the literature. Furthermore, this study performs reliability analysis and verifies the three design values of 600 MPa grade steel yield strength in relation to the experimental performance and recommends the appropriate design values of 600 MPa grade steel yield strength. Research results show that when the measured values of yield strength of the steel bars and concrete strength are used, the ratio of the measured failure moment value to the calculated value for various beams based on different codes is nearly 1.0, demonstrating the high degree of fitting. Finally, the reliability analysis shows that the design yield strength of the 600 MPa grade high‐strength steel bars should be taken as 520 MPa.