Bar Length Research Articles

Degradation of flexural bond of CFRP bar in UHPFRC after exposure to elevated temperature

This paper investigated degradation of flexural bond of a ribbed carbon fiber reinforced polymer (CFRP) bar in ultra-high-performance fiber reinforced concrete (UHPFRC) after exposure to elevated temperatures. For this purpose, the mechanical properties of UHPFRC and thermal properties of CFRP bars after exposure to elevated temperatures were investigated, and a total of 16 groups of hinged beams were fabricated with variables of embedment length (4db, 10db, 20db, and 40db), bar type and exposed to elevated temperatures (200 °C, 300 °C, 400 °C, 600 °C). The mechanical properties of UHPFRC increased until elevated temperatures reached 400 °C and it was shown that the reduction of the ultimate tensile strength of CFRP bars were not notable after exposure to elevated temperatures of up to 300 °C. The ultimate moment of ribbed CFRP bars after exposure to elevated temperatures at 200 and 300 °C was similar. After exposure to an elevated temperature of 400 °C, it decreased by about 29–63 % compared to non-heated specimens, with bar rupture. Although similar decomposition temperatures of ribbed and sand coated CFRP bars occurred, the residual flexural bond strength of the ribbed CFRP bar was larger than that of the sand coated CFRP bar after exposure to elevated temperature at 400 °C. In addition, a relatively lower reduction of bond strength occurred in RC-40ED-400 compared to RC-10ED-400 and RC-20ED-400. Based on the test results, development length with consideration of degradation of developed tensile and normalized bond strength of CFRP bars were proposed, and it was found that the required development length of ribbed CFRP bars after exposure to elevated temperatures at 400 °C increased by 294 % compared to ambient temperature.

Investigation of long-term degradation of the interface in the anchorage zone of GFRP-RC beams

In the long-term service process of Glass Fiber Reinforced Polymer – Reinforced Concrete (GFRP-RC) structures, degradation of GFRP bars and concrete materials can occur, leading to a partial loss of the internal bonding performance of the structure. In this paper, a long-term study on the interface performance of GFRP-RC beams was conducted over an 8-year period to investigate the long-term degradation characteristics of the interface materials and the long-term Effective Anchorage Length (EAL) of GFRP bars. Firstly, a comprehensive analysis from a review perspective was conducted on the long-term degradation mechanisms of concrete and GFRP bars that considers the chemical behavior between microscopic molecules, the two-dimensional (2D) structure observed through micro electron microscopy, and the three-dimensional (3D) structure revealed by micro-X-ray imaging. Secondly, a new EAL calculation model is derived, and the long-term variation parameters of EAL under different conditions are determined. It was observed that the influence of alkaline corrosion and sustained loading is relatively small compared to the influence of initial structural defects on EAL. Finally, a comparison with four international standards revealed that the anchorage length design provided by JSCE-97 and ACI 440–1R-15 is overly conservative for GFRP bars, with values approximately 2–3 times the test results. On the other hand, CSA-S806–12 and CSA S6–19 standards are relatively close to the test values. Considering both design rationality and long-term corrosion resistance, it is concluded that the CSA-S806–12 specification is more reasonable.

Innovative Methods to Improve the Seismic Performance of Precast Segmental and Hybrid Bridge Columns under Cyclic Loading

This paper investigates the seismic performance of prefabricated segmental bridge columns (PSBCs) with hybrid post-tensioned tendons and energy dissipation (ED) bars under cyclic loading. PSBCs with unbonded and hybrid bonded prestressed tendons and columns incorporating ED bars are designed to improve the lateral strength, energy dissipation, and limit the residual drift. The PSBCs under cyclic loading were investigated using the three-dimensional finite element (FE) modeling platform ABAQUS. The FE model was calibrated against experimental results, with an overall error of less than 10%. The seismic performance of the proposed PSBCs was evaluated based on critical parameters, including lateral strength, residual plastic displacement, and the energy dissipation capacity. The results show that bonding the tendons in the plastic hinge region as opposed to the overall bonding along the column leads to a better cyclic performance. The lateral strength, and recentering abilities are further improved by bonding tendons up to 2/3 of the length in the plastic hinge region, along with 100–300 mm in the footing. It was also found that selecting a longitudinal length of ED bars crossing multiple precast segmental joints and having a circumferential spread of 70–90% of core concrete results in a higher bearing capacity and energy dissipation compared to ED bars crossing the single joint.

