Bar Diameter Research Articles

4D printing of pH-responsive bilayer with programmable shape-shifting behaviour

4D printing of smart materials has seen remarkable advancements in the domain of biomedical devices, with a particular focus on developing responsive and adaptive programmable structures. In this work, we report the 4D printing of two solvent-responsive hydrogels forming a bilayer that undergoes bidirectional actuation depending on the pH of the solvent. A strong interlayer adhesion between the hydrogels is formed without subjecting either of their surfaces to any chemical modification. These hydrogels have an interfacial toughness of 71.8 J/m2 and undergoes no delamination during actuation inside a solvent. Conventionally, pH-responsive actuators are only limited to simple 2D films prepared by solvent casting. However, our work focuses on the design and fabrication of complex bilayer and patterned structures using Direct-Ink Writing (DIW) approach. These printed structures actuate upon immersion in a solvent medium, and the actuation is reversible in nature. The influence of programmable variables on the morphed structure was studied systematically by modifying the rheological properties (in the range of 102−105 Pa.s) and printing parameters (optimized at a printing speed of 5mm/sec, with the extrusion pressure of 5−6 bar and nozzle diameter of 0.5 mm) of the 3D printed bilayer structure. The physicochemical properties of the printable hydrogel ink were tuned such that the same structure can respond to both acidic and basic pH (with non-morphing point at pH 7), by altering the directionality of actuation. We have demonstrated the applications of these pH-responsive actuators in smart valves.

Mechanical performance and failure mode judgment criteria of grouted sleeve connectors considering large deformation and grouting compactness

Three groups of 36 grouted sleeve connectors (GSCs) with different grouting compactness were experimentally investigated under monotonic tension and large-deformation reciprocating tension-compression. The experimental results showed that the failure mode contained the tensile fracture of the steel bar (Failure Mode I) and bond-slip failure (Failure Mode II). The yield strength, ultimate strength, and elongation of GSCs gradually decreased, while the residual deformation increased as the grouting compactness decreased. The average ultimate strength of GSCs with 90 % grouting compactness was 561.61 MPa, a 124.46 % enhancement over that of GSCs with 60 % grouting compactness. The loading method mainly affected the residual deformation of GSCs, which increased with the cycle number of large-deformation reciprocating loadings at consistent grouting compactness. Subsequently, based on the effects of the grouting compactness and large deformation on the mechanical performance of GSCs, this study combined the critical grouting compactness and fu/fsy to judge the failure mode of GSCs with steel bar diameters of 20 cm, which were determined to be 90 % and 1.4, respectively. These findings provide a foundation for designing assembled structural connections and ensuring the safety of assembled structures.

Effect of alkali silica reaction on the performance of hooked bars

The Alkali-silica reaction (ASR) is a deterioration phenomenon that causes undesirable expansion and cracking in hardened concrete. This reaction usually occurs between certain types of reactive aggregates and high-alkali cement and is reported in a notable number of reinforced concrete (RC) structures worldwide, for which assessing the residual performance is critical. Many of these structures employ hooked bars to provide anchorage, especially in their joint regions. This paper examines the pull-out behavior of hooked bars in RC beam-column joints affected by ASR to help assist with safety evaluation of RC structures impacted by this reaction. A set of 7 full-scale RC columns was fabricated with concrete containing reactive fine aggregates, which incorporated different hooked bar diameters and amounts of transverse reinforcement. The specimens were subjected to pull-out of their hooked bars either in control conditions or after curing in a relative humidity of 100 % and a temperature of 50°C for up to 303 days to achieve different levels of ASR-induced expansions. Results showed that up to an unrestrained uniaxial expansion level of 0.2 %, the ASR-affected hooked bars showed an increase by up to 22 % in their ultimate pull-out capacity but a notable reduction in their ductility. Despite distributed cracking in ASR-affected specimens, their failure mode was relatively similar to that in the control specimen and remained a combination of side and front failure.

