Ultra-high-performance concrete is a promising material for structures in earthquake-prone regions due to its high compressive strength, excellent ductility, and superior energy dissipation capacity. Although extensive research has investigated the monotonic or cyclic behavior of reinforced ultra-high-performance concrete members under combined axial and flexural loads, direct comparisons between their monotonic and cyclic responses remain limited. Furthermore, the flexural strength prediction model for cyclically loaded reinforced ultra-high-performance concrete columns under combined axial and flexural loads has not been well-addressed in the available technical literature. To address these gaps, six reinforced ultra-high-performance concrete specimens with different steel fiber volumes and axial load ratios were tested, including three specimens subjected to monotonic loading and the remaining three subjected to cyclic loading. The results indicate that the specimens with 2

Existing steel-based dowel models may be unreliable for fiber-reinforced polymer (FRP) bars because of their lower transverse strength, reduced axial stiffness, and distinct failure characteristics. This study presents a systematic investigation of the dowel action of glass FRP (GFRP) bars through tests on ten split beam specimens. The investigated parameters included bar diameter, concrete cover, number of bars, reinforcement layers, and distance from the fictitious crack to the first stirrup. The results showed that all specimens failed by spalling of the concrete cover, whereas no rupture of the longitudinal GFRP bars was observed. Increasing the bar diameter from 10 mm to 19 mm and the concrete cover from 20 mm to 65 mm enhanced the dowel strength by 66.3% and 191.1%, respectively, while doubling the reinforcing bar layers increased the dowel strength by 60.1%. In contrast, increasing the number of bars and the stirrup-to-fictitious-crack distance had negligible effects on dowel strength. Based on the experimental observations, a mechanics-based model for predicting the dowel strength of GFRP bars was developed and validated against an expanded database of 43 dowel-action specimens. In addition, a crack-kinematics-based dowel action model was established to describe the relationship between dowel force and relative displacement.

Abstract Accurately capturing the mechanical behavior of externally prestressed steel–concrete composite (EPSCC) girders is challenging due to the unbonded nature of external tendons and the occurrence of slip at the steel–concrete interface. This paper presents a reliable, design-oriented method for estimating tendon stress and flexural stiffness of EPSCC girders under serviceability conditions. First, analytical expressions are derived to determine the slip-induced deflection in EPSCC girders. Subsequently, a beam–tendon deformation model is developed based on global deformation compatibility, from which an analytical model for the stress increment in external tendons is further derived. Using these foundations, an analytical procedure is developed to calculate girder deflection that accounts for the interface slip effect. Then, a segmented line is introduced to depict the distribution of slip-induced strain, which enables the derivation of a straightforward equation for the effective flexural stiffness of the EPSCC girder. Finally, practical design recommendations are proposed for calculating the deflection of continuous EPSCC girders. Comparisons with experimental results from 18 simply supported and 13 continuous EPSCC girders demonstrate that the proposed method offers greater consistency and accuracy than the design methods considered in this study.

To promote the application of fiber-reinforced polymer (FRP) bar-reinforced ultra-high-performance seawater sea-sand concrete static bending tests were carried out on 16 FRP-UHPSSC beams with different reinforcement ratios, cross-section heights, and types of FRP bars to investigate the ultimate load-carrying capacity, the midspan deflection, and the failure modes of the beams. The experimental results show that all the test beams had brittle failure, and the failure mode of the beams is shear failure when the ratio of the actual reinforcement ratio to the balanced one is higher than 2.73. Increasing the reinforcement ratio and the beam section height improve both bending moment at ultimate load and flexural stiffness at the service limit state. The steel-FRP composite bar (SFCB)-reinforced UHPSSC beams have the maximal bending moment at ultimate load, and the basalt fiber-reinforced polymer (BFRP) bar-reinforced UHPSSC beams have the optimal ductility. The deviation of ultimate bending moment and midspan deflection obtained by proposed calculation method is reduced from 7.5 to 2.8%, and from 15 to 3%, respectively, compared with current specifications for FRP-reinforced concrete structures.

Due to the slip effect in the steel-concrete interface and tension stiffness effect in the concrete slab, accurately predicting the flexural stiffness of steel-prestressed concrete composite girders in the hogging moment region is highly challenging. This paper provides a mechanics-based yet practical method for estimating the flexural stiffness of such girders under service load conditions. Firstly, a validated moment-curvature procedure is developed to analyze the tension-stiffening behavior of the girders. The analysis results indicate that the tension stiffening effect in steel-prestressed concrete composite sections is negligible, allowing their moment-curvature response to be idealized as a bilinear graph in which the interface slip effect is considered. Subsequently, a curvature integration-based method is used to derive expressions for the effective flexural stiffness of the steel-prestressed concrete composite girder. Based on this, an expression for the effective flexural stiffness at the critical section is recommended for design purposes. Finally, the proposed method is validated by comparing its predictions against experimental results from 27 composite girders.

