Bridge Pier Seismic Strengthening Using Uhpfrc Cover

Abstract eng:
The paper presents the results of an experimental program aimed at developing an innovative seismic strengthening technique using Ultra-high Performance Fibre Reinforced Concrete (UHPFRC) cover to eliminate splitting failure mode in splice regions with deficient reinforcement details. With the proposed strengthening technique, the concrete around the bars in lap splice regions is first removed using conventional demolition methods, and is replaced by self-levelling UHPFRC. The exceptional tensile properties of UHPFRC allow eliminating splitting cracks thereby allowing transferring lapped bar forces through the surrounding UHPFRC. The testing program included cyclic tests on full-scale rectangular bridge pier specimens with cross-sectional aspect ratios of 2:1 and 4:1. A refined 3D finite element model at rib scale was developed to provide a numerical tool for evaluating the performance of lap splice regions strengthened by UHPFRC cover. The analyses were validated from the experimental program done at local scale on uniaxial tension specimens performed on concrete prisms. Test results led to the following conclusions for nominally confined 24 d b long lap splices: 1) UHPFRC cover allows eliminating the splitting failure mode; 2) drift ductility ratio up to 8 was obtained without any strength reduction for bars up to 45 mm in diameter; 3) longitudinal bar buckling failure mode was eliminated for 300 mm stirrup spacing. Results of the project also suggest that this technique could be applied at other locations in columns where reinforcement details are inadequate. The technique allows keeping the column initial dimension and could thereby be used for columns of any shape. The advanced nonlinear finite element analyses illustrated their capability for explicitly expressing the bond performance of lap splices in UHPFRC according to the measured tensile properties. These models, combined with experimental investigations, could provide precious information on the behaviour of lap spliced in UHPFRC for the future development of design guidelines.

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