Strength Of Beams Research Articles

Performance Prediction of GFRP-Reinforced Concrete Deep Beams Containing a Web Opening in the Shear Span

This study aimed to investigate the nonlinear structural behavior of concrete deep beams internally reinforced with glass fiber-reinforced polymer (GFRP) reinforcing bars and containing a web opening of various sizes and locations within the shear span. Three-dimensional (3D) numerical simulation models were developed for large-scale GFRP-reinforced concrete deep beams (300 mm × 1200 mm × 5000 mm) with a shear span-to-depth ratio (a/h) of 1.04. Predictions of the numerical models were validated against published experimental data. A parametric study was conducted to examine the effect of varying the opening size and location on the shear response. Results of the numerical analysis indicated that the strength of the deep beam models with an opening in the middle of the shear span decreased with an increase in either the opening width or height. The rate of the strength reduction caused by increasing the opening height was, however, more significant than that produced by increasing the opening width. Placing a web opening in the compression zone close to the load plate was very detrimental to the beam strength. Conversely, a negligible strength reduction was recorded when the web opening was placed in the tension side above the flexural reinforcement and away from the natural load path. Data of the parametric study were utilized to introduce simplified analytical formulas capable of predicting the shear capacity of GFRP-reinforced concrete deep beams with a web opening in the shear span.

Numerical modelling of flexural performance of textile reinforced mortar strengthened concrete beams

In recent years, the application of textile reinforced mortar (TRM) as an overlay has become an important method for repairing and strengthening old masonry structures. However, the quantitative analysis and design of TRM-strengthened reinforced concrete (RC) beams are still limited. To address this gap, a nonlinear finite element (FE) model is proposed in this study to simulate the flexural behavior of TRM-strengthened RC beams. The developed model is validated using experimental results and subsequently utilized for the design of TRM-strengthened RC beams. Various TRM design parameters, including the number of textile layers, textile longitudinal length, and textile mesh size, are parametrically investigated. The modelling results reveal that increasing the number of textile layers and longitudinal length while decreasing the textile mesh size can enhance the bending strength of TRM-strengthened RC beams. Furthermore, an analytical model is proposed to predict the flexural strength of TRM-strengthened RC beams, facilitating rapid strength estimation of TRM-strengthened RC beams. The predicted results demonstrate good agreement with the numerical simulation results. The established FE models can predict the bending performance of TRM-strengthened RC beams under different reinforcement conditions, and the simulation outcomes can provide valuable guidance for their design.

Minimally Invasive FRP Strengthening of External Beam–Column Joints

Minimally Invasive FRP Strengthening of External Beam–Column Joints

Novel sustainable techniques for enhancing shear strength of RC beams mitigating construction failure risk

The aim of this study is to evaluate the effectiveness of various innovative and sustainable methods for improving the shear performance of reinforced concrete (RC) beams. The potential risk of failure for such elements is considered a potential threat, therefore, this study addresses it through experimental tests and numerical analyses to be mitigated carefully in order to enhance the safety and sustainability of buildings. A total of eleven specimens, comprising two control specimens and nine strengthened specimens, underwent three-point testing. Several proposed strengthening techniques, each involving multiple parameters, were examined. In the initial approach, glass fiber-reinforced polymer (GFRP) textile embedded in an external fiber-reinforced cementitious mortar (FRCM) jacket was utilized, with an evaluation of the number of the GFRP textile layers (1, 2, and 3 layers). The second technique incorporated near surface mounted (NSM) GFRP bars along with the FRCM jacketing, where the diameter of the GFRP bars (10, 12, and 16 mm) served as the primary parameter. In the final technique, externally bonded stainless-steel strips (SSSs) of varying thicknesses (1, 1.25, 1.50 mm) were affixed to the beams’ surface. The obtained results revealed that the application of the FRCM jacketing method yielded positive results, showing a significant 30.7 % average increase in the crack initiation load and a 17.1 % improvement in the failure load compared to the defected beam. However, issues of debonding beneath the loading point were observed in the FRCM jacket, particularly with three layers of the GFRP textile, leading to the separation of the concrete cover. Moreover, combining the NSM GFRP bars with an FRCM jacket addressed the absence of shear stirrups. The most remarkable improvement was noted utilizing the NSM GFRP bars and an FRCM jacket, followed by employing SSSs with an FRCM jacket.

