Innovation In Structural Investigation


Structural investigative specialist, GBG, has been commissioned by the City Surveyor’s Department of the City of London to monitor the sway and movement of the Lord Mayor’s State Coach over a variety of road surfaces. GBG’s work, which is part of a wider review being carried out by the City Surveyor’s Department of all its historic coaches, is designed to provide information which can be used to help decide the future of the Coach.

Built in 1757, the State Coach is 22 ft long, 8 ft wide and 11 ft high, weighing over two tons. Along the traditional three mile annual journey it is drawn by three pairs of shire horses at which point its full length becomes 65 ft. Some remedial work has been undertaken over the centuries: it was regilded in 1868, interior electric lighting was added in 1939; brakes were fitted in 1951 and it was completely overhauled in 1952.

To carry out the ‘motion and sway’ survey, engineers from GBG attached a variety of motion sensors to the Coach. These included:
  • Geophones - To generate a movement signal
  • Accelerometers - To measure the vibration of the axles
  • Linear Transformers - To measure linear displacement
  • Foil Strain Gauges – To assess the bending of the main beams of the sub-frame
In addition, GBG used a new technique, developed in the USA: a pressure sensitive film was wrapped round the suspension spindles to record the maximum loads in the leather restraining straps which hold the coach in place.

Measurements from all the monitoring devices were collected during a test run of the State Coach prior to its use on the day of the Lord Mayor’s Show, as well as during the Show itself. The data was captured to a laptop concealed beneath the coachman’s seat, and is currently being prepared for conversion and analysis by GBG.

A spokesperson from the City Surveyor’s Department said, “It has been fifty years since the last major refurbishment of the State Coach. The investigation being undertaken by GBG is important in providing us with detailed information to better understand and evaluate the condition of the Coach."

George Ballard of GBG commented, “This is about the oldest vehicle in regular use on Britain’s highways – the Queen’s State Coach is some five younger. Whilst the undercarriage is unsprung the coach itself has a complex suspension system, so the Lord Mayor rides in smooth comfort despite the sway.”

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