Ultra-high Performance Concrete Joint Research Articles

Experimental investigations on the flexural behavior of UHPC wet joints for UHPC light-weight rigid frame arch bridges

Wet joints are critical parts of prefabricated ultra-high-performance concrete (UHPC) light-weight rigid frame arch bridges (LWRFAGs), so their mechanical behavior is important to the structural design and applications of these arch bridges. To explore suitable joint configurations and reinforcement arrangements for connecting UHPC components or arch ribs of a practical UHPC LWRFAG, this paper experimentally investigated flexural behavior of several prefabricated UHPC joint beams with various kinds of wet joints through four-point bending tests. Firstly, four different UHPC joint beams with different joint configurations were designed, including (i) vertical joint; (ii) rhombus joint; (iii) vertical joint with top and bottom strips; and (iv) rhombus joint with top and bottom strips, and their flexural performance were compared with a complete UHPC beam. The experimental results revealed that UHPC joint beam employing the rhombus joint with top and bottom strips exhibited superior flexural behavior and cracking resistance among four UHPC joint beams. Subsequently, to achieve optimal and robust joint configurations, bending performance of one complete UHPC beam and three large-scale UHPC joint beams with rhombus joints but different reinforcement arrangements were experimentally studied. It is observed that the beam with the welded twist reinforcements (specimen V-4) shown optimal flexural performance and cracking resistance. Finally, to explore the load transfer mechanism and effects of reinforcement parameters on flexural behavior of specimen V-4, the parametric studies were comprehensively performed using finite element analyses (FEA). This study could serve as both the experimental and theoretical reference for flexural design of UHPC beams with the rhombus wet joints.

Interpretable ensemble machine learning models for predicting the shear capacity of UHPC joints

Precast ultra-high-performance concrete (UHPC) structures (PUSs) have gained increasing research and application interest in civil engineering owing to the combination of advanced construction materials and methods. UHPC joints are critical parts of PUSs; thus, an accurate prediction of their shear capacity (SC) is essential to ensure structural safety and reliability. However, existing equations for predicting SC have limited accuracy and applicability owing to their simplified assumptions and restricted input parameters. To address these challenges, this study used machine learning (ML) approaches to develop a unified and accurate predictive model for various types of UHPC joints. A well-curated database containing 218 UHPC joints with diverse types and configurations was established. Six ensemble algorithms and four traditional algorithms were employed to develop predictive models, and eight existing equations were compared for performance evaluation. Both correlation-based and SHAP-based feature selection methods were used to optimize the model accuracy. The ensemble algorithms demonstrated better performance than the traditional individual algorithms, with the gradient boosting machine (GBM) model ranked as the best ML model for SC. The ML model outperformed existing equations in all evaluated metrics, demonstrating its accuracy and robustness. Furthermore, Shapley Additive exPlanations (SHAP) analysis was employed to interpret the ML model, thereby providing insights into influential features and their relationships. These findings demonstrate the advantages of ML methods in predicting the SC of UHPC joints and provide valuable guidance for the structural design and research on PUSs.

Reinforced ECC-UHPC-SCC composite modular framed shear wall systems under lateral cyclic loading

The shear strength and deformability of high performance reinforced composite framed shear wall systems made of Engineered Cementitious Composite (ECC), Ultra-High-Performance Concrete (UHPC) and Self-Consolidating Concrete (SCC) subjected to lateral cyclic shear loading to failure were investigated. A total of seven framed shear wall specimens were constructed using combinations of ECC or SCC wall, SCC frame and ECC or UHPC frame joints. The performance of such novel modular forms of walling systems were compared based on experimental results in terms of cracking, failure mode, hysteretic shear load-deformation response, shear load capacity, ductility, bearing capacity degradation, stiffness degradation, dissipated energy, viscous damping capacity, induced wall shear stresses and strain development characteristics. ECC walling system exhibited better structural performance compared to their SCC counterparts showing up to 40% higher load capacity forming significantly higher number of closely spaced diagonal cracks with up to 72% lower crack shear stress, 14% to 21% higher ductility, up to 2 times higher energy dissipation capacity and lower rate of stiffness/bearing capacity degradation through both hysteretic and damping actions. The incorporation of ECC and ECC or UHPC joint in frame significantly improved shear strength capacity of infill wall and overall framed shear wall system. ECC incorporated framed shear walls even with frames made of SCC and UHPC joints also exhibited superior performance. This study confirmed the superior performance of ECC material for the construction of reinforced framed shear wall with boundary frame made of ECC/SCC/UHPC combinations for better seismic resistance.