Is processing superiority a universal trait for all threats? Divergent impacts of fearful, angry, and disgusted faces on attentional capture

Fearful, angry, and disgusted facial expressions are evolutionarily salient and convey different types of threat signals. However, it remains unclear whether these three expressions impact sensory perception and attention in the same way. The present ERP study investigated the temporal dynamics underlying the processing of different types of threatening faces and the impact of attentional resources employed during a perceptual load task. Participants were asked to judge the length of bars superimposed over faces presented in the center of the screen. A mass univariate statistical approach was used to analyze the EEG data. Behaviorally, task accuracy was significantly reduced following exposure to fearful faces relative to neutral distractors, independent of perceptual load. The ERP results revealed that the P1 amplitude over the right hemisphere was found to be enhanced for fearful relative to disgusted faces, reflecting the rapid and coarse detection of fearful cues. The N170 responses elicited by fearful, angry, and disgusted faces were larger than those elicited by neutral faces, suggesting the largely automatic and preferential processing of threats. Furthermore, the early posterior negativity (EPN) component yielded increased responses to fearful and angry faces, indicating prioritized attention to stimuli representing acute threats. Additionally, perceptual load exerted a pronounced influence on the EPN and late positive potential (LPP), with larger responses observed in the low perceptual load condition, indicating goal-directed cognitive processing. Overall, the early sensory processing of fearful, angry, and disgusted faces is characterized by differential sensitivity in capturing attention automatically, despite the importance of these facial signals for survival. Fearful faces produce a strong interference effect and are processed with higher priority than angry and disgusted ones.

Bond properties of steel bar with engineered geopolymer composites under monotonic load

AbstractEngineered geopolymer composites (EGC) featuring extraordinary tensile ductility are a potential alternative to engineered cementitious composite. In this study, the local bonding properties of steel bars in EGC were investigated. Monotonic loading tests of the 120 specimens were performed using the pullout test method. The study examined the ultimate tensile strain of EGC, diameter and anchorage length of the steel bar on bond performance. The results showed that the EGC, with an ultimate tensile strain of 4.57%, had the highest peak bond strength. By comparing the test results of rebar to ordinary concrete bond performance provided in several previous literature, it was demonstrated that EGC has superior bond performance with rebar compared to ordinary concrete. Based on this, suggestions were provided for the design of rebar anchorage length in EGC. Finally, a mathematical model suitable for determining the bond–slip curve between EGC and steel bars is proposed.

Bond performance of NSM FRP–concrete interfaces with epoxy under chloride‐salt conditioned environments

AbstractConcrete in coastal areas is susceptible to structural damage caused by corrosion and expansion of reinforcement. Near‐surface mounted (NSM) fiber‐reinforced polymer (FRP) bars have become effective for strengthening damaged reinforced concrete structures. The bonding performance of NSM FRP bars in concrete is a key factor limiting their application and promotion in civil engineering. In this study, the influences of the conditioned environment, such as the chloride salt concentration, immersion time, and bond length of the FRP bar, on the bonding performance were investigated experimentally. First, material properties in a conditioned environment were studied. Subsequently, the failure mode, bond stress–slip curve, and bond strength of the NSM FRP bar in concrete were investigated. Finally, the microstructure and chemical composition of the materials were revealed using scanning electron microscopy and energy‐dispersive spectroscopy (EDS) images of the materials under environmental conditions. The transfer mechanism of NSM FRP bars in concrete with epoxy was revealed. The results showed that the failure modes of the pullout specimens can be divided into epoxy splitting failure and basalt fiber‐reinforced polymer (BFRP) pulling failure. The chloride‐salt concentration was a critical factor affecting the bond properties, and the longer the bond length, the lower the bond strength. The microstructure clearly shows that the degradation of the bonding behavior at the interface of the NSM FRP bar in concrete in a conditioned environment is attributable primarily to the resin damage of the epoxy, resulting in pit corrosion. There was no significant damage to the fibers in the FRP bar, and the degradation was primarily due to resin matrix damage and interfacial debonding. The EDS results showed that the degradation of the epoxy resin and BFRP bars was caused by CO bond and SiO bond fractures, respectively.

