Experimental study on the behavior and strength of 180 ° hooked bar lap splices in precast concrete slabs

초록

This study experimentally investigates the behavior and splice performance of 180-degree hooked bar lap splices in precast concrete (PC) slabs. In thin members such as slabs, the limited thickness constrains straight bar development, making 180-degree hooks a rational alternative. However, current codes are based on single anchored bars and lack a basis for direct application to lap splices. Four-point bending tests were therefore conducted on 18 specimens, with splice length, bar diameter, concrete compressive strength, and splice spacing as variables. The wide slab section prevented continuous side-splitting, but in specimens failing before yielding, flexural cracks concentrated at the hook bend and reduced the bearing section, leading to pull-out failure with local cover splitting. The rate of strength increase with splice length was markedly lower for the larger D19 bars, which required a disproportionately longer splice. Under KDS 14 20 52 and ACI 318–25, the mean test-to-prediction ratio was 0.84, with 94% of specimens unconservative. Expressing the measured strength in the form of the development-length equation showed that the current provision underestimates the required splice length for hooked bar lap splices in slabs, so a longer splice length than the current provision is required. These results provide experimental evidence of an unconservative tendency in current hooked-bar provisions rather than a calibration database.

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