Ultra High Performance Concrete Beams Research Articles

Experimental Investigation on Shear Behavior of Non-Stirrup UHPC Beams under Larger Shear Span–Depth Ratios

Due to the extraordinary mechanical properties of ultra-high-performance concrete (UHPC), the shear stirrups in UHPC beams could potentially be eliminated. This study aimed to determine the effect of beam height and steel fiber volume content on the shear behavior of non-stirrup UHPC beams under a larger shear span–depth ratio (up to 2.8). Eight beams were designed and fabricated including six non-stirrup UHPC beams and two comparing stirrup-reinforced normal concrete (NC) beams. The experimental results demonstrated that the steel fiber volume content could be a crucial factor affecting the ductility, cracking strength, and shear capacity of non-stirrup UHPC beams and altering their failure modes. Additionally, the height of the beam had a considerable effect on its shear resistance. French standard formulae were more accurate for the UHPC beams with larger shear span–depth ratios, PCI-2021 formulae greatly overestimated the shear capacity of UHPC beams with larger shear span–depth ratios, and Xu’s formulae were more accurate for the steel fiber-reinforced UHPC beams with larger shear span–depth ratios. In summary, French standard formulae were the most suitable formulae for predicting the shear capacity of UHPC beams in this paper.

Machine and deep learning-based prediction of flexural moment capacity of ultra-high performance concrete beams with/out steel fiber

Machine and deep learning-based prediction of flexural moment capacity of ultra-high performance concrete beams with/out steel fiber

Effect of high-strength and stainless steel reinforcement on the flexural behavior of UHPC beams

Ultra-high performance concrete (UHPC) is an advanced cement-based composite which shows remarkable properties including very high compressive strength, increased tensile resistance, impressive toughness and excellent durability. One promising application of UHPC is in heavily-loaded beams and slabs where its use can allow for increased design efficiency and improved durability. Conversely, the high bond capacity of UHPC can lead to early bar fracture failures, especially when using low amounts of ordinary steel reinforcement. This paper examines the influence of reinforcement grade on the flexural ductility of UHPC beams. As part of the study, three beams built with either Grade 400MPa ordinary steel reinforcement, Grade 690MPa high-strength reinforcement or Grade 520MPa stainless steel reinforcement, are tested under flexural loading. The key test parameters include the influence of concrete type (UHPC vs. conventional high-strength concrete) and steel type (high-strength or stainless steel vs. ordinary steel). The results show that the flexural strength and ductility of the UHPC beams is influenced by the steel grade/type. The beam with ordinary steel shows a well-defined yield point but fails by bar rupture. Increased resistance by 47% is observed when using high-strength bars, however bar rupture occurs owing to the low strain-capacity of this steel type. Combining UHPC with higher ductility stainless steel does not increase capacity, but leads to remarkable ductility by 75%. As part of the numerical study the behaviour of the beams is predicted using FE modelling and the effects of tension steel ratio, UHPC tensile strength and high-strength or stainless steel type are investigated.

Predicting shear strength in UHPC beams through an innovative neural network with SHAP interpretation

Ultra-High performance concrete (UHPC) has garnered considerable attention in the construction industry due to its exceptional mechanical properties and durability. In the design of UHPC beams, accurately predicting shear strength is crucial. Inspired by the dense blocks in DenseNet, this paper proposes a novel neural network for predicting the shear strength of UHPC beams. A comprehensive database of UHPC beams was initially established through extensive literature data collection, amassing 619 experimental data samples. Preprocessing was subsequently conducted using mahalanobis distance (DM) to eliminate outliers. Subsequently, the database underwent detailed parameter analysis. In practical testing, the novel neural network model exhibited superior accuracy in predicting the shear strength of UHPC beams, surpassing traditional machine learning (ML) models and empirical formulas. Furthermore, it demonstrated excellent generalization capabilities, achieving an R2 value of 0.988 in the training set and 0.964 in the test set. The study introduced the shapley additive explanations (SHAP) method to conduct global and local interpretability analysis of the network model, demonstrating the contributions of each input parameter to the model predictions. Finally, based on this network model, a graphical user interface (GUI) was developed for researchers engaged in UHPC beam design, enabling users to easily input relevant parameters and obtain shear strength predictions. The findings of this study are expected to promote the application of ML models in predicting the complex nonlinear behavior of UHPC structures, providing strong support for engineering practice.