Flexural behavior of RC beams externally strengthened with side-bonded CFRP laminates with variable internal reinforcement

This study investigates the flexural behavior of reinforced concrete (RC) beams externally strengthened with bottom- and side-bonded carbon fiber-reinforced polymer (CFRP) sheets with variable steel ratio. The choice of applying the CFRP sheets in a bottom- or side-bonded configuration depends on the accessibility of the beam. This experimental investigation is aimed at studying and comparing the efficacy of bottom- and side-bonded CFRP sheets for flexural strengthening of RC beams with variable internal steel ratios. The effect of steel reinforcement ratio, and the number of CFRP plies are examined by testing 10 RC beams under a four-point bending configuration. The results in terms of load-deflection response, ultimate load-carrying capacity, failure modes, and ductility are studied and compared with control unstrengthened beams. The study revealed that side-bonded beams provided flexural capacity comparable to the bottom-bonded beams for both ratios of internal reinforcement used in the study. The study also showed that both strengthening configurations were more effective when the internal steel ratio was low. In terms of ductility, the side-bonded scheme provided ductility indices comparable to the bottom-bonded beams. The findings of this study confirm the feasibility of using side-bonded fiber-reinforced polymer (FRP) sheets as a strengthening technique for RC beams when the soffit of the beam is inaccessible.

Effect of Rice Husk Ash (RHA) and slake-lime as partial replacement of cement in the production of concrete

This study examines the utilization of rice husk ash (RHA) and slaked lime as substitutes for a portion of the cement in manufacturing concrete. The RHA was acquired from a nearby source, subjected to calcination at temperatures ranging from 500 to 700 °C, and then passed through a sieve to obtain particles with a size of 150 microns. Concrete mixes were made using Ordinary Portland cement (OPC), fine and coarse aggregates, and water, with different amounts of RHA and slaked lime. The concrete mix design adhered to established standards, with a mix ratio of 1:1.5:3 (cement: fine aggregate: coarse aggregate). The experiment was designed using response surface methods, with RHA, slaked lime, and cement as factors, each having five levels. Concrete cubes were formed using 100 mm steel moulds and then submerged in water to assess their workability. The compressive strength was measured using universal testing equipment after 7, 28, and 90 days of cure. The flexural strength of concrete beams was assessed after 7 and 28 days. Samples were subjected to scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) examination after 28 days. The compressive and flexural strengths increased as the curing period progressed, with the 10% RHA substitution showing the maximum strength. The SEM analysis showed that RHA10 exhibited the maximum concentration of silicon, which corresponds to the recommended 10% replacement level of OPC and meets the concrete specifications specified by ASTM M20 grade. Utilising RHA decreases expenses and minimises the amount of concrete that is discarded. The most effective replacement for OPC was 10% RHA, which produced long-lasting and strong concrete.

Bamboo and palm leaves as sustainable alternative to steel reinforcement in concrete beams

A massive urban development is recognized worldwide, resulting in an increased demand for building materials such as reinforcing steel, which is one important material in the construction industry. Due to the high cost of reinforcing steel and its scarcity in many countries, researchers leaned towards finding an alternative, less expensive, renewable and environmentally friendly material. Synthetic and natural fibers, such as glass fiber, bamboo and plam leave, had been under study to serve as reinforcing steel alternatives. This research studies the bending behavior and strength of concrete beams reinforced with bamboo and palm leaves. Six samples were prepared, three of which were reinforced with palm leaves and three with bamboo. A reference beam sample was also prepared for comparative purposes. Three-point bending test was carried out and bending behavior and collapse mechanism were studied. The results showed that the use of palm leaves and bamboo as an alternative to steel reinforcement in concrete improves the beams’ structural behavior. The palm leaves and bamboo reinforced samples showed distinctly different patterns of failure.