Flexural performance of UHPC-filled narrow joints between precast concrete bridge slabs

The deck slabs narrow joints in concrete bridges filled with Ultra-high performance concrete (UHPC) have the potential for wide application and high-efficiency promotion, but there is limited research available on this topic. This paper conducted flexural tests on the new joints. Ten precast concrete deck panels were designed and manufactured for concrete bridges. These panels were connected using UHPC-filled narrow joints. Combined with stress analysis, this study investigates the influence and mechanism of various factors on the mechanical performance of UHPC joints. These factors include the geometric shape of the joint, the roughness of the joint interface, the filling material used in the joint, the width of the joint, and the configuration of joint reinforcement (including the shape and length of lap reinforcement). The test results show that the panel with the UHPC joint filled with steel fibers has excellent flexural and bonding capacity. The jointed panel with a lap length of 140 mm and 120 mm has better flexural performance than the one with a lap length of 90 mm. The straight-jointed panel has a higher flexural capacity compared to the complex triangular-jointed panel. Additionally, reducing the joint width can achieve similar mechanical properties as before. A method has been proposed for calculating the flexural capacity of a jointed panel, utilizing the strut-and-tie model (STM). This method can accurately predict experimental results.

Bending performance of wet joints in negative moment zone of prefabricated small-box girder bridges: Experimental and numerical study

The prefabricated small-box girder (PSBG) structure adopts the construction method of simple supporting beam transforming to continuous beam, which results in negative bending moment on the box girder supports and large tensile stress on the top of the longitudinal wet joints. Due to the relatively low tensile strength of concrete, the top plate of the bridge in the negative bending moment zone is susceptible to cracking under the load of vehicles, as well as due to the shrinkage and creep of concrete. This poses a risk to the safety, applicability, and durability of the bridge structure and may lead to a reduction in these aspects. Ultra-high performance concrete (UHPC) has excellent tensile performance and stronger crack control capability, which can effectively improve the anti-cracking and durability of the wet joints of the PSBG. In the present study, the research focused on the negative bending moment zone of a three-span continuous small–box girder bridges. This zone was selected as the research object and served as the basis for designing a stepped wet joint girder, where UHPC is partially cast on the top plate. By conducting three-point bending tests, we compared the bending mechanical properties of the joint girders when poured with normal concrete (NC) and UHPC in the joint top area. Further, the key factors affecting the anti-cracking performance and bearing capacity, including the length and thickness of the UHPC layer and the width of the wet joint, were analyzed by finite element simulation. The results show that the contribution of the top plate UHPC to tensile stress cannot be ignored. Compared with the NC joint girder, the UHPC joint girder has better toughness and plasticity, and the cracking load and bearing capacity increased by 28.6% and 9.7%, respectively. According to the simulation results, as the increase of the length and thickness of the UHPC layer and the width of wet joint, the anti-cracking and bearing capacities of the PSBG with the wet joint were enhanced. The thickness and length of the UHPC layer had a significant effect on improving the anti-cracking performance of the wet joint, and the joint width only needed to meet the transfer length of rebar bond stress.

