Ultra-high Performance Concrete Bridge Research Articles

Comparative sustainability and seismic performance analysis of reinforced conventional concrete and UHPC bridge piers

Ultra-high performance concrete (UHPC) boasts excellent mechanical properties, but it comes at a high cost and has a significant environmental impact. This study conducts a comprehensive life-cycle analysis (LCA) on reinforced concrete bridge piers to investigate the environmental implications of integrating conventional concrete (CC) and UHPC in seismic design. The analysis covers both materials and members. At the material level, the global warming potential (GWP) from UHPC manufacturing is calculated using a comprehensive database that includes UHPC mixture details, fiber quantity, geometry, mixing and curing processes, loading age, and compressive strength. At the member level, seismic performance is assessed through capacity-to-demand ratios of strength and ductility. A total of 1280 CC and 2240 UHPC bridge piers are virtually tested with comparable functional unit values, and their GWPs are calculated. The study reveals a proportional relationship between GWP per m3 of UHPC manufacturing and its compressive strength. The GWP of CC and UHPC piers designed using the strength-based approach increases with the capacity-to-demand ratio. When the capacity-to-demand ratio is relatively large, the GWP exhibits rapid nonlinear growth. Adding more reinforcement to achieve a higher capacity-to-demand ratio is inefficient. Moreover, both CC and UHPC piers designed using the ductility-based approach show no strong correlation between GWP and the capacity-to-demand ratio. Surprisingly, using a higher grade of UHPC does not improve seismic resistance; instead, it leads to increased GWP. Effective strategies, such as reducing cross-sectional area and increasing the reinforcement ratio, prove beneficial in enhancing material efficiency and reducing GWP. Additionally, the utilization of a specific pipe section enhances material efficiency, improves seismic resistance, and results in lower GWP.

Concept and flexural performance of non-prestressed steel plate-UHPC-NC composite girder bridge

A novel non-prestressed composite girder bridge, incorporating steel plates, ultra-high performance concrete (UHPC), and normal concrete (NC), is proposed for small and medium-span bridges. For the proposed steel plate-UHPC-NC composite bridge, UHPC girders are reinforced with steel plates on the bottom in lieu of part of closely-spaced rebars in the beam. Cast-in-situ NC deck slab is adopted to ensure its transverse integrity and to reduce costs in comparison with UHPC bridge deck. To verify the performance of the proposed novel composite bridge, three types of UHPC-NC composite beams with same reinforcement ratio (reinforced with only rebars, only steel plates, both rebars and steel plates) were first conducted with bending test. The impact of various reinforcement types on the flexural behaviors of UHPC-NC composite specimens was identified, including failure mode, crack distribution pattern, and crack width development. The findings demonstrated that the UHPC girder reinforced with both steel plates and rebars would significantly enhance the crack resistance of UHPC girders during bending in comparison with the other two. In addition, the composite girder reinforced with steel plates and rebars can achieve a nominal stress of 31.41 MPa at the serviceability limit state (with a UHPC crack width of 0.05 mm). The commercial software DIANA is then utilized to numerically simulate the mechanical properties of the proposed composite beam. The deviation between the finite element (FE) results and the experimental load-bearing capacity is within 1.9 %. Parameter analysis demonstrates that the bridge deck's strength has negligible influence on the load-carrying capacity of the proposed composite beam. Finally, a design scenario for a 30 m-span simple-supported bridge is conducted, and the initial cost analysis indicates that the proposed steel plate-UHPC-NC composite girder is 2 % lower than the conventional prestressed concrete T-girder. The proposed non-prestressed steel plate-UHPC-NC bridge presents notable benefits, including cost-effectiveness, strong crack resistance, and the prospect of complete prefabrication, offering a feasible alternative for small and medium-span bridges.

