Reliability-based performance indicators for structural members

The implementation of reliability methods for designing new structures and assessing the safety and evaluating the performance of existing structures and infrastructure systems has gained widespread acceptance. Consequently, reliability-based design specifications in the form of load and resistance factor design (LRFD) methods have dominated the development of current codes and standards. This paper reviews the reliability-based performance criteria used to calibrate design and evaluation codes and standards for assessing the strength, serviceability, and fatigue resistance of structural components. The review shows that large differences exist in the target reliability levels adopted for evaluating the strength of various types of structural members and materials. These differences result from many factors, including (1) intended structure design and service life; (2) expected member modes of failure (e.g., ductile or brittle); (3) importance of the individual member to overall system integrity (secondary member, column, or connection); (4) experiences with previous designs; (5) material and construction costs; (6) structure type and occupancy; and (7) risk tolerance of the engineering community and the public within a code’s jurisdiction. For other than seismic hazards, current specifications remain primarily focused on the evaluation of individual structural members and components, although recently proposed performance-based design (PBD) procedures apply varying target member reliability levels that depend on structure categories, modes of failure, and required levels of structural performance. The implementation of reliability-based durability criteria in design standards is still a subject of research owing to difficulties encountered in modeling material degradation mechanisms and their interactions and in the collection and mapping of long-term site-specific data on degrading agents. Because of large epistemic uncertainties, the evaluation of the fatigue safety of structural components in engineering practice still relies on conservative basic models of damage accumulation using S-N curves or basic fracture mechanics crack growth models. Overall, reliability-calibrated structural standards are producing designs that offer a good balance between safety and cost. The future implementation of risk-based methods will further enhance the ability to meet structure-specific performance requirements set by owners and users

Ciência e ensino médico no Brasil (1930-1950) Science and medical education in Brazil (1930-1950)

Este artigo aborda o papel da ciência e seu impacto no currículo dos cursos das escolas médicas entre 1930 e 1950, delineando-se a rede de relações construídas em torno dessas instituições e evidenciando a ligação entre a conformação curricular e o contexto sociopolítico e econômico vigente. As concepções de ciência, na época em estudo, influenciaram o desenvolvimento das instituições de ensino universitário em geral, representando importante elemento na formação médica, em particular. Nesse período, promoveu-se, no país, a atuação da Fundação Rockefeller, especialmente no campo da educação e da saúde. A ciência, como conceito e método de trabalho, mas também como categoria ideológica, foi importante fator na conformação curricular das escolas médicas brasileiras, especialmente em relação à pesquisa.<br>This article discusses the role of science and its impact on the curricula of medical schools between 1930 and 1950, sketching out the web of interrelations built up around these institutions, and bringing to light the connection between the contents of the curricula and the prevailing social, political and economic context. The scientific concepts at the time influenced the development of university level institutions, and had particular significance in medical education. In this period, the political and economic ties with the USA were manifested by the Rockefeller Foundation, especially in the arena of education and health. As a concept and working method as well as an ideological category, science was an important factor in standardizing the curricula of Brazil's medical schools, especially as concerned basic research