Several studies on tension lap splices have shown the improvement of bond strength using Ultra-high performance Fibre Reinforced Concrete (UHPFRC). The results also confirm the applicability of the method for strengthening lap-spliced regions of wide elements-such as slabs, shear walls, and wall-bridge piers-without having to provide any confinement.
The results demonstrate that an appropriate casting method combined with a self-compacting UHPFRC with an appropriate fiber content ensure the efficiency of the strengthening technique for providing for the continuity of lapped bars and for enabling a high ductility capacity under monotonic or cyclic loading. The levels of ductility reached for the highest fiber content meet the requirements for high ductility demand, such as in seismic design. The result indicates that UHPFRC with a fiber content of 2 or 3% can significantly increase the bond strength of splice bars without confinement. The beam specimens are tested at four points, bending with a constant-moment region along the splice length.
Lap splice free#
For isolating the UHPFRC contribution, the splice regions are free of any confinement. One type of fiber, three fiber contents, two bar diameters, and two bar arrangements are considered. The strengthening technique consists of replacing normal concrete around lapped bars in the splice region by UHPFRC, which allows for keeping the original member geometry. Specimen reinforcement consists of two pairs of deformed bars spliced at midspan on both tension and compression faces.
The objective of this experimental work is to determine the efficiency of this strengthening technique on wide flexural elements (beams, slabs, walls, or wall columns) subjected to reverse cyclic loading.
Lap splice series#
The experimental program is based on the findings of previous test series carried out in the same research program that demonstrated the ability of UHPFRC to eliminate bond failure in deficient lap splices of beams and wall-type bridge columns. The cyclic behavior of six full-scale reinforced concrete (RC) beams with a deficient lap splice strengthened with ultra-high-performance fiber-reinforced concrete (UHPFRC) is experimentally investigated. Direct comparison with existing pullout setups in the literature shows that bond strength measurements of the DTP formulation are more conservative and illustrate clearly the effect of bar cover on bond strength. Striking improvements were observed on the measured HPFRC and ECC bond strength and failure mode over bond of conventional (unconfined) concrete. relationship of bar and concrete strains with the rate of slip along the anchorage), and to study the effect of enhanced fracture energy supplied by the fibers on bond mechanics. Strain fields obtained from digital image correlation (DIC) were used to verify the kinematic hypotheses traditionally used in solving the field equations of bond (i.e. The behavior of the test-specimens was analyzed in detail using nonlinear finite element modeling and an extensive database of published bond tests in high-performance strain-hardening cementitious matrices. Study variables included the bar cover thickness and the type of FRC matrix used. The test setup was selected so as to minimize unaccountable confinement owing to support conditions and to eliminate out-of-plane effects due to flexural curvature.
Bond specimens were tested in a direct tension pullout (DTP) setup in order to quantify a lower bound for bond strength of bars in high performance fiber reinforced cementitious (FRC) matrices with tension-hardening properties, where the bar is developed in a tension stress field. In order to evaluate and quantify the bond strength of bars embedded in novel cementitious materials, a combined experimental and analytical study was conducted using 13 specimens fabricated with high-performance concrete materials containing either steel or PVA fibers. The internal confinement that occurs in high-performance fiber reinforced concrete enhances the bond strength to such an extent that very short anchorage lengths suffice to develop a standard steel reinforcing bar. The bonded interface is highly sensitive to any passive confinement that occurs normal to the contact area. Bond is the complex interaction that occurs at the interface of reinforcement and concrete, enabling force transfer between the two materials.
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