Predicting UHPC Structural Response at Ultimate Limit State through Numerical Simulation Technique

Ultra-high performance concrete (UHPC) is being considered as an alternative ductile material to be used in the expected plastic hinge regions of structural components in buildings and bridges. Although several experimental studies of reinforced UHPC structural elements have been conducted for proof-of-concept seismic application, quantification of the plastic hinge length and associated rotation at ultimate limit states remains the most significant aspect for the ductile design of UHPC components in new structures. To that end, this study utilizes two-dimensional finite element models incorporating recently developed bond-slip constitutive model, which aids in simulating multiple damage states, such as yielding of reinforcement and reinforcement fracture. Several finite element models with variations in geometrical properties and loading scheme were simulated to compute the equivalent plastic hinge length values for reinforced UHPC flexural members. The existing empirical equations available for reinforced concrete and reinforced highperformance fiber-reinforced cementitious composite (HPFRCC) were found to over-predict the equivalent plastic hinge length in reinforced UHPC members. In addition, a mechanics-based approach was used to estimate the ultimate rotation capacity utilizing the plastic hinge length values obtained from numerical simulation techniques. This study can be used as starting point to develop a more robust empirical expression of plastic hinge length for reinforced UHPC flexural members and formulate a simplified approach to compute non-linear modeling parameters for displacement-based seismic design of UHPC structural components.