Strength Of Bars Research Articles

Experimental and numerical investigations on seismic performance of HTRB630 high-strength steel bars reinforced concrete columns

Heat-treated ribbed bar 630 (HTRB630) is a new type of the main 630 MPa reinforcing steel produced in China. To explore the possibility of using HTRB630 high-strength steel bars to replace HRB400 steel bars in reinforced concrete structures, experimental and numerical investigations on seismic performance of HTRB630 high-strength steel bars and HRB400 steel bars reinforced concrete columns are presented in this article. Firstly, the pseudo-static experiment of HTRB630 and HRB400 steel bars reinforced concrete columns is carried out. Secondly, an efficient modeling method is proposed to simulate and analyze the seismic performance of reinforced concrete columns on OpenSees platform based on the measured mechanical properties. ConcreteCM model and Reinforcing Steel model are applied to accurately simulate the uniaxial constitutive relationship of concrete and steel bars respectively. The constitutive parameters of confined concrete of specimens are calculated using the iterative algorithm method to effectively consider the degree of improvement of concrete performance in the core area by transverse steel reinforcements. Considering the bond-slip effect and shear deformation of reinforcements, a rotation spring element and a shear spring element are introduced on the fiber model. Finally, the applicability and accuracy of the numerical simulation results are verified by the experiment results on the hysteresis curves, normalized skeleton curves, bearing capacity, displacement ductility, energy dissipation capacity and degradation of stiffness. The experimental results indicate that the failure modes of the reinforced concrete column specimens are all bending failure. Hysteresis loops of the specimens reinforced HTRB630 and HRB400 steel bars are all bow-shaped. After the equal strength of HTRB630 steel bars, the shape of the hysteresis curve is not changed significantly. HTRB630 high-strength steel bars reinforced concrete columns can achieve good seismic performance under the premise of reasonable reinforcements. The numerical results indicate that the finite element model has a good simulation effect on most seismic performance indicators. For specimens with relatively low axial pressure and insignificant pinching, the error of the simulated hysteresis curve is larger; for specimens with relatively high axial pressure and obvious pinching, the error of the simulated hysteresis curve is smaller. The simulation errors of those seismic performance indicators are about 10%.

Bond Behavior of FRP Bars in Lightweight SCC under Direct Pull-Out Conditions: Experimental and Numerical Investigation.

In recent decades, lightweight aggregate concrete (LWC) became a popular building material due to its desired properties. However, various attributes of LWC, such as bond behavior of used reinforcing, have not been described thoroughly. In this regard, LWC produced with 0%, 50%, and 100% expanded clay aggregate was designed, and the physical–mechanical properties were assessed for material characterization. Subsequently, the bond behaviors of LWC reinforced with steel, glass fiber reinforced polymer (GFRP), and basalt fiber reinforced polymer (BFRP) bars were evaluated by pull-out tests. The results of the experimental program allowed the effects of expanded clay aggregate incorporation on LWC properties to be quantified. The bond strength of BFRP bars was not affected by the replacement of coarse aggregate by expanded clay aggregate, whilst the GFRP bars showed lower bond strength values of LWC specimens. Contrarily, in the case of steel bars, both the bond strength and bond stiffness were higher for LWC specimens than for those of normal concrete. Finite element software ATENA 3D was used for simulation of the bond behavior of LWC, and the model validated by the experimental results referred to reasonably corresponding outputs.

Neural network model for bond strength of FRP bars in concrete

Interest in FRP composite bars as reinforcement to concrete has increased over the years as it showed solutions to the drawbacks of steel such as its corrosion issues and vulnerability when employed in adverse environmental conditions. However, it is still not widely incorporated as a replacement to conventional steel primarily due to the complexity of its bond strength mechanism. This, therefore, imposes the need to establish a comprehensive relationship for the bond property of the FRP reinforced concrete. This paper developed a novel Artificial Neural Network (ANN) bond strength prediction model for FRP reinforced concrete using 184 hinged beam database from various existing experiments. From series of simulations performed, the model N 7-10-1 with ten nodes in the hidden layer appeared to be the best fit with the experimental results yielded the most favorable performance among other existing models. From the parametric analysis conducted, the compressive strength of the FRP reinforced concrete has proved to be the most dominant parameter in evaluating its bond behavior as determined by relative importance of 17.82%. Overall, the proposed ANN model has demonstrated the best prediction for FRP bond strength in comparison to previous studies and code equations.

