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.

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.

This research investigates the potential of a new technique designated as Partially Embedded Bars (PEB) for shear-strengthening of existing reinforced concrete (RC) bridge girders. In this technique, shear strengthening is achieved by inserting steel or FRP bars into holes bored through a partial depth of the girder cross-section and then bonded with an epoxy adhesive. The PEB approach is a modification of an existing retrofit technique, referred to as Deep Embedment (DE) or Embedded Through Section (ETS) technique. Experimental studies by previous researchers have been limited to the DE or ETS method wherein steel or CFRP bars are inserted through the full depth of the RC girder, which can be time-intensive (since access to the bottom of the bridge is necessary) and uneconomical. In addition, most of the reported studies are limited to small-scale testing or comprise configurations that do not resemble typical highway bridges or Caltrans practice. A preliminary exploratory experimental program is first carried out comprising pull-out testing to examine the several options that exist to implement the PEB approach – both in terms of the strengthening bar material type (steel or FRP) and the type of bonding material (epoxy or grout) to be used to anchor the bar into the girder web. The pull-out test campaign comprising thirty rectangular concrete blocks with embedded uncoated traditional Steel (Grade 60 ksi), uncoated High Strength Steel (HSS) Grade 80 ksi, and sand-coated and smooth carbon fiber reinforced polymer (CFRP) bars bonded with either epoxy or grout was performed to determine the most effective strengthening material option. Findings from the direct pull-out testing revealed that the specimens with sand-coated CFRP bars bonded with the epoxy performed remarkably better than the specimens with other strengthening materials.

Next, an experimental program comprised of three-point load bending testing to failure of full-scale RC T cross-section girders strengthened in shear was carried out. The tested girders represent an existing prototype bridge from the Caltrans bridge inventory. The girders were strengthened in shear with the PEB technique utilizing CFRP bars and epoxy adhesive using two options. The primary goal of the first option was to evaluate the effectiveness of the PEB method as a shear-strengthening technique, whereas the second option investigated the effect of increasing the shear reinforcement ratio on the shear capacity gain associated with employing the PEB method. Results from the two tests demonstrated that the PEB method is an effective shear-strengthening technique. An increase of 53% and 30% was observed in the shear capacity of the strengthened specimen compared to the control specimen. Results from the second test revealed that increasing the shear reinforcement ratio has an adverse effect on the shear strength gain associated with utilizing the PEB technique. Finally, the experimental testing was supplemented with numerical simulations to provide additional insight into the shear capacity gain as a result of implementing the PEB method. Observations of the two tests were supported by the three-dimensional nonlinear finite element modeling (FEM) which resulted in good correlations with global and local behaviors of the experimentally tested girders. The validated model can be utilized to generate a parametric study that can eventually lead to the development of a step-by-step design guideline to help bridge engineers estimate the gain in shear capacity of RC girders strengthened with the PEB method.

Performance-based seismic evaluation and retrofit of existing buildings documented in ASCE 41, a professionally recognized standard, contain guidelines and provisions that extend over several analysis procedures. The consistency between the linear and nonlinear analysis procedures outlined in the standard was investigated through the detailed assessment of four existing steel moment frame and concrete shear wall buildings in California. The buildings were instrumented by the California Strong Motion Instrumentation Program, which allowed for the calibration of the structural simulation models against recorded data from past earthquakes. The primary ASCE 41 based assessments of the calibrated models were followed by a comprehensive incremental dynamic analysis (IDA) of each building based on FEMA P-695 to evaluate the collapse probability inherent in the ASCE 41 Collapse Prevention performance level. Finally, a correlation between a system-based drift demand parameter and Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) was established for the four buildings.

This dissertation addresses some of the core issues in ASCE 41 through comprehensive case studies of 3-story and 6-story steel moment frame buildings, and 3-story and 5-story reinforced concrete shear wall buildings. First, options for modeling of the primary structural components are explored, followed by a system-based calibration of the model against displacement and acceleration time histories in past earthquakes recorded at the site. For the steel buildings, a major focus was on obtaining the nonstructural stiffness contribution at low intensities, and understanding how the contribution of nonstructural components diminishes during strong shaking. For the concrete buildings, extensive effort was devoted to modeling options for flexural-controlled versus shear-controlled walls.

The ASCE 41 assessments demonstrated inconsistency between the four analysis procedures. The linear static and linear dynamic procedures produce similar component demands, drifts, and performance levels but were shown to be conservative compared to the nonlinear procedures. The nonlinear static and nonlinear dynamic procedures differed significantly in component-demands and drift patterns, and the static procedure underestimated the demands in the upper stories of the six-story steel building. These basic assessments were followed by incremental dynamic analyses and collapse probability fragility curves were developed based on an assumed collapse condition at 6% story drift. Results from the simulation studies indicate that the current component-based Life Safety and Collapse Prevention performance levels are conservative and a quantified comparison is presented using a drift-based approach. Findings from this research work indicate the need to modify the current acceptance criteria for each performance level to include a system-based demand criteria. The dissertation concludes with recommendations for future research focused on developing methodologies to augment acceptance criteria as well as the need for improved guidelines for shear-controlled walls and ground motion scaling for hazard-consistent assessments.