Strength Of Bars Research Articles

The dynamical state of bars in cluster dwarf galaxies: the cases of NGC 4483 and NGC 4516

ABSTRACT Dwarf barred galaxies are the perfect candidates for hosting slowly rotating bars. They are common in dense environments and have a relatively shallow potential well, making them prone to heating by interactions. When an interaction induces bar formation, the bar should rotate slowly. They reside in massive and centrally concentrated dark matter haloes, which slow down the bar rotation through dynamical friction. While predictions suggest that slow bars should be common, measurements of bar pattern speed, using the Tremaine–Weinberg method, show that bars are mostly fast in the local Universe. We present a photometric and kinematic characterization of bars hosted by two dwarf galaxies in the Virgo Cluster, NGC 4483, and NGC 4516. We derive the bar length and strength using the Next Generation Virgo Survey imaging and the circular velocity, bar pattern speed, and rotation rate using spectroscopy from the Multi-Unit Spectroscopic Explorer. Including the previously studied galaxy IC 3167, we compare the bar properties of the three dwarf galaxies with those of their massive counterparts from literature. Bars in the dwarf galaxies are shorter and weaker, and rotate slightly slower with respect to those in massive galaxies. This could be due to a different bar formation mechanism and/or to a large dark matter fraction in the centre of dwarf galaxies. We show that it is possible to push the application of the Tremaine–Weinberg method to the galaxy low-mass regime.

Bar properties as a function of wavelength: a local baseline with S4G for high-redshift studies

ABSTRACT The redshift evolution of bars is an important signpost of the dynamic maturity of disc galaxies. To characterize the intrinsic evolution safe from band-shifting effects, it is necessary to gauge how bar properties vary locally as a function of wavelength. We investigate bar properties in 16 nearby galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S4G) at ultraviolet, optical, and mid-infrared wavebands. Based on the ellipticity and position angle profiles from fitting elliptical isophotes to the two-dimensional light distribution, we find that both bar length and ellipticity – the latter often used as a proxy for bar strength – increase at bluer wavebands. Bars are 9 per cent longer in the B band than at 3.6 μm. Their ellipticity increases typically by 8 per cent in the B band, with a significant fraction (>40 per cent) displaying an increase up to 35 per cent. We attribute the increase in bar length to the presence of star-forming knots at the end of bars: these regions are brighter in bluer bands, stretching the bar signature further out. The increase in bar ellipticity could be driven by the apparent bulge size: the bulge is less prominent at bluer bands, allowing for thinner ellipses within the bar region. Alternatively, it could be due to younger stellar populations associated with the bar. The resulting effect is that bars appear longer and thinner at bluer wavebands. This indicates that band-shifting effects are significant and need to be corrected for high-redshift studies to reliably gauge any intrinsic evolution of the bar properties with redshift.

Durability of glass fiber reinforced thermoplastic polypropylene composite bars under the coupling effect of seawater and sea sand concrete environment and sustained bending

AbstractThe long‐term interfacial shear strength (IFSS) and flexural strength of GFPP bars under the coupling effect of bending and immersion in the simulated seawater and sea sand concrete (SWSC) solution were studied by an acceleration experiment. Three temperatures and three bending stress levels (0%, 9.8%, and 29.4% of the maximum flexural strain of GFPP bars) were used to accelerate the experiment. Results indicate that the degradation of mechanical properties of GFPP bars is relatively sensitive to the immersion temperature. Low bending stress did not accelerate the degradation of GFPP bars compared with unbent GFPP bars while high bending stress dramatically accelerated the degradation. Microscopic tests found there is corrosion of glass fibers and debonding between glass fibers and polypropylene but no obvious chain breaks of polypropylene occurred. Based on the Arrhenius theory, long‐term stable retention rates of the IFSS of GFPP bars with zero and low bending stress immersed in the simulated SWSC solution are 42.4% and 52.3%.Highlights Low‐stressed GFPP bars degraded similarly or even slower than unbent GFPP bars. GFPP bars degraded mainly due to interfacial debonding and fiber corrosion. Long‐term IFSS of GFPP bars under a coupling effect was predicted.