Using four-point flexure test to investigate effects of temperature and bar size on the tensile properties of GFRP bars

Glass fibre reinforced polymer (GFRP) bars have been increasingly used in structures due to their advantages However, the effect of temperature variation is likely to degrade their mechanical behavior. In this experimental study, the tensile strength and modulus of elasticity of four types of GFRP bars with different diameters at 20 °C under four-point flexure test are initially investigated and their results are compared with those of a direct tensile test. Then, the tensile strength of GFRP bars with different diameters is obtained in low and high temperatures (-40 to 80 °C) using four-point flexure test. The experimental results indicate that the tensile strength variation of GFRP bars with different diameters obtained from four-point flexure test are slightly different from those obtained using direct tensile test. Furthermore, the highest reduction in tensile strength under flexure test occurred at -40 °C for most diameters. The obtained tensile strength from four-point flexure test, on average, reduced about 21, 31 and 38% at temperatures of 0, -20, and -40 °C and 11, 20 and 29% at temperatures of 40, 60, and 80 °C, respectively. In addition, the contribution of each parameter (bar diameter and temperature) was examined using a probability model, including the Analysis of variance. Models show that the bar diameter has significant effect on the GFRP bars’ tensile strength variations when subjected to temperature fluctuations. Finally, by applying the non-linear regression analysis, an equation has been developed to determine the tensile strength of GFRP bars with different diameters at different temperatures.

Effects of natural minor corrosion levels on mechanical property and bond anchorage behavior of CRB600H steel bars

Mechanical property tests and bond anchorage tests of the natural minor corrosion CRB600H steel bars were carried out, and corrosion levels of the steel bars were 0.0%, 1.8%, and 2.1%, respectively. The mechanical property test results showed that the yield strength of the CRB600H steel bars with corrosion levels of 1.8% and 2.1% was approximately 10% and 15% lower than that of intact steel bars, respectively. Still, the strains at the maximum force of the two corrosion levels showed no noticeable change with intact steel bars. The yield strength formula of the natural minor corrosion CRB600H steel bars was regressed. The load-slip curves, failure modes, bond toughness, and bond strength influential factors of natural minor corrosion bond specimens were analysed in the bond anchorage tests. Compared with the control bond anchorage specimens, the bond strength of the specimens with steel bar corrosion levels of 1.8% and 2.1% decreased by 5.4% and 6.3%, respectively. The ultimate bond strength of the natural minor corrosion CRB600H steel bars embedded in concrete was regressed. The development length of the natural minor corrosion CRB600H steel bars satisfying the reliability requirements was calculated using the first-order second-moment method. Based on the calculation results, the calculation formula of the development length for the natural minor corrosion CRB600H steel bars in concrete was regressed.

Revisiting the role of bars in AGN fuelling with propensity score sample matching

The high luminosity displayed by an active galactic nucleus (AGN) requires that gas be transported to the centre of the galaxy by some mechanism. Bar-driven processes are often pointed out in this context and a number of studies have addressed the bar–AGN connection, but with conflicting results. Some of the inconsistencies can be explained by the different spatial- and timescales involved in bar-driven gas inflows, accretion by the central black hole, and AGN emission. However, the discrepant results could also be due to sample biases, because both the AGN activity determination and the bar detection are influenced by the method employed. We revisit the bar–AGN connection in a sample of galaxies from SDSS, looking for evidence of the influence of bars on AGN activity. We determine AGN activity by emission line diagnostics and the properties of the bar were previously estimated withBUDDA, which performs 2D bulge–bar–disk decomposition. Before comparing active and inactive galaxies, we made a careful selection of the sample to minimise selection biases. We created control samples by matching them with the AGN sample using propensity score matching. This technique offers an analytical approach for creating control samples given some object parameters. We find that AGN are preferentially found in barred galaxies and that the accretion rate is higher in barred galaxies, but only when differentM–σrelations are used to estimate the black hole massM•in barred and unbarred galaxies (from the central velocity dispersionσ). On the other hand, we find no correlation between activity level and bar strength. Altogether, our results strengthen theoretical predictions that the bar is an important mechanism in disc galaxies, creating a gas reservoir to feed AGN, but they also indicate that other mechanisms can play a major role, particularly at scales ≲100 pc.

