Probabilistic seismic assessment of bridges

Tese de doutoramento. Engenharia Civil. Universidade do Porto. Faculdade de Engenharia. 201

An Overview of Deterministic and Probabilistic Analytical Approaches for Non-Linear Seismic Risk Assessment of Structures

Performance-based earthquake engineering (PBEE) is a framework that seeks to improve decision-making for seismic risk mitigation through assessment and design methods featuring performance metrics that meet the diverse needs and objectives of owners/users and society. The selection of seismic design analysis approach depends on several factors such as the size and layout of the structure, design objectives, seismic design category, and the value of the structure. Generally, analysis methods can be categorized into two major groups: static and dynamic analysis, both of which are possible to be conducted as linear or nonlinear analysis. This paper presents an overview of the procedures of the nonlinear analysis methods, namely the nonlinear static analysis (NL-SA) and nonlinear dynamic analysis (NL-DA), in addition to the development of fragility curves for a probabilistic seismic risk assessment

Development of fragility curves for RC bridges subjected to reverse and strike-slip seismic sources

. This paper presents a probabilistic fragility analysis for two groups of bridges: simply supportedand integral bridges. Comparisons are based on the seismic fragility of the bridges subjected toaccelerograms of two seismic sources. Three-dimensional finite-element models of the bridges were createdfor each set of bridge samples, considering the nonlinear behaviour of critical bridge components. When theseismic hazard in the site is controlled by a few seismic sources, it is important to quantify separately thecontribution of each fault to the structure vulnerability. In this study, seismic records come from earthquakesthat originated in strike-slip and reverse faulting mechanisms. The influence of the earthquake mechanismon the seismic vulnerability of the bridges was analysed by considering the displacement ductility of thepiers. An in-depth parametric study was conducted to evaluate the sensitivity of the bridges' seismicresponses to variations of structural parameters. The analysis showed that uncertainties related to thepresence of lap splices in columns and superstructure type in terms of integral or simply supported spansshould be considered in the fragility analysis of the bridge system. Finally, the fragility curves determine theconditional probabilities that a specific structural demand will reach or exceed the structural capacity byconsidering peak ground acceleration (PGA) and acceleration spectrum intensity (ASI). The results alsoshow that the simply supported bridges perform consistently better from a seismic perspective than integralbridges and focal mechanism of the earthquakes plays an important role in the seismic fragility analysis ofhighway bridges

Planning and management of actions on transportation system to address extraordinary events in post-emergency situations. A multidisciplinary approach

The main aim of the work is the design and implementation of an integrated procedure for the identification of optimum action plans (satisfying expenditure constraints) on a road transportation system to minimize the impact produced on it by extraordinary events, in particular earthquakes. The attention is focused particularly on post-emergency situations related to effects on transportation networks caused by extraordinary events; the effects are considered with reference to bridges. Addressing the transition from physical effects to functional effects (relating to mobility) on the single infrastructure element calls for a commitment which has appeared challenging in view of the strongly innovative content involved. The analysis process consists in different steps. At the first step an effort must be made in order to acquire knowledge about the characteristics of the set of infrastructures (bridges) and about a set of possible seismic scenarios. By using fragility curves of bridges, the damage state of the network links (in which bridges are included) can be obtained. By making a series of hypotheses on how a bridge damage state can influence links’ functionality, a set of “damaged” (lower capacity) road network models has been carried out. At the next step of the process, interaction between transportation supply and demand, by way of static or dynamic traffic assignment models, allows to measure the performance of the system, or rather, its overall response to extraordinary events using suitable performance indexes. Then, the network risk curve (probability of the seismic action vs. transportation system performance indexes) is derived. At the end of the process a cost-effective retrofit strategy has been identified. The procedure has been applied to a test network at regional scale in the north-east of Italy

Collapse Vulnerability and Fragility Analysis of Substandard RC Bridges Rehabilitated with Different Repair Jackets under Post-Mainshock Cascading Events

Past earthquakes have signaled the increased collapse vulnerability of mainshock-damaged bridge piers and urgent need of repair interventions prior to subsequent cascading hazard events, such as aftershocks, triggered by the mainshock (MS). The overarching goal of this study is to quantify the collapse vulnerability of mainshock-damaged substandard RC bridge piers rehabilitated with different repair jackets (FRP, conventional thick steel and hybrid jacket) under aftershock (AS) attacks of various intensities. The efficacy of repair jackets on post-MS resilience of repaired bridges is quantified for a prototype two-span single-column bridge bent with lap-splice deficiency at column-footing interface. Extensive number of incremental dynamic time history analyses on numerical finite element bridge models with deteriorating properties under back-to-back MS-AS sequences were utilized to evaluate the efficacy of different repair jackets on the post-repair behavior of RC bridges subjected to AS attacks. Results indicate the dramatic impact of repair jacket application on post-MS resilience of damaged bridge piers—up to 45.5 % increase of structural collapse capacity—subjected to aftershocks of multiple intensities. Besides, the efficacy of repair jackets is found to be proportionate to the intensity of AS attacks. Moreover, the steel jacket exhibited to be the most vulnerable repair intervention compared to CFRP, irrespective of the seismic sequence (severe MS-severe or moderate AS) or earthquake type (near-fault or far-fault)