Post-Earthquake Damage Repair and Probabilistic Damage Control Approach for Reinforced Concrete Bridges
AdvisorSaiidi, Mehdi Saiid
Civil and Environmental Engineering
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The main objectives of the study were to develop post-earthquake repair methods using carbon fiber reinforced polymers (CFRP) and probabilistic damage control approach (PDCA) for reinforced concrete (RC) bridges. To develop repair methods, first repair objectives were defined. To define repair objectives, internal earthquake damage was quantified and correlated to a series of visible damage states (DSs). Bridge columns are designed to be the primary source of energy dissipation through nonlinear action under seismic loading and experience a wide range of apparent damage. Therefore, in the present study, DSs for bridge columns were used as a guide to define damage states for other bridge components. The degree of damage in columns depends on the earthquake level (seismic demand). Due to uncertainties in seismic demand and response, damage to bridge columns is probabilistic in nature. In the present study, in addition to bridge repair, a probabilistic damage control approach PDCA was developed for new and repaired bridge columns by incorporating the extent of lateral displacement nonlinearity defined by "Damage Index" (DI) and reliability analysis. The performance objective was defined based on predefined apparent DSs and the DSs were correlated to damage indices based on a previous study at the University of Nevada, Reno. The correlation between DI and DS was determined from a statistical analysis (resistance model) of over 140 response data measured from testing of 22 bridge column models subjected to seismic loads.To accomplish the objectives of this study, the present study was divided into seven parts. The first part was to conduct a detailed review of damage and repair methods in past earthquakes to identify gaps in repair methods. The second part was to develop practical methods to access the condition of an earthquake damaged bridge structural components in terms of apparent DS's. In the third part, repair design recommendations and design examples were developed to aid bridge engineers in quickly designing the number of CFRP layers based on the apparent DS. The fourth part was to establish a resistance model for the reliability analysis to develop a probabilistic based seismic design of bridge columns. In the fifth part, a load model was developed by conducting a large number of non-linear dynamic analyses on bridge bents. The uncertainties in ground motions, site class, bent configuration, earthquake return period were included in the analyses. In the sixth part of the study, the results of the reliability analyses were investigated, and a direct probabilistic design procedure was developed to calibrate design DI based on target reliability against failure. Finally, the PDCA methodology that was developed for conventional columns was used to extend the PDCA and reliability analysis approach to earthquake-damaged columns that have been repaired. Through this study, a new simple non-iterative method was developed for design of CFRP fabrics used in repair of concrete members. The step-by-step repair methods for bridge components that were developed as part of this study address a gap in rational and systematic repair tools that are needed subsequent to moderate and strong earthquakes. The PDCA that was developed and investigated provides design tools enabling designers and researchers to detail bridge columns for a target expected damage with an associated probability of occurrence and a reliability index.