Prediction of Impact Strength of TIG Welded Cr-Mo Steel Using Artificial Neural Networks

Welding is a critical and energy-intensive process with significant importance in the manufacturing industry, enabling the creation of joints capable of withstanding diverse loads without failure. Accurate prediction of welding parameters' effects on the thermal cycle and strength of metals during and after welding is essential to ensure the reliability of welds. This study investigates the influence of welding parameters such as welding current, material thickness, number of weld passes, and electrode diameter on the impact strength of Cr-Mo steel bars. Pure tungsten with 2% thoriated Tungsten Inert Gas (TIG) electrodes was used to join the metal sheets autogenously. Artificial neural network (ANN) was used in creating the model that predicts the impact strength of the steel. Sample with welding parameters of 15 mm thickness, 90 A current, 3 weld passes, and Ø2.4 mm electrode size exhibited the highest impact strength. Furthermore, the analysis of variance (ANOVA) results show that the material thickness and number of weld passes contribute significantly to the impact strength of the steel. The ANN model trained by the Levenberg-Marquardt algorithm had an average training dataset root mean square error (RSME) of 4.12%. This study contributes to the reliability and performance of welded joints in various applications.

Seismic behavior of precast columns with unbonded prestressed tendons and energy-dissipating bars: physical and numerical investigations

The study of the strength and failure modes of construction components has become increasingly important with the advent of industrialized construction. Recently, because of the need to promote the survivability of both structures and persons, it has encompassed failure modes associated with seismic threats. This study reports the seismic behavior of precast segmented columns designed with both unbonded prestressed tendons (UPTs) and energy-dissipating (ED) bars. A physical specimen was subjected to a quasi-static cyclic test; this permitted the evaluation of the damage mode and behavior of the energy dissipation mechanism, and permitted the establishment and verification of a fiber beam element simulation model. The model was then used to evaluate the effects of the variation of the design parameters on the behavior of precast assembled columns. The test specimen exhibited stable energy dissipation and a pinching effect during cyclic loading. An analysis using the fiber beam element model with varying design parameters revealed that high-strength concrete could mitigate the concrete damage and residual deformation after an earthquake, and that the concrete strength and steel bar strength should be matched when enhancing the seismic resilience of precast columns with high-strength steel bars. It was determined that increasing the prestress mechanism, namely the ratio of the UPTs, could greatly improve the residual deformation, while the ratio of ED bars is the key factor in enhancing the energy dissipation capacity of the precast columns. Suitable ratios of UPTs and ED bars are the keys to ensuring stable energy dissipation and low residual drifts. Moreover, an increased axial load ratio and prestress level are able to restrain the joint opening and improve the bearing capacity of the precast columns; however, an excessive axial load or prestressing force would result in the rapid degeneration of the carrying capacity and larger residual displacements.

Experimental study of initial damage to steel bars due to bending process and the resulting performance deterioration

Brittle fracture of stirrups, due to effects such as diseased concrete expansion, is frequently reported and poses a potential threat to the load-bearing performance of structures. The brittle fracture was speculated to be directly related to the initial damage formed to bent steel bar during the bending process. However, few researches have been carried out on the formation of initial damage and its effect on mechanical performance. In this study, bending processes were conducted based on commonly used crescent-shaped steel bars; the effects of bending parameters and rib morphologies on the degree of initial damage were investigated in combination with data on bamboo-shaped steel bars, which often undergo brittle fracture. At the same time, tensile tests were carried out using V-shaped bent steel bars. The results show that as the bar diameter increases and the bending diameter decreases, the degree of initial damage in the bent steel bar increases. For example, for a crescent-shaped steel bar with a diameter φ of 16 mm, the initial damage when bending with a diameter 2.0φ was 430 µm, which exceeded the extent of the bamboo-shaped steel bar. At the same time, the ultimate tensile strength of bent steel bars was reduced by 20% compared to straight steel bars, and can be reduced by approximately 90% in severe cases; the deformation capacity of bent steel bars after yielding was also reduced by a maximum 90%. SEM analyses showed that the fracture surfaces of bent steel bars exhibit typical brittle fracture morphologies with the cleavage and quasi-cleavage fracture, indicating influences of initial damage and its propagation. Finally, based on the study results, some recommendations are made regarding the improvement of the transverse rib morphology, construction measures and the design of mechanical performance for bent steel bars, to prevent, for example, the premature failure of stirrups and the concrete components in which they are located.

