Ultra-high Performance Concrete Layer Research Articles

Data-driven moment-carrying capacity prediction of hybrid beams consisting of UHPC-NSC using machine learning-based models

This paper presents, for the first time in the literature, a study on the development of data-driven machine learning (ML) models to predict the moment-carrying capacity of ultra-high performance concrete (UHPC)-normal strength concrete (NSC) hybrid beams. A database of 56 specimens of rectangular-section UHPC-NSC hybrid beams subjected to flexural loading is adopted to train the models. In this context, ten ML algorithms that are most preferred in structural engineering applications are selected to develop prediction-based models: linear regression (LR), lasso regression (LASSO), ridge regression (RR), support vector regression (SVR), multilayer perception (MLP), random forest (RF), extremely randomized trees (ERT), extreme gradient boosting (XGBoost), K-nearest neighbors regression (KNN), and adaptive boosting regression (AdaBoost). Moreover, the Shapley additive explanation (SHAP) method is used to assess the impact of the input features on the prediction results. Lastly, user-friendly a graphical user interface (GUI) has been developed to ensure the interpretability of the prediction models and to overcome the "black box" problem of ML methods. The GUI, which is designed based on the model with the most effective prediction ability obtained from this work, allows design engineers to analyze their own data and customize the parameters of the model for the prediction of the moment-carrying capacity of UHPC-NSC hybrid beams. The results indicated that ML models can be an effective tool for predicting the moment-carrying capacity of UHPC-NSC hybrid beams. In this regard, notably, the XGBoost model exhibited superior performance in terms of prediction accuracy and generalization ability (R2 = 0.996 and 0.945 in the training and test datasets, respectively). On the other hand, according to the SHAP analysis results, the three most important input parameters influencing the moment-carrying capacity of UHPC-NSC hybrid beams are the effective depth (d), UHPC thickness at the bottom of the beam (UHPCbottom layer) and compressive strength of UHPC (fc,UHPC), respectively. Moreover, it has been found that the placement of the UHPC layer at the bottom of the beam rather than at the upper part of the beam is more effective in enhancing the moment-carrying capacity of UHPC-NSC hybrid beams.

Numerical and experimental study of a segmentally prefabricated orthotropic steel–ultra-high-performance concrete composite deck for long-span cable-stayed bridges

Utilizing the high strengths, toughness, and durability of ultra-high-performance concrete (UHPC), a segmentally prefabricated orthotropic steel–UHPC composite deck (POSUCD) system has been developed for long-span cable-stayed bridges. The deck system combines an orthotropic steel deck (OSD) with a reinforced UHPC layer using notched perfobond strips (NPBLs). The UHPC layer is prefabricated onto the OSD of the girder segment in the factory to form the POSUCD. After the precast UHPC layer is cured, the girder segments are transported to the bridge site and assembled. The precast UHPC layers are then connected via transverse wet joints before tensioning stay cables. Against the background of the Danjiangkou Reservoir Bridge with a main span of 760 m, finite element (FE) analysis was conducted to examine the stress state and flexural tests were carried out on local full-scale models to verify the feasibility of POSUCD. The results show that the prefabricated UHPC layer reduces the maximum static compressive stress of the steel deck in the girder system by 21%, and the stress ranges at fatigue-prone details of the steel deck are decreased by 28%–90% compared to traditional OSDs with asphalt overlay. Since the prefabricated UHPC layer helps withstand dead axial load in the main girder, the high compressive strengths of UHPC can be utilized more effectively than in deck systems with UHPC only used as a cast-in-situ overlay to resist vehicular wheel loads. The transverse wet joint interfaces were identified as the weakest aspect of the POSUCD, whether under tension or compression; however, their nominal flexural strengths along the longitudinal direction meet the required design standards. The shear resistance of NPBLs was also well confirmed by the minimal interfacial slip on the specimen when it reached the ultimate capacity under positive bending moment.

