Peter Tanner

The aging of infrastructure necessitates a robust and rational methodology for the assessment of existing structures. Design codes provide general models which cover different design scenarios and are thus overly conservative. Also, such design approaches lack field data and, if applied directly to existing works, often lead to unnecessarily expensive retrofits or pre‐mature decommissioning of in‐service assets. This paper presents a comprehensive, data‐driven framework for tailored assessment of the design resistance of existing structures. Central to this approach is the role of field measurements, comprising not only material and geometrical data, but also structural response. This allows considering Bayesian inference to combine a priori knowledge and actual structural update on the reliability analysis. On that basis, the potential of splitting the model uncertainty is highlighted, particularly if governing and if it can be updated by site testing. This approach is applied to a real case in which failure tests were performed on existing prestressed girders. To that aim, several Levels‐of‐Approximation for structural analysis and reliability formats are investigated to determine the design values of the failure resistance. As a result, a series of practical conclusions is drawn, providing engineers with a pragmatic tool for making informed decisions on structural safety.

Statistische Auswertungen von Brückeneinsturzdaten zeigen, dass Massivbrücken signifikant seltener einstürzen als Brücken aus Stahl oder Holz. Da weltweit die Hauptursache für Brückeneinstürze Hochwasser und damit verbundene fluviale Prozesse wie Auskolkung, Muren etc. und Anpralle sind, liegt die Vermutung nahe, dass die hohe Eigenlast der Massivbrücken zu einem insgesamt robusteren Verhalten bei diesen Ereignissen führt. Im Rahmen dieses Beitrags soll geprüft werden, ob die IABSE‐Einsturzdatenbank diese These bestätigt und Hinweise auf weitere Ursachen identifiziert werden können. Dazu wird die IABSE‐Einsturzdatenbank mittels Verfahren der Künstlichen Intelligenz und des maschinellen Lernens (KI/ML) untersucht. Die KI/ML‐Analyse bestätigt die bisherige These allerdings nicht. Im Weiteren werden Ursachen für die Ablehnung der These, wie z. B. die Repräsentativität der Daten, diskutiert. Es wird eine Erweiterung der Datenbank für Ereignisse mit großen Einsturzzahlen empfohlen.

Both when designing new and when evaluating existing structures, methods of analysis must be based on established engineering theory and practice. Also, the general principles of structural reliability regarding the treatment of uncertainties when verifying the established requirements apply to both, design and assessment. Taking further into account that new or existing civil engineering works are usually unique, either because they are prototypes or because they are exposed to specific conditions, from an engineering point of view, structural analysis and verification must be carried out, both in the design and in the assessment, under case-specific conditions according to the same principles. However, important differences exist between assessment and design, for example regarding the state of information and its updating through different types of information, the structural condition, reliability requirements, verification methods or decision options. Such differences, which are briefly summarized in the contribution, can often lead to a high level of conservatism when using design-oriented methods for assessment purposes. There is therefore a need to develop a generally recognized, coherent and harmonized set of rules for the assessment of existing structures. The CEN Technical Specification for assessment and retrofitting partially closes this gap, but only establishes principles on assessmentspecific reliability aspects. The consistent application of these generic assessment rules in practice requires further assumptions, or even case-specific developments. Practical applications are therefore of paramount importance in identifying relevant issues to consider in the future development of assessment methods and codes.

Current structural standards like the Eurocodes do not provide a coherent framework for design or assessment of structures under tem-porary use conditions. The reliability requirements for temporary systems put forward in the present study seek to ensure the same risk levels per unit of time that are accepted for permanent structures in accordance with current best practice. The results obtained show that the target reliability index for structural members rises significantly with declining risk exposure times. Conversely, the design values for variable actions may be lowered in keeping with the duration of the temporary activity, as illustrated in a case study, the analysis of the movable scaffolding system for bridge used for the construction of the Pumarejo bridge access viaduct. (c) 2022 Hormigon y Acero, the journal of the Spanish Association of Structural Engineering (ACHE). Published by Cinter Divulgacion Tecnica S.L. This is an open-access article distributed under the terms of the Creative Commons (CC BY-NC-ND 4.0) License

La evaluación de las estructuras existentes es un tema prioritario, de gran importancia económica, en un número creciente de países de todo el mundo ya que en muchos lugares una parte cada vez mayor del mercado de la construcción se centra en las actuaciones relacionadas con edificios, puentes y otras obras de ingeniería civil que ya existen. Actualmente, los Eurocódigos, que se utilizarán en todos los estados miembro del Comité Europeo de Normalización, CEN, y posiblemente en más y más países fuera de este espacio, están principalmente enfocados al proyecto de nuevas estructuras. El empleo de métodos orientados al dimensionado para evaluar las estructuras existentes a menudo conduce a un alto grado de conservadurismo. Las consecuencias económicas, ecológicas y sociopolíticas podrían ser significativas si se condenaran como inseguras unas estructuras cuyas prestaciones son satisfactorias, llevando a una inversión innecesaria de recursos en su rehabilitación o desmantelamiento y sustitución. Por esta razón, la evaluación de las estructuras existentes a menudo requiere el uso de métodos refinados que van más allá del alcance de las reglas normalizadas para el proyecto de nuevas estructuras. Consecuentemente, en los últimos 20 años, se han desarrollado métodos para la evaluación de las estructuras existentes en muchos países a nivel nacional. Sin embargo, estos métodos aún no se han coordinado entre sí y su implementación en la práctica diaria suele ser escasa. Existe por ello una necesidad urgente de fusionar los diversos enfoques nacionales en un conjunto de reglas generalmente aceptadas, coherentes y armonizadas para las estructuras existentes que complementen las reglas para el proyecto de nuevas estructuras. CEN tomó la iniciativa de iniciar un proyecto para desarrollar nuevas normas técnicas europeas para la evaluación y la rehabilitación de las estructuras existentes. Está previsto que el desarrollo de la parte correspondiente del Eurocódigo se logre en tres pasos. Ya se han completado dos de estos pasos, a saber, la preparación de un Informe Científico y de Política y, una vez adoptado por los Organismos Nacionales de Normalización de los estados miembro, la conversión de este documento en una Especificación Técnica de CEN. El tercer paso, la evolución de la Especificación Técnica en una Parte del Eurocódigo, EN, está actualmente en progreso. Sobre este trasfondo, en el presente artículo se analizan las diferencias más relevantes entre la evaluación y el proyecto desde el punto de vista de la fiabilidad estructural y se identifican algunos aspectos que deberían dar lugar a unas reglas adicionales en futuras normas dedicadas a las estructuras existentes.