Experimental study on flexural performance of composite slabs with bent bars and postcast ultrahigh‐performance concrete joints

AbstractThis paper describes the use of joints with bent bars and postcast ultrahigh‐performance concrete (UHPC) joints to enable formwork‐free and support‐free construction of composite slabs. To investigate their flexural performance, static loading tests on three full‐scale simply‐supported slabs and one monolithic slab were carried out. Flexural capacity, stiffness, and crack development were recorded, resulting on flexural failure experienced by all specimens. Main cracks of composite specimens developed along the UHPC–normal concrete interface, and cracks on both sides of the UHPC joint developed evenly, similar with that of the monolithic specimen. Besides, composite slabs and a monolithic slab showed similar flexural capacity. UHPC joint was not cracked when failure occurred, and bottom bars were anchored and connected in the UHPC joint, proving that the flexural anchorage method is feasible. The average strain of the composite specimen across the UHPC joint was still consistent with the assumption of plain section, and there was an approximate linear relationship between the expansion width of the joint at the bottom of the slab and the maximum crack width at bottom bars. Moreover, middle bars contributed to the flexural capacity and stiffness of composite specimens, while horse stool reinforcement may effectively prevent the interface shear failure on the composite interface. Based on test results, the formula to control cracking of UHPC is given in this paper. The design methods on flexural capacity, stiffness, and expansion width of composite slabs are also presented and discussed.

Cyclic behavior of UHPC corner beam-column joints under bi-directional bending

Design codes contain special provisions for anchorage lengths of flexural reinforcement and amount of transverse reinforcement in beam-column joints, to safeguard against joint failure and possible structural collapse. However, those stipulations could lead to congested joints with construction problems such as segregation. This study leverages experimental testing of eight corner beam-column joints under constant axial and cyclic bi-directional bending loads. In addition to being one of few on corner joints under a complex and practical loading, the study’s main aim is to evaluate the effectiveness of ultra-high-performance concrete (UHPC) as a joint fill in lieu of normal strength concrete (NSC). Brittle failure, either by pure shear or shear combined with yielding of beam reinforcement occurred in all NSC joints and varied in shape and intensity depending on the column depth-to-beam longitudinal bar diameter (hc ⁄db) ratio and spacing of transverse beam/column reinforcement. Ductile failure characterized by the yielding of beam reinforcement and plastic hinge at the beam-joint interface occurred in all UHPC joints and was independent of the two aforementioned variables. The application of UHPC in the joint region resulted in increasing the joint ultimate strength by 27.6–54.8%, energy dissipation by 24–163%, and stiffness by 20 to 50%, compared to NSC joints. Such results were obtained when no transverse reinforcement is used in the joint, and only half transverse reinforcement is used in the beam/column members, and with hc ⁄db relaxed to 38% of the code recommended ratio, highlighting the advantages of UHPC joints. Predictions of ACI-ASCE 352R code were found to be overly unconservative and in need of future improvement.

Experimental study on fatigue behavior of UHPC joint in negative moment region of π-shaped steel–concrete composite beams

To improve the crack resistance of concrete bridge decks in the negative moment region of π-shaped steel–concrete composite beam, a novel ultra-high performance concrete (UHPC) joint was first proposed. Based on an actual bridge, a 1:2 scale model was then designed as the specimen. A fatigue test was conducted to investigate the variation of its structural properties during fatigue loading, and a static test was performed to evaluate its residual bearing capacity. The test results show that the new UHPC joint has good crack resistance under fatigue loading and can meet the engineering requirements. The stiffness of the specimen significantly decreases after 3 million fatigue cycles. However, without significant fatigue damage on the surface of specimen, plenty of stiffness is reserved. It is found that there is no significant slip between the concrete deck and steel girder, and between the UHPC and normal concrete in the static test after fatigue, indicating that the studs inside the π-shaped steel–concrete composite beam are arranged reasonably and the interaction of the overall structure is reliable. Furthermore, the ultimate bearing capacity of the specimen decreased by only 9.4% from its design value after being subjected to 3 million fatigue cycles. It is revealed that the application of UHPC in the composite beam effectively improves its crack resistance, resulting in a smaller reduction in bearing capacity. This paper can provide theoretical foundation for the preparation and application of the π-shaped steel–concrete composite beams with UHPC joints.