Durability of seawater sea sand concrete beams reinforced with carbon nanotube-modified BFRP bars in a marine environment

In this study, the durability of seawater sea sand concrete (SWSSC) beams reinforced with basalt fiber-reinforced polymer (BFRP) bars in a marine environment was investigated. To improve the durability of the SWSSC beams, different types of reinforcements, namely, carbon nanotube (CNT)-modified BFRP longitudinal bars, CNT-modified BFRP stirrups, and sand-coated BFRP stirrups, were introduced to replace steel bars and ordinary BFRP bars. Moreover, the durability of the CNT-modified BFRP bars under an SWSSC environment and the durability of the bond strength between the CNT-modified BFRP bars/sand-coated BFRP bars and SWSSC under the marine environment were assessed. The results showed that the modification using CNTs effectively slowed down the degradation rate of the tensile strength of the BFRP bar and the bond strength between the BFRP bar and SWSSC concrete in the marine environment. Additionally, the load-carrying capacity of the SWSSC beams reinforced with BFRP bars exhibited obvious degradation after exposure to the seawater environment. With the increase in corrosion age, the SWSSC beams suffered from shear-compression failure owing to the decrease in the bond strength between the BFRP stirrups and the surrounding concrete. Replacing ordinary BFRP stirrups with CNT-modified BFRP stirrups prevented the occurrence of shear-compression failure in the early stage of corrosion, but the effect disappeared after 9 months. A similar improvement in the shear durability of SWSSC beams by using sand-coated BFRP stirrups was also observed.

The effects of AGN feedback on the structural and dynamical properties of Milky Way-mass galaxies in cosmological simulations

ABSTRACT Feedback from active galactic nuclei (AGNs) has become established as a fundamental process in the evolution of the most massive galaxies. Its impact on Milky Way (MW)-mass systems, however, remains comparatively unexplored. In this work, we use the auriga simulations to probe the impact of AGN feedback on the dynamical and structural properties of galaxies, focusing on the bar, bulge, and disc. We analyse three galaxies – two strongly and one unbarred/weakly barred – using three setups: (i) the fiducial auriga model, which includes both radio and quasar mode feedback, (ii) a setup with no radio mode, and (iii) one with neither the radio nor the quasar mode. When removing the radio mode, gas in the circumgalactic medium cools more efficiently and subsequently settles in an extended disc, with little effect on the inner disc. Contrary to previous studies, we find that although the removal of the quasar mode results in more massive central components, these are in the form of compact discs, rather than spheroidal bulges. Therefore, galaxies without quasar mode feedback are more baryon-dominated and thus prone to forming stronger and shorter bars, which reveals an anticorrelation between the ejective nature of AGN feedback and bar strength. Hence, we report that the effect of AGN feedback (i.e. ejective or preventive) can significantly alter the dynamical properties of MW-like galaxies. Therefore, the observed dynamical and structural properties of MW-mass galaxies can be used as additional constraints for calibrating the efficiency of AGN feedback models.

Refined modeling of the interfacial behavior between FRP bars and concrete under different loading rates

Fiber-reinforced polymer (FRP) bar can be served as a promising alternative to steel rebars due to its lightweight, high corrosion resistance and wider working temperatures, etc., especially for the structure sensitive to weight or in aggressive environments. In order to lay the foundation for a more scientific design of structures reinforced with FRP bars, the bond behavior of FRP bars to surrounding concrete subjected to pull-out loadings with different loading rates was investigated with a refined numerical model in the present study. In the model, the surface features of FRP bars and the heterogeneity of concrete were explicitly reflected. The interaction between the two materials was modeled with a surface-to-surface contact strategy. The effectiveness of the model was verified by the good agreement between the simulation results and the available experimental observations. With the help of the numerical model, taking basalt FRP (BFRP) bars as an instance, the cracking process and failure patterns, bond-slip curves, bond strength and peak slip at the FRP bar to the concrete interface were simulated and analyzed. The influences of fiber types and surface characteristics of FRP bars were discussed. Based on the simulation results, an empirical formula was given to predict the dynamic bond-slip relationships of FRP bars in concrete. It was indicated that the failure patterns of the FRP bar to concrete interface under various strain rates do not show much difference within the scope of the present study. The elastic modulus of FRP bars mainly affects the bond stiffness and peak slip instead of bond strength. The density of FRP bars has a slight influence on the bond strength and peak slip while ignorable on bond stiffness. The variation in rib height of FRP bars changes the bond strength and the descending part of bond-slip curves, showing no regularity on bond stiffness and peak slip. The influence of rib spacing on bond performance is irregular. As the strain rate increases, the bond strength of FRP bars to concrete is increased continuously while the peak slip is reduced firstly and then increased. The empirical formula in the form of two power functions, considering the strain rate effect of bond strength and peak slip, can reasonably reproduce the dynamic bond-slip relationships between FRP bars and concrete to a certain degree.

