Important decisions have to be taken on the suitability and cost effectiveness of materials and repair techniques for the £6 M repair programme currently being implemented on the Tay Road Bridge. These require the accurate and continuous monitoring of bridge behaviour with respect to temperature, wind, loading, etc. before, during and after repairs. The paper deals in particular with the development and application of a microcomputer based hardware and software package for data collection and analysis of bridge deck joint movements, deflections and column substructure deflections. Tayside Regional Council Roads and Transport Department, as Engineer to the Tay Road Bridge Joint Board, decided on the requirements: where, when and why, and then invited the Department of Civil Engineering at Dundee College of Technology to assist in development of the monitoring package.

The selection of a monitoring package splits into three main sections; the specification of transducers, the means of logging and the processing of data. It was decided to use hybrid potentiometric transducers to measure expansion joint movement because of their good linearity, low temperature response and high, noise resistant output. Deck temperatures are being recorded using Platinum Resistance Thermometers, again with high output and good noise resistance qualities even when remote from the data logger. The section of an "autonomous" data logger sited on the bridge as close as possible to the transducers was done for many reasons including the following:-

• The shortest possible, transducer to logger, signal transmission length.
• Storage of readings in memory within the logger, thus leaving the computer free for data processing.
• Minimising the risk of transmission problems on the 1200 m long cable between the transducers on the bridge and the computer on shore.

An important principle followed was that, whenever possible, tried and tested versatile proprietary equipment was employed to increase reliability and to minimise "down time" in the event of breakdown. The versatility of the equipment made it possible to add on data logging of tilt sensors during the contract. On the data handling side, the vast quantities made it essential that software "tools" such as spread sheets and graphical packages were used to manipulate and present the data.

The current phase of development is to combine all relevant data within a management information data base to achieve a full understanding of bridge behaviour before, during and after major repair works.

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