Eurocodes and Their Implications for Bridge Design: Background, Implementation, and Comparison to North American Practice

Codes and standards used for guiding structural design of buildings and bridges traditionally have been prescriptive and quantitative. In an era of gradual change in design and construction technologies, this traditional approach to structural design generally served the public and the profession well. However, prescriptive standards do not accommodate technological advances and innovations easily, and in the last three decades, such occurrences have changed the nature of building design and construction rapidly. At the same time, the performance of buildings and other structures during extreme manufactured events and natural phenomena hazards, such as hurricanes and earthquakes and flooding, has led to intense public and professional scrutiny and criticism of current engineering and construction practices. Finally, uncertainties are invariably present in structural engineering, and standards that do not take these uncertainties into account consistently (or, worse, do not account for them at all) are an obstacle to advancing structural engineering practice. With the advent of structural reliability as a tool for the treatment and analysis of uncertainty, the decades of the 1970s and 1980s brought the realization that although absolute safety is an unattainable goal, uncertainties in structural performance could be quantified (in terms of uncertainties in structural actions and response and in material strength and stiffness characteristics) and risk-informed structural design criteria could be developed that were consistent with a desired level of performance. With this realization, practical structural design standards that reflected these reliability principles evolved quite rapidly. Not only did this transition in thinking regarding structural safety and serviceability evolve rapidly, it evolved in most modern, postindustrial societies at about the same time. Modern building and bridge codes used in structural engineering practice are based on the notions of probability-based limit states design (PBLSD). In the bridge arena, these include the AASHTO LRFD Bridge Design Specifications (AASHTO 2012), the Canadian Highway Bridge Design Code (Canadian Standards Association 2006), EN 1990 [European Commission for Standardization (CEN) 1990] and EN 1991-2 (CEN 1991), and EN 1992-2 (Eurocode 2) (CEN 1992a). There are some differences in the way that PBLSD has been implemented in the countries that have adopted it, but its fundamentals are similar in all countries. In addition to the quantitative modeling of uncertainties using probabilistic models and statistical data, the developers of PBLSD bridge standards have strived to base such standards on present day principles of structural load modeling and to use models of structural behavior that are founded on sound principles of structural mechanics in order for the structural response to be modeled as accurately as possible (within the constraints of practical design). Not surprisingly, PBLSD has opened the door to new research opportunities and challenges. For one, there are differences in code format; in theUnited States, the LRFD format is practically universal, whereas in Europe, a format that involves partial material factors and companion action factors has been adopted. From the viewpoint of the practicing structural engineer, these differences are superficial rather than substantive and stem from country-dependent traditional design practices that predate the introduction of PBLSD. The collection of papers presented in the December 2013 special section on “Eurocodes and Their Implications for Bridge Design: Background, Implementation, and Comparison to North American Practice” reflects a broad spectrum of the commonalities and differences that have arisen in Europe, North America, and elsewhere as part of the move toward implementing PBLSD in practical bridge engineering. Marti-Vargas and Hale (2013) compare the treatment inNorthAmerican andEurocode standards of strand transfer length in prestressed concrete construction. The American Concrete Institute model is based only on the strand parameters, whereas the Eurocode 2 approach considers concrete properties as well, leading to a model that is more conservative in its predictions of required transfer lengths. Walbridge et al. (2013) focus their attention on United States, Canadian, Eurocode, and Swiss approaches to assess fatigue in metallic bridge structures using a simulation approach to show that simultaneous vehicle crossings, which currently are not considered in fatigue assessment, might increase fatigue damage substantially. Granata et al. (2013) consider the effects of creep and shrinkage on prestressed concrete girders usingNorth American and European approaches, concluding that the Eurocode predictions underestimate final deflections and the extent of stress redistribution among girders. Kappos et al. (2013) present a methodology for evaluating response modifications factors for earthquake-resistant design of concrete bridges in Europe and find that the available force-reduction factors for seven typical bridges are higher than those used for design, indicating that the strength reserves are typically larger than those provided by Eurocode 8 (CEN 1992b) or the AASHTO Bridge Design Specifications (AASHTO 2012). A broad comparison by Maiorana and Pellegrino (2013) of design provisions for steel bridge connections in Eurocodes and North American, Australian, and Japanese bridge standards reveals vast differences in assumptions regarding bearing/shear, slip, and minimum edge and end distances and indicated that the Eurocode provisions are the most conservative for typical steel connections in bearing and friction shear and in tension. Anitori et al. (2013) review current and proposed methods for assessing robustness and redundancy of bridge structures in Europe andNorth America; although noting that the North American provisions are more specific in this regard, they recommend that future bridge codes should be based on quantifiable measures of risk. The paper by Gara et al. (2013) on slab cracking in continuous bridge decks advocates the modular ration approach in

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