Multi-objective optimization design of anti-roll torsion bar using improved beluga whale optimization algorithm

PurposeThis study aims to reduce the redundant weight of the anti-roll torsion bar brought by the traditional empirical design and improving its strength and stiffness.Design/methodology/approachBased on the finite element approach coupled with the improved beluga whale optimization (IBWO) algorithm, a collaborative optimization method is suggested to optimize the design of the anti-roll torsion bar structure and weight. The dimensions and material properties of the torsion bar were defined as random variables, and the torsion bar's mass and strength were investigated using finite elements. Then, chaotic mapping and differential evolution (DE) operators are introduced to improve the beluga whale optimization (BWO) algorithm and run case studies.FindingsThe findings demonstrate that the IBWO has superior solution set distribution uniformity, convergence speed, solution correctness and stability than the BWO. The IBWO algorithm is used to optimize the anti-roll torsion bar design. The error between the optimization and finite element simulation results was less than 1%. The weight of the optimized anti-roll torsion bar was lessened by 4%, the maximum stress was reduced by 35% and the stiffness was increased by 1.9%.Originality/valueThe study provides a methodological reference for the simulation optimization process of the lateral anti-roll torsion bar.

Development of asymmetric ceramic membranes for dairy wastewater treatment – A comparison between co-sintering and conventional firing process

Ceramic membranes have high potential for wastewater recovery. However, the high cost of raw materials and the high energy consumption for manufacturing, limit their use. This study aimed to prepare ceramic membranes using kaolin and alumina, emphasizing firing in a single step. On the support, corn starch was used as a porogenic agent and to evaluate the performance of the membrane, a simulation was used for the dairy industry effluent. The supports were manufactured by the extrusion process, which were sintered (1100, 1200 and 1300 °C), for the analysis of their properties. A suspension was applied to the inner surface of the green supports, and the cosintering process was employed. The supports containing 15 % corn starch sintered at 1100 °C showed high porosity (48 %), pure water permeate flux of 1385 L/h.m2 at 2 bar and mechanical strength of 8 MPa. The active layer exhibited pore sizes that indicate that the membrane can be used in the microfiltration process, with a permeate flux of 897 L/h.m2. The membrane showed adequate microfiltration performance for the removal of components present in the milk solution and responsible for the turbidity of the permeate, with a permeate flux stabilized at 30 L/h.m2.

Effects of pre-cracked width and seawater erosion on the cracking behavior of SFRC beams with BFRP bars subjected to cyclic loading

This study aims to explore the effects of various pre-cracked widths, seawater erosion and BFRP reinforcement ratios on the cracking behavior of steel fiber reinforced concrete (SFRC) beams with Basalt Fiber Reinforced Polymer (BFRP) bars subjected to cyclic loading. Pre-cracked beams were made by applying loads to obtain a predetermined crack width, such as 0.02 mm, 0.2 mm, and 0.4 mm crack widths. Eleven beams were poured and tested by a four-point bending load under cyclic loading. The crack pattern and load-crack width curves of beams were drawn and analyzed. The effects of pre-cracked width, seawater erosion, and BFRP reinforcement ratio on crack behaviors of beams were investigated and discussed. The results showed that the tensile strength of BFRP bars degenerated after seawater corrosion, and its degradation rates increased with the increase of diameter. The failure mode of beams after seawater erosion may transform from concrete crushing failure to BFRP tensile failure; The maximum crack width of all beams under service load was less than 0.5 mm. Increasing the BFRP reinforcement ratio can significantly improve the crack resistance of beams, but pre-cracked width and seawater erosion had adverse effects on the crack behavior. Existing codes overestimated the crack width of SFRC beams reinforced with BFRP bars. Finally, a new calculation model of crack width of SFRC beams with BFRP bars after seawater corrosion was proposed, and its results were closer to the experimental results.

