Copyright Transport Research Foundation 2002. All rights reserved INTELLIGENT MONITORING OF JACK ARCH STRUCTURES: THE RESULTS OF A PRELIMINARY STUDY Dr J G Kavanagh & Dr K C Brady TRL Limited Old Wokingham Road Crowthorne Berkshire RG45 6AU jkavanagh@trl.co.uk KEYWORDS: Jack arch; cast iron; bridges; acoustic emission; monitoring ABSTRACT A cast iron beam, instrumented with deflection gauges, strain gauges and two acoustic monitoring systems, was subjected to a series of load cycles. The aim of the test programme was to determine whether acoustic emission (AE) techniques could be used to form the basis of an intelligent monitoring system. The results support the view that AE was generated by a load-related mechanism - most likely due to micro-cracking of the cast iron - and so AE techniques might indeed form the basis of a monitoring system, but further work is required to develop a practical system. INTRODUCTION The research reported in this document was commissioned as part of the Transport Research Foundation's ongoing programme of scientific research. All rights to the intellectual property within the document remain with the Transport Research Foundation. Many old jack arch structures are still in service as short-span road bridges over canals and railways. Cast iron beams manufactured in the 19 th century are also still in service in major public buildings, textile mills and warehouses. The structural condition of such bridges and beams is difficult to assess. Owners, and those charged with the maintenance of such structures, therefore, have a problem with managing such assets. On the one hand it is essential to identify sub-standard structures that pose a risk to users, but on the other it is desirable to minimise expenditure on the strengthening of perfectly adequate structures. As part of the Transport Research Foundation’s reinvestment programme, a project was initiated at TRL Limited to examine various techniques for monitoring the in-service performance of cast iron structures. These might form the basis of an intelligent system that, ideally, was capable of continuously monitoring a structure so that it could forewarn of structural deterioration and thereby trigger remedial works. As a necessary precursor to field trials, various techniques were used to monitor the performance of a cast iron beam in a load test carried out in the laboratory. The beam was instrumented with strain gauges, deflection gauges and two acoustic monitoring systems. Details of the test set-up are provided herein. A summary of the results of the test is also provided, along with recommendations for further work. CAST IRON Cast iron is any iron alloy that has a carbon content of between 2 and 4 per cent, and a silicon content of between 1 and 3 per cent. It might also contain trace amounts of manganese, phosphorus and sulphur. As the name implies, cast iron products are made by pouring molten alloy into a mould and allowing it to solidify. There are two basic types of cast iron. Grey cast iron forms as a result of relatively slow cooling, in which case some of the carbon solidifies as graphite flakes sitting in a matrix of what approximates to steel. White cast iron (or chill iron) forms as a result of relatively rapid cooling, in which the carbon is unable to