Behavior Of Beams Research Articles

Shear behavior of high-strength concrete beams reinforced with carbon fiber-reinforced polymer bars

This study experimentally investigates the shear performance of high-strength concrete (HSC) beams reinforced with carbon fiber-reinforced polymer (CFRP) bars. Thirteen HSC beams were tested under four-point monotonic loading until failure, focusing on parameters such as the shear span-to-depth (a/d) ratio, longitudinal reinforcement ratio, transverse reinforcement ratio, and the type of longitudinal reinforcement (CFRP, steel, and hybrid CFRP-steel). The study analyzed failure modes, shear cracking patterns, cracking load, ultimate shear capacity, and load-deflection responses. Results indicated that shear failures in CFRP-reinforced HSC beams can occur suddenly due to the brittle nature of both FRP and HSC. Adding longitudinal steel bars alongside CFRP bars significantly enhanced the ultimate shear capacity while balancing both ductility and durability. The ultimate shear capacity was primarily influenced by the longitudinal reinforcement ratio and the a/d ratio. Specifically, the ultimate shear capacity decreased by approximately 72 % as the a/d ratio increased from 1.0 to 3.0. Furthermore, the maximum midspan deflection increased by 135 %, rising from 4.0 mm to 9.4 mm with the same change in the a/d ratio. Conversely, increasing the longitudinal reinforcement ratio from 0.6 % to 1.7 % led to a 43 % increase in ultimate shear strength due to enhanced dowel action mechanism and improved crack control, which contributed to a higher shear resistance in the concrete beam. Both CFRP and steel-reinforced beams exhibited similar shear capacity, indicating comparable shear transfer mechanisms. Additionally, a proposed shear model based on regression analysis of 139 FRP-reinforced HSC beams demonstrated better predictive accuracy than existing design codes.

Experimental investigation and analytical model for the shear behavior of composite beams with prefabricated U‐shaped RPC permanent formworks

AbstractThis study aimed to investigate the shear performance of composite beams with prefabricated U‐shaped reactive powder concrete (RPC) permanent formworks with normal strength concrete poured inside. Three‐point bending tests were performed on eight composite beams with prefabricated U‐shaped RPC‐reinforced formworks and one reinforce concrete beam. Additional parameters, such as the stirrup spacing, shear span ratio, and inner core concrete strength, were evaluated. The test results indicated that the prefabricated U‐shaped RPC permanent formworks increased the shear capacity of the composite beams. Under the same configuration, the bending cracking load, stirrup yield load, and peak load of the composite beams increased by 51.54%, 88.02%, and 78.38%, respectively. An analytical model was proposed to predict the shear strength of composite beams with prefabricated U‐shaped RPC formwork and validated using the experimental results.

Numerical study on the flexural and shear behavior of steel fiber and high‐strength steel combination in ultra‐high‐performance fiber‐reinforced concrete beams under cyclic loading

AbstractFiber‐reinforced concrete consists of hydraulic cement, water, aggregate, and discrete fibers, making it a composite material. These fibers, available in different shapes, sizes, and materials such as steel, polymer, glass, and natural fibers, are commonly utilized in structural applications. The tensile strength of conventional concrete tends to decrease as micro‐cracks develop rapidly under applied stresses. However, incorporating closely spaced fibers can hinder the progression of micro‐cracks, leading to a substantial improvement in both tensile and flexural strengths of concrete. Furthermore, fibers can delay the initiation of tensile cracks, effectively enhancing concrete's ability to withstand tensile strains before failure. As a result, fiber‐reinforced concrete exhibits increased durability and enhanced resistance to impacts compared to plain concrete. This study aims to evaluate and compare the cyclic flexural behavior of a cantilever beam constructed from ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) using reinforcing bars made of high‐strength steel (HSS). The beams contain varying relative proportions of longitudinal reinforcement and steel fibers. Various key performance parameters of the cantilever beam were thoroughly examined, such as load capacity, flexural ductility, failure mode, hysteresis response, energy dissipation, and hardness. The study demonstrated that UHPFRC beams with HSS exhibit good cyclic flexural performance prior to failure.

