International Concrete Abstracts Portal

From the very beginnings of time mankind has been intrigued with the potential applications of light and the possibilities that it could bring about. The origins of optical fibers probably go back to mid 19th century when the scientists tried to guide, bend, and transmit the light from one location to another. Now, optical fibers have found widespread usage in telecommunications as well as in medical and sensing applications. This article provides a summary review of principles involved in sensing with discrete optical fibers such as Bragg gratings and specific methods more prevalently employed in monitoring of bridges. The focus will be in application examples including monitoring of the masonry vaults of the Brooklyn Bridge, deformation of cable stays, and fiber optic accelerometers for testing of bridges.

Needs for structural health monitoring in the last decades were rapidly increasing, and these needs stimulated developments of various sensing technologies. Distributed optical fiber sensing technologies have reached market maturity and opened new possibilities in structural health monitoring. Distributed strain sensor (sensing cable) is sensitive at each point of its length to strain changes and cracks. Such a sensor practically monitors one-dimensional strain field and can be installed over the entire length of the monitored structural members, and therefore provides for integrity monitoring, i.e. for direct detection and characterization of local strain changes generated by damage (including recognition, localization, and quantification or rating). The aim of this paper is to help researchers and practitioners to get familiar with distributed sensing technologies, to understand the meaning of the distributed measurement, and to learn on best performances and limitations of these technologies. Hence, this paper briefly presents light scattering as the main physical principle behind technologies, explains the spatial resolution as the important feature for interpretation of measurements, compares performances of various distributed technologies found in the market, and introduces the concept of integrity monitoring applicable to various concrete structures. Two illustrative examples are presented, including applications to pipeline and bridge.

Structural health monitoring (SHM) is a process aimed at providing accurate and timely information concerning structural health condition and performance. The information obtained from monitoring is generally used to plan and design maintenance activities, increase the safety, verify hypotheses, reduce uncertainty, and widen the knowledge concerning the structure being monitored. The technologies used to perform the SHM are continuously developing, and researchers and practitioners are not always aware of their market maturity, performances, and applicability. The papers included in this CD, 1) Identify the state-of-the-art SHM technologies, including their performances, applications, and market maturity; 2) Generalize the use of SHM technologies for various classes of problems and structures; 3) Examine how the SHM technologies can be used in evaluation of the current conditions and performances of concrete structures; and 4) Analyze the benefits of SHM technologies regarding the preservation and safety of concrete structures and long-term management activities in general. This CD consists of 10 papers that were presented at a technical session sponsored by ACI Committee 444 at the ACI Convention in Cincinnati, Ohio in October 2011. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-292

This paper describes the development, implementation and evolution of applied research by the Iowa DOT to better understand how SHM may be used to more effectively manage their bridges. Bridge management is a critical responsibility for highway agencies. Fortunately, advances in technology have allowed for the development and deployment of many types of monitoring schemes. Selected case studies are presented to help describe how the Iowa DOT effectively integrated SHM in their current responsibilities. SHM has been used on wide range of bridge applications in Iowa such as capacity evaluation of deficient or damaged structures, construction phase monitoring, in-service assessment of vulnerable details, security and many others. Working with researchers at Iowa State University (ISU), initial efforts utilized existing technologies for short term monitoring and then advanced into the development of the state of art systems for long term monitoring using fiber optic (strain-based). The SHM system autonomously records, processes and evaluates strain data, and assesses damage in essentially real-time. More recent research has focused on development of broader based monitoring systems that assess both structural and non-structural conditions.

An important challenge for widespread application of structural health monitoring (SHM) in civil engineering is the creation and implementation of algorithms for automatic and reliable detection of unusual structural behavior. Branko, the lead role and the second author of this paper has been in charge of data analysis of a 19-storey tall building. Observation of the data from the instrumentation has over the years, convinced Branko that there is an ongoing differential settlement of one of the base columns, in apparent contrast with his initial expectations. This conclusion matured gradually not only as a consequence of the monitoring results, but also based on verbal information received from a design engineer. Thus, besides the quantitative data provided by the monitoring system, including in the data analysis algorithms the engineer’s knowledge and experience has also been of value. In this study we propose an approach based on Bayesian logic as an effective tool to allow such a blend of field knowledge and SHM results. We show how the whole cognitive process followed by Branko can be suitably reproduced using Bayesian logic. In particular, we discuss to what extent the prior knowledge and potential evidence from inspection, can alter a perception of building behavior based on SHM data alone.