Performance of GFRP Sheets in Strengthening Concrete Beams in Flexure

Plain concrete beam repair and strengthening are increasingly important in structural strengthening and retrofitting. This study examines the glass fibre-reinforced polymer (GFRP) sheets in plain concrete beams under flexural behaviour by using its patching sheets. Through the implementation of a symmetrical four-point static loading technique, a series of tests were conducted on plain concrete beams that had been externally joined with GFRP sheets. These beams were subjected to rigorous testing until they reached their ultimate failure point. The experimental test consists of casting nine plain concrete beams with identical specifications. Three beams are utilised as control beams; three are reinforced with GFRP sheets measuring 50 mm × 100 mm, and another three are reinforced with GFRP sheets measuring 100 mm × 200 mm. The flexural test is designed to determine the tensile strength of concrete under bending. Compared to the control beams, the specimens strengthened with GFRP sheets demonstrated a significantly enhanced ultimate load capacity. The beams with larger GFRP sheets exhibited a higher ultimate load of 14.84 kN, while those with smaller sheets showed an ultimate load of 8.54 kN, marking an appreciable improvement in performance. Moreover, the smaller area GFRP-reinforced beams failed at a 45% higher shear stress compared to those with a larger area GFRP, indicating a differential impact based on the size of the reinforcement used. This study highlights the effectiveness of GFRP sheets in enhancing the structural performance of plain concrete beams, providing crucial insights into the benefits of different sizes of reinforcement.

Experimental behaviour, FE modelling and design of large-scale reinforced concrete deep beams shear-strengthened with embedded fibre reinforced polymer bars

Reinforced concrete (RC) deep beams are widely used in buildings and bridges. However, research on shear strengthening of RC deep beams with embedded fibre reinforced polymer (FRP) bars is limited. This paper presents the first comprehensive study on the experimental behaviour, nonlinear finite element (NLFE) modelling and design of large-scale RC deep beams strengthened in shear with embedded carbon or glass FRP (CFRP or GFRP) bars. An experimental investigation comprising three large-scale RC deep beams was conducted. Subsequently, a three-dimensional NLFE model was developed and validated against the experimental results. The validated NLFE model was used to perform a parametric study, examining the influence of FRP bar type and steel-to-FRP shear reinforcement ratio on shear strength enhancement. The results of the parametric study were utilized to calibrate and validate a novel design model. The results showed that embedded FRP bars can enhance the shear force capacity of large-scale RC deep beams by up to 40 %. The effect of FRP bar type on the shear strength enhancement was insignificant. However, there was 13 % reduction in shear force gain due to the increase in steel-to-FRP shear reinforcement ratio from 0.77 to 10.0. The novel design model reproduced the NLFE results with a mean ratio of 0.921 and a standard deviation of 0.018. Finally, the ability of the design model to capture the effect of the investigated parameters was demonstrated.

Horizontal shear behavior of self-compacting lightweight concrete composite beams with dry joints and unbonded reinforcements

This study aims to investigate the horizontal shear behavior of self-compacting lightweight concrete (SCLC) composite beams with dry joints and unbonded transverse reinforcement. For this, the experimental program included different concrete types, joints configurations, and the use of unbonded high-strength bars with varying levels of prestressing and transverse reinforcement ratios in composite beams. Two precast beams were fabricated using a match-cast method and integrated horizontally to form composite beams, utilizing unbonded transverse reinforcements. The composite beams incorporating lightweight aggregates (LWA) instead of normal weight aggregates (NWA) exhibited a decreased ultimate shear strength of 19.5 %; however, the addition of steel fibers into the mixtures mitigated this decrease, resulting in a 22.8 % increase in strength compared to mixture without steel fibers. The vertical prestressing level significantly influenced the horizontal shear behavior and failure mode of composite beams, with adequately prestressed composite beams exhibiting similar ductile behaviors to the monolithic beam. Composite beams with keyed joints exhibited higher horizontal shear strength, up to 65.3 % more than the beam with flat joint, attributed to the interlock provided by the shear keys. Increased slip between two precast beams activated the dowel action of unbonded reinforcements, effectively resisting horizontal shear. Predictions of the horizontal shear strength, as per current codes, were compared to the experimental results. The results indicate that the design approach in Eurocode 2 provides reasonable estimations of the strengths of composite beams with dry joints and unbonded reinforcements.