Forming analysis and process study for a 6082 aluminum alloy automobile control arm in the process of forging

To reduce the weight of vehicles and save on fuel consumption, the forming analysis and process study for a 6082 aluminum alloy automobile control arm were conducted, and the results are reported here. First, the parameters of the constitutive equation of the 6082 aluminum alloy are determined, and the forming process and the dies of the stretch rolling, bending, and die-forging are proposed and discussed according to the given contours of the control arm. Then, the control arm is simulated by means of Deform-3D, the experiment results of the automobile control arm are compared with the simulation results, and the tensile strength, yield strength, and elongation of the test bars obtained from the control arm can meet the mechanical performance requirements based on the tensile test rig. Finally, the relationship of the die load, die wear, workpiece damage, and workpiece equivalent stress with different processing parameters are analyzed, and the effects of different solid solution times on the strength of control arm are discussed. The results show that when the friction coefficient is 0.3, the die temperature is 250°C, the forging velocity is 230 mm/s, the strain rate is 1s−1 and the solid solution time is 30 min, the die load, die wear, workpiece damage, workpiece equivalent stress, and the mechanical strength are then in a good state. The results of this research provide a reliable basis and analysis method for the forging of aluminum alloy automobile control arms.

Sectional Analysis of Reinforced Engineered Cementitious Composite Columns Subjected to Combined Lateral Load and Axial Compression

The ultra-high tensile ductility of ECC provides an alternative way to enhance the ductility of structural members by using high-ductile matrix material instead of simply increasing reinforcements. However, the application of ECC members is still limited due to the relatively short research time and the lack of design specifications. Being equivalent to eccentric compressive members, a sectional analysis of RECC columns subjected to combined lateral load and axial compression are proposed in this paper. Based on the design theory of load capacity of eccentric compression columns and the unique constitutive model of ECC, the calculation equations for the sectional load capacity of RECC columns are derived. The analytical prediction of the load capacity of RECC column is evaluated in comparison with that of experiments that confirm the capacity of the proposed calculation method to capture the behavior of the RECC column accurately. The strength-interaction diagrams showing the axial force-moment (N-M) interaction curves are then constructed for analysis using the proposed calculation equations. A parametric study is also carried out by using the proposed calculation equations, demonstrating the effects of ultimate tensile strain of ECC, compressive and tensile strength of ECC, yield strength of steel bar, and reinforcement ratio on the N-M interaction curves of RECC columns. The investigations exhibited in this paper are expected to provide insight into the design principles of RECC columns.

Assessment of Bond Strength of GFRP Bars Embedded in Fiber-Reinforced Cementitious Composites

Assessment of Bond Strength of GFRP Bars Embedded in Fiber-Reinforced Cementitious Composites

Theoretical Analysis Method of Variable Thickness GFRP Tray.

Glass-fiber reinforced polymer (GFRP) bars are increasingly widely used in slope support instead of steel bars or steel pipes. GFRP Bars are generally connected with the slope by combining conical nut and tray, but the tray stress still lacks corresponding theoretical calculation and strength verification methods. Therefore, assuming that the tray is an equal thickness thin plate, the internal force distribution of the tray is calculated using the thin plate bending and cavity expansion theory, and compared with the finite element numerical analysis results of the tray. The calculation and analysis show that the elastic theoretical solution of internal force distribution of equal thickness tray is basically the same as the numerical simulation solution of variable thickness tray. The tray loading and free surface are controlled by hoop tensile and radial compressive stress, respectively. The inner wall of the free surface of the tray is the weakest part of the tray, and the ultimate strength of a GFRP tray is 35.81–53.00% of the standard tensile strength of Φ20 GFRP bars by distortion energy density. This theoretical method can be used for stress analysis of variable thickness trays and has played technical support for promoting the application of GFRP bars in slope support.

