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Precast Ultra-High-Performance Concrete (UHPC) segmental bridges (PUSBs) are among the most promising structural systems owing to their potential for application in advanced philosophies, such as green and intelligent construction technology, industrialization, prefabrication, and automation. The joints, where precast segments are connected, play a significant role in the construction and structural performance of PUSBs. This study reviews the state-of-the-art knowledge on the shear behavior of UHPC joints, which includes the following aspects: (1) the introduction of joints in PUSBs, including their role, types, experimental methods, and typical shear responses; (2) the development of the experimental database of the push-off tests conducted on UHPC joints; (3) a discussion of the influence of critical factors (e.g., UHPC strength, joint type, confining stress, fiber characteristics, and shear key design) on the shear behavior of UHPC joints; (4) a summary and evaluation of the current analytical models and formulae for predicting the shear resistance of UHPC joints; and (5) the identification of current challenges and recommendations of future research directions for UHPC joints. This review is expected to comprehensively understand the shear performance of UHPC joints and facilitate the research and application of UHPC structures. [Display omitted] • A state-of-the-art review is conducted on the shear performance of joints in precast UHPC members. • The critical factors affecting the shear behavior of UHPC joints are discussed. • Analytical models for predicting the shear strength of UHPC joints are summarized and compared. • Existing formulae for the shear strength of UHPC joints are evaluated based on the experimental database. [ABSTRACT FROM AUTHOR]

• An updated database consisting of 532 UHPC beams that failed by shear is established. • Ten ML models with different algorithms are developed to predict the shear strength of UHPC beams. • The performance of the ML models is evaluated and compared to empirical models. • The ML models are interpreted using the SHAP methods. • The impact of critical features on the shear strength of UHPC beams is identified. To provide more accurate and reliable predictions of the shear strength of ultrahigh-performance concrete (UHPC) beams, in this study, the machine learning (ML) approaches were employed to develop the data-driven models, and the ML models were interpreted using the Shapley additive explanations (SHAP) method. It was found that the ensemble models, particularly CatBoost, outperform individual ML models and traditional empirical models. The geometric dimensions and shear span-to-depth ratio were the most influential features for predicting the shear strength of UHPC beams, followed by the parameters of reinforcement and material properties of the UHPC. [ABSTRACT FROM AUTHOR]

• The shear behavior of externally prestressed UHPC beams without stirrups is experimentally investigated. • Effects of the a / d ratio, stirrups, and longitudinal reinforcement ratio are discussed. • An equation for predicting the shear-cracking strength of prestressed UHPC beams is proposed. • Effects of key parameters on the shear strength of prestressed UHPC beams without stirrups are analyzed. • Prediction equations of shear strength of prestressed UHPC beams without stirrups are proposed. Externally prestressed ultra-high-performance concrete (UHPC) beams without stirrups (EPUBs-WS) that simplify the reinforcement design and construction procedure are becoming a competitive option in bridge engineering. To investigate the shear behavior of EPUBs-WS, five specimens were designed and tested considering several critical parameters, such as the shear span-to-depth ratio (λ), shear stirrups, and longitudinal reinforcement ratio. The EPUBs-WS exhibits diagonal tension failure as the fibers pull out and the specimen shears off into two parts along the critical diagonal crack. However, the beam with λ = 3.67 exhibited flexural failure due to the large λ. The stiffness, shear-cracking strength, and shear strength of EPUBs-WS decrease as λ increases. Stirrups enhance the shear resistance of EPUBs but result in a more brittle shear failure mode. A higher reinforcement ratio augments the dowel action in EPUBs-WS, which contributes to a ductile shear failure mechanism. The web-shear cracking force accounts for 46% to 87% of the shear capacity, implying that the shear-cracking strength is a significant factor in the design of EPUBs-WS. An equation for predicting the shear-cracking strength of prestressed UHPC beams is proposed and validated using a database of experimental results reported in the literature. A parametric analysis is performed using 40 available specimens to investigate the effects of compressive strength, λ , reinforcement ratio, fiber reinforcing index, and prestressing level on the shear strength of prestressed UHPC beams without stirrups. By considering the key parameters, equations for estimating the shear strength are proposed and exhibit good accuracy. [ABSTRACT FROM AUTHOR]