Experimental and numerical studies on shear behavior of prefabricated bridge deck slabs with compact UHPC wet joint

Ultra-high performance concrete (UHPC) as a joint material for precast bridge decks might reduce the width of the joint and improve its connection performance and durability. This study proposes a type of compact UHPC wet joint based on the mechanical properties of UHPC and the force characteristics of transverse joints in prefabricated bridge decks. The shear behavior of the novel joint was investigated through experimental study and numerical simulation. In addition, the shear properties of compact UHPC wet joints were compared with epoxy joints. The results indicated that the shear resistances of compact UHPC joints are comparable to those of epoxy joints. The failure process of the precast bridge deck with new joint might be divided into three stages: elastic stage, working stage with cracks, and yield stage. No interface cracks or reinforcement slippage was observed throughout the loading process, indicating that the UHPC joint and the epoxy joint exhibited adequate shear resistance. The ultimate load capacity and corresponding mid-span deflection of UHPC joint specimens were respectively increased by 8.6 % and 75.0 %, when compared with the epoxy joint specimens. Finite element analysis reveals that the transverse shear transfer range of the compact UHPC joints is within 57.1 %. Bending failure due to the yielding of the transverse reinforcement at the bottom of the precast bridge deck is the primary failure mode for both specimens. Moreover, the stresses applied to the deck system have good continuity at the joint.

Corrosion of steel rebars across UHPC joint interface under chloride attack

Corrosion of steel rebars across ultra-high-performance concrete (UHPC) joint interface under chloride attack is experimental investigated in the present study. The cases of concrete joint interface with normal concrete (NC) and high-performance concrete (HPC) are also investigated as the contrast. Twelve specimens are prepared and subjected to corrosion test. The corrosion potential and corrosion current density are measured to monitor the corrosion evolution of steel rebars. The effects of chloride concentration and cracking on the corrosion of steel rebar across the concrete joint interface are clarified. And the corrosion characteristic of steel rebars with a high corrosion loss are further investigated through the accelerated corrosion method. Results show that steel rebars across joint interface trend easily to be corroded for all the three cases with NC, HPC and UHPC. Corrosion of steel rebar across UHPC joint interface is just a little slower or slighter than the other cases across NC and HPC joint interface. The corrosion of steel rebars is highly centralized and localized at the joint interface for the case with UHPC, but relatively uniform without significant difference around the joint interface for the other cases with NC and HPC. Corrosion of steel rebars across concrete joint interface is sensitive to chloride concentration and interface cracking, especially for the case with UHPC.

Experimental and numerical investigations on direct shear performance of UHPC dry joints

Ultra-high performance concrete (UHPC) has great prospects in the field of precast segmental bridges. The excellent mechanical properties of dry joints between the UHPC segmental have become the focus of scholars all over the world. Currently, there are few studies on UHPC dry joints with a compressive strength between 120 MPa and 140 MPa. In this study, the direct shear performance of UHPC dry joints was tested and simulated with parameters of steel fiber content, confining stress, key number, shear key interlocking depth-height ratio (the depth-height ratio was used later), and key height. The results showed that the cracking resistances and ultimate strength of UHPC joints could be significantly improved with the increase of steel fiber content. All the UHPC specimens showed a little brittleness behavior with the average cracking load being 78.4% of the average ultimate load. Different cracking patterns occurred in single-keyed UHPC dry joints, while sequential failure arose for multi-keyed UHPC dry joints. Compared with monolithic specimens, the direct shear strength of keyed UHPC dry joints was reduced with a range of 51.4%–66.0%, and the decreasing trend was alleviated with the increase of the key number. The direct shear capacity of UHPC dry joints increased with the increase of key height and depth-height ratio, and the optimized depth-height ratio was 0.40–0.50. Compared the calculated results of existing formulae with the test results incorporated with the previous studies, it was found that Jiang's formula predicted the shear capacities of UHPC dry joints more accurately than the other formulae. In addition, the influence of the depth-height ratio on the direct shear capacities of UHPC dry joints cannot be reflected by the existing formulae, which need further improvement.