Prediction of residual tensile strength of glass fiber reinforced polymer bars in harsh alkaline concrete environment using fuzzy metaheuristic models

The long-term durability of glass fiber reinforced polymer (GFRP) bars in harsh alkaline environments is of great importance in engineering, which is reflected by the environmental reduction factor in various structural codes. The calculation of this factor requires robust models to predict the residual tensile strength of GFRP bars. Therefore, three robust metaheuristic algorithms, namely particle swarm optimization (PSO), genetic algorithm (GA), and support vector machine (SVM), were deployed in this study for achieving the best hyperparameters in the adaptive neuro-fuzzy inference system (ANFIS) in order to obtain more accurate prediction model. Various optimized models were developed to predict the tensile strength retention (TSR) of degraded GFRP rebars in typical alkaline environments (e.g., seawater sea sand concrete (SWSSC) environment in this study). The study also proposed more reliable model to predict the TSR of GFRP bars exposed to alkaline environmental conditions under accelerating laboratory aging. A total number of 715 experimental laboratory samples were collected in a form of extensive database to be trained. K-fold cross-validation was used to assess the reliability of the developed models by dividing the dataset into five equal folds. In order to analyze the efficiency of the metaheuristic algorithms, multiple statistical tests were performed. It was concluded that the ANFIS-SVM-based model is robust and accurate in predicting the TSR of conditioned GFRP bars. In the meantime, the ANFIS-PSO model also yielded reasonable results concerning the prediction of the tensile strength of GFRP bars in alkaline concrete environment. The sensitivity analysis revealed GFRP bar size, volume fraction of fibers, and pH of solution were the most influential parameters of TSR.

Side-Face Blowout Strength of Two-Layer Headed Bars Embedded in Exterior Beam-Column Joints

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A novel technique to improve the compressive strength and ductility of glass fiber reinforced polymer (GFRP) composite bars

Glass fiber reinforced polymer (GFRP) composite bars have excellent durability compared to traditional steel reinforcements but their strength contribution in the design of compression members is generally neglected. The non-homogeneous and anisotropic nature of GFRP bars including their complex behavior in compression and the lack of standard testing procedure have hindered their use as compressive reinforcements. To improve their behavior and strength in compression, a novel technique has been developed by winding additional GFRP layers around the longitudinal fibers. One, two and three winding layers with a thickness of 1.5 mm for each layer and a winding angle of ± 83.3° have been used. Compressive strength tests have then been conducted on 20 mm and 30 mm high GFRP bars with a core diameter of 20 mm to determine the improvement in compressive strength, ductility, and failure behavior. Test results showed that the 20 mm core diameter GFRP bars have shown promising improvement in the compressive strength and ductility with the increased number of winding layers wherein the compressive strength of the 20 mm and 30 mm high bars increased by 74% and 63%, respectively for bars with three winding layers. Comparison of the mechanical properties in compression and tension showed that the optimum strength and ductility improvement can be achieved with two winding layers. A simple theoretical strength model has been developed which can reliably predict the compressive strength of the winded GFRP bars.

Predicting tensile strength of spliced and non-spliced steel bars using machine learning- and regression-based methods

Mechanical properties of steel reinforcement bars, which have a critical effect in the overall performance of reinforced concrete (RC) structures, should be reported and assessed before being used in structural elements. Determining bars’ properties could be time-consuming and expensive specifically in the case of incorporating splices. Therefore, this study aims to predict tensile strength of bars using machine learning-based methods including nonlinear regression, ridge regression and artificial neural network. To this end, a comprehensive database including over 200 tests on non-spliced and spliced steel bars by mechanical couplers was collected from the available peer-reviewed international publications. Bar size, splice method, steel grade, temperature and splice characteristics (length and outer diameter of couplers) were the input parameters considered for predicting tensile strength. The efficiency of the models was evaluated through Taylor diagram and common performance metrics namely coefficient of determination (R2), root mean square error (RMSE), mean absolute error (MAE) and mean absolute percentage error (MAPE). The results demonstrated that the predicted values agreed well with the actual values reported in the experimental studies used for collecting the database. A parametric study was also conducted in order to examine the influence of coupler length, coupler outer diameter and temperature on the tensile strength of spliced bars. Based on the parametric study results, three different equations were suggested for calculating tensile strength of spliced bars using the mentioned parameters. The outcomes of this study can assist practitioners to effectively and accurately estimate tensile strength of spliced and non-spliced steel bars in reinforced concrete structures without the need to carry out expensive and timely physical tests.