On the Factors That Determine the Bond Behaviour of GFRP Bars to Concrete: An Experimental Investigation

It is becoming accepted that glass-fibre-reinforced polymer (GFRP) is a credible and effective replacement for steel in reinforced concrete (RC) to meet structural requirements whilst addressing durability concerns posed by steel over the long term. A better understanding of the bond behaviour between GFRP and concrete is essential for reliably and efficiently designing concrete structures with reinforced GFRP bars. This paper presents a parametric study of the bond behaviour of GFRP bars to concrete where the effects of the length, diameter, concrete strength, concrete cover thickness and rebar surface morphology of GFRP bars were investigated via a series of pull-out tests. The test results indicate that the bond strength of GFRP bars is predominantly influenced by their surface morphology, embedment length and diameter. On the other hand, the effects of concrete strength and cover thickness appear to have a limited impact on the bond strengths of GFRP rebars to concrete. It is shown that ribbed GFRP bars exhibit the highest bond energy of 89.4 Nmm and an average bond strength of 11.9 MPa. Moreover, the analysis of failure modes indicated the unique effect of GFRP surface morphology on failure mode. It is shown that 100% of ribbed GFRP failed due to concrete split, while 85% of sand-coated bars experienced failure due to bar slip. This examination of failure modes and their corresponding bond strengths provides a unique perspective on the bond behaviour between GFRP bars and concrete.

Experimental and Theoretical Shear Strength of Simply Supported Reinforced Concrete Beam

The study was conducted to evaluate the experimental and theoretical shear strength of a simply supported reinforced concrete beam with and without shear reinforcement in accordance with Eurocode 2 design criteria. Fifteen (15) reinforced concrete beams of dimension 750mm x 150mm x 150mm reinforced with diameter 12mm size bars were cast at various reinforcement ratios (i.e. 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%), while preliminary and mechanical tests were conducted on the materials (i.e. cement, fine and coarse aggregate, and reinforcement bars) in accordance with relevant codes and standards. The outcome from the findings showed that the cement, fine aggregate and coarse aggregate used to cast the reinforced concrete beam were well graded and satisfies the requirement of code specification. More results showed that the average diameter of the reinforcement bars are 11.67mm, the mean tensile and ultimate strength of the reinforcement bars are 389.73N/mm2 and 640.80N/mm2 respectively, while the mean reinforcement steel elongation is 14.23% which mostly met code requirement indicating suitability of the reinforcement bars usage in concrete. Furthermore, the result from the findings showed that the Eurocode 2 (EC2) design criteria of beams without shear reinforcement were lower than the experimental value, while EC2 design criteria for beams with shear reinforcement was close to the experimental value.

Early-growing Supermassive Black Holes Strengthen Bars and Boxy/Peanut Bulges

Using N-body simulations, we explore the effects of growing a supermassive black hole (SMBH) prior to or during the formation of a stellar bar. Keeping the final mass and growth rate of the SMBH fixed, we show that if it is introduced before or while the bar is still growing, the SMBH does not cause a decrease in bar amplitude. Rather, in most cases, it is strengthened. In addition, an early-growing SMBH always either decreases the buckling amplitude, delays buckling, or both. This weakening of buckling is caused by an increase in the disk vertical velocity dispersion at radii well beyond the nominal black hole sphere of influence. While we find considerable stochasticity and sensitivity to initial conditions, the only case where the SMBH causes a decrease in bar amplitude is when it is introduced after the bar has attained a steady state. In this case, we confirm previous findings that the decrease in bar strength is a result of scattering of bar-supporting orbits with small pericenter radii. By heating the inner disk both radially and vertically, an early-growing SMBH increases the fraction of stars that can be captured by the inner Lindblad resonance (ILR) and the vertical ILR, thereby strengthening both the bar and the boxy-peanut-shaped bulge. Using orbital frequency analysis of star particles, we show that when an SMBH is introduced early and the bar forms around it, the bar is populated by different families of regular bar-supporting orbits than when the bar forms without an SMBH.