Structural behavior of shear deficient high performance reinforced concrete exterior joints under bending

Structural performance of shear deficient reinforced concrete exterior beam-column connections made with Engineered Cementitious Composite (ECC) and Ultra-high Performance Concrete (UHPC) is investigated experimentally and compared with those made of Self-Consolidating Concrete (SCC). Beam-column connections of 1/3rd scale made entirely of ECC, SCC and UHPC as well as ECC-SCC and UHPC-SCC combinations (joint core zone made of ECC and UHPC while the rest made with SCC) are tested under monotonic flexural loading to failure. The performance is compared in terms of failure mode, ductility, energy absorption capacity, stiffness, load/moment-displacement/rotation response, stress–strain characteristics, crack patterns/widths, member flexural/shear strength and joint shear strength. SCC and SCC-UHPC joint specimens have non-ductile beam shear failure and shear failure of the SCC part of the connection respectively, while all others have joint flexural failure. Code based equations significantly under predicted the shear strength of ECC and UHPC joint members. All connections made fully or partially with UHPC and ECC have exhibited higher ductility (1.2 to 1.7 times), energy absorption capacity (3.1 to 15.7 times) and reserve joint strength compared to those with SCC. UHPC incorporated connections exhibited higher strength and energy absorbing capacity, those with ECC showed higher ductility and better crack control characteristics and incorporation of ECC/UHPC can induce desired flexure dominated failure in a shear deficient joint.

Shear behavior of joints in precast UHPC segmental bridges under direct shear loading

The joints in precast ultra-high-performance concrete (UHPC) segmental bridges (PUSBs) play significant roles in the structural performance of PUSBs, which require systematic investigation to establish a thorough understanding of their shear behavior. To this end, the push-off tests for 11 UHPC joints, including 9 epoxy joints and 2 dry joints, were carried out to obtain the failure modes, crack distribution, and the load-relative vertical displacement relationships. The confining stress, number of shear keys, and joint types were the critical test parameters considered in this study. Experimental results show that the failure mode of flat epoxy joints was the spalling of the epoxy, and no visible damage was observed on the surface of joints. For the keyed epoxy joints, the brittle shear-off of shear keys led to the failure of joints. However, dry joint specimens showed severe damage and spalling of UHPC. The shear capacity of UHPC joints effectively improved as the confining stress and number of keys increased, and the epoxy joints exhibited a higher shear capacity than the dry joints. The shear strength formulas of UHPC joints were developed and the calculated results from the proposed formulas agreed well with the test results with an average ratio of 1.05 and a coefficient of variation of 0.079. Moreover, four calculation models for the UHPC joint shear strength were proposed based on the forms of existing shear strength formulas of UHPC joints and 61 push-off test results available in the previous studies were used to evaluate the calculation models.

Direct shear performance of UHPC Multi-Keyed epoxy joint

The modular Ultra-High Performance Concrete (UHPC) girder elements show outstanding potential to produce lightweight superstructure with high quality, low lifecycle cost and excellent durability for precast segmental bridge; and the required connection between segments is critically important to ensure desirable overall structural performance. This paper presents the results of direct shear tests on 18 UHPC joint specimens considering the influence of the number of shear keys, confining stress, depth of shear key, steel fiber volume content of UHPC and joint type. The shear behavior was characterized in terms of load-slip response, shear resistance, cracking pattern, and failure mode. Two types of failure modes, namely synchronous and stepwise shear failure, were observed. These specimens with stepwise shear failure showed smaller shear resistance and higher ductility compared with those with synchronous shear failure. And the ultimate shear stress decreased with the increase of key number, while the positive effect from confining stress was identified for the shear resistance in general. In addition, an updated model based on the existing ones was proposed and validated against the test data (standard deviation of 0.11).