Shear behavior of pre-damaged RC beams strengthened with steel plate and UHPC

To address the deficiencies in the durability of the bonded connection, an innovative strengthening method combining steel plates with UHPC (ultra-high-performance concrete) is proposed. In this method, the UHPC layer is located between the steel plate and the original damaged RC (reinforced concrete) structures, mainly acting as a binder to enhance the bonding effect. To verify the effectiveness of the proposed method, five RC beams are manufactured and carried out to investigate the shear characteristics and capacity. In this experiment, some factors that may affect the strengthening effect are considered, such as the initial damage degree (represented by different crack widths), steel plate thickness, and strengthening method (two-side or one-side). The experiment results show that the proposed strengthening method can significantly improve the shear capacity (increased by at least 56%) of pre-damaged RC beams without significantly enlarging the cross-section and self-weight. In addition, during the load test, there is no peeling phenomenon for the steel plate-UHPC interface and the UHPC-RC interface. This demonstrates that it is feasible for the UHPC layer to replace epoxy resin glue as a bonding agent to enhance the bonding effect between steel plate and RC. The proposed strengthening method shows promising applications in strengthening old/defective bridges. Moreover, a simple formula for predicting the shear-bearing capacity of strengthened beams is derived. The shear-bearing capacity predicted by the proposed formula is in good agreement with the experimental results.

Early-age shrinkage characteristic of UHPC in strengthening stone masonry arch: Influence of restraint from arch structure

Ultra-high performance concrete (UHPC) is frequently employed in strengthening existing bridges, due to its extremely high mechanical qualities and exceptional durability. Nevertheless, the early shrinkage of UHPC layer restrained by the arch structure may result in the risk of cracking, when used for strengthening masonry arch bridges. This paper aimed to investigate the shrinkage and cracking potential of ultra-high-performance concrete (UHPC) at early age under restraint from masonry arch structure. For that, different types of masonry model arches were respectively strengthened by using UHPC and then the shrinkage behaviors of UHPC layer were tested. The effects of four different strengthening modes, i.e., F-hoop (wrapping for four sides), T-hoop (wrapping for three sides), Intrados and Extrados, three different rise-span ratios, i.e., 1/5, 1/4, 1/2 and two different arch ring widths, i.e., 0.42 and 0.15 m, were considered. Results indicate that the shrinkage strain time-varying curve of UHPC layer was not only related to the material characteristics, but also negatively related to the change in external environment temperature. For different strengthening methods, the final shrinkage strain of UHPC layer follows: F-hoop < T-hoop < Intrados < Extrados. The shrinkage strain was unaffected by different strengthening modes along the thickness and arch axis directions. The shrinkage effect of UHPC generates the maximum tensile stress value (1.0–2.0 MPa) at the arch top of the strengthening layer, which was significantly less than the tensile strength of UHPC during the same risk period. The arch foot is the most complex area under stress and should be taken seriously.

Experimental study on thermal behaviors of two-layered functionally graded concrete slabs subjected to fire

In order to improve structural thermal performances, this paper designed a two-layered functionally graded concrete (FGC) slab composed of an ultra-high performance concrete (UHPC) layer and a lightweight aggregate concrete (LWAC) layer. UHPC layers are used as structural layers to bear loads while LWAC layers are used for thermal insulation. Fire tests were conducted to investigate the fire resistance behaviors of the FGC slabs with different LWAC thicknesses under the ISO834 heating regime while homogeneous UHPC and normal concrete (NC) slabs were prepared as a contrast. The experimental results revealed that the LWAC could significantly reduce the temperature transferred to UHPC layers, where the interfacial temperatures of FGC slabs with 40 mm and 30 mm thick LWAC layers were 197 °C and 325 °C respectively. Meanwhile, the maximal mid-span deflections ranged from 26.1 mm to 31.5 mm respectively, approximately 55%-65% lower than those of homogeneous material specimens. Besides, FGC slabs presented good explosive spalling resistance, no delamination or debonding occurred at interfacial regions, and LWAC layers adhered to UHPC layers in the form of “multi-point attachment”. The studies provided a solution to the fire resistance design of reinforced concrete structures under high temperature based on the structural level, and the thickness of LWAC layers was optimized by finite element analyses.