Shear strengthening of self-compacting lightweight concrete beams with steel fibers and unbonded prestressing bars

This study aims to investigate the shear behavior of self-compacting lightweight concrete (SCLC) beams strengthened with steel fibers and unbonded prestressing bars. For this, the experimental program included the use of hooked-end steel fibers with volume fractions of 0.5 %−0.75 %, and high-strength prestressing bars with varying prestressing forces and transverse reinforcement ratios. The addition of steel fibers in SCLC significantly increased the normalized shear capacity of beams, reaching up to 2.50 times higher values, whereas the substitution of normal coarse aggregates with lightweight aggregate resulted in a decrease of up to 10.1 %. The shear strengthening of SCLC beams with unbonded prestressing bars provided a substantial increase in the ultimate shear capacity up to 2.06 times higher than that of beam without reinforcement. Increasing the prestressing force of bars effectively restrained the occurrence of critical shear cracking, consequently enhancing the shear capacity. Utilizing hybrid reinforcement with fibers and prestressing bars resulted in a transition of failure mode from shear to flexural, attributed to the improved shear capacity. For the SCLC beams reinforced with steel fibers, the shear strengths were predicted by previous prediction models. When modifier for lightweight concrete was considered, the Imam’s model most precisely predicted the shear strengths with an average vu/vn ratio of 1.00 and SD of 0.07. The fib model Code, based on the modified compression field theory, provided accurate predictions for the shear capacities of SCLC beams with unbonded prestressing bars, exhibiting an average Vu/Vn ratio of 1.00 and SD of 0.09. The fiber-resisting component was reasonably considered in the model with an average Vu/Vn ratio of 1.02 and SD of 0.07.

Flexural behavior of RC beams strengthened with CFRP grid-reinforced engineering cementitious composite

Flexural strengthening of RC beams by replacing the tension part with carbon fiber reinforced polymer (CFRP) grid‐reinforced engineering cementitious composite (ECC) matrix has been proved to be a reliable way in the marine environments. However, few studies have been conducted on the arrangement of CFRP grids so far, which is supposed to be a possible way to deal with the premature fracture of CFRP grid and debonding of strengthening layer. In this paper, the flexural behavior of RC beams strengthened with CFRP grid‐reinforced ECC matrix is experimentally studied. The location of CFRP grid and the number of CFRP grid layers were specially discussed. Results from experiments indicated an improvement range of 66.67 %∼100 % in the peak load of strengthened RC beams, with a higher initial cracking load from 4.72 %∼20.47 % when compared to the reference beam. The generating of initial cracks was delayed with the CFRP grid close to the bottom, whereas the development of cracks was accelerated. The bearing capacity showed a nonlinear relationship with the distance from CFRP grid to the beam bottom, and a linear relationship with the number of CFRP grid layers. Finally, the formulas for the flexural capacity of strengthened beams were developed, considering the plasticity and cracking of concrete.

Flexural strengthening of RC beams using PGFRP bars embedded in strain-hardening cementitious composites (SHCC)

The application of the near surface mounted (NSM) fiber reinforced polymer (FRP) as an additional reinforcement at tension side of flexural members is efficient to upgrade the flexural strength. However, this technique must be applied to concrete beams having hard concrete cover to avoid premature failure induced by concrete cover deterioration. The current research aims to improve and evaluate the flexural behavior of reinforced concrete (RC) beams strengthened with embedded prestressed glass fiber reinforced polymer (PGFRP) bars, based on replacement of weak concrete cover with a layer of strain hardening cementitious composites (SHCC). For this investigation, one reference beam (without strengthening) and nine flexural strengthened beams were tested under a four-point bending scheme. All beams had the same reinforcement and geometry, 150 mm width, 300 mm total depth, a total length of 3000 mm and the effective span was 2700 mm. The test parameters were: (1) the strengthening technique (conventional NSM-PGFRP bars, NSM-PGFRP bars covered with external SHCC layer and PGFRP bars embedded in SHCC replaced cover), (2) the prestressing levels in the GFRP bars (0, 10 % and 20 % of the ultimate bar strength) and (3) the thickness of the SHCC layer (30, 40 and 50 mm). Compared to the conventional NSM strengthened beams, the conjunction of SHCC with PGFRP bars not only prevented the spalling of the concrete cover but also increased the load carrying capacity up to 26.5 % and the ductility up to 16 %. A model for the prediction of flexural capacity of the strengthened beams having SHCC replaced cover was conducted, the predicted ultimate loads have a good consistency with the test results.

Exploring Damage Patterns in CFRP Reinforcements: Insights from Simulation and Experimentation.