Shear Strength of Ultra-High-Performance Concrete Beams without Stirrups—A Review Based on a Database

This paper presents a comprehensive study on ultra-high-performance concrete (UHPC) beams without stirrups, where the test data of 487 beams were collected, and an experimental database was established. Four distinct shear strength calculation models for UHPC beams were examined in the study. These models were created from national specification guides. The results indicate that while the code equation is useful for predicting UHPC beam shear capacity, it consistently underestimates actual values, with a mean experimental-to-calculated ratio above 1.5. The database was also used to study the impacts of the compressive strength of UHPC, the shear span-to-depth ratio, the fiber volume fraction, and the reinforcement ratio on the shear strength of UHPC beams. The findings showed that the shear span-to-depth ratio significantly affected the shear load-bearing capacity of UHPC beams. The increase in the compressive strength of UHPC, fiber volume fraction, and reinforcement ratio positively affected the shear strength of UHPC beams to varying degrees. Additionally, there were size effects for beams with a shear span-to-depth ratio of less than 1.5 and an effective depth of more than 300. In addition, coefficients accounting for fiber influence and the shear span-to-depth ratio were incorporated to develop an enhanced formula for UHPC beams. The empirical data from the database tests revealed that the average ratio of the beams’ experimental shear capacity to the values predicted by the modified equation is 1.3, with a standard deviation of 0.74. These results suggest that the refined equation offers improved calculation precision and broader applicability. Eventually, a summary of the issues pertaining to the shear performance of UHPC beams and the key future research directions is provided to facilitate a clearer comprehension and awareness of emerging concepts for scholars within the discipline.

Comparative study on flexural performance of ultra‐high performance concrete beams reinforced with steel rebar and steel plate

AbstractTo enhance the mechanical and constructional performance of the ultra‐high performance concrete (UHPC) beams, the steel plate placed at the bottom surface of the UHPC beam is utilized to replace the ordinary steel rebars. In this paper, four 3.2 m UHPC T‐shaped beams with different reinforcement patterns of ordinary steel rebars and external steel plate were fabricated and comparatively tested under flexure loading. Their damage patterns, load versus deflection behavior, flexural capacity, load versus strain behavior, moment versus curvature behavior, stiffness, and crack development were investigated. The flexural experiments indicated that the external steel plate, positioned at the bottom surface of the UHPC members, could resolve the difficulty of installing ordinary steel rebars in slender UHPC components and improve its constructional performance. Compared with the inside steel rebar reinforcement, the employment of the steel plate at the bottom surface of the UHPC beam can effectively increase the distance from the neutral axis to the tensile reinforcement at the serviceability and ultimate states, thereby improving its flexural capacity and stiffness. Additionally, the configuration of the external steel plate was beneficial to reduce the tensile stress level of the tensile reinforcement and limit the opening of UHPC crack width, and thus their crack resistance can be effectively enhanced. Moreover, increasing the thickness of the steel plate or rebar ratio can also significantly improve the flexural capacity, stiffness, and cracking resistance of UHPC beams.

Investigation of shear response due to variation of fiber volume fraction, transverse steel, and placement method on short span R/UHPC beams

This study investigates the response of small-scale, reinforced ultra high performance concrete beams. Seven specimens were cast and experimentally tested. Steel fiber volume fraction, amount of longitudinal and transverse steel reinforcement, and casting direction varied between specimens. High longitudinal reinforcement ratios of 4.1% and 9.5% were expected to drive relatively large shear demands and low steel fiber volume fractions of 0.5% and 1% were expected to decrease the UHPC’s ability to resist tension, shear, and compression. Specimens were either cast at one end or mid-span. All specimens failed in shear, as expected. R/UHPC beams with only 0.5% fibers and a stirrup spacing equal to half the beam’s depth carried more ultimate load than beams with 1% fibers and twice the stirrup spacing. At a 0.5% fiber volume fraction, UHPC performed well, exhibiting fiber bridging in tension and resisting spalling in compression. As longitudinal reinforcement ratio increased from 4.1% to 9.5%, load carrying capacity generally increased, but not proportional to the increase in steel. Placement method did not influence fiber orientation in the R/UHPC beams when measured in 2D planes transverse or longitudinal to the specimens’ major axis. The longitudinal and transverse reinforcement interrupted fiber flow and prevented significant fiber alignment; combined with the short span of the beams, these factors mitigated the influence of placement method.

