The use of carrier phase kinematic GPS (global positioning system) has evolved into a reliable technique to measure both the three-dimensional magnitudes and frequencies of movements of structures. Techniques have been developed that tackle errors caused by multipath, tropospheric delay and issues relating to satellite geometry. GPSderived movements compare well with data from both design predictions and structural models. Results from field trials carried out on the Forth Road Bridge are presented. This paper brings together key results that outline the procedure as well as a series of new data that indicate other potential applications. GPS data were collected continuously over a period of 46 h at a minimum rate of 10 Hz. During the trials wind speed, wind direction, relative humidity and temperature were also recorded. Frequently there was very heavy traffic flow, and at one point a special load (a 100-t lorry) passed over simultaneously to the heavy daytime flow of traffic. Data from a planned load trial during a brief bridge closure are reported and compared with the limited results available from a finite element model. Measured vibration frequencies are also computed from GPS data and compared with those given in the literature. In addition, results indicating the change in structural characteristics are also presented -in particular changes of mass associated with changes in traffic loading are observed. The results show the performance of GPS as it has developed in recent years, and that it can now reliably be used as a significant part of structural health monitoring schemes, giving both the magnitude of quasi-static deflections in known time periods and hence the frequency of dynamic movements of structures.

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Forth Road Bridge is a suspension bridge with a main span of 1006 metres and side spans of some 408 metres. Approach viaducts to the north and south bring the total length of the structure to just under 2500 metres. The bridge crosses the Firth of Forth some 16 km to the north and west of Edinburgh and was opened in 1964. Traffic has grown significantly from 4 million vehicles using the crossing during its first year of operation to the 24 million vehicles using the bridge last year. This paper lists major projects that have been carried out to strengthen and improve the structure and replace major components and makes reference to continuing major maintenance schemes such as bridge painting and resurfacing. The discovery of significant corrosion in the main cables has resulted in the implementation of a dehumidification scheme to halt or slow down the deterioration and this scheme is described. The preliminary findings of a study to examine the feasibility of replacing or augmenting the main cables and to investigate the long term structural integrity of the anchorages are also detailed.

Forth Road Bridge main cables: replacement/augmentation study B. R. Colford CEng, MICE and C. A. Clark CEng, MICE, MAPS The 1800 m long suspended structure of the Forth Road Bridge spans the Firth of Forth in Scotland. It forms an integral part of the roads network, carrying in excess of 24 million vehicles each year. Since its opening in 1964, the bridge has received a high level of continuous maintenance and, when required, retrofitting to enhance the capacity of the structure. In 2004, as part of this maintenance and inspection regime, the Forth Estuary Transport Authority (FETA) undertook the first internal inspection of a main cable of a suspension bridge in the UK. This inspection revealed significant corrosion in the wires forming the cable, and a subsequent inspection in 2008 confirmed these findings. To combat progression of the corrosion, the authority retrofitted dehumidification systems on the main cables, and acoustic monitoring has been fitted to monitor wire breaks within the cables. As a precautionary measure, FETA also commissioned a study into the feasibility of augmenting or replacing the bridge's main cables. This paper outlines the processes undertaken in this study, the options for undertaking the works and the conclusions reached to date.

Over the past few decades, engineers working in design offices have become much better at designing for constructability. The use of the design and build form of procurement has, in many ways, been instrumental in this change. The use of accelerated bridge construction in the USA, although primarily a method of reducing traffic impact, has also helped engineers become better at designing for constructability. However, it can be argued that engineers have not made the same progress in designing bridges to make future inspections and maintenance easier. In fact, unless an employer's requirements for inspection and maintenance are clearly prescribed in detail in the contract, then the design and build form of procurement is perhaps the least advantageous when considering the service life of a structure. Over the lifespan of a bridge, the service life costs, including inspection and maintenance, can account for a significant percentage of the lifecycle costs of the bridge. Therefore, the importance of not only ensuring that an adequately funded proper inspection and maintenance regime is established but also that sufficient attention is paid to the provision of inspection and maintenance during the design stage cannot be overstated. This paper examines and compares current practice in the UK and USA and considers ways of improving the design process to assist the future inspection and maintenance of bridges.