Due to the slip occurring at the interface between the steel beam and the concrete slab, accurately predicting the deformation behavior of steel-concrete composite beams is rather complicated. In this paper, a mechanics-based yet simplified design approach is proposed to determine the short-term service deflection of simple and continuous composite beams. First, analytical solutions for the interface slip-induced strain of composite beams under positive moments are derived. On this basis, a multifold line is assumed to represent the distribution of the slip strain, which is then used to derive the effective flexural stiffness of the composite beams. Considering the interface slip effect and the tension stiffening effect in the reinforced concrete slab, a design equation for the effective flexural stiffness is formulated for the composite beams under negative moments. Finally, a design recommendation for the deflection calculation of continuous composite beams is proposed. By comparing the predictions with available experimental results from 57 simply supported beams subjected to positive moments, 14 simply supported beams subjected to negative moments, and 15 continuous beams, it is found that the proposed approach is more consistent and accurate than the design guidelines or models considered in this study.

The primary objective of this paper is to investigate the mechanical behavior of shear stud connections through flexural tests and to assess the flexural stiffness of steel-concrete composite girders under negative moments. To accomplish this, five steel-concrete composite girders were tested under both negative and positive moments, with a particular emphasis on their behavior under negative moments. The test parameters included the spacing of shear connectors, the longitudinal reinforcement ratio in the concrete slab, and the type of concrete. Detailed measurements of the steel-concrete interface slip and the strain along the stud shear connections were conducted to evaluate the local moment distribution along the connectors and to identify the underlying load transfer mechanisms. The results showed that the use of high-performance concrete reduced the slip in the hogging moment zone, thereby enhancing the beam’s flexural stiffness. During negative moment testing, it was observed that the local moments exerted on the connector reached their maximum hogging values near the root and maximum sagging values near the mid-height. Finally, by considering the slip effect at the steel-concrete interface and the tension-stiffening effect in the reinforced concrete slab, a design equation for the effective flexural stiffness of composite girders under negative moments was proposed.

This paper aims to investigate the flexural behavior of steel-prestressed concrete composite girders under negative moments and to develop a reliable approach for calculating their flexural stiffness. Experimental tests were conducted on four steel-prestressed composite girders and one non-prestressed composite girder until failure. The test results indicate that post-tensioning the concrete slab effectively delays crack initiation and enhances the post-cracking stiffness of the composite girders. When the shear connection degree exceeds 1.0, further reducing the shear connector spacing has a negligible impact on the hogging moment capacity but improves the girders' flexural stiffness. The flexural stiffness predictions for cracked sections in current design guidelines were found to be conservative at low service load levels but unconservative at higher service load levels. To address this, a design equation for the effective flexural stiffness of prestressed composite beams is proposed, considering the slip effect at the steel-concrete interface and the tension-stiffening effect in the prestressed concrete slab. Finally, a database of 14 steel-prestressed concrete composite girders was compiled to validate the accuracy of the proposed equation.

This paper discusses the shear-transfer mechanism of continuous concrete deep beams reinforced with glass fiber-reinforced polymer (GFRP) bars. Five large-scale two-span continuous GFRP reinforced concrete deep beams, each measuring 5040 mm in length and 600 mm in height, were tested to failure. The test parameters were the GFRP shear reinforcement ratio and the shear span-to-effective depth ratio (a/d). Digital image correlation equipment was employed to monitor crack patterns and kinematics throughout the loading process. Based on detailed measurement data, the contributions of various shear-transfer mechanisms were quantified by employing relevant constitutive models. It was found that all beams experienced shear failure following the appearance of the critical shear crack (CSC) within the interior shear span. Decreasing the a/d ratio or increasing the amount of GFRP stirrups traversed by the CSC led to an enhancement in shear strength. The results confirmed that the dominant shear-transfer mechanism was attributed to the GFRP stirrups, with a percentage contribution to the shear strength ranging from 65.7 % to 96.2 %. However, the contributions of aggregate interlock, dowel action and the uncracked compression zone to the shear strength of the beam with GFRP stirrups were insignificant, each accounting for less than 16.0 %. The sum of these contributions consistently matched the tested shear strength, with an assessed-to-applied load ratio ranging from 88.2 % to 114.8 %.