Performance-based seismic design of Ultra-High-Performance Concrete (UHPC) bridge columns with design example – Powered by explainable machine learning model

Ultra-high-performance concrete (UHPC) has rapidly become a material of choice in modern construction owing to its favorable properties, such as superior strength, toughness, and durability. Yet, accurate quantification of damage states using appropriate engineering demand parameters (EDPs) remains a significant challenge in the performance-based seismic design (PBSD) of UHPC columns. This gap is especially evident in the scarcity of research focused on the PBSD of UHPC columns. Therefore, this study aims to develop an explainable machine learning (ML) powered predictive model for the drift ratio limit states of UHPC bridge columns across four damage states. To achieve this, a fiber-based numerical model was developed and then validated against large-scale experimental results of UHPC columns tested under reverse cyclic loading. The Latin hypercube sampling method is employed to generate a comprehensive database of UHPC bridge columns (10,000 UHPC columns), considering uncertainties across a spectrum of design factors, including column geometry, material characteristics, reinforcement ratio, and axial load ratio. The drift ratios at the initiation of four damage states are determined using the numerical model. Subsequently, the power of the ML algorithm is leveraged to introduce drift ratio limit states for UHPC columns that capture the onset of four different damage states. The efficacy of the developed model is assessed using a range of statistical metrics, including the composite fitness score, DX% metrics, coefficient of determination, root mean squared error (RMSE), normalized RMSE, and mean absolute error, which demonstrated high predictive accuracy of the drift ratio limit states on both the training and unseen or test datasets. Furthermore, a model-agnostic Shapley Additive exPlanation (SHAP) is used to explain the output of the model and examine the influence of various design factors on drift ratio across the damage states. Notably, the axial load ratio and aspect ratio are found to be major factors in determining the drift ratios across the damage states. The developed model is deployed into a software tool in order to enable its practical application. Additionally, the implementation of the developed model in the context of PBSD is illustrated through a design example. Furthermore, the study proposed capacity uncertainty parameters to aid the fragility assessment of UHPC columns. Finally, the proposed model, along with capacity uncertainty parameters, is used for the fragility assessment of UHPC columns reinforced with varying steel bar grades. The results demonstrate the less vulnerability of UHPC columns reinforced with higher bar grade, yet the effect of bar grade lessens at severe damage levels.

Modeling life expectancy and cost effectiveness for UHPC bridge retrofitting techniques

Bridge components are subject to both structural loads and environmental stressors, rendering them susceptible to accelerated deterioration and potential collapse in the absence of effective maintenance and rehabilitation strategies. Moreover, the phenomenon of wet-dry cycling, coupled with elevated chloride concentrations prevalent in coastal regions, further expedites the degradation process of bridges, thereby escalating maintenance frequency and repair costs. In response to this challenge, the integration of innovative materials such as Ultra High-Performance Concrete (UHPC) is being explored for the development and implementation of maintenance and rehabilitation strategies. This study presents a comparative analysis between conventional methods and UHPC applications for bridge repairs, utilizing Life Cycle Cost Analysis (LCCA) to encompass both agency and user costs, and applies Monte Carlo simulation to account for the variability of the modeling factors. A practical case study illustrates the applicability of the LCCA methodology, revealing that the utilization of UHPC contributes to a reduction in the total life cycle cost for bridge maintenance and rehabilitation. Life expectancy, Average Daily Traffic (ADT), and the duration of construction activities during rehabilitation emerge as the most influential factors affecting life cycle costs. The main contributions of the study are the development of the life-expectancy model and step-by-step Life-Cycle Cost Analysis (LCCA) methodology. Findings from this study aim to identify cost-effective retrofitting techniques for maintaining bridges in a “State of Good Repair.”

Shear performance of headless studs in ultra-high performance concrete bridge deck

Conventional stud connectors were proved to be inconvenient for the later disassembly and replacement in ultra-high performance concrete (UHPC) bridge decks. In this study, the headless studs which is a type of studs with their heads removed were employed as a substitute for conventional stud connectors, aiming to enhance the detachability of the bridge decks on the premise of ensuring the anti-lift bearing capacity of the decks. Three push-out specimens containing the headless studs with a diameter of 13 mm were carried out to study the mechanical properties of headless studs. In addition, the finite element model was developed to reveal the failure mechanism of headless studs in UHPC. Results indicated that the load-slip curve of headless stud connector can be divided into elastic stage, plastic stage and failure stage. The failure mode of headless studs was the shear fracture at the root of stud shank. Headless stud connections under cyclic loading can produce greater plastic deformation. The ultimate shear capacity and shear stiffness of headless studs were lower than those of conventional studs. Additionally, the UHPC slabs configured with headless studs have a small quantity of separation at the steel-UHPC interface, so it is suggested to use headless studs and conventional studs together in UHPC slabs to ensure the necessary anti-lift bearing capacity. Finite element analysis indicated that in the elastic stage, the bearing capacity of the push-specimen was dominated by the material properties of the headless stud. After entering the plastic stage, the bearing capacity of the push-specimen was mainly controlled by the UHPC below the headless stud.

