Structural effectiveness of NSM aluminum bars combined with UHPC/ECC overlays in strengthening RC slabs against punching shear

ABSTRACT This study investigates the structural performance of reinforced concrete slabs strengthened using ultra-high-performance concrete (UHPC) and engineered cementitious composite (ECC) overlays combined with near-surface-mounted (NSM) aluminum bars. An experimental program comprising multiple strengthening configurations was conducted to assess improvements in punching shear resistance, stiffness, and failure mechanisms. Complementary finite element models were developed and calibrated using the Concrete Damaged Plasticity approach to simulate the nonlinear behaviour of the strengthened slabs and validate the experimental findings. An analytical case study further examined the contribution of NSM aluminum bars to punching shear capacity and demonstrated the practical applicability of the proposed system. Results show that the UHPC overlay with orthogonal NSM bars achieved up to a 121% increase in ultimate load and a shift from brittle punching failure toward a more ductile flexural response. The combined experimental, numerical, and analytical outcomes highlight the effectiveness and practical potential of the UHPC–NSM strengthening technique for enhancing slab punching resistance.