Experimental study of the tensile behaviour of GFRP reinforcing bars at elevated temperatures

Understanding and quantifying the behaviour of glass fibre reinforced polymer (GFRP) bars when exposed to elevated temperatures is of great importance to predict the fire resistance of GFRP–reinforced concrete structural members. However, the experimental results available about the tensile properties of GFRP bars at elevated temperatures still do not cover a sufficiently wide range of temperatures likely to be attained during a fire incident. In fact, very few data has been reported for temperatures above the decomposition temperature of the polymeric resin, and the reduction of the tensile strength and elastic modulus of GFRP bars above 500 °C still remains largely unknown. This paper presents an experimental and analytical study about the tensile behaviour of GFRP bars exposed to elevated temperatures up to 715 °C. Tensile tests were performed at different elevated temperatures, under steady-state conditions, on four different types of GFRP bars provided by different manufacturers. The degradation of their tensile strength and elastic modulus with increasing temperatures was assessed and compared with data available in the literature. Such data was then used to propose analytical models describing the reduction of the tensile properties of GFRP bars with temperature. The results obtained show that the tensile strength is considerably more degraded with temperature than the elastic modulus, especially during the glass transition and after the decomposition of the resin. At 715 °C, after full decomposition of the resin, the tensile strength was reduced to 4% of the value at ambient temperature, while the remaining elastic modulus was still 66%.

Baryon-driven decontraction in Milky Way-mass haloes

ABSTRACT We select a sample of Milky Way (MW) mass haloes from a high-resolution version of the EAGLE simulation to study their inner dark matter (DM) content and how baryons alter it. As in previous studies, we find that all haloes are more massive at the centre compared to their dark matter-only (DMO) counterparts at the present day as a result of the dissipational collapse of baryons during the assembly of the galaxy. However, we identify two processes that can reduce the central halo mass during the evolution of the galaxy. First, gas blowouts induced by active galactic nuclei feedback can lead to a substantial decrease of the central DM mass. Secondly, the formation of a stellar bar and its interaction with the DM can induce a secular expansion of the halo; the rate at which DM is evacuated from the central region by this process is related to the average bar strength, and the time-scale on which it acts determines how much the halo has decontracted. Although the inner regions of the haloes we have investigated are still more massive than their DMO counterparts at z = 0, they are significantly less massive than in the past and less massive than expected from the classic adiabatic contraction model. Since the MW has both a central supermassive black hole and a bar, the extent to which its halo has contracted is uncertain. This may affect estimates of the mass of the MW halo and of the expected signals in direct and indirect DM detection experiments.

Properties of Fast and Slow Bars Classified by Epicyclic Frequency Curves from Photometry of Barred Galaxies

Abstract We test the idea that bar pattern speeds decrease with time owing to angular momentum exchange with a dark matter halo. If this process actually occurs, then the radii of the corotation resonance and other resonances should generally increase with time. We therefore derive the angular velocity Ω and epicyclic frequency κ as functions of galactocentric radius for 85 barred galaxies using photometric data. Mass maps are constructed by assuming a dynamical mass-to-light ratio and then solving the Poisson equation for the gravitational potential. The locations of Lindblad resonances and the corotation resonance radius are then derived using the standard precession frequency curves in conjunction with bar pattern speeds recently estimated from the Tremaine–Weinberg method as applied to integral field spectroscopy data. Correlations between physical properties of bars and their host galaxies indicate that bar length and the corotation radius depend on the disk circular velocity while bar strength and pattern speed do not. As the bar pattern speed decreases, bar strength, length, and corotation radius increase, but when bars are subclassified into fast, medium, and slow domains, no significant change in bar length is found. Only a hint of an increase in bar strength from fast to slow bars is found. These results suggest that bar length in a galaxy undergoes little evolution, and is determined instead mainly by the size of the host galaxy.