Load-Path Redistribution and Damage Asymmetry in Reinforced Concrete Beams Under Eccentric Drop-Weight Impact: A Coupled SPH-FEM Study

Reinforced concrete (RC) beams under impact are commonly assessed using central-impact configurations, but practical impacts may deviate from midspan and create unequal shear spans. This study investigates how impact eccentricity changes force transfer and damage development using a validated coupled smoothed particle hydrodynamics–finite element method (SPH-FEM) model. Concrete is modeled with SPH particles, while reinforcement, supports, and the impactor are modeled with FEM solid elements. After validation against central drop-weight tests, full-span eccentric-impact cases are compared with matched short-span references. The first contact-force peak changes only slightly with eccentricity, whereas the later response distribution changes more substantially. At the largest eccentricity, shorter-span shear reaches up to 2.23 times the central-impact value, showing shear-dominated redistribution. Absorbed energy per unit length also localizes on the shorter-span side and reaches up to 4.29 times the longer-span side value. Matched references show that full-span eccentric beams can develop up to 18.4kN higher local shear than symmetric short-span beams. Damage fields shift from symmetric central damage to asymmetric shorter-span-side damage with clearer fragmentation in low-strength cases. For off-midspan accidental-load assessment, the central-impact force level should be considered together with side-specific shear demand, the shorter-span shear-transfer path, and asymmetric damage.