Studying the Effect of Skew Angle on the Behavior of Concrete Slab Under Repeated Load

This study experimentally and numerically investigates how skew angle affects the structural behavior of reinforced concrete slabs under monotonic and repeated loading. Eight simply supported slab specimens were divided into four groups corresponding to skew angles of 0°, 15°, 30°, and 45°, with one specimen in each group tested under monotonic loading and the other under repeated loading. All specimens had plan dimensions of 1400 × 1400 mm and a thickness of 100 mm and were subjected to a concentrated load at mid-span. The repeated-loading protocol consisted of stepwise quasi-static loading–unloading cycles with the peak load increased by 5 kN in each successive cycle until failure. All specimens exhibited predominantly flexural failure, with major cracking concentrated within the middle region of the slabs. The first-cracking loads under repeated loading were approximately 9.1–12.0% lower than those of the corresponding monotonic specimens. The effect of repeated loading on yield and ultimate response depended on skew angle and did not exhibit a uniform trend. However, increasing skew angle generally reduced load resistance and increased deformation. Under repeated loading, the ultimate load decreased by approximately 13.2%, 27.6%, and 33.1% for skew angles of 15°, 30°, and 45°, respectively, relative to the zero-skew specimen. Under monotonic loading, the 45° specimen exhibited approximately 24.9% lower ultimate resistance than the zero-skew specimen. The displacement ductility response was non-monotonic; under monotonic loading, maximum ductility occurred at 30°, and under repeated loading, at 15°. A simplified equivalent-strip analytical model was used as a preliminary reference, while three-dimensional nonlinear finite-element models were developed using ANSYS. The finite-element predictions of ultimate load differed from the experimental results by approximately 5.6–15.2%, although larger differences were observed in the load–deflection response and crack distribution. Overall, the experimental findings suggest that skew angle and loading history may influence deformation, stiffness, and ultimate resistance. However, since only one specimen was tested for each configuration, the reported differences should be considered descriptive observations rather than statistically validated relationships. Further experimental investigations with replicate specimens are required to confirm these trends.