Investigation on shear behavior of large diameter short stud connectors in steel- thin UHPC bridge deck

Ultra-high performance concrete (UHPC) is a promising alternative for improving the mechanical performance of the steel and reinforced concrete composite bridge deck. Because of the excellent compression and tensile strength as well as the superior durability, the thickness of the UHPC slab can be effectively reduced. Therefore, large diameter short headed stud connector was proposed in this study to match the thin UHPC slab. To investigate the shear behavior of the large diameter headed studs in steel-thin UHPC composite bridges, 6 groups of 12 push-out specimens were designed and tested under the static loading. During the test, the failure mode, load-slip curves, the ductility, shear stiffness and shear strength of the specimens were emphatically focused. Besides, the influences of the aspect ratio of the stud, the thickness of the UHPC slab and the number of the stud in one position on shear behavior of the specimens were evaluated. Furthermore, the ABAQUS software has been used to analyse the large diameter short stud. A proposed modelling strategy used for further parametric analysis was validated with the test results. For the parametric research, different aspect ratio of stud and ultimate strength of stud were evaluated. Test and FEM results showed that the specimens failed in the failure of the root of the stud and the crushing of the concrete. With the increasing of the diameter of the stud, the thickness of the UHPC slab and the ultimate strength of stud, the shear strength and the shear stiffness of the specimens increased. Under the same cross-sectional area of the stud, the shear behavior of a single large diameter short stud connector could be comparable to that of two conventional stud connectors. Finally, after evaluating the results obtained from existing formulas, a predictive equation for the shear bearing capacity of large diameter short studs was proposed, and the accuracy of the calculated results was verified.

Performance of UHPC bridge piers subjected to heavy vehicle collisions and probability analysis of damage level

Heavy vehicle collisions have been reported as one of the major causes of normal concrete (NC) bridge pier failure due to its low crashworthiness. Ultra-high performance concrete (UHPC), which has been demonstrated as a promising engineering material to resist high strain rate loadings, is deemed as an alternative material to improve the collision performance of bridge piers that would be impacted by heavy vehicles. In this study, the performance of the UHPC pier subjected to heavy vehicle collisions is investigated by using the finite element (FE) modelling approach. Firstly, the damage and energy absorption characteristics of NC and UHPC piers are comparatively studied. The results show that the NC pier is dominated by plastic failure, whereas the UHPC pier essentially presents brittle damage. The kinetic energy of the vehicle is mainly dissipated by the steel reinforcement for UHPC piers whereas by the concrete for NC piers. Then, a comprehensive parametric analysis, with respect to the vehicle weight and velocity, pier diameter, and longitudinal and transverse reinforcement ratios, is performed to investigate the impact performance of UHPC piers. An analysis of the Pearson correlation coefficient for the involved parameters shows that the vehicle weight and velocity are key influential parameters to the peak impact force. Finally, to facilitate the evaluation of the bridge column subjected to heavy vehicle collisions, three regression surrogate models, SVR (support vector regression), kriging, and RBF (radial basis function), are established to predict the equivalent static force (ESF) of the peak impact force on UHPC piers with promising accuracy. Among the presented five damage levels, the probabilities of slight and moderate damages are remarkably larger when UHPC piers are impacted by heavy vehicles. This study can provide guidance for the revision of AASHTO and future engineering practices with considering UHPC piers subjected to heavy vehicle collisions.