Structural Behavior of Self-Compacting Bendable Mortar Beams reinforced by GFRP Bars under Monotonic Loads

Flexible or bendable concrete is an Engineered Cementitious Composite (ECC) that exhibits ductile material properties, in contrast to the brittle nature of conventional concrete. The material composition of conventional concrete is modified in order to impart a flexible nature to the material. This research presents the findings of an experimental study examining the flexural response of self-compacting bendable concrete beams reinforced by Glass Fiber Reinforced Polymers (GFRP) bars under a symmetrical two-point load. The experimental work comprised the casting of eight reinforced beams. The dimensions of all beams were identical: an overall height of 150 mm, a width of 100 mm, and a total length of 1,000 mm. The beams were classified into three groups based on the type of variables adopted and the type of the strengthening method employed, the percentage of steel fibers (1%, 1.5%, and 2%), and the percentage of Polyvinyl Alcohol (PVA) (0.2%, 0.3%, and 0.4%) were also considered. The following measurements were taken: the first cracking load, midspan vertical deflections, concrete surface strains, and the ultimate load capacity. Additionally, the crack patterns were recorded and the failure mode was observed, in addition to the mechanical properties of self-mortar bendable concrete (both fresh and hardened). The results indicated that an increase in the PVA ratio from 0.2% to 0.3% and 0.4% resulted in a notable rise in the modulus of rupture and modulus of elasticity, by approximately 16% and 40%, respectively, and 0.09% and 2%, respectively. The ductility of the beams increased with the steel fiber ratio due to enhanced flexural and splitting properties, which is a positive outcome. This allows for more caution to be exercised before the beam reaches its limit of stability. Furthermore, the value of deflection at maximum load increases with the increase of steel fiber content due to the increase in load capacity.

Structural Behaviour of Built-Up I-Shaped CFS Beams

Structural Behaviour of Built-Up I-Shaped CFS Beams

Numerical study of the effect of circular openings in the upper surface of rectangular hollow flange steel beams on the sectional moment capacity

Rectangular Hollow Flange (RHF) steel beams may have openings drilled in their top surface to pass some plumbing and electrical wiring inside the RHF cavity. These openings affect the behavior of these steel beams and may reduce their resistance to bending moment. To investigate this effect, Finite Element Modeling (FEM) was used to simulate RHF steel beams with and without flange openings with several variables in geometric dimensions. The FEM results were examined using 8 experimental test specimens of RHF steel beams obtained from previous studies without flange openings. The results showed high accuracy in modeling these RHF steel beams in structural behavior and ultimate bending moment capacity. Current design codes were applied to predict the capacity of these RHF steel beams without flange openings, both from FEM results and experimental tests. The prediction values were always less than the ultimate capacity of RHF steel beams without flange openings. After verifying the results, 98 RHF steel beams with different flange opening diameters were modeled. The reduction ratios in ultimate capacity in steel beams with hollow flange openings are directly proportional to the opening diameter, hollow flange height, and steel yield stress, while they are inversely proportional to the thickness and width of the hollow flange and the steel beam web height. The reduction ratios in the ultimate capacity for RHF steel beams with flange openings are small in the compact category, and these ratios increase with the non-compact and slender categories.

Effect of Bar Surface Geometry on Bond Behavior in GFRP-Reinforced Concrete Beams: Experiments and Design Implications

Effect of Bar Surface Geometry on Bond Behavior in GFRP-Reinforced Concrete Beams: Experiments and Design Implications

Shear behavior of FRP-UHPC composite beams enhanced by FRP shear key: Experimental study and theoretical analysis

To investigate the shear behavior of FRP (fiber reinforced polymers)-UHPC (ultra-high performance concrete) composite beams, four-point bending tests were conducted on seven FRP-UHPC specimens and two FRP-NSC (normal strength concrete) specimens, having different width and depth of concrete flange as well as FRP shear key (FSK) spacing. The slip between FRP profiles and concrete flange was controlled by employing FSK and epoxy resin bonded hybrid connection. The failure pattern, load-deflection/strain curves, and sliding response of composite beams were analyzed to study the influence of concrete type, FSK spacing, width and thickness of concrete slab. The results indicate that FRP-UHPC composite beams exhibited shear failure, while FRP-NSC composite beams experienced bending-shear failure. The composite beams demonstrated shear-lag effect, which became more pronounced with the increasing of the concrete slab width. The use of UHPC, reducing FSK spacing, and increasing the size of cross-section of concrete flange can effectively enhance the shear performance and reduce interface sliding. Formulae were developed to predict the shear capacity and deflection, considering shear deformation. The results predicted by the formulae developed match well with the experimental results.

