Lateral Drop-Weight Impact Response of SRC Columns with Built-In L-Shaped Steel: Role of Impact Velocity, Axial Compression Ratio, and Stirrup Spacing

L-shaped steel-reinforced concrete (SRC) columns are commonly used as edge and corner members in bridge piers and high-rise buildings. However, systematic experimental evidence on their dynamic behavior and detailing effects under lateral impact remains limited. This study presents a parametric drop-weight impact program on seven SRC columns with built-in L-shaped steel sections. The effects of impact velocity (v), axial compression ratio (n = 0–0.2), and stirrup spacing in the non-densified region (s = 100–200 mm) were examined in terms of damage evolution, impact-response indices (Fmax, Fave, Δmax, Δres, T), and energy absorption efficiency (η = Eab/E). The results show that impact velocity was the dominant parameter governing both response amplitude and damage severity. Increasing v from 7.67 to 9.90 m/s increased Δmax and Δres by 92.6% and 144.3%, respectively, while η increased from 60.7% to 74.6%. Within the investigated range, axial compression improved resistance and suppressed residual deformation. As n increased from 0 to 0.2, Fmax and Fave increased by 17.5% and 30.4%, respectively, whereas Δres decreased by 32.1%. The effect of stirrup spacing on η was non-monotonic. The intermediate spacing (s = 150 mm) yielded the highest energy absorption ratio (60.7%) and the most balanced overall response among the tested cases, rather than representing a definitive optimum. No global buckling of the embedded steel section was observed, and all specimens maintained overall structural integrity under high-energy impact. These results provide experimental evidence for the response assessment and preliminary transverse detailing of asymmetric SRC columns under lateral impact.