UBC Theses and Dissertations
Performance-based seismic design and assessment of concrete bridge piers reinforced with high-strength steel rebar Aldabagh, Saif Maad
Utilizing high-strength steel (HSS) rebars in concrete bridge columns in seismic applications is greatly restricted primarily due to the lack of appropriate seismic design guidelines. The purpose of this study is to use a combination of analytical and experimental methods to evaluate the seismic performance of concrete bridge columns reinforced with HSS rebars, and thereby make appropriate design recommendations. ASTM A1035 Grade 690 steel was the primary focus of this study, however, other types of HSS were also considered in a number of assessments for comparison purposes. In this study, a comprehensive analytical program with an overarching objective of proposing simplified expressions to predict drift ratio limit states for circular concrete columns reinforced with HSS was first carried out. A machine learning-based symbolic regression was used to fit the resulting data into simplified numerical expressions. The proposed simplified expression provided adequate predictions of the drift ratio limit states obtained from the numerical analysis as well as those measured in previous experimental programs. In addition, a comprehensive experimental study was carried out to examine the low-cycle fatigue performance of ASTM A1035 Grade 690 rebars under cyclic-strain reversals. Existing strain and energy-based fatigue-life models’ constants were calibrated using the generated experimental fatigue data. Previously established low-cycle fatigue life models of HSS rebars were utilized as a part of an analytical program to identify conditions under which such rebars can achieve adequate performance in comparison to that of benchmark ASTM A706 Grade 420 steel bars in concrete bridge columns. Irrespective of the spacing-to-bar diameter ratio, ASTM A1035 Grade 690 rebars demonstrated adequate low-cycle fatigue performance for crustal earthquakes up to a displacement ductility level of 2. Design codes were found overly restrictive in not permitting the use of HSS in seismic applications based on their low-cycle fatigue performance. Lastly, analytical seismic fragility curves were developed for a concrete bridge pier alternately reinforced with HSS and conventional normal-strength steel. Comparisons between fragility curves were made to evaluate the applicability of certain clauses of the Canadian Highway Bridge Design Code to bridge piers reinforced with HSS.
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