Study on the bond-slip behavior between steel bar and rammed earth

The steel bars significantly enhance the mechanical properties of rammed earth, as they together withstand external loads. In order to investigate the bond performance between steel bars and rammed earth, the pull-out tests were conducted on 60 specimens. This study investigated the distribution of bond stress along the anchorage length of steel bars by embedding strain gauges inside the bars. The effects of four types of anchorage length, three types of cover thickness, three types of steel bar diameter and three types of compressive strength of rammed earth on the bond-slip behavior were investigated. Through experimental research and theoretical analysis, the distribution law of the bond stress along the anchorage length was obtained. The transfer mechanism of the bond stress and the failure mode of the specimens were analyzed. An improved bond-slip constitutive model was proposed to reflect the influence of the position function of bond stress distribution. Furthermore, a theoretical formula for the bond strength was proposed based on the analytical approach of elastic solid mechanics and the failure modes of the specimens, and its accuracy was validated by experimental results.

Experimental investigation of the bending creep behavior of glulam beam reinforced with near surface mounted steel bars

ABSTRACT In this study, the pull-up tests of glued-in steel bar were conducted, and the results showed that ensuring the anchorage length of the steel bar can obtain desired mechanical behavior of the glued-in steel bar. The creep tests were performed on two unreinforced glulam beams with different stress ratios and four glulam beams reinforced with near surface mounted steel bar. After 65-day test periods, the test results found that mounting the steel bar at both compression and tension sides of the glulam beam can decrease the creep coefficients by at least 0.32 when compared to the unreinforced glulam beam. By employing the power function, Burger and proposed modified model, it was found that the proposed modified model had the best goodness of fit, followed by thepower function model. Through the analysis of the creep coefficients predicted by the modified model, it was found that values of the creep coefficients for the reinforced glulam beams were almost half of those for the unreinforced glulam beams. Thus, it was recommended that the glulam beam reinforced with smaller diameter steel bar mounted at compression or tension side can be usedfor the long-term design of the glulam beam in practice.

Experimental study on bond performance between vertical deformed steel bar and modern rammed earth based on in-situ pull-out test

This study investigates the bond strength–slip behavior between vertical deformed steel bar and modern rammed earth in modern rammed earth wall. Firstly, in-situ pull-out tests were conducted on seven modern rammed earth walls, taking into account the effects of the relative anchorage length of steel bars, the cube compressive strength of modern rammed earth, and the diameter of steel bars on the bond strength and slip of vertical deformed steel bars and modern rammed earth. The experimental results indicate that the bond force–slip behavior between vertical deformed steel bars and modern rammed earth can be divided into four stages: elastic bonding stage, nonlinear rising stage, nonlinear decreasing stage, and residual stage. Based on the experimental results, six characteristic values were defined: ultimate bond strength τu, cracking bond strength τs, residual bonding strength τr, ultimate bond slip Su, cracking bond slip Ss, residual bond slip Sr. An average bond strength-slip constitutive model for vertical deformed steel bars and modern rammed earth was proposed. The model was compared with the experimental results and can be used to predict τu, τs, Su, Ss. Due to the anisotropic characteristics of modern rammed earth, there will be a large deviation in the prediction of τr and Sr. There are three types of failure in the pull-out specimens, namely, pull-out failure, splitting failure and conical failure. The relative anchorage length of steel bar, the cube compressive strength of modern rammed earth and the diameter of steel bar have different degrees of improvement on τu, τs, but have little effect on τr. Due to the brittle failure of modern rammed earth specimens, the above three factors have little effect on the slip value.

New Computerized Planning Algorithm and Clinical Testing of Optimized Nuss Bar Design for Patients with Pectus Excavatum.

BACKGROUND Computer-aided design (CAD) has been used in the Nuss procedure to determine the bar length and shape. Despite computer aid, the shape and design remain quite intuitive. We tested a new algorithm to determine the optimal bar shape. MATERIAL AND METHODS The normal sterno-vertebral distance was defined on computed tomography (CT) scans of patients without pectus excavatum (PEx) at the same level where the deepest depression was found on CT scans of 97 patients with PEx. Four points were marked on the CT scan of 60 patients with PEx at the deepest deformity: P1: edge of the vertebra; P2: edge of the deformity; P3: the expected contact point of the bar and the rib; and P4: the expected end of the bar. The algorithm generated 3 circles upon these points, and the fusion of the arcs drew the line of the ideal bar. Corrected and normal sterno-vertebral distance values were compared with the Mann-Whitney U test. Ten bars were bent manually guided by a 1: 1 printout of the designed bar and were implanted in 10 adolescents. RESULTS The shortest sterno-vertebral distance was 3 cm below the intermammillary line in PEx patients. The normal mean sterno-vertebral distance at this level was 10.16±1.35 cm in non-PEx patients. The mean virtually corrected sterno-vertebral distance was 10.28±1.27 cm. No significant difference was found (P=0.44). The bars were seamless and were successfully implanted. No bar needed adjustment, the operation time was shorter, and the patient satisfaction score was 9.4/10. CONCLUSIONS With our new algorithm, an optimal Nuss bar can be designed.