Blast retrofit of shear-deficient high-strength concrete beams with ultra-high performance concrete

This research has investigated the ability of ultra-high performance concrete (UHPC) to improve the blast performance of high-strength concrete (HSC) beams. As part of the study 4 shear-deficient HSC beams built without stirrups and with dimensions of 125 mm × 250 mm × 2440 mm were retrofitted with a UHPC jacket and tested under simulated blast loads using a shock-tube. The retrofit involved replacing the existing cover with a cast in-situ UHPC jacket (with thickness of 20–40 mm). A companion set of beams was also tested under quasi-static four-point bending. The results from the blast and static tests are compared to a control set of HSC beams built without and with stirrups to examine the ability of UHPC to increase shear and flexural resistance, respectively. The effect of steel ratio (ρ = 1.6% or 2.4%), an important parameter which affects the behavior of HSC and UHPC beams, was also investigated in beams with 15M and 20M bars. Under static loading, the results show that the UHPC jacket was able to prevent shear failure, and improve flexural performance by increasing strength by 40–125%, stiffness by 80–100% and overall toughness by 56–144%, when compared to the companion HSC beams. Under blast loading, the UHPC increased shear capacity, prevented shear failure and improved blast performance by reducing displacements, increasing overall blast capacity and improving damage tolerance. For example, in the 20M set, the UHPC-retrofitted beam showed reductions of 26–63% in maximum displacements, and 88–100% in residual displacements under varying blast intensities. The steel ratio was found to play an important role on the failure mode of the retrofitted beams under static loading, with bar fracture observed in the beam with lower steel ratio of 1.6%. As part of the numerical study, the blast response of the UHPC retrofitted beams was predicted using 3D finite element (FE) modeling. The FE models were able to predict the failure modes and maximum displacements of the control and UHPC retrofitted beams, with an average numerical-to-experimental displacement ratio of 1.03 and an average error of 8%.

Experiment study on flexural performance of steel concrete composite beams under salt freeze-thaw cycles in negative moment sections

Bridge structures in cold climates face significant challenges due to freeze-thaw cycles and salt-induced corrosion. This study investigates the degradation mechanisms of the negative bending behavior of steel-concrete composite beams using normal concrete (NC) and ultra-high performance concrete (UHPC) under salt freeze-thaw cycles (SFTC), considering the impact of different stud arrangements. The results indicate that UHPC significantly enhances the cracking performance in the negative bending region of the composite beams and demonstrates high resistance to SFTC. Before undergoing SFTC, the cracking moment of the UHPC beams increased by an average of 210.5%, and stiffness by 37.3%, compared to the NC composite beams. After 150 SFTCs, the NC beams showed a significant decline in performance, with a 62.1% reduction in cracking moment, a 6.2% decrease in load-carrying capacity, and a 5.6% reduction in stiffness. In contrast, the flexural performance of the UHPC beams was almost unaffected, with only a 17.5% reduction in cracking load. Moreover, beams with a double-row stud configuration exhibited better negative bending resistance compared to those with a single-row stud configuration. Based on experimental results and data from reference, a reasonable formula for predicting the composite beams under the effect of SFTCs was proposed and proved to have satisfactory accuracy.

Experimental investigation on UHPC-NSC composite beams

A hybrid beam composed of ultra-high performance concrete (UHPC) and normal strength concrete (NSC), is experimentally evaluated. The layout optimizes cost and performance by placing the UHPC full-depth section at mid-span of the hybrid beam. The length of the UHPC section compared to the span length (Lu/L) as well as the angle between the UHPC and NSC interface is varied experimentally, and the performance evaluated against fully NSC and fully UHPC control beams. The fully UHPC beam (BU) had an ultimate load 63.5% higher compared to the NSC beam (B). All three hybrid UHPC-NSC beams B0.5, B0.6, and B0.5I, having Lu/L ≥ 0.5, achieved ultimate loads of 92.3%, 95.8% and 94.2% of the fully UHPC beam ultimate load respectively. The failure of the hybrid beam with the inclined joint (B0.5I) was more gradual when compared with the beam with the straight joint (B0.5) having the same volume of UHPC. The hot joint between UHPC and NSC in the hybrid beams showed no joint separation. The developed 3D FE model was able to predict the load-deflection behaviour as well as crack locations and crack localization. In hybrid UHPC-NSC beams, steel yielding can initiate near the UHPC-NSC joint location, where unlike within the UHPC portion, the steel rebars are required to carry the entire tensile force. An analytical method is proposed to provide conservative design loads considering the different failures expected from the hybrid UHPC-NSC beam.