Carbon Fiber Reinforced Polymers (CFRP) have become increasingly significant in real-world applications due to their superior strength-to-weight ratio, corrosion resistance, and high stiffness. These properties make CFRP an ideal material for reinforcing concrete structures, particularly in scenarios where weight reduction is crucial, such as in bridges and high-rise buildings. The transformative potential of CFRP lies in its ability to enhance the durability and load-bearing capacity of concrete structures while minimizing maintenance costs and extending the lifespan of the infrastructure. This research explores the impact of reinforcing structural elements with advanced composite materials on the strength and durability of concrete and reinforced concrete structures. By integrating Carbon Fiber Reinforced Polymer (CFRP) reinforcements, we subjected both rectangular and T-section concrete beams to comprehensive three-point bending tests, revealing a substantial increase in flexural strength by 45% and crack resistance due to CFRP reinforcement. The study revealed that CFRP reinforcement increased the flexural strength of concrete beams by 45% and improved crack resistance significantly. Additionally, the load-bearing capacity of the beams was enhanced by 40% compared to unreinforced specimens. These improvements were validated through finite element simulations, which showed a close alignment with the experimental data. Furthermore, an innovative simulation study was conducted using a finely tuned finite element numerical model within the Abaqus calculation code. This model accurately replicated the laboratory specimens in terms of shape, dimensions, and loading conditions. The simulation results not only validated the experimental observations but also provided deeper insights into the stress distribution and failure mechanisms of the reinforced beams. Novel aspects of this study include the identification of specific failure patterns unique to CFRP-reinforced beams and the introduction of an enhanced interaction model that more accurately reflects the composite behavior under load. In CFRP-reinforced beams, specific failure patterns were identified, including flexural cracks in the tension zone and debonding of the CFRP sheets. These patterns indicate the points of maximum stress concentration and potential weaknesses in the reinforcement strategy. The study revealed that while CFRP significantly improves the overall strength and stiffness, careful attention must be given to the bonding process and the quality of the adhesive used to ensure optimal performance. These findings contribute significantly to the understanding of material interactions and structural performance, offering new pathways for the design and optimization of composite-reinforced concrete structures. This research underscores the transformative potential of composite materials in elevating the structural integrity and longevity of concrete infrastructures.

Correction: Pour et al. Enhancing Flexural Strength of RC Beams with Different Steel–Glass Fiber-Reinforced Polymer Composite Laminate Configurations: Experimental and Analytical Approach. Infrastructures 2024, 9, 73

In the published publication [...]

Improving Shear Strength Prediction in Steel Fiber Reinforced Concrete Beams: Stacked Ensemble Machine Learning Modeling and Practical Applications

Existing machine learning (ML) models often encounter challenges in accurately predicting the shear strength of steel fiber reinforced concrete (SFRC) beams, mainly due to a lack of generalization. This study introduces an advanced stacked ensemble ML architecture to overcome this limitation by utilizing a comprehensive data set of 394 experimental observations and a 20-feature matrix. The model exhibits exceptional performance with a mean absolute error of 0.391 and a correlation coefficient (R2) of 93.7%, and surpasses traditional ML algorithms. Furthermore, a sensitivity analysis of the developed model yields that shear strength is highly responsive to the shear span-to-effective depth ratio, with an increase from 1 to 4 resulting in a significant reduction (about 50%) in strength. Increasing the percentage of longitudinal steel from 1 to 2% leads to a 14.6% gain, whereas doubling its yield strength has a more modest 3.7% effect. Increasing the compressive strength of concrete from 25 to 50 MPa, notably increases the shear strength by 19.6%. Fiber length, diameter, and aspect ratio exhibit varying impacts, with shear strength most influenced by the fiber volume fraction, which leads to a peak enhancement of 30.7% at 2% fibrous volume; however, the tensile strength of fibers minimally affects the shear strength. Additionally, this research presents a simplified empirical model to predict the shear strength of SFRC beams based on the key determinants. This model employs the iterative Gauss–Newton algorithm, demonstrates reasonable predictive capability, and boasts an R2 of 83.3% and mean prediction-tested strengths of around 1.039. The practical implications of these findings are substantial for the construction industry as they enable a more accurate and reliable design of SFRC beams, optimize material usage, and potentially reduce construction costs as well as enhance structural safety.