The improvement of the threaded-based mechanical splice by modifying the threaded system: Study of techniques cold rolling and rotating friction welding

In this study, by modifying the method of making a threaded splice and combining it with rotary friction welding, two types of patches are introduced. The aim is to modify the failure area of the coupler with a threaded bar and use it in the plastic hinge areas of ductile members in seismic areas. The splice area in the suggested method is oversized. To enlarge the splice area, two techniques-cold rolling and rotating friction welding are used. In total, 96 samples (including three repeated samples of each type) were tested. Threaded couplers (TC), oversize-threaded couplers (OTC), rotary friction welding splices with threaded couplers (RFWTC), and non-spliced reference specimens underwent uniaxial tensile and cyclic testing with and without concrete (NS). The sensitivity to bar diameter, as well as bar strength, ductility, energy absorption, and failure mode performance, were evaluated. In terms of strength, ductility, energy absorption, and failure mode, the RFWTC and OTC performed the best and are suited for usage in high seismic zones. Additionally, the TC is appropriate for use in low-to-medium seismic zones. Also, the predicted model is sufficient to estimate the ultimate tensile strength of the threaded couplers.

Compressive response of GFRP and BFRP bars at different temperatures and quasi-static rates

The adoption of fiber-reinforced polymer (FRP) bars in concrete structures has increased due to their superior mechanical properties and durability. However, the compressive response of FRP bars at high temperatures remains unclear. This article presents an experimental study on the behavior of glass FRP (GFRP) and basalt FRP (BFRP) bars subjected to compressive loads at different elevated temperatures and deformation rates. The study considers four different temperature conditions: ambient temperature (25 °C), 50 °C, 100 °C, and 150 °C, and two different deformation rates: 0.5 mm/min and 1000 mm/min. Digital Image Correlation (DIC) was used to accurately measure strains at high temperatures by generating a suitable speckle pattern over the specimen surface for full-field deformation measurements. The study results revealed that the modulus of elasticity and compressive strength of both GFRP and BFRP bars degraded as the temperature increased from 25 °C to 150 °C. The compressive strength reduction was higher at 150 °C compared to 100 °C, and the reduction was more significant for BFRP bars than GFRP bars. The compressive strength of GFRP bars was comparable under both strain rates for all temperature conditions. However, the elastic modulus of the bars showed a slight variation between the different load rates, especially at an elevated temperature of 150 °C. For the BFRP bars, the study found that different strain rates at ambient temperature resulted in significant deviation in the compressive strength and modulus of elasticity results. At higher temperatures, the reduction in mechanical properties was more pronounced. In summary, the study provides valuable insights into the behavior of GFRP and BFRP bars under compressive loads at elevated temperatures, which is useful for designing and assessing the performance of FRP-reinforced structures under fire conditions.

