Probabilistic seismic demand models of RC bridge columns retrofitted with shape memory alloy spirals

Shape memory alloys;Demand model;Confinement;Performance based design;Retrofit;Seismic;Damage index

Deogekar, Pratik Sharad ; Andrawes ; Bassem

关键词: Shape memory alloys;    Demand model;    Confinement;    Performance based design;    Retrofit;    Seismic;    Damage index;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/99438/DEOGEKAR-THESIS-2017.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The breakdown of critical bridge infrastructure in past earthquakes has often been attributed to the failure of reinforced concrete (RC) bridge columns due to lack of flexural ductility. Despite the revision of structural design standards to accommodate the lessons learned from these earthquakes, a significant number of RC bridge columns, built prior to these revisions, are vulnerable to failure under moderate and high intensity earthquakes. Recent studies have shown that retrofitting these vulnerable RC bridge columns by applying lateral active confinement using shape memory alloy (SMA) spirals can significantly improve their ductility, resulting in enhanced seismic performance. The research work done till date in this area is limited to exploring experimentally the efficacy of this new retrofit technique on a material and component level. In order to aid the implementation of this retrofit technique in actual construction practice, this thesis initiates the development of a performance-based-design framework for SMA retrofitted columns by creating seismic demand models which relate the intensity measure (IM) of an earthquake with the demand imposed by the earthquake on SMA retrofitted RC columns, which is quantified in terms of demand measures (DM).An array of vulnerable RC bridge columns, susceptible to flexural failure due to inadequate lateral confinement, is created using Latin hypercube sampling and 6 columns with varying time periods and reinforcement ratios are chosen. These columns are retrofitted with SMA spirals in their plastic hinge region and subjected to a suite of bi-directional ground motion records. The performance of the retrofitted columns is assessed using 4 DM including maximum drift, residual drift, an energy-based concrete damage index and a steel damage index based on low-cycle fatigue. The suitability of 8 IMs for the development of probabilistic demand models to predict the DMs is explored. The optimal IM, which predicts the DM with least uncertainty, is found to be a function of the fundamental period of the retrofitted columns. The final demand models, developed using the optimal IM, are presented and compared to understand the effect of lateral active confinement. The results indicate that increasing the confinement reduces the damage in concrete substantially while the damage associated with low-cycle fatigue of steel is also reduced. Higher levels of active confinement are also seen to be effective in reducing the residual drifts of long period columns.