Flexural behavior of the hollow slab girders strengthened with ultra-high performance concrete: Field full-scale experiment and analysis

Due to high strength and well durability, ultra-high performance concrete (UHPC) can be designed to strengthen damage hollow slab girder. The main objective of this study is to evaluate reinforcement feasibility of compression zone of hollow slab girder via field full-scale experiments and finite element (FE) analysis. To this end, UHPC layer was firstly proposed to reinforce top plate of damaged hollow slab girder. Then, four-point bending tests were conducted to investigate flexural behavior of hollow slab girder with/without UHPC layer. FE models were developed to simulate bending failure process of hollow slab girders. The deflection, crack propagation and stress distribution of hollow slab girders were analyzed as well as failure modes. The results show that UHPC layers can significantly improve flexural stiffness of hollow slab girder, and it results in an increase of 11.5% in cracking load and 23.7% in ultimate load, respectively. Moreover, reinforced girder exhibits well ductility and relatively high flexural bearing capacity. Furthermore, the parameter analyses were performed to investigate the effects of the thickness of UHPC layer and prestress on flexural behavior of reinforced girder. The results show that the prestress significantly affects the ductility and cracking load. Whereas, it seems to be independence of ultimate load. Finally, theoretical analysis was performed to obtain calculation formulas, which determine cracking and ultimate loads of reinforced hollow slab girder. Overall, this study has verified effectiveness of proposed reinforcement method in improving stiffness and flexural bearing capacity of hollow slab girder.

UHPC-XPS insulation composite board reinforced by glass fiber mesh: Effect of structural design on the heat transfer, mechanical properties and impact resistance

Extruded foamed polystyrene (XPS) and ultra-high performance concrete (UHPC) are the ideal insulation and structural materials for preparing sandwich composite boards, respectively. However, how to design the multilayer structure of composite board to maximize thermal insulation, mechanical properties and impact resistance has not been clarified yet. In this study, styrene-acrylic emulsion was coated on the surface of XPS to improve its wettability, and glass fiber mesh-reinforced bonding mortar with vac-ethylene copolymer emulsion was used to improve the adhesive properties between UHPC and XPS layers. Then the contribution of each layer in heat-transfer, load-bearing, and impact resistance were investigated and simulated by finite element analysis. By separating XPS and UHPC into serval layers, the midspan displacement at peak load and fracture energy of composite boards increased by 689.4% and 39.1% respectively, then roles of each layer in composite board were discussed. The results provide an effective method to prepare high performance composite board by multilayer structural design, and then promote energy-saving and emission-reduction of prefabricated wall system and even building industrialization.

Shear behavior of short studs in steel-thin ultrahigh-performance concrete composite structures

Steel-concrete composite structures gradually tend to be thinner and lighter in modern bridge engineering. Ultrahigh-performance concrete (UHPC) as an innovative solution has been used to upgrade the behavior of composite structures and accelerate construction, and short stud connectors are the key elements to guarantee the effective connection of steel and concrete components. This study conducted push-out test to explore the failure modes and load-slip relationships of short studs in steel-thin UHPC composite structures (STUCs). The experimental findings revealed that the fracture of the stud shank and local concrete crushing dominated the failure modes of all specimens. Increasing stud diameter could enhance shear strength, while arranging short studs densely and decreasing stud height could result in the reduction of shear capacity of a single stud. The experiment data were employed for the construction and verification of the finite element models. The impact of several parameters on the shear strength was investigated via the validated numerical models. The shear strength increased approximately linearly with stud diameter for short studs in thin UHPC layers, but the cover thickness and UHPC strength had a slight impact. The shear capacity of short studs couldn't be negatively impacted by reducing the aspect ratio to 3.16. In addition, the ultimate shear capacity significantly decreased due to the grouped stud effect for grouped short studs when the spacing between the studs was less than 70 mm. The shear capacity was conservatively predicted by these specifications for short studs in thin UHPC layer, according to the comparison of the simulated data with the existing construction specifications. Finally, a new equation considering multiple parameters was proposed and validated by the test data, which could precisely predict the shear strength of short studs in STUCs.