Experimental and theoretical investigation on bond performance between surface-modified bamboo scrimber bars and concrete

With the aim of facilitating the adoption of eco-friendly bamboo scrimber bars as an alternative to the widely used steel bars in concrete structures, center pull-out tests were conducted on 75 specimens to investigate the bond performance between bamboo scrimber bars and concrete. Two innovative modification methods were employed, including the sand coating modification method with varying particle sizes and a newly proposed method involving wrapping with basalt fiber bundles, with a focus on the impact of bundles spacing on bond strength. Additionally, other influence factors, including the concrete compressive strength, development length, and equivalent diameter of bamboo scrimber bars, were investigated. The test results show that compared to unmodified bamboo scrimber bars, those modified with sand and basalt fiber bundles show increases in bond strength of 5.50–5.96 times and 4.82–6.15 times, respectively. The bond strength was most significantly influenced by the development length, which decreases with increasing development length. Besides, specimens with development length less than 75 mm mainly exhibit pull-out failure, while those with development length equal to 75 mm primarily occur concrete splitting failure. Furthermore, a bond strength prediction formula and a bond stress-slip constitutive model for the interface between bamboo scrimber bars modified with sand coating and concrete were established, which show great agreement with the test results.

Early age bond-slip behavior of reinforcing steel bars in concrete subjected to uniaxial lateral pressure: An experimental study

The bond between reinforcing bars and concrete is a crucial factor concerning the serviceability of reinforced concrete structures, particularly for those during construction in some developing areas where plain bars were still used as reinforcements. Despite numerous studies on early age bond behavior between steel bars and concrete, little research has been conducted to quantify the effect of uniaxial lateral pressures on this bond. This study involved testing a total of 378 pullout specimens to evaluate the early age bond-slip behavior of plain bars in concrete under uniaxial lateral pressure. The main test parameters included the concrete ages (1, 3, 7, 14 and 28 days), lateral pressures (0, 0.1, 0.2, 0.4 and 0.6 times the compressive strengths of concrete), concrete strength grades (C20, C35 and C45), and bar diameters (12, 16 and 20 mm). Based on the experimental results, a series of analytical expressions were developed for bond strength, maximum bond slip and residual bond stress predictions considering the effects of early age and lateral pressure. The results demonstrate that degradation of bond strength at early ages can be effectively mitigated by uniaxial lateral pressures. As the age decreases from 28 to 1 days, the bond strength exhibits a significant decrease of up to 51.59 %, while this adverse effect can be reduced by around 10 % in the presence of lateral pressures. Increasing the pressure level from 0 to 0.4 results in a significant increased early age bond strength by 112.6 % to 199.0 % for different bar diameters. However, the residual-to-maximum bond stress ratio remains nearly constant at 0.49 regardless of age and lateral pressure, as the pressure primarily contributes to frictional forces at the bar-concrete interface. An age-dependent bond-slip constitutive model considering the effect of uniaxial lateral pressures was finally proposed and verified with the test results. The paper concludes that given the concrete compressive strength at 28 days, the proposed bond strength and bond stress-slip models can predict the early age bond responses of plain bars in concrete under uniaxial lateral pressures with reasonable accuracy.

Steel stresses and shear forces in reinforcing bars due to dowel action

AbstractReinforcing bars in structural concrete are typically designed to carry axial forces. Nevertheless, due to their bending stiffness, the bars can also carry transverse forces, that are associated with the localized bending mechanism (dowel action) resulting from the relative displacements (or slip) wherever a crack interface or a discontinuity interface (between two concrete parts cast at different times) intercept the bar. Such localized bending induces stress concentrations in both the bars and the concrete. The relative displacement can occur at interfaces either perpendicular to the bar or inclined with respect to its axis. Thanks to steel ductility, the bending stresses in the bars due to dowel action do not impair the sectional capacity at the ultimate limit state. Fatigue verifications, however, require an accurate evaluation of these stresses under imposed transverse displacements or shear forces. As well known, dowel action can be described by means of the traditional unidimensional Winkler's model (beam on an elastic foundation), where the bearing stiffness of the concrete embedment is typically introduced through a couple of parameters, namely the bar diameter and the concrete strength in compression. The actual behavior of a dowel, however, is definitely more complex and for such a reason, improvements are needed for the Winkler's model to introduce other parameters typical of actual structures. Hence, a new formulation is introduced in this study for the bearing stiffness, that is calibrated based on mechanical considerations and measurements with optical fibers. The proposed formulation also accounts for the following parameters: angle between the crack and the bar, concrete‐cover thickness, number of load cycles and the softening effect caused by the local secondary cracks radiating from bar ribs during the pull‐out process. The predictions of the model—implemented with the proposed bearing stiffness—fit fairly well the test results under both monotonic and cyclic loads, in terms of shear force–transverse displacement response and peak stress in the reinforcing bars.

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.