A morphological segmentation approach to determining bar lengths

ABSTRACT Bars are important drivers of galaxy evolution, influencing many physical processes and properties. Characterizing bars is a difficult task, especially in large-scale surveys. In this work, we propose a novel morphological segmentation technique for determining bar lengths based on deep learning. We develop U-Nets capable of decomposing galaxy images into pixel masks highlighting the regions corresponding to bars and spiral arms. We demonstrate the versatility of this technique through applying our models to galaxy images from two different observational data sets with different source imagery, and to RGB colour and monochromatic galaxy imaging. We apply our models to analyse SDSS and Subaru HyperSuprime Cam imaging of barred galaxies from the NA10 and Sydney AAO Multi-object IFS catalogues in order to determine the dependence of bar length on stellar mass, morphology, redshift and the spin parameter proxy $\lambda _{R_e}$. Based on the predicted bar masks, we show that the relative bar scale length varies with morphology, with early type galaxies hosting longer bars. While bars are longer in more massive galaxies in absolute terms, relative to the galaxy disc they are actually shorter. We also find that the normalized bar length decreases with increasing redshift, with bars in early type galaxies exhibiting the strongest rate of decline. We show that it is possible to distinguish spiral arms and bars in monochrome imaging, although for a given galaxy the estimated length in monochrome tends to be longer than in colour imaging. Our morphological segmentation technique can be efficiently applied to study bars in large-scale surveys and even in cosmological simulations.

Natural and Forced Convective Heat Transfer Enhancement for Solid Cylinders with Different Geometrical Shapes

Enhancing heat transfer for both natural and forced convection is a common issue for any heat transfer process. Experimental studies have been carried out for six different geometrical shapes of solid bars for natural convection and forced convection with four different air velocities while keeping the same perimeter and length of the solid bars, which means the lateral surface area of the bars is the same. Results reveal that both the natural and forced convective heat transfer characteristics are greatly influenced by the geometrical shape in terms of Nusselt number (Nu), heat transfer coefficient (h), and heat transfer rate (q). In addition, isosceles and cylindrical shape geometry contribute to the lowest and highest heat transfer, respectively. As well, it is obtained from the results that convective heat transfer characteristics are directly related to the cross-sectional area, even if the perimeters are the same. Moreover, among the different geometrical shapes, the isosceles and hexagonal shapes take the shortest and longest duration to attain the steady-state condition in the conductive heat transfer process. The convective heat transfer characteristics are well-validated, with available results for both natural and forced convection heat transfer.

Measuring the dynamical length of galactic bars

ABSTRACT We define a physically motivated measure for galactic bar length, called the dynamical length. The dynamical length of the bar corresponds to the radial extent of the trapped orbits that are the backbone supporting the bar feature. We propose a direct observational technique well suited to integral field unit spectroscopy to measure it. Identifying these orbits and using the dynamical length is a more faithful tracer of the secular evolution and influence of the bar. We demonstrate the success of our observational technique for recovering the maximal bar-parenting orbit in a range of simulations, and to show its promise we perform its measurement on a real galaxy. We also study the difference between traditionally used ellipse fit approaches to determine bar length and the dynamical length proposed here in a wide range of bar-forming N-body simulations of a stellar disc and dark matter halo. We find that ellipse fitting may severely overestimate measurements of the bar length by a factor of 1.5–2.5 relative to the extent of the orbits that are trapped and actually comprise the bar. This bias leads to overestimates of both bar mass and the ratio of corotation radius to bar length, i.e. the bar speed, affecting inferences about the evolution of bars in the real Universe.