Flexural Behavior of Beams Reinforced with Hybrid Steel Rebars using Sea-Water Mixed concrete

Flexural Behavior of Beams Reinforced with Hybrid Steel Rebars using Sea-Water Mixed concrete

Flexural behavior of steel/GFRP reinforced concrete beams having layered sections integrated with normal and rubberized concrete

Rubberized concrete (RuC) is one of the possible sustainable solutions to the problem of quickly disposing of old tires. This study introduced a new coating material (metakaolin, MK) for crumb rubber (CR) at a controlled temperature to avoid decreasing the RuC mechanical properties. Additionally, to prevent the possible reduction in the RuC strength on the RC beam behavior, the functionally graded material (FGM) approach was applied (layered beam section with RuC at 67 % of the beam section and normal concrete (NC) at the top one). The influence of RC beams on the tensile reinforcement (glass fiber-reinforced polymer (GFRP) instead of steel) was also examined. The experimental investigation comprised several concrete combinations: conventional concrete and RuC integrated uncoated and MK-coated CR replacing sand with percentages (0 %, 5 %, 15 %, and 25 %). The mechanical characteristics of concrete mixtures under compression and splitting tension tests were examined. Moreover, fourteen RC beams were experimentally loaded in flexural to investigate the impact of proposed parameters on the beam response. Following that, Finite Element (FE) modeling was carried out to examine the influence of the additional parameters on the RC beams' performance. The results demonstrate a notable improvement in the compressive strength of concrete by 17.4 % and a 25.4 % rise in split tensile strength due to the use of MK-coated CR compared to the uncoated CR. The impact of MK-created CR was more prominent in increasing the GFRP RC beam loads than the steel RC ones. In addition, using the FGM approach could eliminate the CR effect and exhibit nearly the same NC beam load.

Shear behaviour of deep beams strengthened with high-strength fiber reinforced concrete jackets

The study addresses the pressing need for effective strengthening of reinforced concrete (RC) members, specifically focusing on shear-critical deep beams. One of the most effective methods for strengthening RC members is the fiber reinforced concrete (FRC) jackets. However, limited number of studies have been conducted on deep beams strengthened with FRC. To address this gap, this paper presents an experimental investigation for strengthening of shear-critical deep beams using high-strength fiber reinforced concrete (HFRC) jackets. The experimental program involves testing three large-scale deep beams, including a reference specimen and two strengthened beams with thin HFRC jackets of different thicknesses (34 mm and 26 mm). The HFRC jackets featured straight steel fibers with a volumetric ratio of 1.13 %. According to the experimental results and analysis, it is found that an HFRC jacket of 34 mm thickness upgraded the strength by around 25 % and enhanced the crack control by reducing crack widths by around 50 % at the same absolute load with respect to the reference specimen. From the measured deformed shapes of the compression zone of the specimens, it is concluded that the main principles of the two-parameter kinematic theory of deep beams remain valid for HFRC-strengthened members, and these principles can be used to establish a complete modelling approach for such members.