Characterization of interface properties for modeling the shear behavior of T-beams strengthened with ultra high-performance concrete

The application of Ultra high-performance concrete (UHPC) lateral layers on normal-strength concrete (NSC) beams substantially improves their shear performance. However, the impact of the NSC-UHPC interface properties on the shear performance has been scarcely studied and may hinder the strengthening efficiency and modify the failure mode. This study has characterized the complete shear and tensile behavior of interface specimens and evaluated the effect of anchors at the interface. Then, the complete curves of the interface allowed calibration of an interface concrete fracture (CF) model that was introduced in finite element (FE) simulations replicating the shear behavior of UHPC-strengthened T-beams tested in the same project. Parametric studies were then made with FE simulations. Results showed the FE simulations with the CF model better capture the stiffness evolution and failure mode of strengthened beams than that with the perfect bond model. The increase of UHPC layer thickness up to 80 mm and anchor spacing at the interface smaller than 300 mm considerably increased the stiffness and shear capacity of the strengthened beams. Existing dead load on beams did not impair UHPC strengthening and a substantial increase in shear capacity can still be achieved in real-size strengthened T-beams.

Fatigue life prediction of orthotropic steel deck strengthened with UHPC under stochastic traffic load

In recent years, the ultra-high performance concrete (UHPC) has been increasingly used to strengthen orthotropic steel decks (OSD) to solve the cracking problems at fatigue-prone details and pavement damage. In this paper, the fatigue life of a cable-stayed orthotropic steel decks bridge under stochastic traffic loads is calculated before and after the orthotropic steel decks strengthened with the ultra-high performance concrete layer. The traffic data of the real bridge for 1 week is first obtained based on the weigh-in-motion system. Then, a stochastic traffic load on the bridge is simulated for its service life by the Monte Carlo method. A fatigue life analysis framework, which includes the traffic load simulation, a refined finite element model, the S-N curve and Miner linear cumulative damage criterion, is proposed for fatigue life prediction of orthotropic steel decks. For the bridge before reinforcement, the predicting results for the fatigue life of three fatigue-prone details, including the scallop cutout, rib-to-diagram and rib-to-deck joint are basically consistent with that of the actual bridge inspection results. After strengthening by ultra-high performance concrete, the fatigue life of the three structural details are increased from 15.87, 13.89, and 32.26 years to more than 100 years, respectively, as compared with the original orthotropic steel decks structure.

Potential of Ultra-High-Performance Concrete (UHPC) for Refurbishment of Bridges

In many countries, the bridge infrastructure suffers from damaged bridges that need to be rehabilitated or replaced. This means that the state or the institutions responsible for this must make extensive investments. Are there other ways to address the problems caused by the damaging effects of de-icing agents, by fatigue due to high vehicle loads and frequencies on the load side or by lack of fatigue strength of, for example, orthotropic bridge decks? Yes, UHPC surface courses can be used as a protective barrier against aggressive substances such as chlorides. They can also be load-bearing and contribute to improved bearing capacity while providing durability. In addition, a single layer can replace the foundation of multiple layers required for sealing and trafficability. The following article shows the potential of such UHPC layers for improving existing bridges, be they concrete or steel bridges.