Seismic performance of novel bolt-connected precast concrete walls strengthened by UHPC

Existing bolted precast concrete walls (PCWs) have shown disadvantages in terms of high precision in production or insufficient seismic performance compared with cast-in situ walls. Based on this background, new bolt-connected PCWs enhanced by ultra-high performance concrete (UHPC) and connected by spliced bolted joints for use in low-to mid-rise residential systems were proposed. Seven specimens, including one monolithic concrete wall and six bolt-connected PCWs, were tested at a low axial compression ratio and reversed cyclic loads. The effects of the UHPC enhancement area, bolt arrangement, joint position and bolt hole shape of the steel plate on the seismic performance of the PCW were evaluated. The test results indicate that three types of failure patterns could be observed in PCWs, i.e., wall toe compressive failure, joint shear failure and flexural failure. The PCW enhanced by UHPC was able to achieve equivalent performance to the monolithic wall in terms of lateral resistance and energy dissipation. In addition, theoretical calculations for the flexural strength of PCWs corresponding to different failure modes were proposed. The predicted results approximated the test values and were all within the safe range.

Experimental Study on Seismic Performance of Precast Pretensioned Prestressed Concrete Beam-Column Interior Joints Using UHPC for Connection.

The traditional connections and reinforcement details of precast RC frames are complex and cause difficulty in construction. Ultra-high-performance concrete (UHPC) exhibits outstanding compressive strength and bond strength with rebars and strands; thus, the usage of UHPC in the joint core area will reduce the amount of transverse reinforcement and shorten the anchoring length of beam rebars as well as strands significantly. Moreover, the lap splice connections of precast columns can be placed in the UHPC joint zone and the construction process will be simplified. This paper presented a novel joint consisting of a precast pretensioned prestressed concrete beam, an ordinary precast reinforced concrete (RC) column, and a UHPC joint zone. To study the seismic performance of the proposed joints, six novel interior joints and one monolithic RC joint were tested under low-cyclic loads. Variables such as the axial force, the compressive strength of UHPC, the stirrup ratio were considered in the tests. The test results indicate that the proposed joints exhibit comparable seismic performance of the monolithic RC joint. An anchorage length of 40 times the strands-diameter and a lap splice length of 16 times the rebar-diameter are adequate for prestressed strands and precast column rebars, respectively. A minimum column depth is suggested as 13 times the diameter of the beam-top continuous rebars passing through the joint. In addition, a nine-time rebar diameter is sufficient for the anchorage of beam bottom rebars. The shear strength of UHPC in the joint core area is suggested as 0.8 times the square root of the UHPC compressive strength.

Long-term performance of a continuous box-girder bridge constructed using precast segments with wet ultra-high-performance concrete (UHPC) joints

Although the precast segmental construction (PSC) technique can relieve age-dependent difficulties and accelerate bridge construction as compared to the cast-in-situ construction (CSC) technique for long-span prestressed concrete box-girder bridges (LSPCBB), the ordinary concrete joints between adjacent precast segments are risky. In order to improve the bond strength at the joint interface and enhance structural reliability, ultra-high-performance concrete (UHPC) can be used to fill joints as a new cementitious material with high strength, ductility, and durability. Thus, the effect of the naturally cured UHPC shrinkage and creep on the bridge's long-term performance should be evaluated. The present study numerically investigates the long-term bridge performance constructed by the PSC technique with wet UHPC joints. One cast-in-place segment using the CSC technique is replaced by one precast segment and one cast-in-place UHPC joint using the PSC technique in the bridge model. A creep coefficient equation in an existing code and a shrinkage strain equation fitted from the test data for the UHPC are verified, and an equivalent temperature drop method is used for simulating pretension forces of the prestressing strands in the numerical model. Through comparison with the CSC technique, the technical advantages in reducing long-term deflection, rotation, prestress losses, and improving normal cross-sectional stresses are quantitatively highlighted for the UHPC enhanced PSC bridge.

