The highway bridge infrastructure system within the United States is rapidly deteriorating and a significant percentage of these bridges are approaching the end of their useful service life. Deterioration mechanisms affect the load resisting capacity of critical structural components and render aging highway bridges more vulnerable to earthquakes compared to pristine structures. While past literature has traditionally neglected the simultaneous consideration of seismic and aging threats to highway bridges, a joint fragility assessment framework is needed to evaluate the impact of deterioration mechanisms on bridge vulnerability during earthquakes. This research aims to offer an efficient methodology for accurate estimation of the seismic fragility of aging highway bridges. In addition to aging, which is a predominant threat that affects lifetime seismic reliability, other stressors such as repeated seismic events or simultaneous presence of truck traffic are also incorporated in the seismic fragility analysis. The impact of deterioration mechanisms on bridge component responses are assessed for a range of exposure conditions following the nonlinear dynamic analysis of three-dimensional high-fidelity finite element aging bridge models. Subsequently, time-dependent fragility curves are developed at the bridge component and system level to assess the probability of structural damage given the earthquake intensity. In addition to highlighting the importance of accounting for deterioration mechanisms, these time-evolving fragility curves are used within an improved seismic loss estimation methodology to aid in efficient channeling of monetary resources for structural retrofit or seismic upgrade. Further, statistical learning methods are employed to derive flexible parameterized fragility models conditioned on earthquake hazard intensity, bridge design parameters, and deterioration affected structural parameters to provide significant improvements over traditional fragility models and aid in efficient estimation of aging bridge vulnerabilities. In order to facilitate bridge management decision making, a methodology is presented to demonstrate the applicability of the proposed multi-dimensional fragility models to estimate the in-situ aging bridge reliabilities with field-measurement data across a transportation network. Finally, this research proposes frameworks to offer guidance to risk analysts regarding the importance of accounting for supplementary threats stemming from multiple seismic shocks along the service life of the bridge structures and the presence of truck traffic atop the bridge deck during earthquake events.

The form of the energy function (i.e. Total, Hellinger-Reissner, Hu-Washizu or Complementary energy functions) has a significant influence on FEM performance. Motivated by the ability of the force-based method to satisfy the equilibrium equation and ability of the displacement-based method to satisfy compatibility equation, this thesis proposes a mathematical framework, namely the ‘Hybrid Force-Based Method’ which employs two physical concepts; the Total and Complementary Potential Energy functions. Satisfaction of both the Total and Complementary Potential Energy function is critical to the success of the Hybrid Force-Based Method. The Hybrid Force-Based Method is constructed using these two independent energy functions in order to perform inelastic structural analyses. The method has been proposed, implemented and evaluated across the entire structure, element, section and material domains first considering each domain separately and then in combination. The equilibrium and compatibility equations are satisfied simultaneously by discretisation of these two equations, and accuracy is controlled by specifying the upper and lower bounds of the results. Outcomes following evaluation of the proposed method can be classified into the following three categories: (i) structure-level performance (see Chapter 2), (ii) material-level performance (see Chapter 3), and (iii) element level performance (see Chapter 4). The proposed Hybrid Force-Based Method is constructed by deriving the governing equations directly from the Total and Complementary Potential Energy functions, leading to two distinct variants of the hybrid approach (i) the so-called ‘augmented Hybrid Force-Based Method’, and (ii) the so-called ‘unaugmented Hybrid Force-Based Method’. A number of numerical posterior process tests were devised and used to demonstrate the performance of these two variations of the hybrid method (see Sections 2.9.4.1 and 2.9.5.1) to demonstrate those methods ability in convergence in contrast to the Large Increment Method. Due to the occurrence of numerical instabilities experienced when using various established solution algorithms in solving the fundamental equations at the material level, within implicit approach (such as the Standard Implicit Method, the Cutting Plane Method, and the Closest Point Projection Method). A new form of the constitutive equation solver is proposed in Sections 3.9, referred to as the General Implicit Method (GIM). It is shown that the GIM can be implemented both in the strain and stress domains, and is therefore appropriate for use in both the displacement- and the force-based solution family of methods. The GIM is then evaluated by comparing its predictions to those of other common solution algorithms for inelastic analysis. Performance evaluation involves the use of a new error indicator that guarantees the uniqueness and accuracy of a solution in both the stress and the strain domains. Three iso-error maps serve to emphasis the accuracy, reliability, and computational performance of the General Implicit Method as a solution method compared to those are evaluated for the defined Stress Increment Ratio. The fundamental equations at the element level are followed, based on structured fibre discretisation. The decomposition of the various degrees of freedom into deformational and rigid-body motion serve as a mechanism by which independent equilibrium equations can be determined for each element. The subsequent equation is able to involve axial force, torsion, and both in and out of plane moments while a general form of shear strain distribution is also involved. The original form of the solution at the cross section of the elements leads to novel governing equations that are based on the characteristics of the hybrid force-based approach. The numerical evaluation in Section 4.11.7.1 demonstrates the performance of the proposed method. The newly defined error indicators demonstrate the accuracy and computational performance of the method and the uniqueness of the solution in satisfying both the equilibrium and compatibility equations for Euler-Bernoulli, Timoshenko, and Reddy strain distributions across the element section. Further to the structured fibre, distributed, semi-distributed and concentrated inelastic approach elements, as a simplified form of the element are implemented and evaluated. Although performance of those original formulations is evaluated independently in in comparison with the conventional approaches, compatibility of those as an important issue is followed as well. The numerical evaluation demonstrates higher accuracy and reliability by following the proposed method, further to the higher computational performance respect to the conjugate approaches.

This thesis examines the development of a superstructure for a slab-on-girder wood-concrete composite highway bridge. Wood-concrete composite bridges have existed since the 1930's. Historically, they have been limited to spans of less than 10 m. Renewed research interest over the past two decades has shown great potential for longer span capabilities. Through composite action and suitable detailing, improvements in strength, stiffness, and durability can be achieved versus conventional wood bridges. The bridge makes use of a slender ultra-high performance fibre-reinforced concrete (UHPFRC) deck made partially-composite in longitudinal bending with glued-laminated wood girders. Longitudinal external unbonded post-tensioning is utilized to increase span capabilities. Prefabrication using double-T modules minimizes the need for cast-in-place concrete on-site. Durability is realized through the highly impermeable deck slab that protects the girders from moisture. Results show that the system can span up to 30 m while achieving span-to-depth ratios equivalent or better than competing slab-on-girder bridges.

This thesis examines the development of a superstructure for a slab-on-girder wood-concrete composite highway bridge. Wood-concrete composite bridges have existed since the 1930's. Historically, they have been limited to spans of less than 10 m. Renewed research interest over the past two decades has shown great potential for longer span capabilities. Through composite action and suitable detailing, improvements in strength, stiffness, and durability can be achieved versus conventional wood bridges. The bridge makes use of a slender ultra-high performance fibre-reinforced concrete (UHPFRC) deck made partially-composite in longitudinal bending with glued-laminated wood girders. Longitudinal external unbonded post-tensioning is utilized to increase span capabilities. Prefabrication using double-T modules minimizes the need for cast-in-place concrete on-site. Durability is realized through the highly impermeable deck slab that protects the girders from moisture. Results show that the system can span up to 30 m while achieving span-to-depth ratios equivalent or better than competing slab-on-girder bridges.