Opposite Peak Ratio to Characterize Ground Motion Loading History for Performance-Based Design

Recent studies have revealed the impact of ground motion loading history on performance limit states of reinforced concrete (RC) bridge columns such as reinforcement bar-buckling and residual drift ratio. Conventional hazard characterizations such as peak ground acceleration, spectral acceleration, and spectral displacement only capture peak values of ground motion hazard and, therefore, fall short of providing the necessary information to account for these limit states. In this study, a parameter termed as the opposite peak ratio (Rop) is defined, explored, and shown to be useful in reproducing loading history characteristics of ground motions for displacement-based design. Several past ground motion records were analyzed to develop empirical models that can estimate Rop. These models provide the mean and confidence intervals of Rop as a function of earthquake magnitude, epicentral distance, structural period, hysteretic model, and displacement ductility. To motivate practitioners to make use of Rop, a design scenario and two case studies are discussed. In an RC bridge column design scenario, it is shown that having prior information about the expected Rop at the site could reduce the structural cost of the bridge. Next, case studies designed to investigate correlations between Rop and the performance limit states of RC bridge columns are discussed. By analyzing the results of nonlinear time-history analyses of numerical RC column models, it is established that Rop could potentially be a significant variable in generating fragility models for these limit-states.

Numerical analysis of axial load effects on RC bridge columns under blast loading

Blast load and its effects on transportation infrastructure especially bridge structures have received considerable attention in recent years. The RC bridge columns are considered as the most critical structural members because their failure leads to collapse of the bridge. Although RC bridge columns are typical axial load-carrying components, the studies on blast-resistant capacity of RC bridge columns usually neglect the axial load effect since it is commonly assumed that neglecting the axial load leads to conservative predictions of column responses. This assumption is true when column failure is governed by flexural response since axial compressive load generates a prestress in column which compensates concrete tensile stress induced by bending response. When subjected to blast loads, column response however could be governed by shear response. In this case neglecting axial loading effect does not necessarily lead to conservative predictions of column responses. In this study, high-fidelity finite element (FE) models for both non-contact explosion and contact explosion were developed in LS-DYNA. The FE models were validated with field blast test data. Subsequently, intensive simulations of the RC bridge columns with and without axial load subjected to a wider range of blast loading scenarios, including far-field, near-field and contact explosion were conducted. The influence of axial load on the dynamic performance of RC bridge columns corresponding to different blast loading scenarios was discussed.