A novel coupled modeling approach of UHPC-NC components based on peridynamics

Ultra-high performance concrete (UHPC) is recognized for its exceptional mechanical properties. Due to its relatively high cost, it is often combined with normal concrete (NC) to improve cost-efficiency in engineering. Notably, the complex interaction mechanisms in UHPC-NC materials present significant challenges for accurate simulation. This paper presents a novel coupled modeling approach to accurately and efficiently simulate the complex mechanical properties of UHPC-NC components using bond-based peridynamics (BPD). This approach uses a coupled adhesive-frictional interaction (AFI) element to accurately study the relative slip and damage at interfaces between the UHPC and NC. Secondly, a fiber-matrix coupled (FMC) element is developed to simulate the pull-out behavior of fibers embedded into the UHPC matrix, which is constructed with fictitious nodes to avoid increasing degrees of freedom. Moreover, the matrices of UHPC and concrete are modeled based on BPD theory to investigate the damage and cracking behavior in detail. The above modeling framework has been implemented in OpenSees, and combined with a CPU parallel computing strategy for efficient execution of implicit static analysis. Three application examples are used to validate the efficiency of the proposed approach. This study illustrates that the UHPC/NC material and its interface properties significantly influence the mechanical performance and failure modes of composites. The results show that fiber bridging significantly suppresses crack propagation and enhances ductility. Increasing UHPC content or interface roughness improves strength and damage resistance. The model accurately captures early-stage interfacial degradation, nonlinear crack evolution, and load transfer mechanisms, while achieving higher computational efficiency. This study provides a valuable analytical approach for optimizing UHPC-NC material design in engineering applications.