Numerical and digital image correlation study of the flexural behavior of prestressed ultra-high-performance concrete beams made from locally available materials

This paper presents finite element simulations of the flexural behavior of three prestressed ultra-high-performance concrete (UHPC) beams based on the concrete damaged plasticity model (CDPM) available within Abaqus. A novel numerical model that applies the prestressing force through surface traction is proposed. The flexural deformation of the prestressed UHPC beams is simulated from the application of the prestressing force through failure under flexural loading. Material properties were measured and informed values for CDPM input parameters. The model was compared with four-point loading tests previously conducted to study the flexural behavior of large-scale prestressed UHPC beams. Digital image correlation (DIC), supplemented with traditional sensors, was used during the test to monitor behavior. The primary results based on the numerical modeling are as follows: • The model is validated to accurately simulate the flexural behavior of prestressed UHPC beams, both in global deflection and local strain. • The prestressing process, including camber deformations, is effectively simulated. • The new approach to apply prestressing force in the model can be applied in scenarios requiring large prestressing forces. • The numerical results are also validated through comparison with DIC results. The new numerical modeling approach will be effective for guiding experimental studies and design of prestressed UHPC beam elements.

An Adaptive Crack Width Prediction for Flexural Steel Reinforced UHPC Beams

The crack pattern of steel reinforced ultrahigh performance concrete (UHPC) beam is usually characterized by many densely distributed fine cracks (i.e., multiple microcracks) along with localized macrocrack, and the crack width development rate along the beam height is smaller than that of normal concrete since steel fibers and steel reinforcement bars are supposed to be effective in controlling crack width propagation of the UHPC beam. However, an effective crack width prediction formula is still underdeveloped for steel reinforced UHPC beam. The present study aims to formulate a crack width prediction equation based on the equations in Chinese code GB50010 where the parameters can be regressed and calibrated. Ten UHPC beams with different steel fiber volumes and reinforcing ratios are experimentally tested to collect crack width and spacing data for comparison and validation purposes. Nonuniformity distribution coefficient of rebar strain and average crack spacing are calibrated by the test data. Also, rebar stress is calculated with considering residual tensile strength of UHPC based on a sectional analysis. The modified crack width equation is validated with the test results, showing the best prediction accuracy of 0.97 and standard deviation of 0.11 for the test beams in this study compared to those predicted by JTG 3362, CECS 38, MC and AFGC. This study is emphasizing crack width prediction and control in designing UHPC structures.

Flexural and cracking performance of ultra-high performance concrete beams with high-strength steel reinforcements

In this study, the flexural and cracking performance of ultra-high performance concrete (UHPC) beams reinforced with high-strength steel reinforcement (HSSR) is investigated. Four beam specimens, including two UHPC beams and two normal-strength concrete (NSC) beams with different HSSR ratios were tested under flexure. The effect of concrete type and HSSR ratio on the flexural behaviour was evaluated. The failure mode, load-deflection response, stiffness, ductility and strain of the concrete and HSSR were discussed. Test results show that UHPC coupled with HSSR achieved better flexural performance and the ability to limit the development of the crack. The flexural capacity, deflection and stiffness for the UHPC beams were increased but the ductility was decreased as the HSSR ratio increased. The flexural behaviors of UHPC beams were predicted by section analysis. The flexural performance of HSSR-UHPC beams should consider the contribution of steel fibre to the tensile strength. Considering the influence of steel fibre, an equation was proposed to predict the average crack spacing. UHPC beams showed excellent agreement with the experimental results. The maximum crack width of 630 MPa reinforced UHPC beams was calculated by NF P 18-710 in accordance with the test results.

