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PREFACE:

Bridges are the flagships of our transportation infrastructure, on which society heavily depends. Operation and maintenance have become more and more complex with the increased age of our bridge stock. Structural Health Monitoring, as part of lifecycle management procedures, experienced a growth in importance recently. 

To maintain and improve the high quality and high level of service to the public it is essential to know the lifecycle performances of structures to ensure long service life and durability. Structural Health Monitoring of bridges comprises too many approaches and aspects to be completely covered in one publication.

 This book therefore concentrates on the current practice and methodologies of dynamic monitoring. The theorem that the health of a structure is expressed in its dynamic characteristic is exploited. 

Other sectors like mechanical engineering or aeronautics are operating in conditions where the properties of their structures are well known and are operating under controlled conditions. Civil engineering has to account for numerous non-linearities as well as dominating environmental factors that are able to hide useful information in the records. 

This leads to the situation that the results carry a portion of uncertainty that we have to deal with as effectively as possible. It is most likely that one or the other approach will be overruled by future research work and the methodologies considerably improved.

 It therefore is of highest importance that the raw data of any monitoring campaign are stored properly in order to apply new algorithms in the future, or to enable qualitative comparison between subsequent measurements. It further has to be mentioned that bridge management approaches are dominated by political factors or incidents like bridge collapses. This might hinder the best possible exploitation of the methodologies. It further has to be recognized that currently a search for proper bridge management procedures is underway, which might lead to adaptation of the described approach

 The vision for structural health monitoring of bridges is an integrated decision support system, web based and featuring a most user friendly surface. It contains the following elements:

 • A display embedded in a GIS environment reporting the status of any structure in a network 

• A database with web interface 

• Permanent and mobile monitoring units

 • Data handling, transfer and cleaning routines 

• A knowledge and history base for statistical comparison 

• A database on dynamic bridge simulation including automatic model update routines 

• A case based reasoning system to compute the proposals for decision making 

• Interfaces to existing bridge databases and relevant codes and standards.

The key to success is high quality data combined with realistic identified models and deterioration laws quantitatively supported by monitoring.

 The output can either be a reliability index, a safety level, a graphic symbol or any other output value as desired by the bridge owners. 

Due to the complexity of the subject there will be limitations to this approach that can be narrowed in combination with engineering judgment. There is a long way ahead of us before the computerized SHM systems will be superior to the experience of a senior bridge engineer. It is doubtful that the human input can be replaced in civil engineering entirely and a fruitful combination is proposed. 

The proposed SHM is to be seen as a tool and support for the bridge engineer as well as an indicator to the bridge operators when critical situations are developing and a human expert ought to be called.