Properties of barred galaxies with the environment

Context. Barred structures are widespread in a considerable fraction of galactic disks, spanning diverse environments and galaxy luminosities. The environment likely exerts a significant influence on bar formation, with tidal interactions leading to the emergence of elongated features resembling bars within galaxy disks. It is plausible that the structural parameters of bars resulting from tidal interactions in high-density galactic environments differ from those that formed through internal disk instabilities in isolated galaxies. To empirically test this scenario, a viable approach is to compare the structural parameters of bars in galaxies situated within distinct environments. Aims. The objective of this study is to study environmental effects on the properties of bars by conducting a comparison between the two key structural parameters of bars, namely strength and radius, in galaxies situated within the Virgo cluster and galaxies of comparable luminosities found in environments characterized by lower galaxy densities. Methods. We have collected data on the bar radius and bar strength for a sample of 36 SB0 and SBa galaxies located within the Virgo cluster. These galaxies exhibit a large range of magnitudes, with values ranging from Mr = −22 to Mr = −17. Additionally, we analyzed a sample of 46 field galaxies with similar morphologies and luminosity ranges. The measurements of bar parameters were conducted by employing Fourier decomposition on the r-band photometric images of the galaxies. Results. The analysis reveals that the bar radius exhibits a correlation with the galaxy luminosity, indicating that larger bars are typically found in more luminous galaxies. When comparing galaxies with fixed luminosities, the field galaxies display larger bar radii compared to those in the Virgo cluster. However, when the bar radius is scaled by the size of the galaxy, the disparity diminishes and the scaled bars in the Virgo cluster and the field exhibit similar sizes. This is because galaxies of similar luminosities tend to be larger in the field environment compared to the cluster and because the bars adapt to the disks in which they live. Regarding the bar strength, no significant differences were observed for bright galaxies (Mr < −19.5) between those located in the Virgo cluster and those in the field. In contrast, faint galaxies (Mr > −19.5) show stronger bars in the field than in the cluster. Conclusions. The findings of this study indicate that the size of galaxies is the parameter that is influenced by the environment, while the bar radius remains independent of the environment when scaled by the galaxy size. The findings of this study indicate that the environment influences the size of galaxies rather than the bar radius, which remains independent of the environment when scaled by the galaxy size. Regarding the bar strength, there is no influence of the environment for bright galaxies. However, bars in faint galaxies are weaker in the cluster environment. This could be explained by an enhancement of disk thickness in dense environments which is more efficient in faint galaxies. These results support the notion that the internal dynamics and intrinsic characteristics of galaxies play a dominant role in the formation and evolution of bars, regardless of the surrounding environment.

Study on the Bending Performance of High-Strength and High-Ductility CRE-Reinforced Concrete Beams

Constant resistance energy (CRE) steel reinforcement has a yield strength of up to 750 MPa and an ultimate elongation of more than 20%. CRE reinforcement overcomes the contradiction between high yield strength and high uniform elongation of ordinary high-strength bars. This paper explores the flexural performance and load-carrying mechanisms of CRE-reinforced concrete beams through a series of experiments, while also presenting a theoretical analytical method for such specimens. Flexural tests on six CRE-reinforced concrete beams and two control tests on hot-rolled ribbed bar 400 (HRB400)-reinforced concrete beams were conducted in this paper. The study examines the influence of the shear–span ratio and reinforcement type on the mechanical response of the beams, including cracking load, yield load, and ultimate load, while analyzing the variation patterns of concrete strain and reinforcement strain. The experimental results demonstrate that as the shear–span ratio decreases, the crack resistance and load-carrying capacity of CRE-reinforced concrete beams improve. Under equivalent conditions, CRE-reinforced concrete beams exhibit higher load-carrying capacity compared to HRB-reinforced concrete beams, surpassing the latter by approximately 43% in terms of ultimate load. Additionally, this paper proposes a calculation method for the mechanical response of NPR-reinforced concrete beams and compares the theoretical values with the experimental values. The differences between the two are within 13%, which proves the reliability of the calculation method.

Sub-zero temperature flexural and flexural fatigue behaviour of glass fabric /epoxy composite tubular anti roll bars

Flexural and flexural fatigue reliability of glass fabric/epoxy composites used in anti-roll bars in room and sub-zero temperature regions at +25 °C, +10 °C, 0 °C, −10 °C, −20 °C, −30 °C, and −40 °C are investigated. The mean flexural strength of anti-roll bars substantially varies and improves in the sub-zero flexural property assessment (+25 °C to −40 °C). The fixed amplitude pulsating mode fatigue test was carried out at temperature points, i.e., 25 °C and −40 °C. The improvement in fatigue strength was observed 3.5 times at a sub-zero temperature of −40 °C. The fatigue durability of glass/epoxy composite anti-roll bars is observed to be longer at sub-zero temperatures due to residual stresses building up, an increase in glass transition temperature, and a lack of molecular mobility leading to higher chain stiffness in the epoxy matrix. The structural properties like flexural rigidity and modulus were calculated with reference to the shape factor and test temperatures for better correlations. These lifetime prediction studies under unpredictable operating conditions for automotive are crucial in the development of robust designs. Automotive performance under service conditions and environmental extremes will become increasingly important as lighter weight, longer life, and higher structural performance continue to evolve.