Reliability evaluation of flexural capacity design provision for UHPC beams reinforced with steel rebars/prestressing tendons

This study investigated the reliability of the flexural capacity prediction models for ultra-high performance concrete (UHPC) beams in various standards, including the Chinese UHPC Code (draft), Chinese standards JGJ/T 465–2019 and JTG 3362–2018, Swiss standard SIA 2052–2016, and French standard NF P18–710–2016. The research was based on two comprehensive databases of 110 reinforced and 47 prestressed UHPC beams. Correlation analysis of the model errors of the flexural capacity formulae was conducted at first. Then, the reliability of the prediction models was analyzed through Monte Carlo simulation (MCS) and first-order second-moment (FOSM) method, considering the design parameters such as material strength, live-to-dead load ratio, longitudinal reinforcement ratio, and prestressing tendon ratio. The results indicated that the prediction model in Chinese UHPC Code (draft) could accurately predict the flexural capacity of reinforced and prestressed UHPC beams among the five specifications, with the mean model errors of 1.06 and 1.02, respectively. The reliability indexes of Chinese UHPC Code (draft), Swiss standard SIA 2052–2016, and French standard NF P18–710–2016 for both the reinforced and prestressed UHPC beams were significantly higher than the specified value of 4.2 in the Chinese standard. The sensitivity analysis showed that the reliability index increased with the increase of live-to-dead load ratio, but it was not significantly influenced by UHPC compressive strength. In addition, the reliability index decreased as the longitudinal reinforcement ratio and prestressing tendon ratio increased. Material partial factor of flexural resistance of the formula in Chinese UHPC Code (draft) was calibrated, and γc= 1.30 was recommended for UHPC beams for safety.

Flexural strength of ultra-high performance concrete beams with stainless steel wire mesh: experimental and finite element analysis

The addition of a stainless steel wire mesh (SSWM) at the bottom of ultra-high performance concrete (UHPC) was proposed for improving the flexural strength of UHPC and solving the problem of low initial cracking performance. A method combining experiments and numerical simulations was used to study the ability of the SSWM to enhance the flexural strength of UHPC and evaluate its cracking resistance. The wire diameter, mesh size, number of steel wire mesh layers, and length of the SSWM were the geometric parameters considered in the experiments. The experimental results showed that the flexural strength of UHPC is improved by SSWM, and the load–deflection curve, ductility, strain distribution, and failure mode of UHPC were assessed. The flexural strength and failure modes of UHPC were evaluated accurately using a numerical model. The wire diameter, mesh size, number of steel wire mesh layers, and wire mesh length parameters were analyzed using the model. The relationship between the flexural strength and the geometric parameters was obtained through an in-depth study of the parameter analysis results using multiple linear regression.

Reinforced ultra-high performance concrete beam under flexure and shear: Experiment and theoretical model

This paper investigated the influence of different shear span ratios, longitudinal (LR) and stirrup (SR) reinforcement ratios, and material types on the flexural and shear performance of reinforced ultra-high performance concrete (UHPC) beams. A series of bending tests with shear span ratios of 4.0, 1.5, and 1.0 were conducted. Results reveal that UHPC beams with a LR ratio of 2.53% exhibit 1.66, 2.00, and 1.45 times higher load capacity than that of the beams with a LR ratio of 1.34% at shear span ratios of 4.0, 1.5, and 1.0, respectively. A SR ratio of 1.40% can achieve 15% and 35% enhancement in load capacity of UHPC beams at shear span ratios of 1.5 and 1.0, respectively. The UHPC beams made with hybrid polyethylene and straight steel fibers have the highest load capacity compared to the beams with straight steel fibers and hooked steel fibers. The enhancement can achieve 8%, 5%, and 15% at shear span ratios of 4.0, 1.5, and 1.0, respectively. Furthermore, cross-section analysis, a novel truss-arch model, and strut-and-tie model were employed to theoretically calculate the load capacity of the UHPC beams with different failure modes. The relative errors of the cross-section analysis and truss-arch model are smaller than 9% and 25%. The findings of this work could provide guidelines for the structural design of UHPC beams under different loading conditions.