Experimental and numerical study on flexural behaviors of damaged RC beams strengthened with UHPC layer using the bonding technology of post-installed reinforcing bar

Due to the outstanding mechanical and durability properties, Ultra-high performance concrete (UHPC) has been popularly used for strengthening of existing reinforced concrete (RC) beams. To improve the reliability of UHPC strengthening RC beams and enhance the effectiveness of its usage on site applications, bonding technology of post-installed reinforcing bar was proposed to connect the RC beams with UHPC layers. In this paper, a push-out test program was firstly carried out to study the shear properties of interface between UHPC and normal strength concrete (NSC) using the post-installed reinforcing bar connection technology, and to select suitable embedment length of the post-installed reinforcing bar in UHPC layer. Then, a bending test program consisted of three damaged RC beams strengthened with UHPC layers and one control RC beam was conducted to investigate the flexural behaviors of the damaged RC beams strengthened by UHPC layers using the bonding technology of post-installed reinforcing bar. Thereafter, three-dimensional FE models were developed to simulate the flexural performance of the strengthened RC beams, and the crucial parameters were investigated. The results of the present study revealed that the strengthening with reinforced UHPC layers could effectively improve the cracking and flexural performance of damaged RC beams. All the strengthened beams using the bonding technology of post-installed reinforcing bar failed in the typically flexural failure and no obvious interface cracks caused by the interface connection were observed throughout the bending test process.

Fatigue behavior of reinforced UHPC-NC composite beams

Ultra-high-performance concrete (UHPC) can be strategically applied in the lower part of a beam and combined with normal-strength concrete (NC) to achieve a more cost-effective design. The purpose of this research was to assess the effects of the UHPC layer thickness, reinforcement ratio, reinforcing bar type, and load level on the enhancement of the fatigue performance, as well as their interaction effects on the contribution of the UHPC layer. Four-point bending tests were conducted on eleven 500-mm-deep and 4400-mm-long T-beams under cyclic and monotonic loading. The test results indicated that the fatigue performance of the beam is strengthened by increasing the UHPC layer thickness, whereas the efficiency of the strengthening decreased as the thickness increased from 200 to 360 mm. The benefits of the UHPC layer on the fatigue resistance was magnified as the load levels decreased, which was also influenced by reinforcement ratio and reinforcing bar type. A method of deflection prediction was suggested, considering the contribution of the UHPC layer and effect of cyclic loading. Meanwhile, a fatigue relationship was established for reinforced UHPC-NC beams.

High-velocity projectile impact resistance of reinforced concrete slabs with ultra-high performance concrete strengthening - A numerical study

This paper adopted numerical simulations to explore the high-velocity projectile impact (HVPI) performance of 180 mm thick reinforced concrete (RC) slabs with ultra-high performance concrete (UHPC) strengthening. Finite-element modelling of the RC slab and UHPC layer subjected to HVPI was firstly performed to verify the numerical model related to the local damage and projectile residual velocity. Then, the slab configuration parameters concerning the steel rebar layer number and grid size in the UHPC layer, the spacing between the RC slab and UHPC layer, and the layout positions of the UHPC layer were investigated to determine the optimal strengthening strategy to resist projectile perforation. The numerical results demonstrated that snugly placing the UHPC layer without steel rebars upon the impact face of the RC slab was the most effective and efficient strengthening strategy. With the optimal slab configuration, the influences resulting from the unconfined compressive strength of UHPC, projectile mass and nose shape on the projectile perforation of UHPC strengthened RC slabs were explored. For each influencing factor, the relations between the projectile residual velocity and UHPC layer thickness were obtained at various projectile striking velocities. In the light of the simulated data, an empirical formula was established to estimate the ballistic limit of the 180 mm thick RC slab with UHPC strengthening..