Behavior of RC interior beam-to-column joints with FRP-strengthened beam web openings under cyclic loading

Despite the widespread adaption of the design criterion of strong column and weak beam (SCWB) in reinforced concrete (RC) frames, many existing RC frames cannot meet the design requirements of SCWB. Therefore, a novel beam opening (BO) technique for retrofitting RC frames that violate the SCWB design philosophy was proposed. The BO technique involves the creation of a web opening at the beam end near the joint to weaken its flexural capacity. In order to offset the reduced shear capacity due to the web opening, a fiber-reinforced polymer (FRP) shear strengthening system also needs to be applied around the opening. However, all previous relevant studies have been focused on the behavior of RC beams with FRP-strengthened web openings. To further verify the effectiveness of this technique, this study conducted experimental and numerical evaluations of RC joints with beam web openings under cyclic loading. Three full-scale RC interior beam-to-column joints were fabricated and tested under lateral cyclic loading and the results were evaluated in terms of failure modes, hysteresis behavior, ductility, energy dissipation, and stiffness degradation. The test results indicated that the inclusion of beam web openings successfully changed the failure mode of the joint from column-end failure to beam-end failure. Subsequently, finite element models of the three test specimens were established and the simulation results agreed well with the test results.

Flexural Behavior of Innovative Glass Fiber-Reinforced Composite Beams Reinforced with Gypsum-Based Composites

Glass Fiber-Reinforced Composite (GFRP) has found widespread use in engineering structures due to its lightweight construction, high strength, and design flexibility. However, pure GFRP beams exhibit weaknesses in terms of stiffness, stability, and local compressive strength, which compromise their bending properties. In addressing these limitations, this study introduces innovative square GFRP beams infused with gypsum-based composites (GBIGCs). Comprehensive experiments and theoretical analyses have been conducted to explore their manufacturing process and bending characteristics. Initially, four types of GBIGC—namely, hollow GFRP beams, pure gypsum, steel-reinforced gypsum, and fiber-mixed gypsum-infused beams—were designed and fabricated for comparative analysis. Material tests were conducted to assess the coagulation characteristics of gypsum and its mechanical performance influenced by polyvinyl acetate fibers (PVAs). Subsequently, eight GFRP square beams (length: 1.5 m, section size: 150 mm × 150 mm) infused with different gypsum-based composites underwent four-point bending tests to determine their ultimate bending capacity and deflection patterns. The findings revealed that a 0.12% dosage of protein retarder effectively extends the coagulation time of gypsum, making it suitable for specimen preparation, with initial and final setting times of 113 min and 135 min, respectively. The ultimate bending load of PVA-mixed gypsum-infused GFRP beams is 203.84% higher than that of hollow beams, followed by pure gypsum and steel-reinforced gypsum, with increased values of 136.97% and 186.91%, respectively. The ultimate load values from the theoretical and experimental results showed good agreement, with an error within 7.68%. These three types of GBIGCs with significantly enhanced flexural performance can be filled with different materials to meet specific load-bearing requirements for various scenarios. Their improved flexural strength and lightweight characteristics make GBIGCs well suited for applications such as repairing roof beams, light prefabricated frames, coastal and offshore buildings.

Flexural behaviors of GFRP-wood sandwich beams with recycled wood formwork cores

The escalating consumption of wood products has inevitably led to a rapid accumulation of waste wood, of which a large amount has been landfilled. An innovative concept has been therefore proposed to repurposes waste wood formwork as the core material of Glass Fiber Reinforced Polymer (GFRP)-wood sandwich beams. A series of four-point bending tests were conducted on these sandwich beams, with the thicknesses and orientations of strengthening GFRP layers as the main test parameters examined. The test findings indicated that the GFRP-waste wood sandwich beams failed in either buckling of compression zone or rupture of GFRP covering. In addition, the increase in the number of GFRP layer resulted in a significant increase in the both bending stiffness and flexural strength, and the beams strengthened with three-layer GFRP sheets exhibited the bending stiffness and flexural strength up to respectively 4.7 and 6.5 times greater than those without such GFRP strengthening. The analytical and numerical predictions of flexural properties of sandwich beams are in a good agreement with the test results, thereby validating the accuracy of the models employed in the present study.