Behavior of Ultrahigh-Performance Concrete Bridge Decks with New Y-Shape FRP Stay-in-Place Formworks

Behavior of Ultrahigh-Performance Concrete Bridge Decks with New Y-Shape FRP Stay-in-Place Formworks

Bonding performance between ultra-high performance concrete and asphalt pavement layer

The bonding performance between the ultra-high performance concrete (UHPC) and asphalt pavement layers is crucial to prevent the interface of asphalt pavement and bridge deck from falling off. In order to improve the bonding performance between UHPC and asphalt pavement layers, the surfaces of UHPC specimens were treated using four different techniques: spreading gravels, spreading steel balls, pickings and grooving. Through the pull-out and shear tests, the bonding performance between UHPC and asphalt pavement layers was evaluated. The pull-out strength and shear strength were used to evaluate the influence of different surface patterns on the bonding performance between UHPC and asphalt mixture layers. Additionally, the MATLAB software was employed to extract the digital image characteristic parameters of UHPC surfaces, and the neural network was constructed using the characteristic parameters to predict the bonding performance between UHPC and asphalt pavement layers. Results show that the spreading gravels, spreading steel balls, broom picking, cutting machine picking and grooving can all improve the bonding performance. Among the techniques, the cutting machine picking has the most obvious improvement on the pull-out strength and shear strength. The accuracy of neural network prediction model is reliable, and the correlation between the predicted value and the measured value is high. The result is of great significance to enhance the bonding performance between UHPC bridge deck and asphalt pavement layer, thus improving the durability of UHPC bridge structures.

Numerical study on the seismic performance of precast UHPC bridge columns considering the buckling behavior of replaceable energy dissipaters

This paper aims to explore the seismic performance of a novel earthquake-resilient bridge column with replaceable elements, including external ultra-high-performance concrete (UHPC) cover plates and internal steel dissipaters, based on a numerical model including local and overall levels. The overall model was established to assess the seismic behavior of the bridge columns considering the buckling behavior of steel dissipaters adopting the modified material constitutive relationship, of which the parameters were determined according to the results of the local model. The numerical model was verified with reported experimental results. A parametric analysis was conducted to investigate the effects of three parameters. The results show that the numerical model can effectively evaluate the seismic performance of the bridge columns. The buckling behavior of steel dissipaters dominates lateral deformation capacity of the bridge columns. The steel dissipater's initial defect direction and gap gradient can accelerate the failure of cover plates. Reasonable upper and lower limits are required for the length-to-diameter ratio of the fuse part as well as the gap between the fuse part and surrounding concrete, while only a suitable lower limit is needed for the thickness of cover plate to ensure the superior seismic performance of the bridge columns.

Fatigue performance of UHPC bridge deck system with field-cast dovetail joint

The Fifth Nanjing Yangtze River Bridge had adopted accelerated bridge construction utilizing precast systems to connect the prefabricated plate with the cast-in-place ultra-high performance concrete (UHPC) wet joint. Wet joints are prone to crack under fatigue load. In this study, the steel wire mesh (SWM) treatment method was adopted to enhance the interface crack resistance, and add coarse aggregate (CA) to UHPC to reduce cost. Decks were tested under static and fatigue loadings to study the effects of CA, SWM interface treatment, and stress level on fatigue performance. Results indicate that the fatigue performance of wet joints using UHPC with CA was similar to that using regular UHPC. Dovetail wet joints using SWM interface treatment effectively guarantee the bridging effect of the fiber at the interface and disperse fatigue cracks. Overloading affected the fatigue performance, and the fatigue damage was linear to the upper limit of stress when the stress ratio was fixed. Secant stiffness was used to evaluate the fatigue damage of decks, and the calculated damage was in good agreement with the actual bearing capacity loss. This study verified that the innovative dovetail wet joint is practical, economical, and guarantees fatigue performance.

