Precast segmental bridges made of ultrahigh-performance concrete (UHPC) have gained wide research attention and application. The shear transfer of dry joints between UHPC segments is one of the major concerns due to the discontinuity and interruption of the reinforced bars. In this study, direct shear tests of UHPC joints were conducted. Parameters included confining stress, concrete type, joint type, joint shape and number of keys, and arrangement of steel reinforcement. Crack-formation sequences, cracking patterns, ultimate shear load, and vertical slippage were obtained, and typical normalized shear stress–relative displacement curves were calculated. The results show that a higher shear strength of UHPC joints can be achieved with higher confining stress, higher matrix tensile strength, and the addition of steel fibers. Concrete joints with fibers exhibited a limited area of concrete crushing compared with joints without fibers. Large-keyed joints showed a minor increase in shear capacity (9.7%) compared with three-keyed joints. A calculation method for the shear strength of concrete dry joints based on Mohr’s circle was established, and a simplified formula for calculating the shear strength of UHPC dry joints with different compressive strengths was developed. The results of the proposed calculation method were found to agree well with the experimental values. The average ratio of the calculated results to the experimental results was found to be 1.01, with a standard deviation of 0.14. The simplified formula for UHPC joints was also found to have better agreement with the shear test results, with an average ratio of 0.96 and a standard deviation of 0.24, compared with 1.41 and 0.38, respectively, in the AASHTO provisions.

This paper evaluates the seismic responses of a super-span cable-stayed bridge subjected to near-fault ground motions. A new method, record-decomposition incorporation (RDI), is proposed to synthesize the artificial near-fault pulse-type ground motions by combining the high-frequency background record (BGR) with simple equivalent pulses. The effects of forward-directivity pulses and fling-step pulses on the responses are assessed for the Sutong cable-stayed bridge (with a main span of 1,088 m) in China. The results show that the near-fault pulse-type ground motions generate larger displacement and internal force to the bridge compared with the nonpulse ground motions, and the fling-step ground motions are more damaging to the bridge than those of the forward-directivity ground motions. The high-frequency components of near-fault records have a significant effect on the responses of the bridge. Subsequently, the longitudinal displacement and bending moment of the tower induced by artificial ground ...

A theoretical method, termed the mesoscale fiber-matrix discrete model (MFDM), has been developed that can be used for estimating the shear contribution of steel fibers and calculating shear strength of ultrahigh-performance fiber-reinforced concrete (UHPFRC) beams. In the proposed model, an effective fiber distributed region (EDR) along the critical diagonal shear crack, where fibers are efficient at providing shear resistance, is defined. The total quantity of fibers within EDR is calculated by the EDR volume proportion of the beam based on a uniform distribution of steel fibers. Two concepts to determine the width of EDR are proposed: (1) probability theory and (2) the basis of the pullout load slip relationship. The bond strength between a single fiber and the matrix is determined by the probability method based on a uniform distribution of fibers. Combining the number of efficient fibers and the bond strength of a single fiber, the shear contribution of fibers is derived. The shear contributi...

The concept of an equivalent plastic-hinge model was used to evaluate the lateral behavior of precast segmental ultra-high-performance concrete (UHPC) bridge columns. The columns consist of precast UHPC segments that were integrated by unbonded post-tensioning (PT) tendons and complemented with energy dissipation (ED) bars. The equivalent constitutive relationships of the PT tendons and the ED bars were analytically derived to meet the plane section assumption for the sectional analysis. Cyclic loading tests were conducted on three specimens to validate the proposed equivalent plastic-hinge model. The test results revealed that the proposed model showed good accuracy for predicting the lateral skeleton curve, stiffness, and opening at the base joint. Using the validated model, a parametric study was conducted to investigate the effects of nine main design parameters on the lateral behavior of the column. The parametric study showed that increasing the PT level is more economical to enhance the PT force than relying on the larger ratio of the PT tendons when the PT level is no more than 44% of the yield strength. Finally, a simplified formula for the effective stiffness was developed through regressive analysis. The effective stiffness depended on the aspect ratio, the number and unbonded length of ED bars, and axial loading ratio.