Seismic behavior of resilient concrete column-base connection with SMA bolts and RSPs

This paper presented a novel resilient concrete column-base connection with shaped memory alloy (SMA) bolts and rectangular slotted plates (RSPs) to achieve the demountable and recoverable capabilities in precast concrete columns. Quasi-static tests were conducted on one monolithic and three resilient concrete connections to investigate the effects of RSP number and yield strength on seismic behavior. Results showed that the resilient connection with both flange and web RSPs had superior lateral capacity, ultimate drift ratio, and energy dissipation compared to the monolithic connection. The resilient connection also exhibited minimal concrete damage and smaller residual deformation. However, low-yield-strength flange RSPs significantly reduced lateral capacity, initial stiffness, and energy dissipation, which should be considered in engineering design. Additionally, adjustment coefficients for rocking interface rotations were determined from digital image correlation (DIC) data using a fitting method. A formula was proposed to predict the flexural capacity of resilient specimens, assuming a plane section in the compression zone. The predictions closely matched the test data, with differences within 10 %, demonstrating the formula's effectiveness. The length, diameter, and material yield strength of the anti-shear steel bar (ASB) had a significant impact on the shear capacity of the interface.

Shear performance of perfobond leiste (PBL) connectors in engineered cementitious composites (ECC)

Substituting normal concrete with ductile Engineered Cementitious Composites (ECC) is a promising way to address the safety and durability issues caused by cracking in steel-concrete composite structures. To realize a synergistic deformation behavior between steel and ECC, Perfobond Leiste (PBL) shear connectors are preferred to be used owing to their superior shear resistance, shear stiffness, and excellent fatigue performance. This research comprehensively investigated the shear performance of PBL connectors in ECC through experimental, numerical, and analytical approaches. Firstly, the shear load-slip relationships of PBL connectors in ECC and concrete were studied through push-out tests of 36 H-shaped specimens. It indicated that the fracture of penetrating bars dominated the final failure of PBL connectors in ECC, whereas premature concrete spalling happened in concrete specimens. By establishing a refined finite element model, the parametric study was then conducted to clarify the influence of the compressive strength of ECC, hole diameter, penetrating bar diameter, and penetrated plate thickness on the shear characteristics of PBL connectors in ECC. Finally, an analytical model for predicting the shear carrying capacity of PBL connectors embedded in ECC was derived, matching well with the test results.

The shear performance of DSCW-RC joints with lap-spliced steel bars

The double steel plate concrete composite shear wall (DSCW) structure combines the advantages of steel and concrete, offering high strength, stiffness, and durability. The joint formed by the DSCW and reinforced concrete foundation (RC foundation) was often unavoidable in engineering practice. Research related to the mechanical behavior of the DSCW-RC foundation is limited. This paper investigated the shear performance of DSCW-RC joints with lap-spliced steel bars. A total of seven specimens were designed and tested. The influences of steel plate thickness, steel bar arrangement, and stud spacing on the shear behavior of the joints are elucidated. The test results indicate that the predominant failure mode of the specimens occurred in the upper part of the local steel plate, with reinforcement yielding. While steel bar diameter and stud spacing minimally affected the shear strength, they significantly influenced the failure displacement at the joint interface. The failure deformation increased with increasing steel bar diameter and decreased with increasing stud spacing. Moreover, the thickness of the steel plate profoundly impacted structural shear strength and deformation, with both deformation and bearing capacity increasing with plate thickness. In addition, this study explores the force-transferring mechanism of such joints under shear load, offering a crucial reference for subsequent analyses of the composite force mechanism of DSCW - RC foundation joints.

Contribution of spatially variable pitting corrosion on fatigue life prediction of RC beams

Pitting corrosion induces stress concentration in steel bars, significantly reducing the fatigue life of reinforced concrete (RC) beams. Moreover, spatially variable pitting corrosion can cause fatigue fractures in tensile steel bars at various cross-sections of beams, not just at the mid-span section. This will further increase the failure probability of beams but is rarely considered by existing studies. Thus, this study proposes a fatigue life prediction method for RC beams experiencing spatially variable pitting corrosion. First of all, the spatial variability of pitting corrosion in tensile steel bars in RC beams is simulated through the three-dimensional laser scanning method and the spectral representation method, in which the steel bar diameter, length, distance, corrosion level, and the correlation between corrosion pits are systematically considered. Subsequently, the fatigue crack initiation and propagation of pitting corroded steel bars are modeled based on fracture mechanics. The spatial analysis is then conducted on corroded RC beams until fatigue failure occurs. The proposed prediction method is verified with results from existing references. The findings highlight that neglecting the spatial variability of pitting corrosion leads to an overestimation of the fatigue life of corroded RC beams, especially under uniformly distributed loadings and high corrosion levels. This study provides a reasonable prediction for the lifespan of corroded RC beams.