Effect of shrinkage-mitigating materials, fiber type, and repair thickness on flexural behavior of beams repaired with fiber-reinforced self-consolidating concrete

While self-consolidating concrete (SCC) has emerged as a highly effective approach for the repair of concrete structures, there have been few investigations regarding the effect of the combination of different fiber and shrinkage-mitigating material types (shrinkage-reducing admixture, SRA; superabsorbent polymer, SAP; and expansive agent, EA) on the flexural behavior of repaired structures. This study aims to explore the influence of three different shrinkage-mitigating materials (1.25%–2.5 % SRA, 4%–8% EA, and 0.2%–0.4 % SAP), four fiber types (two macro synthetic fibers, MSFA and MSFB; 5D hooked steel fibers, 5D; a combination of 80 % 3D hooked steel +20 % short steel fibers STST) on fresh and hardened properties, cement hydration, and drying shrinkage of fiber-reinforced self-consolidating concrete (FR-SCC). Specifically, the effect of different shrinkage-mitigating materials, fiber types, and two repair thicknesses corresponding to 1/3 and 2/3 of the total height of prismatic element on the flexural performance of composite specimens repaired using FR-SCC was studied. The bond strength between existing concrete and FR-SCC was also investigated to reveal the flexural behavior of the composite beams. The results indicate that prismatic specimens repaired with FR-SCC made with 1.25 % SRA showed excellent flexural performance compared to those repaired using FR-SCC made with 4%–8% EA and 0.2%-0.4%SAP. The adverse effect of the incorporation of 4%–8% EA and 0.2%–0.4 % SAP on flexural behavior of repair specimens can be attributed to a lower existing concrete-FR-SCC interfacial and fiber-matrix bond strengths. Using SRA, EA, or SAP in FR-SCC improved bond strength with substrate by 10%–60 % compared to FR-SCC without any shrinkage-mitigating materials. The use of 1.25 % SRA showed the highest bond strength, which increased by 10%–37 % and 33%–44 %, respectively, compared to that made with SAP and EA. As the increase in the repair thickness of specimens, the incorporation of SRA, EA, or SAP had different efficiencies to enhance the flexural toughness and residual strength of the repair specimens. Furthermore, the incorporation of 5D fiber and 1.25 % SRA in SCC showed excellent flexural performance, followed by MSFA, STST, and MSFB fibers. The increase in the repair thickness from 1/3 to 2/3 of the total height of the composite beam enhanced the flexural toughness and residual strength by a maximum of 133 % and 160 %, respectively, attributing to fiber type and the increase in fiber volume at the cross-section of specimens.

Experimental investigation on the effect of natural fire exposure on the post‐fire behavior of reinforced concrete beams using electric radiant panel

Experimental investigation on the effect of natural fire exposure on the post‐fire behavior of reinforced concrete beams using electric radiant panel

Numerical investigation on bending characteristic and ductile fracture of AA7075 thin-walled beam using advanced orthotropic plasticity and fracture models

Thin-walled structures manufactured from the 7075 aluminum alloy are gaining tremendous attention in the automotive industry for their potential to reduce vehicle weight. However, the bending characteristics and rupture behavior of the AA7075 thin-walled beams under unexpected collision events have not been extensively studied. This study aims to fill that gap through a detailed numerical investigation of the bending deformation and failure mechanism of AA7075 thin-walled beams under quasi-static three-point bending at room temperature. Full-size, three-dimensional numerical simulations of laboratory-scale AA7075-T6 hat-shaped beam were conducted using the ABAQUS/Explicit solver. The material elastic–plastic response is described by a rate-independent constitutive description, incorporating advanced non-quadratic orthotropic plasticity and anisotropic ductile fracture criteria via VUMAT subroutines. Results indicate that the simulations accurately reproduced experimental observations, including the loading-displacement curves and deformation patterns. The bending behavior of the AA7075-T6 thin-walled beams aligns with typical bending collapse mechanisms, consistent with Kecman’s theory. The rupture process exhibits ductile fracture characteristics, with heterogeneous stress distribution across the material thickness affecting crack initiation rates between the upper and lower surfaces. Notably, the stress state at the fracture’s half-thickness section approximates an equi-biaxial tension condition. These findings provide essential insights into the bending deformation and failure mechanisms of AA7075 thin-walled structures under unexpected impact loading.