A flexural design methodology for composite heterogeneous and homogeneous UHPC bridge beams prestressed with bonded strands

A non-iterative flexural design methodology for composite, heterogeneous, and homogeneous ultra-high performance concrete (UHPC) bridge beams prestressed with bonded strands is presented. One key feature of the proposed methodology is the development of closed-form equations for calculating strain in concrete at the most extreme compression fiber at the ultimate limit state, εc, as a function of various parameters. Separate formulations for predicting εc are provided for homogeneous and composite cross-sections. The predicted concrete strain, together with the maximum usable tensile strain for UHPC, εtu, at the most extreme tension fiber are used to calculate cross-sectional curvature and the distribution of strains and stresses. Force equilibrium is then used to determine the depth to the neutral axis and the nominal moment capacity of the beam. The flexural failure mode for the majority of beams considered is a fiber tension controlled failure. From a beam flexural strength perspective, the compressive strength of the deck or top flange for composite and heterogeneous beams, respectively, does not need to exceed 28 MPa. Any excess compressive strength will remain either unutilized or will result in marginal or negligible increases in moment capacities. The magnitude of the cracking strength of UHPC plays an important role in the contribution of UHPC to the moment capacity of the beam and determines whether this contribution is higher or smaller than that provided by the prestressing strands. The strand stress at the ultimate limit state, fps, varied from 1688 MPa to 1743 MPa and was past the linear elastic branch of the assumed stress-strain curve. The parameter that had the highest influence on fps was εtu. The proposed methodology is validated using test data as well as results from validated nonlinear finite element models and strain compatibility analysis.

Concrete Bond and Behavior of Nonproprietary Ultrahigh-Performance Concrete Bridge Slab Joints

The purpose of this study was to evaluate a nonproprietary ultrahigh-performance concrete (UHPC) mix design in terms of bond strength and behavior as a slab joint material. Composite modulus of rupture and direct pull-off tests were conducted to evaluate bond strength using sandblasted, wire-brushed, and exposed aggregate substrates. The two methods for obtaining a saturated substrate included covering the substrate with wet burlap or power washing the substrate and either leaving pooled water or patting the surface dry. In addition, several specimens were constructed by joining two full-scale normal strength concrete slabs with a UHPC joint containing shortened reinforcing bar embedment lengths. These specimens were used to evaluate structural behavior when subjected to both static and cyclic loadings. Each test was compared to an identical test using the proprietary UHPC product Ductal. Bond testing showed that power washing of the substrate was required to produce comparable bond strengths to Ductal. For full-scale slabs, the nonproprietary mix performed comparably to Ductal as a bridge joint material, despite having lower compressive strength.

Probabilistic seismic vulnerability and loss assessment of a seismic resistance bridge system with post-tensioning precast segmental ultra-high performance concrete bridge columns

Precast segmental ultra-high performance concrete (UHPC) columns with post-tensioned (PT) tendons can effectively protect the compression toe from damage and enhance energy dissipation (ED) capacity of column compared to conventional segmental concrete columns. Extensive experiments and numerical studies have been carried out to explore the cyclic response of segmental UHPC columns in the existing literature; however, the effect of such novel columns on the seismic safety of bridge structures has not been thoroughly understood. This study aims to numerically assess the seismic fragility and seismic life-cycle loss of bridge structures supported by the precast segmental UHPC columns. For comparison, the seismic performance of the same bridge with monolithic reinforced concrete (RC) piers are also evaluated. Here, three-dimensional (3D) numerical models are generated to simulate these two bridge types. A performance-based earthquake engineering (PBEE) framework is used to evaluate and compare their seismic performance. The segmental UHPC column model is validated with the previous experimental studies. The validated model is combined into the whole bridge. Numerical results showed that the precast segmental UHPC bridge experiences similar peak acceleration and larger peak displacement in comparison to the monolithic RC bridge. The segmental UHPC bridge pier experiencing lower residual deformation can effectively reduce the damage probability and life-cycle loss of a bridge compared to the conventional monolithic RC pier. Under the design event (2475-year return period) and maximum considered event (5000-year return period), the expected losses of the segmental bridge in the lifetime were approximate 92% and 84% of that of the monolithic bridge, respectively. The segmental UHPC bridge has a noticeable economic benefit when such a bridge is constructed in regions of high seismicity.

