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The collapse of a column for public street lighting is a rare but not unusual event that can lead to extremely severe consequences for the Authority in charge of looking after the system. Cases involving loss of life have been reported.
When such an event occurs, corrosion at the base joint is always involved, because, as a rule, a sound steel post is a very sturdy structure that can withstand heavy loads, much greater than the reasonably predictable ones.
Only a corrosion attack can reduce its strength to such an extent that it collapses under the load of a strong wind or of a weak impact. Corrosion in the buried portion is particularly treacherous, as it not only it affects the most stressed section of the pole, but can start and progress till collapse without any visible indication. For a long time the only possible pre-emptive actions have been periodic replacement of the posts or a series of sample checks involving the demolition of the post base and subsequent visual inspection, but both actions are-time consuming, expensive and scarcely reliable.
Since 1990 RENCO S.p.A. has studied, developed and patented method for the corrosion rate assessment of the buried portion of lampposts, traffic lights posts and similar structures. The method is based on the measurement of the Linear Polarisation Resistance using the Stearn-Geary equation (LPR Method). The site test is non-destructive, fast and reliable; collected data are processed with a dedicated software and the final result is a certificate where the warranted residual life of every inspected structure is reported. As a supplementary service, the mapping of the structures can also be supplied.
Every step of the procedure, from the site test to the data processing and data management is carried out to the highest achievable standards and is monitored according strict quality control procedures, as RENCO holds certifications according to ISO 9001 and ISO 14001 This monitoring technique offers considerable advantages, identifying the level of damage for individual structures, as well as the risk areas where intervention through suitable checks or pre-emptive maintenance works can optimise means and resources, and hence it is particularly pertinent to the needs of authorities in charge of large networks with a high number of structures.
According to our experience, based on the test of more than 60,000 structures, about 0.2% of the posts present in a typical metropolitan area are in danger of sudden collapse and need immediate replacement, whilst 5% are more or less damaged but can be regenerated with fast and economical maintenance interventions. Since its introduction in 1990 the method has been having growing success and has been adopted in the largest Italian cities as well as in many small towns.
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