Experimental and Numerical Investigation of CFRP-Strengthened Reinforced Concrete Slabs with Mechanical Anchorage Systems Under Repeated Low-Velocity Impact Loading

Reinforced concrete (RC) slabs in buildings and protective structures are vulnerable to repeated low-velocity impacts caused by falling objects, vehicle collisions, industrial accidents, and successive debris strikes. Such repeated impacts can result in cumulative damage, progressive stiffness degradation, and eventual structural failure. Although externally bonded carbon fiber-reinforced polymer (CFRP) sheets have been widely adopted to improve the impact resistance of RC members, their effectiveness under repeated impact loading is often limited by premature debonding, while the contribution of mechanical anchorage systems to mitigating debonding and improving structural performance remains insufficiently understood. Accordingly, this study experimentally and numerically investigates the repeated low-velocity impact behavior of RC two-way slabs strengthened with externally bonded CFRP sheets incorporating boundary and distributed mechanical anchorage configurations. Four slab groups were investigated: unstrengthened control slabs (SL1), CFRP-strengthened slabs (SL2), CFRP-strengthened slabs with boundary anchors only (SL3), and CFRP-strengthened slabs with distributed anchors across the entire slab area (SL4). Repeated impact tests were conducted using a 92 kg drop weight released from progressively increasing heights until failure. The outcomes showed that strengthening of RC slab with CFRP sheets significantly improved the impact resistance at a 1.50 m drop height by reducing the residual displacement, crater diameter, and indentation depth by up to 67%, 55%, and 70%, respectively, compared with the control slabs. The incorporation of mechanical anchors further delayed premature CFRP debonding, maintained the CFRP–concrete bond, and enhanced the structural response, achieving maximum reductions of 77%, 63%, and 85%, respectively. Furthermore, the anchored slabs withstood repeated impacts from a 2.50 m drop height, whereas both the control and unanchored CFRP-strengthened slabs failed at a 2 m drop height. The developed finite element model accurately captured the structural response, CFRP debonding, anchorage failure, and damage evolution of the RC slabs, with good agreement between the numerical predictions and the experimental observations in terms of failure patterns, damage characteristics, and residual displacements. The proposed strengthening strategy and validated numerical model provide a reliable framework for assessing the effectiveness of different mechanical anchorage configurations and predicting the progressive failure behavior of CFRP-strengthened RC slabs subjected to repeated low-velocity impacts.