Editorial

Abstract

Welcome to this themed issue of Bridge Engineering on the subject of assessing the capacity of existing bridge structures.Many parts of the world continue to provide opportunities for major new bridge construction. These include the massive investment in infrastructure in China and the Far East; the urban metro schemes in India and the Middle East; and the high-speed rail lines in Europe and the USA.However, many countries now have extensive stocks of mature bridge assets. A typical example is provided by the paper in this issue by McKoy (2016) on London Underground, which has a stock of approximately 8000 bridges and other assets, of which nearly half were constructed before 1900.Assessment is a key tool for the management of existing bridges. Assessments may be undertaken to check that bridges are safe under the loads they are already experiencing. In addition, increasing traffic capacities and loading often require the evaluation of the carrying capacity of existing structures. Changes to structures, such as modifications or external damage or deterioration, may need to be assessed.Bridge assessment, although a challenging subject, can also be a rich field that offers opportunities for research, innovation and the development of technical expertise. The rewards can also be significant: analytical approaches are generally less costly than structural strengthening, so there can be many benefits in progressing sophisticated investigation and analysis methods to justify the strength of structures.This issue of Bridge Engineering includes five papers from across this full range of endeavours. Papers include a discussion of an asset owner's assessment programme spanning three decades; a methodology for evaluating the potential benefit of installing structural monitoring systems; techniques for controlling proof test loading using acoustic emission; development and calibration of a finite-element approach to service-level assessment of masonry arch bridges; and a case study of a project to assess a 620m-long steel-composite box girder viaduct by deploying Eurocode methods. Olaszek et al. (2016) consider the on-site assessment of bridges supported by acoustic emission. In situ tests show that sometimes bridges have a reserve strength that is not accounted for in design codes of standard assessment methods, since the codes may conservatively neglect contributory mechanisms. Full-scale load testing can demonstrate these reserves of strength. However, proof load testing up to the design load may have risks of inducing cracking or damage in the structure if it is not properly performed and controlled, owing to the high level of load in the bridge.Acoustic emission has been identified as a useful technique to stop the load increase before any damage can be inflicted on the bridge. The paper presents tests on a three-span bridge at Barcza, Poland, and shows that monitoring with acoustic emission sensors made it possible to evaluate the cracking limits of the concrete members and stop the load increase prior to the onset of...