Time-sensitive networking (TSN), as a solution to the nondeterministic communication of traditional Ethernet, meets the real-time and deterministic communication requirements of intelligent automobiles. There are three traffic types in intelligent automobiles, including time-triggered (TT) flows, audio-video-bridging (AVB) flows, and best-effort (BE) flows, and TSN proposes the gate control list (GCL) to control the transmission of the above traffic. The current GCL synthesis usually serves the hard real-time TT flows but ignores the delay of non-TT flows; and it introduces guard bands to ensure the noninterference transmission of TT flows, inevitably wasting bandwidth. Therefore, this article proposes a design synthesis and optimization strategy to improve the transmission of AVB flows and bandwidth utilization while ensuring the real-time performance of TT flows. This strategy first adopts the initial time window design to allocate the antecedent time windows for AVB flows, then transmits AVB flows according to the deadline to enhance the scheduling of AVB flows, and finally flexibly adjusts the time windows of TT flows and AVB flows according to the size of AVB flows to improve bandwidth utilization. Experimental results show the effectiveness of the proposed strategy in improving the transmission of AVB flows and bandwidth utilization compared to the state-of-the-art methods.

The bridging mechanism of steel fibers in ultra-high performance concrete (UHPC) significantly enhances the post-cracking stiffness of prestressed UHPC beams. Despite this beneficial effect, most existing design guidelines neglect the contribution of steel fibers when determining service deflections. This paper proposes a mechanicsdriven yet practical approach for predicting the instantaneous deflection of prestressed UHPC beams under service loads. Firstly, a validated moment-curvature procedure is developed to explicitly capture the steel fiber bridging effect in analyzing the tension-stiffening behavior of beams at service loads. The analytical results reveal that prestressed UHPC sections exhibit an almost fully sustained tension-stiffening response. Subsequently, a curvature integration-based method is employed to derive design equations for the effective moment of inertia of prestressed UHPC beams. Then, a critical section-based effective moment of inertia is recommended for design purpose. Finally, the proposed approach is evaluated by comparing its predictions with experimental data from 38 prestressed UHPC beams. The mean values of experimental-to-predicted deflection ratio for two selected service load levels are 0.914 and 0.952, with the corresponding standard deviations being 0.173 and 0.198, respectively.

Although several confinement strength models have been proposed for concrete confined by fiber-reinforced polymer (FRP) transverse reinforcements, these models show considerable scatter and discrepancies in the estimation of experimental data. Machine learning (ML) techniques may present an alternative prediction approach, but challenges arise due to insufficient experimental data. This study, therefore, develops a transfer learning-based model for predicting the confinement strength of concrete confined by FRP transverse reinforcements. Firstly, a literature review was conducted to collect a target dataset of FRP-confined concrete columns and a source dataset of steel-confined concrete columns used for knowledge transfer. Subsequently, a transfer learning algorithm was proposed to construct an ML confinement strength model for FRP-confined concrete. Finally, the performance of the proposed model was compared to that of six ML models and seven physics-based models. The model evaluation based on one-time random split indicated that the proposed model provided more accurate predictions for the confinement strength than other models considered in this study, achieving an R2 of 0.9089 on the test dataset. Shuffle split evaluation demonstrated that the proposed model exhibited superior stability and robustness compared to other models considered. Based on the proposed transfer learning-based model, the importance of the input parameters was obtained, further confirming the robustness of the proposed model.

This work studied and compared the evolutions of irradiation-induced microstructural defects in five high-entropy carbide ceramics (HECCs) at room temperature to reveal the irradiation resistances of HECCs and corresponding underlying mechanisms. The five HECCs exhibit high phase stabilities and no amorphization is observed up to 40dpa. In-situ 800keV Kr ion irradiation reveals similar evolutions of irradiation-induced defects. The densities of dislocation loops show non-monotonic variations, which reach the maximum at ~ 2dpa and then decrease due to the interactions with each other. In contrast, the sizes of dislocation loops increase monotonically with dose. (NbTaZrW)C exhibits the lowest defect densities and highest defect sizes, which is probably due to the high lattice distortion and its induced high defect recombination efficiencies. Based on the characterization results, it is deduced that the species of constituent elements play more important role in the defect behaviors than the number of constituent elements.