Enhancing Flexural Resistance in Pre-Damaged RC Beams with Near-Surface Mounted GFRP Bar and Bolt Anchoring System

The objective of this research was to explore the mechanical properties and failure mechanisms of reinforced concrete beams (RC beams) strengthened with near-surface mounted (NSM) glass fiber-reinforced polymer (GFRP) bars. This study focused on evaluating the effect of various factors on the load-deflection response and failure patterns of RC beams, including pre-existing damage, end anchorage, bar length, bar number, and the condition of concrete cover. The tested RC beams were divided into three groups. The first group included undamaged and damaged control beams. The second group involved the strengthening of beams after inducing damage, with variations in bar length, number, and cross-sectional area. This group also included beams strengthened by GFRP bars with and without anchors. In the third group, the effects of different cover materials, cover bonding techniques, and anchor bolts on the strengthening bars were examined. The results of the experiment indicated a notable decrease in both cracking and maximum load capacity for beams that were pre-damaged. The inclusion of anchor bolts appeared to have a noticeable effect, enhancing the load-carrying capacity and reducing mid-span deflection. Opting for two bars proved to be more effective than using three bars, leading to a higher maximum load and improved ductility. Moreover, prioritizing the bonding of the concrete cover at the end of the bars was found to be more important than bonding in the area of maximum moment.

Looking for a needle in a haystack: Measuring the length of a stellar bar

One of the challenges related to stellar bars is to accurately determine the length of the bar in a disc galaxy. In the literature, a wide variety of methods have been employed to measure the extent of a bar. However, a systematic study on determining the robustness and accuracy of different bar length estimators is still beyond our grasp. Here, we investigate the accuracy and the correlation (if any) between different bar length measurement methods while using an N-body model of a barred galaxy, where the bar evolves self-consistently in the presence of a live dark matter halo. We investigate the temporal evolution of the bar length, using different estimators (involving isophotal analysis of de-projected surface brightness distribution and Fourier decomposition of surface density), and we study their robustness and accuracy. We made further attempts to determine correlations among any two of these bar length estimators used here. In the presence of spirals, the bar length estimators that only consider the amplitudes of different Fourier moments (and do not take into account the phase-angle of m = 2 Fourier moment) systematically overestimate the length of the bar. The strength of dark-gaps (produced by bars) is strongly correlated with the bar length in early rapid growth phase and is only weakly anti-correlated during subsequent quiescent phase of bar evolution. However, the location of dark-gaps is only weakly correlated to the bar length, hence, this information cannot be used as a robust proxy for determining the bar length. In addition, the bar length estimators, obtained using isophotal analysis of de-projected surface brightness distribution, systematically overestimate the bar length. The implications of bar length over(under)estimation in the context of determining fast and slow bars are further discussed in this work.

The bar pattern speed of the Large Magellanic Cloud

Context. The internal kinematics of the Large Magellanic Cloud (LMC) have been studied in unprecedented depth thanks to the excellent quality of the Gaia mission data, thus revealing the disc’s non-axisymmetric structure. Aims. We seek to constrain the LMC bar pattern speed using the astrometric and spectroscopic data from the Gaia mission. Methods. We applied three methods to evaluate the bar pattern speed by measuring it via: the Tremaine-Weinberg (TW) method, the Dehnen method, and a bisymmetric velocity (BV) model. These methods provide additional information on the bar properties, such as the corotation radius as well as the bar length and strength. We tested the validity of the methods with numerical simulations. Results. A wide range of pattern speeds are inferred by the TW method, owing to a strong dependency on the orientation of the galaxy frame and the viewing angle of the bar perturbation. The simulated bar pattern speeds (corotation radii, respectively) are well recovered by the Dehnen method (BV model). Applied to the LMC data, the Dehnen method finds a pattern speed of Ωp = −1.0 ± 0.5 km s−1 kpc−1, thus corresponding to a bar that barely rotates and is only slightly counter-rotating with respect to the LMC disc. The BV method gives a LMC bar corotation radius of Rc = 4.20 ± 0.25 kpc, corresponding to a pattern speed of Ωp = 18.5−1.1+1.2 km s−1 kpc−1. Conclusions. It is not possible to determine which global value best represents an LMC bar pattern speed with the TW method, due to the strong variation with the orientation of the reference frame. The non-rotating bar from the Dehnen method would be at odds with the structure and kinematics of the LMC disc. The BV method result is consistent with previous estimates and gives a bar corotation-to-length ratio of 1.8 ± 0.1, suggesting that the LMC is hosting a slow bar.