Preparation of ultra-high performance concrete containing waste foundry sand and its application in structures

The resourceful recycling of waste foundry sand (WFS) has aroused continued interest. In this research, the feasibility of application of WFS in ultra-high performance concrete (UHPC) beams was explored. Firstly, the material properties of 12 groups UHPC consisting of 4 replacement levels of WFS for aggregate and 3 water-binder (W/B) ratios were tested. Then, the flexural tests on 6 UHPC beams were conducted and the structural response were analysed. Finally, theoretical analysis was performed to guide the design of UHPC beams with WFS. It has been proved that the UHPC beams containing appropriate content of WFS could achieve satisfactory performance. There was an 11.4% and 9.3% improvement of the compressive and tensile strength of UHPC containing 20% WFS with the W/B ratio of 0.18 compared with that without WFS. In addition, the cracking load, yield load and ultimate load of the UHPC beam increased by 25.9%, 23.3% and 12.2%, respectively. Meanwhile, the ductility, stiffness and crack resistance also exhibit a certain degree of enhancement. The average values of the ratios of prediction and test results of cracking moment, flexural capacity and crack width of UHPC beams containing WFS are 0.96, 0.93 and 1.04, respectively, indicating that the equations have satisfactory accuracy.

Flexural behavior of high-strength steel bar reinforced UHPC beams with considering restrained shrinkage

Despite the excellent mechanical properties of ultra-high performance concrete (UHPC), UHPC beams with a conventional reinforcement ratio consistently demonstrate limited ductility. Therefore, this study aims to enhance the ductility of reinforced UHPC beams by regulating the tensile interaction between steel fibers and reinforcement. Six UHPC beams with varying fiber volume fractions and reinforcement ratios were tested under flexure. The effect of restrained shrinkage on flexural behavior was emphatically investigated. A cracked section analysis was also implemented to predict cracking behaviors of UHPC beams and was verified by experimental results. The test results revealed an increase in the ductility of UHPC beams with an increasing reinforcement ratio, while a decrease was observed with an increasing fiber volume fraction. The contribution of UHPC tensile capacity decreased significantly with the increase in the reinforcement ratio because of the restrained shrinkage. The stiffness and crack control capacity of reinforced UHPC beams reaches a plateau when the sum of reinforcement ratio and fiber volume fraction exceeds 3.1%. Increasing the fiber content is more effective than increasing the reinforcement ratio in limiting crack development, whereas the converse is true for improving the flexural capacity.

Prediction of shear strength in UHPC beams using machine learning-based models and SHAP interpretation

To provide more accurate and reliable predictions of the shear strength of ultrahigh-performance concrete (UHPC) beams, in this study, the machine learning (ML) approaches were employed to develop the data-driven models, and the ML models were interpreted using the Shapley additive explanations (SHAP) method. It was found that the ensemble models, particularly CatBoost, outperform individual ML models and traditional empirical models. The geometric dimensions and shear span-to-depth ratio were the most influential features for predicting the shear strength of UHPC beams, followed by the parameters of reinforcement and material properties of the UHPC.

Performance of pre-cracked beams exposed to corrosion environment cast with ultra-high performance concrete

Ultra-high-performance concrete (UHPC) is a unique type of concrete that has a lot of advantages in the construction sector. There is no risk for reinforced UHPC elements in an aggressive environment or coastal region, unless cracking occurs due to extra-loading or inaccurate structural design. For that, there is a need for this study to be considered. The core concentration of this study is towards understanding the shear behavior of pre-cracked beams cast with UHPC as affected by durability. This program presents materials used to reach the main aim of the present study. 72 specimens were conducted to study UHPC physical and mechanical properties to be compared with traditional normal concrete (NC). Moreover, 10 RC beams were cast to investigate the shear behavior of RC-UHPC beams with dimensions of 100 mm, 150 mm, and 1300 mm. Five non-exposure beams and five exposure beams were corroded by an accelerated corrosion cell, and half the potential cell readings were recorded. Obtained results for specimens provide that; UHPC eliminates deflection with high modulus of elasticity, in chloride penetration test UHPC is 200 times less than NC, and the reduction in bond strength test after corrosion exposure is 66.24 % and 1.69 % for NC and UHPC specimens, respectively. For pre-carking UHPC beams at 80 % of experimental ultimate load; cracking resistance for un-corroded beams exceeds the corroded beams by 250 %. The residual flexural capacities for corroded beams pre-cracking up to 80 % of E.U.L. are 61.6 % and 119 % for NC and UHPC beams, respectively. UHPC is much better than NC in corrosive environments.