Shear strength of steel-reinforced ultra-high performance concrete dry and epoxy joints for segmental girders

Joints in precast segmental bridge girders (PSBGs) are the locations of discontinuity and these parts are weaker than those of adjacent monolithic sections within the segment. During the service phase, the compression and shear forces are transmitted at this component. Generally, the keys in this region serve three purposes, namely, to align the segments during erection, to transfer shear force between the sections during service, and to protect the prestressing tendons against corrosion where the tendons pass through the joints. However, as revealed in this study, all the existing provisions tended to significantly over-estimate the ultimate shear capacity of the joint specimens and are developed for normal grade concretes which cannot be used in ultra-high performance fibre reinforced concrete (UHPFRC) joints of PSBGs. The literature review also highlighted that there was no available existing design provision model to calculate the first crack shear capacity of any type of concrete keyed joints. Therefore, the aim of this research was to investigate the shear capacity loads of typical joints (dry and epoxy) used in PSBGs using UHPFRC concrete and to develop the new design provision models for UHPFRC girders based on the failure criterion of Mohr circle theory. Twelve real full-scale shear key joints of UHPFRC specimens (6 dry keyed joint specimens, 6 epoxy keyed joint specimens) were tested experimentally to fail with three variable parameters namely, number of shear keys, confining stress, and the type of joint (dry or epoxy). Enabling shear was used in the test setup and applied across the shear plane with insignificant moment. The experimental results were also compared with five existing shear capacity design provision models, and a numerical FEM analysis model was developed to compare the results against the experimental data to further confirm the failure pattern of the specimens based on all the three variable parameters. In all, the results of the study showed that the capacity of the UHPFRC key joints increased with increasing horizontal pressure applied across the joint (confining stress), number of shear keys and the epoxy layers applied on joints. The results of the new UHPFRC design provision model also compared well with the experimental results for both the dry and epoxy keyed joints at both stages (first crack and the ultimate shear capacity loads). The mean and the coefficient of variation (COV) values of the theory/experimental ratio for dry keyed joints were 0.87 and 7.71% at the first crack shear load stage and 0.7 and 9.96% at the ultimate shear load stage. Meanwhile the mean and the coefficient of variation (COV) values for epoxy keyed joints were 0.95 and 5.31% at the first crack shear load stage and 0.87 and 6.12% at the ultimate shear load stage. In conclusion, this research confirmed that the existing shear capacity design provision models could not be used in the design of UHPFRC precast segmental bridge girder (PSBG) joints. Furthermore, by applying the new UHPFRC shear capacity design provision model in the design of UHPFRC PSBGs, it will ensure both private and governmental bodies that the UHPFRC structures are more affordable, economical, sustainable, and much easier to construct. Lastly, this research will provide an essential contribution to the development of UHPFRC PSBG guidelines in future, particularly in the area of the UHPFRC joint.

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