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Monitoring Techniques

Introduction

The use of wireless monitoring systems often are supposed to have several advantages compared to wired monitoring systems, that is for example easy installation, cost-effectiveness and autonomous operation over longer periods providing remote control and analysis features. Therefore, a lot of research and development activities are ongoing with regard to wireless monitoring systems to be applied on civil engineering structures like bridges as well as on historic structures. At first glance, continuous monitoring with wireless sensor networks seems to be a perfect solution to get more detailed information about structures than from visual inspection only. However, wireless monitoring is often not that simple if the monitoring task is more complex than just acquiring and transferring relatively simple data like temperature or humidity every hour. For such simple tasks many competitive solutions with adequate reliability in form of data loggers, partly also equipped with wireless communication, are nowadays commercially available.

The situation becomes challenging if the desired monitoring is targeted on acquiring and analyzing data like stress, strain, inclination, salt and moisture content inside materials or even vibration or acoustic emissions caused by fracture processes that require higher sampling rates. A main problem in this context is the power supply (mainly primary batteries are used) so that the wireless monitoring hard- and software is subject to several restrictions. To remain cost-effective and practicable, a balance between the monitoring task respectively the expected result from the monitoring and the time and effort to perform the continuous monitoring must be found. This is why wireless monitoring systems mostly have to be customized for the desired monitoring objective. Thus, structural health monitoring is also to be seen as an interdisciplinary engineering task.

Environmental Influences and Damage Processes

Modern civl engineering structures as well as historical structures have been under environmental influence for centuries or even millenniums. These influences induce damage processes in the building materials that lead to a degraded state of the structures eventually. The degradation effects can sum up and destroy the valuable object that structure and monuments authorities try to preserve for the coming generations.

Environmental influences are manifold and have their origin in physical and chemical effects. This comprises decomposition by light, rain, salts, gases and others. To prevent the degradation or the destruction of structures and historic objects, engineers, restorers and conservators try to chemically and physically conserve and protect the object and in some cases have to reconstruct parts. For the engineers, restorers and conservators, it is of great importance to know and understand the main factors responsible for the damage effects.

Benefits of Structural Health Monitoring

By knowing the main causes for damaging effects, best countermeasures for preservation and conservation can be taken and the remedies are adapted to the specific structure. To this end, understanding of environmental effects is necessary. To this effect, all relevant environmental quantities have to be recorded and analyzed by relating the resulting effects to the physical and chemical values. Damage processes are usually slow and medium to long-term measurements are necessary.

The knowledge resulting from the SHM measurements can be used for the discovery and confirmation of general correlations but it can also be used to erect an object specific treatment plan, if correlations are already known but influencing factor for the specific object are unknown.

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Created by: admin. Last Modification: Tuesday 14 of February, 2012 10:32:33 CET by admin.