Concrete bridge deck slabs are the most common form of bridge deck construction in short and medium span bridge
structures in North America. Understanding and monitoring the condition of these bridge decks is an important
component of a bridge management strategy. Progressive deterioration due to fatigue occurs in concrete decks due to
the large number of cycles of heavy wheels loads and normally manifests itself as the progressive growth of cracks in
the top and underside of the deck slab. While some laboratory fatigue testing programs have been reported in the
literature, there is very little information on proposed techniques to monitor this phenomenon.
This paper discusses the issue of how fatigue monitoring may be included as part of a structural health monitoring
system for bridges. The paper draws upon previously published experimental results to identify the main characteristics
of fatigue damage and structural response for concrete bridge deck slabs. Several means of monitoring this response are
then evaluated and monitoring methods are proposed. A specific field structure monitoring program is used to illustrate
the application of the concept. The cases study examines several sensor systems and discusses the various limitations
and needs in this area. The results are of interest to both the general area of structural health monitoring as well as
fatigue monitoring specifically.
To be able to offer services to the world's largest container vessels, commonly known as Post-Panamax vessels, the Halifax Port Authority launched a dredging project to increase the berthing depth at its Nova Scotia facility. To monitor the movement of the existing pier during and after construction, sensors were installed in the sub-sea foundation 14 m below mean sea level. Vibrating wire strain gauges were attached directly to steel sheet piles (positioned adjacent to the existing concrete cribs) and both Bragg grating and Fabry-Perot fibre optic sensors were attached to anchor bolts used to attach the sheet piles to the cribs. Strain monitoring over approximately an eight month period indicated that the sub-sea shoring of the crib foundation has become engaged to resist the slight settlement of the cribs. The resulting stresses are very low, however, confirming that the cribs are performing well within design and functional limits. The project also confirmed the durability and effectiveness of the use of fibre optic sensors in marine environments.
Fibre reinforced polymer (FRP) laminates are used to rehabilitate concrete beams that do not possess the required ultimate flexural capacity. Because this is a new technology, there is a need to use structural health monitoring techniques in many of the field projects to verify their field performance and increase user confidence. This paper discusses the process of developing an SHM system for concrete beams with FRP flexural strengthening laminates. In the specific case of FRP laminates, debonding or delamination is a damage mechanism of specific concern. Through an experimental and theoretical study it is shown that strain monitoring would be the most effective technique for this application. Due to the need for a dense spatial resolution of sensors with low noise, Brillouin scatter or multi-Bragg grating style fibre optic sensors are suggested as the most appropriate for this application. A damage assessment methodology based of the shape of the laminate strain profile is established. While the precise methodology is specific to this application, the process of SHM system development discussed in the paper is adaptable to a wide range of field structures.
Structural health monitoring (SHM) activities in civil engineering grow at a rapid pace and mature in both research and field applications. Internet technology was successfully incorporated into structural health monitoring, which makes it possible to manage real-time sensing data and centralize the remote structural monitoring systems. With the increase in size and complexity of the monitored structures, more sensors and data acquisition equipment is involved. This paper addresses some specific issues related to long distance small signal transmission and Ethernet IP sharing between different devices. The issue of data volume versus storage space and communication bandwidth is discussed especially in the application of web camera image transfer and recording. The approaches are illustrated through reference to two current case studies, which include a bridge and a statue. It can be seen that these practical solutions employed by ISIS Canada are easy to implement and reduce the cost for the maintenance of SHM systems. The paper also discusses future activities and research needs related to the reliability and security of the SHM system.
KEYWORDS: Structural health monitoring, Bridges, Data acquisition, Sensors, Data communications, Telecommunications, Data centers, LabVIEW, Databases, Structural monitoring
Structural health monitoring (SHM) activities in civil engineering are increasing at a rapid pace in both research and field applications. This paper addresses the specific issue of incorporating internet technology into a structural health monitoring program. The issue of data volume versus communication speed is discussed along with a practical solution employed by ISIS Canada. The approach is illustrated through reference to several current case studies which include two bridges and a statue. It is seen that although the specifics of the projects and monitoring needs are different, the manner in which on-line monitoring can be conducted is very similar and easily allows for centralized monitoring. A general framework for website construction integrating sensing data and web camera options are presented. Issues related to simple real-time performance indices versus more comprehensive complex data analysis are discussed. Examples of on-line websites which allow visualization of new and historic data are presented. The paper also discusses future activities and research needs related to centralized remote structural monitoring and management of real-time data.
The concept of steel-free deck slab is discussed along with six field applications in Canada. In particular, the phenomenon of cracking in deck slabs is discussed with reference to laboratory studies as well as field observations, both of which have shown that, notwithstanding the presence of cracks, the fatigue resistance of the steel- free deck slab is very high. The provision of a layer of nominal tensile reinforcement within the thickness of the steel-free deck slab, however, eliminates the unaesthetic wide cracks. Laboratory studies, currently underway, have shown that the technique of acoustic attenuation is very effective in tracking the growth of cracks in concrete deck slabs. The conventional sensors were not successful in this respect.
The Hall's Harbour wharf in Nova Scotia is the first Canadian project to demonstrate the application of fibre reinforced polymer reinforcement, the steel-free concrete deck slab concept and fibre optic monitoring systems to structures in the marine environment. The extreme environmental exposure conditions make the site an excellent location for testing both material performance and sensing system durability. The early results of the monitoring program indicate that the innovative structure is meeting service level performance requirements. Long-term durability assessment is continuing and being complemented by controlled field and laboratory testing programs. Continuous remote monitoring of the fibre optic sensors is producing valuable reinforcement strain information for tracking structural response to ambient conditions. The fibre optic sensors themselves were found to be rugged enough to withstand the construction process and exposure environment; however, further work is required to achieve feasible field units for some types of fibre optic sensing instruments and associated equipment.
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