Numerical modeling and design sensitivity of structural and seismic behavior of UHPC bridge piers

Advanced behavior of Ultra-high performance concrete (UHPC) is attracting a growing interest among the construction industry worldwide. Currently, UHPC is commonly used in precast bridge deck joints and connections. As the UHPC market grows, the material will have a great potential to extend to larger structural applications. However, there is no guidance yet on best practices or optimum structural designs that fully utilize the UHPC superior mechanical properties for larger components. The objective of this study is to better understand the overall behavior, failure mechanism, and effect of reinforcement and design details of UHPC bridge columns using detailed finite element modeling. The pushover response of a two-column bridge pier with the typical geometry and gravity loads obtained from a representative California bridge is investigated when UHPC is used instead of conventional concrete for the columns. A detailed sensitivity/parametric analysis is conducted to assess the effect of different steel fiber ratio, longitudinal reinforcement ratio, and steel grades of reinforcement bars on the overall structural behavior of the columns. The total strain crack model, as readily implemented in DIANA FEA, is utilized with user-defined input to model the UHPC constitutive material behavior. The UHPC stress-strain relationships in tension and compression are independently defined using uniaxial curves from the literature. For comparison, the two-column bent of conventional concrete is modeled and used as the reference case to evaluate the relative increase in load capacity of the UHPC bridge columns.

Design criterion for the self-centering capacity of precast segmental UHPC bridge columns with unbonded post-tensioning tendons

This paper aims to provide a novel quantitative design criterion for the self-centering (SC) capacity of precast segmental ultra-high performance concrete (UHPC) bridge columns based on the concept of the SC factor, which is deemed capable of depicting the formation mechanism of residual drift. A refined numerical model was developed to simulate the seismic performance and was verified by the results of the cyclic loading test. Parametric analysis was conducted to research the influence of seven common design parameters on the SC factor based on the proposed numerical model. According to the results of the parametric analysis, a simplified formula was established to assess the residual drift when the SC factor and the maximum drift were known. Nonlinear dynamic analysis was conducted to validate the simplified formula for precast segmental UHPC bridge columns subjected to far-field, no-pulse near-field, and pulse near-field earthquake motions. A design criterion for the SC capacity was proposed based on the SC factor limits determined by the simplified formula. Research results show that the SC factor corresponding to the ultimate drift is generally conservative for assessing the SC capacity of precast segmental UHPC bridge columns. The residual drift is dependent on the SC factor and the maximum drift. The residual drift decreases with the increasing SC factor or decreasing maximum drift. The proposed formula is verified by the results of nonlinear dynamic analysis to be conservative to calculate the residual drift. According to the proposed design criterion, the SC factor limits are increased with the drift demand up at the same earthquake design level. The adverse effects of pulse near-field earthquake motions on the earthquake resilience of precast segmental UHPC bridge columns should be taken seriously.

Field Testing of a Prestressed Concrete Bridge With High Performance and Locally Developed Ultra-High Performance Concrete Girders

Recent research has developed mixture proportions for ultra-high performance concrete (UHPC) using materials primary local to New Mexico, United States of America (USA). In 2017, a two-span bridge was constructed in Anthony, New Mexico, USA consisting of prestressed girders using the locally developed non-proprietary UHPC, for span one, and high performance concrete (HPC), for the second span. Field tests were conducted on the bridge approximately nine months apart to investigate the performance and behavior of the UHPC and provide baseline data for future studies and condition evaluation of the bridge. The load tests consisted of various load configurations utilizing up to four trucks weighing 267 kN on average. The load paths were designed to maximize strains along the length of the bridge and investigate transverse load distributions between girders. The measured results provide a comparison of the behavior and performance of the UHPC and the HPC girders and were also compared to the American Association of State Highway and Transportation Officials (AASHTO) predicted behaviors. This study is one of the first that compares HPC and nonproprietary UHPC bridge performance subjected to the same environmental conditions and vehicular loading. The findings of the study will aid in the development of recommendations incorporating UHPC into design provisions as well as provide meaningful information of the short and long-term performance between the two materials including durability and load distribution.