A novel analytical model coupling hydrodynamic-structural-material scales for very large floating photovoltaic support structures

Floating solar farms are emerging as a viable option for large-scale solar power production. Considering the sustained wave action and the low deadweight of solar power components, a lightweight and high-stiffness floating platform, composed of an ultrahigh performance concrete (UHPC) surface panel and an expanded polystyrene (EPS) geofoam bottom panel, was designed as a large area and controllable cost bilayered structure. An analytical model coupling hydrodynamic-structural-material multiple scales was proposed for the highly efficient and accurate design of the floating structure. The microstructural and elastoplastic parameters of the UHPC were coupled utilizing the representative volume element (RVE) method, in which the parameterized relations between the microscale configuration and homogenized elastoplasticity of materials were obtained. For the coupling material-structure analysis, an equivalent homogenized model for the dynamics of the floating bilayered structure was deduced according to the heterogeneous interface continuity condition, in which the microstructures of the UHPC layer were introduced through the parameterized relations. A novel hydrodynamic theoretical model coupling of the macro-wave action, mesostructure, and micromaterial was established through this equivalent dynamics method. As an illustration, this hydrodynamic-structural-material coupled analytical model was utilized to design and optimize floating photovoltaic support structures. The dynamic responses and internal strain of a floating bilayer structure were directly calculated, and the plastic area was predicted and optimized for a smaller amplitude, which relied on the interactivity of the material configurations, structural parameters, bilayered features, and wave conditions. The results from the theoretical model not only realized the analysis and optimization of floating structures but also demonstrated that the hydrodynamic-structural-material coupled analytical model has great potential for designing large floating structures of solar photovoltaics.

Flexural behavior of damaged RC beams strengthened with prestressed UHPC layer

Based on ultra-high-performance concrete (UHPC) and prestressed technique, a new flexural strengthening technology using a prestressed UHPC (PUHPC) layer for the damaged reinforced concrete (RC) structure was proposed in this study. To investigate the flexural strengthening efficiency of PUHPC layer, the bending tests of six beams were carried out in this study, including four PUHPC strengthened RC beams with different pre-damaged degrees (PUB), one reinforced UHPC (RUHPC) strengthened control beam (RUB) and one unstrengthened RC control beam (CB). The experimental results showed that the PUB was typical bending failure. The cracking load and ultimate load of PUB increased by 145% to 190% and 90% to 94% compared with that of CB respectively. Similarly, 98% and 38% of improvement of the characteristic loads comparing with RUB were observed. Moreover, the post cracking stiffness of PUB were significantly improved compared with CB and RUB, while the ductility indexes were decreased. However, with the increase of the pre-damaged degree of RC beam, the cracking resistance, flexural stiffness and ductility of PUB decreased correspondingly. It is worth mentioning that the interface between PUHPC layer and RC beam has a high bond strength, and the slight slip at the interface did not lead to debonding failure during the bending test. Also, the calculation model for predicting the ultimate flexural capacity of PUB was developed, which yielded promising predictions with reasonable accuracy.

Key Design Parameters Analysis and Calculation Theory Research on Bending Performance of Steel–UHPC Lightweight Composite Deck Structure

This paper aims to study the influence of key design parameters (e.g., reinforcement ratio, cover thickness, stud spacing, and thickness of the ultra-high-performance concrete (UHPC) layer) on the longitudinal and transverse bending performance, as well as the cracking load and ultimate bearing capacity calculation theory of steel–UHPC lightweight composite deck (LWCD) structure. Four transverse bending tests and four longitudinal bending tests on steel–UHPC composite plates and steel–UHPC composite beams were conducted, respectively. The refined finite element models of components with different key design parameters based on ABAQUS were established. The influences of different key design parameters on the transverse and longitudinal flexural behaviors (e.g., load-mid-span displacement curve, cracking stress, stiffness, elastic limit load, critical slip load, ultimate bearing capacity and ductility) were compared and analyzed in detail. The ultimate bearing capacity can be improved by increasing the thickness of UHPC layer and the reinforcement ratio of longitudinal reinforcement, and reducing the cover thickness and the spacing of studs. According to the longitudinal bending characteristics of the steel–UHPC lightweight composite deck structure, the calculation formulas for the cracking load and the ultimate bearing capacity of the steel–UHPC composite beam are proposed, and the calculated values are in good agreement with test results (the errors are basically within 10%), which is convenient for practical engineering applications.