Calculations of the Radiation Dose for the Maximum Hormesis Effect

To date, the radiation-adaptive response has been reported as a low-dose-related phenomenon and has been associated with radiation hormesis. Well-known cancers are caused by non-radiation active reactants, in addition to radiation. A model of suppression for radiation-specific cancers was previously reported, but the model did not target radiation-nonspecific cancers. In this paper, we describe kinetic models of radiation-induced suppressors for general radiation non-specific cancers, estimating the dose M that induces the maximum hormesis effect while satisfying the condition that the risk is approximately proportional to a dose above NOAEL (No Observed Adverse Effect Level). The radiation hormesis effect is maximal when the rate constant for generation of a risk-reducing factor is the same as the rate constant for its decomposition. When the two rate constants are different, the dose M at which the radiation hormesis effect is maximized depends on both rate constants, but the dose M increases as the two rate constants approach each other, reaching a maximum dose. The theory proposed in this paper can only explain existing experiments with extremely short error bar lengths. This theory may lead to the discovery of unknown risk-reducing factor at low doses and the development of risk-reducing methods in the future.

Bounding the Lagrangian Hofer metric via barcodes

In this paper, we provide an upper bound on the Lagrangian Hofer distance between equators in the cylinder in terms of the barcode of persistent Floer homology. The bound consists of a weighted sum of the lengths of the finite bars and the spectral distance.

Experimental study of the bond behavior of 400MPa grade hot-rolled ribbed steel bars in steel fibre reinforced concrete

Present studies show that steel fibres can improve the bond of steel bar in steel fibre reinforced concrete (SFRC) with a correlation to the fibre factor and the fibre distribution uniformity. As a foundation of high-flowability SFRC working together with 400 MPa grade hot-rolled ribbed (HRB400) steel bar in reinforced structures, the bond between them was evaluated through a series of pull-out testing on 48 specimens with a central arranged steel bar. The bond behaviours of steel bar were estimated with a constant bond length of 5d (d is the diameter of steel bar) embedded in high-flowability SFRC, the main research parameters included the ingot mill steel fibres with a fibre volume fraction varied from 0.8 to 2.0%, the strength grade C40 and C50 of SFRC or referenced conventional concrete, and the diameter of steel bars varied from 14 to 20 mm. Results showed that the high-flowability SFRC compacted with a slight vibration is beneficial to improve the bond failure pattern since steel fibres effectively eliminate the crack appeared on the SFRC blocks during the pulling out of steel bar, leading to all specimens failed with the steel bar pull out of SFRC blocks. The bond strength was dominant by the SFRC strength, and obviously strengthened with the increase of fibre volume fraction, while the peak-slip was slightly influenced by the diameter of steel bar. By conducting analyses of test data, equations for calculating the bond strength and the peak-slip are proposed accounting for the effect of steel fibres. Then the predicting method for the anchorage length is suggested linking with different design codes for concrete structures. Compared with test results of this study, a little shorter anchorage length of steel bar in SFRC is obtained from the specification of Chinese code JGJ/T46, which should be noticed to ensure a rational anchorage of ribbed steel bar in SFRC with ingot mill steel fibres.

Experimental study on bond behavior of steel bar embedded in thin UHPC

Due to the high compressive strength and excellent tensile properties of UHPC, reinforced UHPC with a thickness of 45 mm–60mm and a concrete cover of 15 mm–19mm has been used in the steel-UHPC lightweight composite deck. However, the researches about the bond behaviors of steel bar in UHPC with the concrete cover less than 20 mm were still limited. This paper aimed to study the bond behaviors of steel bars in UHPC with a thinner concrete cover (≤20 mm) and develop the calculation method for the lower bound of bond strength. A program of pullout test was conducted using the tensile test setup mimicking the tensile stress condition of structural members. The effects of concrete cover (10 mm, 15 mm and 20 mm), steel fiber volume fraction (0.5%, 1% and 2%), steel bar diameter (10 mm, 12 mm, 14 mm and 16 mm), embedment length of steel bar (4db, 6db, 8db, 10db) on the bond behaviors of steel bar in UHPC were investigated through 11 groups of pullout test specimens. The test results showed that most specimens failed in concrete cover splitting and the bond strength was influenced to different degrees by the test variates. The bond strength for steel bar in UHPC with a steel fiber volume fraction of 2% varied from 12.29 MPa to 15.88 MPa, and an embedment length of 8db with a concrete cover of 15 mm could ensure the steel bar with a diameter less than 16 mm reached its nominal yield stress of 400 MPa before the bond failure. On the basis of pullout test results in this study and the published test data, an empirical equation was proposed to predicted the lower bound of bond strength for steel bar in UHPC.