The lack of ductility is the main concern in the use of carbon fiber -reinforced polymer (CFRP) reinforcement as prestressing tendon in concrete members. To address this concern, a partially bonded concept has been proposed. In this approach, CFRP tendons are intentionally debonded from the concrete in the middle region of the prestressed concrete beam, while remaining bonded at each end. In this study, eight post -tensioned beams, including five beams with CFRP tendons and three beams with steel tendons, are tested under cyclic loading. Three bond conditions, including fully bonded, partially bonded, and fully unbonded, are considered. The results indicate that increasing the unbonded length of the tendon changed the failure mode from CFRP rupture to concrete crushing. There is a trend that the flexural capacity decreased with the increase of the unbonded length. The displacement ductility (mu) of partially bonded CFRP prestressed beams ranged from 5.38 to 5.70, which is significantly higher than that of the fully bonded beam (mu = 2.83) and slightly lower than that of the fully unbonded beam (mu = 6.10). Finally, by introducing a relative bond length coefficient into the ultimate tensile stress equation for internally unbonded tendons, a modified design approach for estimating flexural capacities of the partially bonded beams is proposed. The experimental flexural capacities are in close agreement with the values predicted using the modified design approach.

The combination of glass fiber-reinforced polymer (GFRP) and ultrahigh-performance concrete (UHPC) to form structural members has generated significant interest due to their excellent durability and mechanical properties. This paper presents the flexural behavior and design methodology of GFRP-reinforced UHPC beams. Eight reinforced UHPC beams were tested to failure, varying in longitudinal reinforcement type (steel and GFRP), flexural reinforcement ratio, and steel fiber volume fraction (1% and 2%). Two flexural failure modes, including crack localization followed by rupture of GFRP (tension failure) and progressive crushing of UHPC followed by rupture of GFRP (compression failure), were observed in the tested GFRP-reinforced beams. Substitution of steel bars with GFRP bars resulted in delayed crack localization and a significant improvement in flexural strength by 54.9% and ultimate displacement by 55.7%. Increasing the GFRP reinforcement ratio showed a trend of increased flexural capacity, ultimate deformation, and energy dissipation capacity. Increasing the steel fiber volume in UHPC improved the flexural capacity of the tension failure-controlled beam, but had a slight effect on the flexural capacity of the compression failure-controlled beam. In addition, two different models were used to calculate beam deflection, and were compared with experimental results at the service load levels. Considering the fiber-bridging mechanism, a flexural strength model for GFRP-reinforced UHPC beams was developed. Finally, a minimum reinforcement ratio was proposed to ensure progressive failure of GFRP-reinforced UHPC beams.

The aim of this paper is to investigate the bond-slip behavior and model of sand-coated deformed glass fiber-reinforced polymer (GFRP) bars embedded in ultra-high-performance concrete (UHPC). For this purpose, a total of 24 pull-out specimens were tested to failure, varying embedded lengths (2 d b,3 d b,4 d b and 5 d b, where d b represents the diameter of the bar) and steel fiber volume fractions (1% and 2%). It was observed that as the embedded length or fiber volume fraction increased, the failure mode changed from progressive pull out of GFRP bars (pullout failure) to rupture of GFRP bars (rupture failure). Both modes of bond failure experienced damage at GFRP-UHPC interface due to the delamination of the outside layer of GFRP bars. The bond-slip response of GFRP bars exhibited four stages: micro slip stage, ascending stage, descending stage, and residual stage. The bond strength of GFRP bars embedded in UHPC exhibited an increasing trend with the fiber volume fraction, while it demonstrated a declining trend with the increasing embedded length. For specimens with fiber volume fraction of 1% and 2%, the bond strength decreased by 24.4% and 8.0%, respectively, as the embedded length increased from 2 d b to 4 d b. In addition, a database consisting of 200 bond specimens including 24 test specimens from this study was established to statistically derive a bond strength equation for GFRP bars embedded in UHPC. Furthermore, a bond-slip model was proposed to describe the bond-slip behavior of sand-coated deformed GFRP bars embedded in UHPC.