Bond-slip behavior of Aluminum Alloy (AA) bars for near-surface mounted (NSM) technique

An experimental study consisting of 22 pull-out tests was carried out to investigate the bond-slip performance and load transfer mechanism between near-surface mounted (NSM) Aluminum Alloy (AA) bars and concrete when the AA bars are inserted into pre-cut grooves on the surface of the host structure and bonded with an appropriate bonding agent. The effects of several design parameters were evaluated including bond length, diameter of AA bars, bar surface treatment, and adhesive type. A digital image correlation (DIC) system was used to measure the slips and surface strain and four failure modes were observed in the tests, being concrete splitting failure, epoxy splitting, debonding at the bar-epoxy interface, and AA bar rupture. Results showed that an increase in bond length could make the failure mode more ductile, while AA bars with rough surfaces exhibited a relatively satisfactory bond-slip behavior when a suitable epoxy was used. Finally, the test data from this study were used to examine three bond-slip models based on fiber reinforced polymers (FRP) for the NSM technique. A new bond-slip model considering the influence of the bar external surface was proposed and validated by the test results from both this study and literature.

The numerical simulation study on the Fe-SMA-strengthened PCCP with broken wires

This paper conducted a full-scale experiment on a PCCP with an inner diameter of 1400 mm and a length of 6000 mm. A finite element model was established on the basis of this experiment, and the influence of different recovery stresses, Fe-SMA bar diameters, and material types on the strengthening effect was investigated. The simulation results indicated a notable enhancement in the strengthening effect upon employing Fe-SMA bars with recovery stresses of 0 MPa, 175 MPa, 330 MPa, and 382 MPa, respectively. With the increased recovery stress, the micro-cracking pressure enhanced 33.8 %, 51.5 %, 72.1 %, and 80.9 % and the visible cracking pressure enhanced 12 %, 24.8 %, 31.6 %, and 33.1 %, respectively, compared to the non-strengthened PCCP. Finally, this paper proposed a design concept for a short-duration, micro excavation PCCP strengthening method based on the self-prestressing of the Fe-SMA.

Experimental investigation on shear behavior of double-row perforated GFRP rib connectors in FRP-concrete hybrid beams

Perforated GFRP rib (PFR) connectors have been used in FRP-concrete hybrid beams due to durability and ease of construction. PFR connectors are parallel FRP plates with predrilled holes positioned in the flange of FRP beams. The optimal plate spacing needs to be determined because it affects the shear performance of PFR connectors. 18 push-out tests were conducted to investigate the effect of plate spacing ( Sl), penetrating GFRP bar diameter ( d), and concrete strength ( fc) on the failure mode, capacity, and shear load-slip (P-S) curves of double-row PFR connectors. Results showed that PFR connectors suffered plate shear failure with the concrete dowel undamaged. Typical P-S curves consisted of micro-slipping and significant-slipping phases. The shear capacity and stiffness of PFR connectors were improved by 33.3% and 45.1%, respectively, by increasing the plate spacing from 1.2 h (where h denotes the plate height) to 3.2 h. The effect of plate spacing on shear capacity and stiffness could be neglected if the ratio ( Sl/ h) was more than 3.2. Specimens with a larger diameter of penetrating bar and higher concrete strength demonstrated higher capacity and stiffness. An empirical equation based on the maximum stress failure criterion was proposed to estimate the capacity of PFR connectors, considering the plate spacing effect, and verified by available data. Additionally, a description of the P-S curve was developed and calibrated by the experimental results.

Pre-and post-heating bar-concrete bond behavior of CFRP-wrapped concrete containing polymeric aggregates and steel fibers: Experimental and theoretical study