Effect of early‐strengthening of RC beams using UHPC layers on their performance against reinforcement corrosion

AbstractIn the present work, the effect of early‐strengthening of reinforced concrete (RC) beam specimens using layers of ultra‐high performance concrete (UHPC) on their performance against reinforcement corrosion was examined. A number of fifteen RC beam specimens were prepared, one beam specimen uncorroded and unstrengthened was considered as a control beam, two beams were corroded and unstrengthened, and twelve corroded and strengthened beam specimens that were divided into two groups. RC beam specimens of the first group were corroded continuously to cause total theoretically targeted mass losses of the steel rebars and then strengthened using UHPC layers. RC beams of the second group were also corroded to the same degrees but in two steps. In the first step, the beams were corroded to cause a portion of targeted theoretical mass losses. Then the beams were strengthened in the same way as the beams of the first group and then subjected to second‐step accelerated reinforcement corrosion to achieve finally the same degrees of total theoretical mass losses as that of the first group. The corroded and strengthened beam specimens were exposed to flexural testing, and then the corroded rebars extracted from the beams were used to conduct gravimetric tests to determine the actual values of the mass losses due to accelerated corrosion. The gravimetric and flexural tests' results were used mainly to observe the influence of early‐strengthening on the actual mass loss and the flexural behavior of the tested beam specimens. Results showed a significant reduction in the values of the actual mass loss and better flexural behavior due to the early‐strengthening of the corroded beams. An analytical model, developed and validated using the data collected from the experimental tests, can be utilized to predict the ultimate load‐carrying capacities of the corroded strengthened RC beam specimens.

Flexural Reinforcement of Over-Reinforced Beam by Ultrahigh Performance Concrete Layer

In order to improve the failure state of over-reinforced beams and enhance their ductility, an innovative reinforcement method was proposed by adding an ultrahigh performance concrete (UHPC) layer on the top surface of the over-reinforced beam to take advantage of the high compressive strength of UHPC. The numerical simulation method was used to carry out the research. The validity of the finite element model was verified by comparing it with the experimental results, and the effectiveness of the new reinforcement method was verified by comparing it with the calculation results after adding the UHPC layer. Then, a detailed parameter study was carried out, including the thickness of the UHPC layer, the cross-section area of longitudinal tension rebar, and concrete strength. The load-deflection curve, flexural bearing capacity, and deflection ductility coefficient were studied. The results show that the bearing capacity of the UHPC-reinforced over-reinforced beams is significantly increased by 88.1%. And the stiffness and ductility of the beams are also significantly increased, with the ductility coefficient reaching 23.85. In addition, flexural bearing capacity increases with the thickness of the UHPC layer and sectional area of longitudinal tension rebar. Finally, a prediction model for the flexural bearing capacity of UHPC layer-reinforced over-reinforced beams is proposed, which further verifies the effectiveness of this method.

Fatigue Performance of Steel–UHPC Composite Bridge Deck System with Large Longitudinal Rib

A critical problem in the development and application of orthotropic steel bridge decks (OSDs) is fatigue cracking, which is determined by the deck’s structural system, mechanical characteristics, load, and external environmental factors. The development of bridge deck systems with high fatigue resistance is increasingly gaining interest in the field of bridge deck design. An effective method for improving the fatigue life of OSDs is the introduction of an ultra high performance concrete (UHPC) layer to enhance OSD’s stiffness. In this study, two types of experiments were performed to investigate the transverse and longitudinal fatigue behaviors of a steel–UHPC composite bridge deck with large longitudinal ribs. The experiments show that the application of a 70-mm-thick UHPC layer effectively reduces the stress intensity at key fatigue details in OSDs. The influence of the UHPC layer on the OSD fatigue performance was evaluated by experiments and finite element analysis. After the formation of microcracks on the UHPC surface layer, the composite bridge deck system continued to exhibit adequate fatigue performance. Moreover, the effects of damage accumulation on the UHPC layer and studs in transverse specimens were evaluated.