Experimental and analytical investigation of the flexural behavior of steel-bamboo composite I-beams with composite connections

A novel steel-bamboo composite (SBC) I-beam with composite connections was presented, in which the pure adhesive bonding steel-bamboo (SB) interfaces at the beam's flanges were reinforced by self-tapping screws (STSs) to avoid the debonding failure and slip behavior of beams. 14 beams with various parameters were prepared and performed four-point bending tests to investigate the bending behavior of beams. The influences of different parameters on the bending behavior were revealed. Finally, analytical models were developed for estimating the interfacial shear stress at the beam flanges in the serviceability limit state (SLS) and ultimate deflection of beams, respectively. The results indicated that the debonding failure and slip behavior of beams were effectively limited, and the flexural and deformation capacities and ductility were significantly improved. The failure mechanism of beams changed from a debonding failure to a bamboo tensile failure. The bending resistance was improved by increasing the diameter and arrangement range of the STS and reducing the STS spacing and steel flange width-thickness ratio. The local buckling behavior was effectively reduced and the ductility was improved for beams reinforced with transverse stiffening ribs (TSRs). Compared to beams with inclined STS reinforced bonding interfaces, the bending resistance was increased for beams with vertical STS reinforced bonding interfaces. The analytical model provided accurate predictions for beams.

Impact of structural adhesive creep on the performance of CFRP-strengthened steel beams

This paper examines the viscoelastic creep response of the structural strengthening epoxy adhesive and develops a viscoelastic constitutive model for numerical analyses to assess its impact on the long-term performance of carbon fibre reinforced polymer (CFRP)-strengthened steel beams. The numerical studies explore the behaviour of CFRP-strengthened steel beams subjected to both three-point and four-point bending over a one-year period, with temperatures ranging from −20 to 60 °C. The results revealed that the stiffeners could reduce the deflection and peak stress in the steel under four-point bending, yet they had the opposite effect under three-point bending. Furthermore, whilst the larger CFRP plates could reduce the slip at the plate ends, they provided only a limited enhancement in the strengthening effectiveness. The impact of viscoelastic creep in the adhesive is more marked and apparent, particularly at higher temperatures. Over time, the increased slip leads to a rise in maximum stress and deflection of the steel beams, thereby diminishing the effectiveness of the strengthening. A low-temperature environment can mitigate these negative impacts, whereas elevated temperatures can significantly exacerbate them. Notably, at a moderate temperature of 30 °C, the maximum CFRP stress can already be reduced by 32.25 %, which corresponds to an increase in steel stress by 4.15 %. Therefore, in practical applications at warm service temperatures, the creep of CFRP-strengthened steel beams should be carefully considered to ensure their long-term safety.

Optimizing flexural strength of RC beams with recycled aggregates and CFRP using machine learning models.

This paper investigates the flexural bearing behavior of reinforced concrete beams through experimental analysis and advanced machine learning predictive models. The primary problem centers around understanding how varying compositions of construction materials, particularly the inclusion of recycled aggregates and carbon fiber-reinforced polymer (CFRP), affect the structural performance of concrete beams. Eight beams, including those with natural aggregates, recycled aggregates, fly ash, and CFRP, were tested. The study employs state-of-the-art machine learning frameworks, including Random Forest Regressor (RFR), XGBoost (XGB), and LightGBM (LGBM). The formation of these models involved data acquisition from experiments, preprocessing of key input features (such as rebars area, cement portion, recycled and natural aggregate masses, silica fume, fly ash, compressive strength, and CFRP presence), model selection, and hyperparameter tuning using Pareto optimization. The models were then evaluated using performance metrics like Mean Squared Error (MSE), Mean Absolute Error (MAE), and coefficient of determination (R2). Outputs focus on load-induced deflection and mid-span displacement. With a dataset of 4851 samples, the optimized models demonstrated excellent performance. The experimental results revealed substantial enhancements in both compressive strength and load-bearing capacity, notably observed in beams incorporating 70% recycled aggregate and 10% silica fume. These beams exhibited a remarkable increase in compressive strength of up to 53.03% and a 7% boost in load-bearing capacity compared to those without recycled aggregate. By integrating experimental analysis with advanced computational techniques, this study advances the understanding of eco-friendly construction materials and their performance, shedding light on the intricate interactions between sustainable construction materials and the flexural bearing behavior of beams.