The present research attempted to explore the impact of steel fibers and carbon fiber-reinforced polymer (CFRP) sheets on the pre-and post-heating bond behavior of steel bars in high-strength concrete incorporating waste polyethylene terephthalate (WPET) by conducting the pullout and beam tests and in both pullout and splitting failure modes. To achieve this aim, one hundred and forty-four cubes and forty-eight prisms were cast for the pullout and beam tests, respectively. The variable parameters included the replacement ratio of the fine aggregates with waste polyethylene terephthalate (WPET) particles (0 % and 10 % by volume), steel-fiber content (0 % and 1 % by volume), bar diameter (12-and 16-mm), target temperature (25, 200, and 600 °C), and confinement level (no confinement or CFRP wrapping applied after the thermal regime). Bond strength, bond stress-slip behavior between rebar and concrete, failure mode, and rebar debonding energy were among the parameters investigated after cooling. The results showed that in contrast with the positive effect of CFRP sheets on debonding energy, steel fibers have a positive effect on debonding energy only at 600 °C. Steel fibers did not offset the negative effect of polymeric aggregate, negatively changed the pullout mode to a mixed pullout/splitting failure at 200 °C, and tended to favor splitting failure mode to mixed mode at 600 °C. Moreover, steel fibers negatively affected the bond strength of pullout specimens in both confined and unconfined conditions, especially at 25 and 200 °C, and were less effective than CFRP sheets in avoiding splitting. Small-diameter bars reduced the negative effect of steel fibers on the bond, while polymeric aggregate tended to enhance the bond strength differences between large- and small-diameter bars. The effect of increasing the bar diameter on the effectiveness of CFRP sheets on the bond strength was not clear, but as a general trend, the effectiveness increased with the increase of the bar diameter. A predictive model based on the experimental results of this study and other studies was proposed as well to introduce the positive effect of the CFRP confinement and the dubious effect of steel fibers and polymeric aggregate on bond strength.

Size Effects in Climatic Aging of Epoxy Basalt Fiber Reinforcement Bar.

The purpose of this study was to obtain information on the influence of the size factor on the climatic aging of circular fiber plastics produced by pultrusion. The kinetics of moisture transfer was obtained in humidification and drying modes at 60 °C in samples of epoxy basalt fiber reinforcement bars: after 28 months of exposure in the extremely cold climate of Yakutsk and 30 months of exposure in the moderately warm climate of Gelendzhik. It was shown that the 2D Langmuir model adequately describes the kinetics. The diffusion coefficients in the reinforcement direction for bars with diameters of 6, 8, 10, 16 and 20 mm turned out to be significantly higher than in the radial direction. To clarify the aging mechanism of the bars and the tensile, compressive and bending strength, the coefficient of linear thermal expansion and the glass transition temperature of the epoxy matrix of the bars with a diameter of 6, 8 and 10 mm after 51 months of exposure in Yakutsk and 54 months of exposure in Gelendzhik were measured. It was shown that after climatic exposure, the deformability of the bars decreased with increasing diameter of the bar; the glass transition temperature increased more significantly in the bar with a smaller diameter. In 6 mm diameter bars, the compressive and bending strength limits decreased by 10-25 % due to the plasticizing effect of moisture. With the same depth of moisture penetration into the volume of the samples, its effect on the strength of thin bars was significant, and for thick bars, it was insignificant. An increase in the glass transition temperature by 6 °C, associated with the additional curing of the polymer matrix, occurred in the surface layer of the epoxy basalt fiber reinforcement bars and was revealed in bars with a smaller diameter.

Experimental investigation on influence of embedment length, bar diameter and concrete cover on bond between reinforced bars and steel fiber reinforced concrete (SFRC)

The bond between reinforced bars and concrete has a significant impact on reinforced concrete structures. Incorporating steel fibers in concrete not only enhances the performance of the concrete but also influences the bond strength of embedded reinforcing bars. In this paper, experiments have been carried out to investigate the influences of different bar diameters, concrete cover and embedment lengths on bond-slip responses between reinforcing bars and steel fiber reinforced concrete (SFRC). Furthermore, pull-out tests with normal concrete were also executed as a comparative group. The bond-slip results of specimens were collected. The impact of embedment length, reinforcing bar diameter, and the existence of steel fibers on the bond behavior of reinforcing bars was comprehensively analyzed. Meanwhile, the results indicate that variations in the ratio of concrete cover to reinforcing bar diameter lead to different effects on the bond behavior of SFRC compared with normal concrete. Different failure modes of specimens were exhibited and discussed. Additionally, a mathematical model for bond strength of bars in SFRC was proposed based on the correction of the bond strength model with normal concrete, which shows good agreement with experimental results.