Effects of fiber content and concrete cover on the local bond behavior of helically ribbed GFRP bar and UHPC

The bond performance of GFRP bar to UHPC is of great concern in GFRP reinforced UHPC elements and structures. In this study, pullout tests were conducted on 45 specimens to investigate the local bond behavior of helically ribbed GFRP bar to UHPC which was characterized by the failure mode, the bond strength and the bond stress-slip curve. The test parameters included the fiber content in UHPC Vf (0 %–3 %) and the concrete cover C (12–66 mm) and their effects on the local bond behavior were accessed. Specimens with C ≥ 36 mm and Vf ≥ 2 % trended to exhibit the direct pullout failure while those specimens with C < 36 mm and Vf < 2 % generally behaved in the splitting pullout failure. GFRP bars with diameter of 18 mm embedded in UHPC had the bond strength of 18.76–54.11 MPa. The bond strength could be significantly enhanced by increasing the fiber content in UHPC or the cover thickness within a certain range. As the fiber content increased from 0 % to 2 %, the bond strength of GFRP bar to UHPC grew by 74.81 %–92.22 %. However, the bond strength showed almost negligible growth when the fiber content further increased from 2 % to 3 %. Similar phenomenon was observed in the effect of cover thickness on the bond strength. The critical cover thickness was found to be approximate 3 times of rebar diameter D in the case of embedment length Le = D. In addition, some interactions were observed in the effects of these two factors on the bond performance. Based on the test results, an updated equation including the influence of fiber content was proposed to predict the bond strength of ribbed GFRP bars embedded in UHPC. Further, a fitted model was developed to describe bond-slip relationship between GFRP bars and UHPC.

Bond characteristics of quartz sand modified enamel coated steel bars with concrete

Porcelain enamel, as a coating material, has a glassy and smooth surface that reduces the bond action with surrounding concrete when applied to steel rebar. In this work, quartz sand modified enamel (QSME) coatings are proposed for the first time to improve the bond action with concrete. The bond characteristics of QSME-coated steel bars in concrete are experimentally investigated by pull-out tests, and the effects of the size and content of quartz sand are considered. The microstructure of the steel bar/concrete interface is characterized by using a scanning electron microscope, and the surface profile is analyzed with a 3D scanner. Results show that QSME coating significantly increases the bond strength, bond stiffness, bond ductility, bond toughness, and residual bond strength of plain steel bars, which increase with an increase in the quartz sand content. The bond strength of QSME-coated deformed steel bars decreases compared with that of uncoated rebars due to the reduced rib height. However, QSME coating improves the bond stiffness, bond ductility, bond toughness, and residual bond strength of deformed steel bars. For QSME-coated steel bars, the bond strength linearly increases with an increase in the surface roughness.

Effect of Macro Polyolefin Fibers on Bond Strength of Tension Lap Splices in RC Beams

The effect of macro synthetic polyolefin fibers on the bond strength of tension lap splices in reinforced concrete (RC) beams is investigated in this study. The bond between the reinforcement and concrete plays a vital role in the strength of RC beams. The presence of polyolefin fibers in the lap splice zone confines the concrete and enhances the bond strength of the steel bars. The use of synthetic fibers is preferable to steel ones since steel suffers from corrosion over time. Tests were conducted on 12 full-scale beam specimens to determine the effect of fiber volume fraction (Vf), bar diameter (db) and concrete cover-to-bar diameter (c/db) on the response. Four volume fractions (Vf = 0, 0.5, 1 and 1.5%) of polyolefin fibers and three bar sizes (db = 16, 20 and 25 mm) with the corresponding (c/db = 2.31, 1.75 and 1.30) were considered to evaluate the bond strength. The test results demonstrated that the polyolefin fibers noticeably enhanced the bond strength and ductility of spliced tension bars. Experimental results were compared with those obtained from two theoretical methods including ACI Committee 318 design provisions. The results showed that the equation proposed by the ACI Committee overestimates the bond strength.