• The mechanism of precast segmental UHPC beams (PUSBs) with epoxy joints subject to combined bending and shear was investigated. • The PUSBs with epoxy joints exhibit comparable structural performance with the monolithic beam. • The effect of the shear span-to-depth ratio, stirrups, and joints on the mechanical behavior of PUSBs were discussed. • Analytical models for predicting the cracking strength and ultimate capacity of PUSBs were proposed. Precast ultra-high-performance concrete (UHPC) segmental bridges (PUSBs) have become a competitive bridge type in modern civil engineering. To establish a thorough mechanistic understanding of PUSBs, seven specimens were fabricated and experimentally investigated. These specimens were designed to have different longitudinal reinforcements, construction methods, joint types, shear span-to-depth ratios (λ), stirrup ratios, and numbers of shear keys. Two failure modes were observed in the tests: flexural failure with crushing of the UHPC at the joints, and shear failure with shear tension sliding and concrete spalling of the web. Additionally, it was found that although the ultimate capacity, stiffness, and cracking load of the segmental beams were slightly lower than those of the monolithic beams, the segmental beams tended to exhibit better ductility and deformation capacity. As λ increased, the ultimate capacity and stiffness of the segmental beams decreased, whereas the growth rates of the deflection and tendon stress increased. Moreover, the stirrups showed a positive effect on the cracking control ability and shear strength of the beams. The three-keyed specimen exhibited better structural behavior than the single-keyed specimen. Finally, calculation methods were proposed to predict the cracking strength and ultimate capacity of PUSBs. [ABSTRACT FROM AUTHOR]

• The UHPC-based precast large-cantilevered thin-walled bent caps were proposed and designed. • The structural performance of two large-scale (12.1 m long) UHPC-based bent caps was experimentally investigated. • The calculation methods for predicting the cracking strength and ultimate capacity of UHPC-based bent caps were proposed. • The design considerations for the UHPC-based bent caps were proposed. This study aimed to develop a new type of precast bent cap by using ultrahigh-performance concrete (UHPC) with prestressed tendons. The UHPC-based bent cap was designed to be lightweight and to exhibit excellent crack control as well as flexural and shear resistance. To this end, two large-scale specimens were designed and tested to identify their crack patterns, failure modes, shear behavior, and flexural behavior. The experimental results indicate that the UHPC bent caps provide excellent cracking resistance and considerable load-carrying potential after cracking, and the flexural strength dominates the design. In addition, calculation methods for the cracking strength and ultimate capacity were investigated and discussed, which can predict the strength of the UHPC bent cap with acceptable accuracy. Moreover, alternative options were proposed from different perspectives considering the construction procedure, weight reduction, and structural performance. Finally, several design considerations, i.e., the optimization of the cross-section and reinforcements, were proposed for prestressed UHPC-based bent caps. [ABSTRACT FROM AUTHOR]

• Shear behavior of UHPC joints was experimentally examined. • The failure modes, crack patterns, and load–displacement responses were obtained. • The effect of test parameters on the shear behavior of UHPC joints was discussed. • The calculation method for the shear strength of UHPC joints was developed. • Four calculation models for the shear strength of UHPC joints were proposed. 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. [ABSTRACT FROM AUTHOR]

Sacrificial concrete shear keys have been recommended and used widely because they can restrain the excessive displacement of the bridge superstructure under normal service loads and protect the substructures from severe damage under the huge earthquake event, whereas the post-earthquake rehabilitation of the traditional shear key (regain its original function) is still a big challenge for bridge engineers. Therefore, this study proposed a replaceable concrete retaining block as an alternative that can provide mostly the same functionality as the sacrificial shear keys. The proposed replaceable concrete retaining block is prefabricated and installed to the cap beam by using the unbonded prestressed tendons. To study the functional feasibility and seismic behavior of the replaceable retaining block, four specimens with identical size were designed and tested under the horizontal monodirectional and cyclical load. The influence of structural materials and forms on seismic failure modes of different blocks was investigated based on both laboratory tests and finite element analysis. It is concluded that the failure modes of the monolithic normal concrete (NC) and the ultra-high-performance-concrete (UHPC) retaining block are the typical diagonal shear failure and the vertical interface damage, respectively. The replaceable NC retaining block performs well in lateral displacement and self-resetting ability, but its final damage is still the unpredictable bending-shear failure mode. The replaceable UHPC retaining block can keep only slight damage but simultaneously satisfy the requirements of higher lateral bearing and displacement capacity. Especially, the self-resetting capacity of the replaceable UHPC retaining block will be greatly improved if the straight joint is used instead of the original mortise-tenon joint. • A novel replaceable concrete retaining block is proposed. • Functional feasibility and seismic behavior of the proposed retaining block are investigated. • Impact of the structural materials and forms on damage mode of the retaining block are assessed. • Finite element models of different retaining blocks are developed. • Replaceable UHPC retaining block is with significant benefit of seismic performance. [ABSTRACT FROM AUTHOR]