Bond-slip behavior of lapped sand-coated deformed GFRP rebars in UHPC under double-row splice test

Novel Ultra-High-Performance-Concrete (UHPC) structures reinforced with Fiber-Reinforced Polymer (FRP) rebars are promising candidates for applications in important infrastructures under exposed environments where normal concrete and steel rebars may falter. This paper aims to assess the bond-slip behavior between lapped sand-coated deformed Glass FRP (GFRP) rebars and UHPC using double-row splice tests, with parameters including bar diameter, splice length and lap clearance. Failure modes including the pullout of GFRP rebars and the splitting of UHPC were identified. For cases of pullout failure, the average bond strengths in samples with splice lengths of 5db were reduced by 17.6–22.1 % compared to those of 2.5db. Increasing the lap clearance from 0 to 1db and 2db led to 11.1 % and 30.2 % increases in average bond strengths. Furthermore, average bond-slip models for lapped sand-coated deformed GFRP rebars in UHPC were developed. The predicted curves matched the experimental ones, showing errors within 20 % for both average bond stresses and slips. When the cover is not less than 2db, the splice length is recommended to be at least 15db for sand-coated deformed GFRP rebars with diameters of 10 mm–16 mm in UHPC, approximately 1.25 times the corresponding development length proposed by the existing research.

Flexural Behavior of Precast Rectangular Reinforced Concrete Beams with Intermediate Connection Filled with High-Performance Concrete

Precast rectangular reinforced concrete (PRRC) beams are joined on construction sites using concrete in situ to achieve the desired length. Limited research exists on the effect of intermediate connection shapes and the types of infilled concrete on the flexural performance of PRRC beams. This paper presents a comprehensive experimental and numerical investigation into the performance of PRRC beams with various intermediate connection geometries and infilled materials under flexural loading. The study examines rectangular, triangular, and semi-circular intermediate connections, along with the performance of beams infilled with normal concrete (NC), engineered cementitious composites (ECC), ultra-high-performance ECC (UHPECC), and rubberized ECC (RECC). The experimental results indicate that the rectangular intermediate connection exhibits superior performance in terms of strength and energy absorption compared to the triangular and semi-circular shapes. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC for any shape of intermediate connection. Moreover, beams with rectangular connections and UHPECC infill exhibited the most significant increase in energy absorption and ultimate load compared to the beams with ECC and RECC. The ultimate load of the beams with UHPECC and tensile reinforcement bar diameters of 10 mm and 12 mm increased by 13% and 29%, respectively, compared to the control beam. The energy absorption of the beams with tensile reinforcement bar diameters of 10 and 12 mm was found to be 75% and 184% higher, respectively, than the control beam. In addition, an increase in tensile bar diameter was found to enhance both the energy absorption and the ultimate load capacity of the beams, regardless of the type of infill concrete. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC. In particular, beams with rectangular connections and UHPECC infill exhibited an increase in energy absorption and ultimate load of up to 184% and 29%, respectively. UHPC was calculated to be as high as 184%, and 29%, respectively, compared to the control beams. In addition, an increase in tensile bar diameter was found to enhance both energy absorption and ultimate load capacity. Finite element modeling (FEM) was developed and validated against the experimental results to ensure accuracy. A parametric study was conducted to study the effects of various concrete types in triangular and semi-circular connections, as well as the influence of intermediate connection length on semi-circular connections under flexural loads. The findings reveal that increasing the length of intermediate connections increases the ultimate load of the beams.

Flexural strengthening of reinforced concrete cantilever beams having insufficient splice length

Structural systems often undergo changes due to variations in the usage, the loading conditions, or the presence of defects in their elements. The problem can be exacerbated when there is insufficient overlap between reinforcing bars in critical moment zones. This article investigates the behavior of reinforced concrete cantilever beams exhibiting insufficient overlap between bars that used as main reinforcing steel bars in the negative moment zone. Various strengthening techniques were employed in order to improve these defected cantilever beams. Eleven beams underwent flexural testing until reaching failure. The experimental parameters encompassed the strengthening scenarios and the bonded length. Three strategies were used: the application of stainless-steel plates (SSPs) as externally bonded reinforcement, near surface mounted (NSM) reinforcement in which additional deformed steel bars were bonded utilizing engineering cementitious composites, and externally pre-stressing technique. The anchorage length was examined at 40, 50, and 60 times the internal bar diameter. It was noted that the most substantial improvement achieved with the NSM method, followed by the externally pre-stressing method. It is worth mentioning that most of the beams failed in a flexural manner, with partial debonding occurring in beams strengthened using external strengthening. Moreover, this article includes the development of a numerical model employing the finite element method to replicate the response observed from the experimentally tested beams. The accuracy of the model was confirmed through the comparison of its outcomes with the experimental data, demonstrating an acceptable level of accuracy with deviations of less than 4.4 %. This successful numerical investigation was also used to conduct a parametric study. From this study it is evident that the effect of debonding on SSPs can be reduced by adding steel anchors at the ends of these plates. Finally, an analytical method was proposed to calculate the ultimate load capacity of strengthened reinforced concrete beams.