Numerical modeling and design sensitivity of structural and seismic behavior of UHPC bridge piers

Advanced behavior of Ultra-high performance concrete (UHPC) is attracting a growing interest among the construction industry worldwide. Currently, UHPC is commonly used in precast bridge deck joints and connections. As the UHPC market grows, the material will have a great potential to extend to larger structural applications. However, there is no guidance yet on best practices or optimum structural designs that fully utilize the UHPC superior mechanical properties for larger components. The objective of this study is to better understand the overall behavior, failure mechanism, and effect of reinforcement and design details of UHPC bridge columns using detailed finite element modeling. The pushover response of a two-column bridge pier with the typical geometry and gravity loads obtained from a representative California bridge is investigated when UHPC is used instead of conventional concrete for the columns. A detailed sensitivity/parametric analysis is conducted to assess the effect of different steel fiber ratio, longitudinal reinforcement ratio, and steel grades of reinforcement bars on the overall structural behavior of the columns. The total strain crack model, as readily implemented in DIANA FEA, is utilized with user-defined input to model the UHPC constitutive material behavior. The UHPC stress-strain relationships in tension and compression are independently defined using uniaxial curves from the literature. For comparison, the two-column bent of conventional concrete is modeled and used as the reference case to evaluate the relative increase in load capacity of the UHPC bridge columns.