This paper attempts to investigate the mechanical behavior of ultra-high-performance concrete (UHPC) under combined tensile and bending action. For this purpose, a total of 72 specimens were tested under axial tension, pure bending, and eccentric tension loads, respectively. The test parameters included the steel fiber content (0%, 1%, 2%, and 3%) and eccentricity ratio (0, 0.1, 0.2, 0.4, 0.8, and ∞). It was found that all the specimens failed due to crack localization. The stresses and strains at cracking, peak, and ultimate load increased as the eccentricity ratio and steel fiber content rose. For specimens with a higher steel fiber content, the eccentricity ratio's effects on cracking and peak strength were more pronounced. For specimens with a commonly used fiber content of 2%, specifically, cracking and peak strength increased by 29% and 63%, respectively, as the eccentricity ratio rose from 0.1 to 0.8. With the aid of full-field measurement on the specimen surface using digital image correlation, the fiber bridging mechanism of UHPC under combined tensile and bending loads was discussed. Then, a calculating method for determining the cracking load was proposed by introducing the plastic influence coefficient, which depended on the eccentricity ratio and steel fiber content. Finally, a unified approach for predicting the coupled strength of UHPC under combined tension and bending action was derived, and its robust applicability was verified through a database collected from the available literature.

The existing literature concerning the behavior of slender columns made of reinforced ultra-high-performance concrete (UHPC) is severely limited. Furthermore, current design standards lack specific guidelines for reinforced UHPC (R-UHPC) slender columns. Based on this, a comprehensive experimental investigation was conducted on four columns with 2% steel fiber content subjected to compression to explore the influence of eccentricity ratios (e/h0 = 0, 0.15, 0.3, and 0.6) on the compression behavior of the R-UHPC slender columns. The results revealed that all R-UHPC slender columns experienced failure due to compressive zone UHPC crushing, with no observed concrete spalling. Moreover, a detailed parametric study was conducted on 3000 R-UHPC slender columns using a validated finite element model. By analyzing the parameters and employing the moment magnification method, a statistically derived design equation for effective flexural stiffness (EI) was formulated. The results indicated that EI decreased with increasing eccentricity ratio and increased with rising slenderness ratio. Additionally, calculation formulas for determining cross-section strength were proposed for R-UHPC slender columns, accounting for the contribution of tensile zone UHPC to the overall section strength. Finally, the proposed design approach was validated by comparing predicted results with available experimental data.

In the present study, pre-deformation at liquid nitrogen temperature (77 K) was applied to introduce twins into Ti–Mo alloys with different contents of molybdenum. The microstructural evolution and mechanical properties with different cryogenic pre-deformation amounts (from 0 to 9 %) were characterized and analyzed. The results show that the twinning activities and the evolution of twinning systems are mainly influenced by β phase stability and cryogenic pre-deformation amount. After cryogenic pre-deformation, the primary and secondary twinning of {332}<113>twins are observed in Ti–12Mo and Ti–15Mo alloys but absent in Ti–20Mo alloy. With the cryogenic pre-deformation amounts increasing, the width and quantity of twins increase constantly. Moreover, {112}<111>twinning is activated in Ti–15Mo alloy pre-deformed by 6 % and 9 %. Twins and high-density dislocations induced by cryogenic pre-deformation cause a significant enhancement in strength of all these three alloys. However, the effect of cryogenic pre-deformation on the elongation of alloys is complicated. For Ti–12Mo alloys, the yield strength increases monotonically (from 527 to 778 MPa) with the increase of cryogenic pre-deformation reduction, while the elongation is completely opposite (from 47 to 20 %). For Ti–15Mo alloys, the optimal matching of strength and ductility is achieved when the amount of cryogenic pre-deformation is 6 %, with a tensile strength of 815 MPa and an elongation of 24 %. Compared with the other two alloys, Ti–20Mo alloy gets a smaller increase in strength and a slight decrease in elongation with the amount of cryogenic pre-deformation increasing.

The use of ultra-high-performance concrete (UHPC) allows for much smaller cross-sections compared to conventional reinforced concrete columns, which may make reinforced UHPC (R-UHPC) columns more susceptible to slenderness effects. Currently, there is no guideline in design standards for the slenderness limit of R-UHPC columns. This paper, therefore, attempts to develop a design provision for determining the slenderness limit of R-UHPC columns. Firstly, a numerical analytical model was proposed for predicting the load-deflection of R-UHPC columns under eccentric loading, which was validated by comparing its predictions with available experimental results from the available literature. Based on the validated model, a parametric study was then conducted to determine the key parameters affecting the slenderness limit of R-UHPC columns. It was found that the slenderness limit corresponding to the 5% strength reduction was sensitive to the ultimate compressive strain of UHPC, the tensile strength of UHPC, and the reinforcement ratio. On this basis, a design equation for the slenderness limit of R-UHPC columns in single curvature was statistically derived. Additionally, the slenderness limit for R-UHPC columns in non-sway frames was also proposed in a convenient form for design procedures.