This research investigates the consequences of two amendments by the California Department of Transportation (Caltrans) of current AASHTO (2017) guidelines related to the determination of the shear resisted by concrete in a post-tensioned (PT) girder containing grouted ducts. Experimental studies by previous researchers have either been limited to small-scale testing or comprise configurations that do not resemble typical Caltrans practice. In this study, load testing to failure of the specimens was carried out on near full-scale cross-sections that represent typical Caltrans PT girders. The experimental testing is further supplemented with numerical simulations to provide additional insight into the effect of grouted ducts in PT girders. Two large-scale specimens were fabricated to achieve the goals of the project and represented a prototype bridge from the Caltrans bridge inventory. Reinforcing details of the specimen were modified so as to induce shear failure prior to flexural yielding of the specimen. Considerable effort was dedicated to the design of a reaction system so that the imposed loading at shear failure of the specimen could be safely distributed to the strong floor of the laboratory. The primary goal of the first test was to examine the consequence of the Caltrans amendment related to the effective web width in calculating the shear resistance of a PT girder with grouted ducts whereas the second test investigated Caltrans practice of bundling more than three ducts that is currently disallowed in the AASHTO bridge design specifications. Findings from the experimental testing indicate that the shear resistance of PT girders with grouted ducts have significant reserve strength beyond the AASHTO-predicted shear capacity.

For the specimens tested in this study, the concrete contribution（Vc）to shear resistance varies between 15 – 25% of the nominal shear capacity and the difference in Vc resulting from the Caltrans amendment for establishing the effective width of the web affects the nominal shear capacity of the girder by less than 5% and consequently has a minor effect in the design of PT girders with fully grouted ducts. There was no visible distress around the duct region at the end of testing for specimen #1 indicating that the corrugated metal duct bonds well to the concrete and remains intact even at loads approaching shear failure of the girder. Minor to moderate distress was observed on the concrete surface along the duct lines for specimen #2, which experienced a dramatic shear failure. The inclination of shear cracks for both specimens during testing varied between 25 - 30 degrees, which is slightly lower that AASHTO estimates, with the angle of newly forming cracks tending to decrease with increasing load. These findings are also supported by the numerical simulations of additional girders with varying duct sizes and number of ducts.

The ShakeCast software platform, utilized by the California Department of Transportation (Caltrans), utilizes near real-time ground shaking maps generated by the US Geological Survey in conjunction with predictive fragility models, encompassing both seismic demand models and component/system capacity models, to evaluate the likely damage to all bridges in the vicinity of an earthquake event. The ability to estimate with reasonable accuracy the likelihood and extent of damage to bridges following an earthquake is crucial to post- earthquake activities such as the mobilization of emergency response. While the development of seismic demand models has seen considerable progress, there is a significant gap in our current ability to correlate demands with capacity limit states, particularly for older California bridges. Whereas modern bridges designed after 1990 are expected to perform well, older bridges, particularly those built before 1971 (and referred to as Era-1 bridges in this dissertation), are vulnerable to damage. It is the goal of this research to address this gap by developing a range of component capacity limit states (CCLS), from minor damage up to collapse, for pre-1971 Caltrans bridge columns through rigorous modeling and comprehensive simulations.A simulation model is developed for non-ductile bridge columns considering potential failure modes such as flexure, shear and mixed shear-flexure and incorporating critical effects at the material level (such as confinement in concrete, bar buckling in reinforcing steel) and sectional level (such as bond-slip due to strain penetration). Given the prevalence of drift-based measures in seismic design and assessment, the first choice considered in the development of the CCLS models was ductility. A strain-based approach was used to correlate damage with capacity limit states for both circular and wide rectangular sections that typify Era-1 bridge columns. Findings from this phase of work exposed a major drawback in using ductility-based measures to characterize capacity limit states under random earthquake-induced loading. Hence, a major effort was dedicated to developing a damage-index based approach to classifying limit states. The proposed damage-based approach to developing CCLS models was validated against experimental data and then applied to single, two and three-column bents. Fragility functions were developed wherein exceedance probabilities of damage states are examined as a function of seismic intensity. The new damage-based methodology was successful in predicting a range of capacity limit states associated with visual damage such as cracking of the cover concrete, spalling of concrete, buckling of longitudinal reinforcement, crushing of the core concrete and multi-bar rupture. Findings from the study will not only assist in post-earthquake emergency response efforts but also in prioritizing strengthening of such nonductile bridges.