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2 2023

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Shear behavior of precast ultrahigh-performance concrete (UHPC) segmental beams with external tendons and dry joints

Ye Meng, Li Lifeng, Yoo Doo-Yeol, Wang Lianhua, Li Huihui, Shao Xudong

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 3

art. no. e143, 2023

In this study, ultrahigh-performance concrete (UHPC) was utilized in precast segmental beams to reduce the self-weight, shorten the construction time, and improve the performance and durability of bridges. Owing to the discontinuity in the joints, shear behavior plays a critical role in the overall structural performance of precast UHPC segmental beams (PUSBs). Therefore, four dry-jointed segmental specimens along with one monolithic specimen were designed and tested under a two-point concentrated load with various joint types, shear span-to-depth ratios (λ), and numbers of shear keys. Two types of shear failure modes were observed in the tests: shear compression failure of the web (λ = 1.44 and 2.56) and local shear failure of the flanges at the joint (λ = 3.67). The shear capacity, stiffness, and cracking load of the dry-jointed segmental specimens were lower than those of the monolithic specimen, and the single-keyed specimen exhibited better shear behavior than the three-keyed specimen. Increasing λ decreased the shear strength and stiffness of the segmental beams and considerably affected their failure modes and crack distributions. Additionally, four UHPC design codes were evaluated for their accuracy in estimating the shear strength of the specimens, and a simplified strut-and-tie model was developed to predict the shear strength of externally pre-stressed PUSBs. Finally, several design recommendations were proposed. This study is expected to facilitate the research and application of PUSBs.

Experimental and theoretical investigation of the shear lag effect in the novel non‑prismatic prestressed CSW-UHPC composite box girders

Li Huihui, Li Lifeng, Yoo Doo-Yeol, Ye Meng, Zhou Cong, Shao Xudong

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 2

art. no. e132, 2023

Due to their featured mechanical and structural merits, such as the light self-weight, excellent prestressing efficiency, appealing appearance, and optimal shear force and bending moment distributions in corrugated steel webs (CSWs) and concrete flanges, the prestressed concrete composite box girders with CSWs (CCBGCSWs) are popularly applied in highway bridges nowadays. To further enhance the cracking resistance of the concrete flanges of conventional prestressed CCBGCSWs, by replacing the regular concrete flanges with that made by ultra-high-performance concrete (UHPC) (i.e., with the much superior mechanical properties), this paper proposed a novel non-prismatic prestressed CSW-UHPC composite box girder to achieve the lighter dead weight, superior spanning capacity, and more rapid and cost-efficient construction for highway bridges. Owing to the differences in both the geometric dimensions and material properties, shear lag behavior of the proposed novel non-prismatic prestressed CSW-UHPC composite box girder could significantly differ from that of conventional prestressed CCBGCSWs. The shear lag effect refers to the non-uniform distributions of the longitudinal bending normal stress within the flanges caused by shear interaction between the webs and flanges, and the improper consideration of the shear lag behavior would impair the safety of thin-walled CCBGCSWs, especially the proposed novel non-prismatic prestressed CSW-UHPC composite box girder. Therefore, to investigate the shear lag behavior of the proposed novel nonprismatic prestressed CSW-UHPC composite box girder during different construction stages, a representative test specimen (5.55 m in length) with different boundary conditions (e.g., simply supported and cantilever) was designed and investigated under five different loading cases using the experimental tests and finite element (FE) analyses. In addition, a modified bar simulation method was proposed for the theoretical analysis of the shear lag behavior of the girder, and its feasibility and effectiveness were demonstrated through the comparisons to the experimental and numerical results. Finally, the results indicated that (i) the shear lag effect of UHPC flanges in the stress concentration region of the proposed novel non-prismatic CSW-UHPC composite box girder was more pronounced than that in the non-stress concentration region under different loading conditions; (ii) the shear lag coefficient (λ) of UHPC flanges in the non-stress and stress concentrated regions of the girder could be conservatively recommended not less than 1.1 and 1.25, respectively; and (iii) the boundary conditions and loading forms had significant influences on the shear lag behavior of the girder. The results of this study could serve as the experimental, numerical, and theoretical references for the shear lag behavior of the novel non-prismatic prestressed CSW-UHPC composite box girders.