Flexural behavior of an innovative dovetail UHPC joint in composite bridges under negative bending moment

The 5th Nanjing Yangtze River Bridge is a three-tower cable-stayed bridge with a main span of 600 m and a composite cross section consisting of a steel box girder- and precast ultra-high performance concrete (UHPC) deck slab. The precast UHPC slabs are connected using cast-in-place UHPC, and joints between the UHPC slabs are prone to cracking under negative bending moment. This paper investigates the flexural behavior of an innovative dovetail UHPC joint in seven UHPC slabs under negative bending moment. An innovative method using steel wire mesh is presented to enhance the interface between precast and cast-in-place UHPC at the joints. Test parameters of the UHPC slabs included interface treatment method, joint material, reinforcing bar overlapping form, and prestressing level. The steel wire mesh generated fibers that bridge the interface between the precast and cast-in-place UHPC, thus significantly enhancing the mechanical performance of the jointed UHPC slabs: (1) the nominal cracking strength was increased by 2.4 MPa; (2) the post-cracking stiffness was retained at about 80% of the initial stiffness; (3) the ultimate stiffness was retained at about 35% of the initial stiffness; and (4) closely-spaced multiple cracks occurred at the joints. A new ductility index defined as the ratio of the ultimate deflection and the flexural cracking deflection is proposed to characterize the post-cracking ductility. The research findings are useful in understanding and improving the flexural behaviors of UHPC bridge decks subjected to negative bending moment.

Experimental Study on Basic Performances of Reinforced UHPC Bridge Deck with Coarse Aggregates

In order to reduce the self-weight of conventional steel-concrete composite girders and to improve the crack-resisting behavior of normal strength concrete (NC) bridge decks for long-span cable-stayed bridges, an innovative steel–ultrahigh performance concrete (UHPC) composite girder was proposed. Coarse aggregates (CA) were added to UHPC to control shrinkage and cost. On the basis of the Fifth Nanjing Yangtze River Bridge (FNYRB), a 2 × 600 m cable-stayed bridge in China, a series of experimental tests was conducted. The studies aimed to reveal the material properties of UHPC with and without CA and the static and fatigue flexural performances of the reinforced UHPC deck with CA. The test results implied that the UHPC with CA had compressive strength and flexural strength comparable to UHPC without CA, but the former exhibited much lower shrinkage strains under the natural curing condition. The static bending test results showed that the steel fibers and steel reinforcement bars could effectively control the propagation of cracks in UHPC. The average nominal cracking strength of the UHPC bridge deck specimens was 13.8 MPa, about 1.97 times the maximum tensile stress in the design requirement of the FNYRB under serviceable design loads. Further, the fatigue bending test results demonstrated that the cracks in UHPC propagated very slowly under cyclic tensile stresses, and the residual flexural loads were only 7.2% and 10.9% lower than the ultimate loads obtained for specimens free from the fatigue loading processes. Thus, the current study verified the safety of applying UHPC with CA to long-span cable-stayed bridges.

Feasible region of post-tensioning force for precast segmental post-tensioned UHPC bridge columns

This paper aims to establish an analytical method to determine the feasible region of post-tensioning (PT) force for precast segmental post-tensioned ultra-high performance concrete (UHPC) bridge columns. Three principles, i.e. no collapse after earthquake, good self-centering capacity, and no shear failure at joints, were put forward to define the feasible region of PT force according to the ultimate state. A calculation procedure was developed to determine the ultimate state and verified by a validated finite element model. With the ultimate state known, an analytical method was established to calculate the feasible region of PT force according to the three principles. Parametric analysis was conducted to quantitatively study the effects of eight common design parameters on the feasible region of PT force. A noniterative calculation method was further given to determine the feasible region of PT force for designers. The results show that the calculation procedure can accurately predict the characteristic values at the ultimate state. There are significant effects of the eight design parameters on the feasible region of PT force, which is actually controlled by the two former principles. The gravity loading can provide sufficient shear resistance at joints without shear keys in general. The feasible region of PT force is mainly distributed between 0.10 and 0.20 for precast segmental UHPC bridge columns with an area ratio of energy dissipation (ED) bars of more than 1.00%. The feasible region of PT force does not exist when the ED bar ratio is more than a critical value (i.e., 2.83% in this research). A noniterative and conservative calculation method to determine the feasible region of PT force can be obtained when the compression zone height of the bottom section at the ultimate state is equal to the wall thickness of the hollow section.