In bridge planning, the successful translation of the many conditioning factors into a solution that meets all safety requirements while also addressing considerations such as economy and elegance is essentially a matter of conceptual design. Despite the utmost importance of that stage, which in addition to an intuitive understanding of load-bearing mechanisms calls for imagination and a sense of form and beauty, creative conceptual thinking is systematically underestimated both in engineering training and everyday practice. The resulting impoverishment of the profession stems not only from growing, need-driven and hardly reversible specialisation, but also from inexorably extensive and opaque standardisation and control. The rules for ensuring robustness reflect the increasing complexity and opacity characterising structural design codes. While the practical importance of designing and building robust structures is universally acknowledged, the codes presently in place are often vague or confusing. Cross-referencing, in turn, may lead to loops around rules that, confounding engineers, are counterproductive. At the same time, however, that lack of clarity may afford opportunities for innovative solutions by building items that ensure robustness into the conceptual design of a structure. This paper proposes an operational design process that deals appropriately with all factors of structural performance, including robustness, without compromising bridge economy or elegance. That process, which combines a number of robustness strategies, including risk-based considerations, is illustrated with a case study of a proposal submitted to a design competition for a viaduct.

The assessment of an existing structure to determine its suitability for present and future use entails different sorts of problems than encountered when designing new structures. The differences revolve essentially around the nature of the information available. In existing structures, deteriorated or otherwise, the accuracy of the models used for such assessments can usually be improved by acquiring more data. The most accurate way to find actual load and resistance would be to conduct a probabilistic analysis using site data. This is a time-consuming process, however, calling for a working knowledge of probabilistic methods that may not be suited to everyday use by practising engineers. For this reason, in the past few years various studies have been conducted to develop assessment approaches, compatible with Eurocodes, which include the same verification format as normally applied for designing new structures. In this paper, the application of several of these approaches is illustrated by means of the reliability verification of one of the main beams of the reinforced concrete structure of an industrial building from the 1940s, recently transformed into a cultural centre. The obtained results are discussed and compared to the findings of a full probabilistic analysis.

Due to its severely damaged condition, former La Laguna cathedral was demolished and rebuilt between 1905 and 1913, saving only its neo‐classical façade. Reinforced concrete, at the time an innovative technology, was deployed to expedite construction and reduce costs. The trade‐off for these benefits was the risk associated with the use of a scantily understood material. Although a reliability‐based assessment of the corrosion‐damaged load‐bearing system showed that structural safety requirements were fulfilled for the future service life, less than 100 years after its reconstruction, the temple was so profoundly deteriorated that the roof had to be replaced entirely. Reconstruction began on the healthy part of the existing columns, underneath the capitals. The solution adopted retains the geometry of the 1913 structure, while improving its ventilation and lighting as well as its aesthetics by reconfiguring the proportions as nearly as possible to the golden ratio. The ribs in the vaults and main dome, characteristic of the neo‐gothic style of the building, were built with self‐compacting concrete, reinforced with glass‐fiber polymer rebars, and joined monolithically to the shells, as well as to the existing walls and columns. The 0.08 m thick shells are also made of a relatively unknown material, self‐compacting concrete reinforced with polypropylene fibers. In order to reduce to acceptable levels the uncertainties associated with innovative technologies, in addition to laboratory tests, a full‐scale prototype of a typical dome was constructed prior to the execution of the new roof. Nearly a century after the previous, negative experience, thanks to modern structural engineering and materials science, new challenges can be assumed.

Load bearing capacity can be predicted by appropriate modeling of material properties, geometry variables, and uncertainties associated with an applied model for the failure mechanism under consideration. The submitted study investigates shear resistance model uncertainties for reinforced concrete beams with and without shear reinforcement, considering large test databases and various levels of approximation offered by fib Model Code 2010. Model uncertainty is treated as a random variable and its characteristics are obtained by comparing test and model outcomes. The sensitivity of model uncertainty with respect to basic variables is analyzed. For beams with stirrups, Level III is recommended for practical applications. Its predictions are shown to be independent of the amount of shear reinforcement and have reasonable bias and dispersion around test results. For beams without shear reinforcement, the use of Level II is advisable and a distinction between lightly reinforced and moderately to heavily reinforced beams should be made.