Numerical and analytical studies of flexural behaviour of prestressed UHPC joints

This study numerically and analytically investigates flexural behaviour of precast ultrahigh performance concrete (UHPC) segments connected by post-tensioned prestressing strands with or without epoxy on keyed joint surfaces. The analytical formulas are proposed for calculation of joint opening load and ultimate flexural capacity, and a numerical model is established to investigate flexural behaviour of the jointed beam. The joint surfaces without epoxy are simulated by a pair of contact elements with a friction coefficient of 0.6. For the joint surfaces with epoxy, besides the contact elements, a spring element is defined for consideration of the epoxy and an optimized force–displacement relationship is first proposed and input for the spring property. The previous test data and data from one intact beam with low reinforcement ratio tested in the present study are used for validation of the analytical and numerical calculations. The numerical results agree well with the test results in terms of load-midspan deflection, load-joint opening displacement as well as failure modes. Based on the validated numerical model, the effect of number of prestressing strands and beam depth on the flexural behaviour of the prestressed jointed beam is investigated. This study will promote prestressed UHPC joints’ application in practical engineering.

Shear strength prediction method of the UHPC keyed dry joint considering the bridging effect of steel fibers

The joints between segments of the precast ultra-high performance concrete (UHPC) segmental bridge (PUSB), which transmit compressive and shear stresses, require special attention in design. The shear strength of these joints is significantly improved in comparison with that of normal strength concrete (NSC) joints due to the excellent mechanical properties of UHPC. Nevertheless, little attention has been paid to predict the shear capacity of UHPC joints directly considering the shear contribution of steel fibers. This paper develops a new shear strength model for UHPC-keyed dry joints incorporating transferring mechanisms of three primary shear component based on previous experimental results and numerical simulation. Based on the modified compression-field theory, the shear contribution by the matrix in UHPC keys is mainly influenced by normal compressive stress and area of all bases of keys. Based on the mesoscale fiber–matrix discrete model, the shear contribution by steel fibers was affected by the steel fiber length, diameter, type, and volume fraction. To obtain more accurate prediction results, a reduction coefficient was utilized for UHPC multi-keyed dry joints in the proposed shear strength formula on grounds of regression analysis. The reliability and accuracy of these results were then verified by experimental results of 27 push-off tests available, with mean and standard deviations between the predicted and experimental shear strength of 0.98 and 0.27, respectively. Thus, the proposed formula can be used to predict the shear strength of UHPC dry joints with single and multiple shear keys.

Experimental study on the tensile behavior of ultra‐high performance concrete fiber continuous joints

AbstractThe application of ultra‐high performance concrete (UHPC) in the bridge deck effectively increases the strength, ductility, and durability of the deck system, while the problem of fiber discontinuity at the joint‐deck interface remains unsolved. This study proposes an innovative UHPC joint to create steel fiber continuity at the interface and experimentally investigates its tensile behavior. Test parameters include fiber content, fiber length and diameter, fiber shape, and fiber strength. Test results indicate that the joint tensile strength increases with fiber content, fiber length, and fiber strength. The specimen with hooked end fibers also develops higher joint tensile strength compared with the specimen with straight fibers. It is recommended to use fibers with a smaller diameter to increase the interfacial bonding area between the fibers and the matrix. High‐strength fibers are also recommended to achieve the best efficiency in a high‐strength matrix, like UHPC. The tensile performance of the joint with a fiber content of no less than 0.5%, and an embedment length of 15 mm (with a fiber length/diameter ratio of 50), and a diameter of 0.3 mm is similar to the performance of the specimen cast as one piece. Therefore, a properly designed UHPC fiber continuous joint is recommended in engineering practice to improve the integrity of the joint‐deck system.