Enhancing the mechanical performance of composite corners through microstructural optimization and geometrical design

Processing carbon fiber-reinforced composites into corner sections through compression molding poses challenges due to the limited flowability of continuous prepregs, resulting in reduced curved beam strength (CBS). The use of discontinuous plies was explored, including random HexMC and unidirectional chopped strand (CS) prepreg. A first comparison on flat UD or Quasi Iso (QI) plates highlighted the potential interest of CS in terms of stiffness and lower strength penalty as HexMC. The iso-thickness corners produced from HexMC reached a CBS of 1 kN while CS QI had a CBS of 2.5 kN, overperforming corners made from neat prepregs (2.1kN) thanks to the improved flowability of the CS. By selecting an optimized geometry at equivalent mass, the CBS of CS corners further increased to 6.6kN. The performance of composite corners can thus be greatly enhanced by a combination of the material microstructural arrangement and the geometrical design of the mold.

Study of the flexural behavior of UHPC-HPC composite beams strengthened with BFRP sheet after chloride secondary erosion

To solve the issue of insufficient durability of reinforced concrete (RC) structures, a new structure of ultra-high performance concrete (UHPC)-high performance concrete (HPC) composite beam was designed, and the flexural performance of the composite beam strengthened with basalt fiber reinforced polymer (BFRP) after pre-damage was investigated. Results indicate that main cracks are formed and developed after the secondary erosion of chloride salt, leading to three forms of failure modes of the beams: BFRP sheet fracture and concrete crushing, BFRP sheet debonding and concrete crushing and BFRP sheet debonding. The test beam failure process can be classified into three stages: linear elasticity, crack development and yield. The maximum cracking and ultimate loads increased by 27.9 % and 35.8 %, respectively. The crack load growth rate of the beam decreased after 7 days (d) of secondary chloride salt erosion. The formula for calculating the peel strength of the UHPC-HPC composite beam was modified. The calculated bending capacity of the beam agrees well with the measured value. This study provides a reference for enhancing the lifespan and calculating the flexural bearing capacity of structures in corrosive environments.

Prediction of flexural strength in FRP bar reinforced concrete beams through a machine learning approach

PurposeThe purpose of this study is to assess the incorporation of fiber reinforced polymer (FRP) bars in concrete as a reinforcement enhances the corrosion resistance in a concrete structure. However, FRP bars are not practically used due to a lack of standard codes. Various codes, including ACI-440-17 and CSA S806-12, have been established to provide guidelines for the incorporation of FRP bars in concrete as reinforcement. The application of these codes may result in over-reinforcement. Therefore, this research presents the use of a machine learning approach to predict the accurate flexural strength of the FRP beams with the use of 408 experimental results.Design/methodology/approachIn this research, the input parameters are the width of the beam, effective depth of the beam, concrete compressive strength, FRP bar elastic modulus and FRP bar tensile strength. Three machine learning algorithms, namely, gene expression programming, multi-expression programming and artificial neural networks, are developed. The accuracy of the developed models was judged by R2, root means squared and mean absolute error. Finally, the study conducts prismatic analysis by considering different parameters. including depth and percentage of bottom reinforcement.FindingsThe artificial neural networks model result is the most accurate prediction (99%), with the lowest root mean squared error (2.66) and lowest mean absolute error (1.38). In addition, the result of SHapley Additive exPlanation analysis depicts that the effective depth and percentage of bottom reinforcement are the most influential parameters of FRP bars reinforced concrete beam. Therefore, the findings recommend that special attention should be given to the effective depth and percentage of bottom reinforcement.Originality/valuePrevious studies revealed that the flexural strength of concrete beams reinforced with FRP bars is significantly influenced by factors such as beam width, effective depth, concrete compressive strength, FRP bars’ elastic modulus and FRP bar tensile strength. Therefore, a substantial database comprising 408 experimental results considered for these parameters was compiled, and a simple and reliable model was proposed. The model developed in this research was compared with traditional codes, and it can be noted that the model developed in this study is much more accurate than the traditional codes.

Experimental and analytical study of shear strengthening of deep RC beams using externally bonded CFRP system

Experimental and analytical study of shear strengthening of deep RC beams using externally bonded CFRP system