PROPOSAL OF A BRIDGE DECK DISPLACEMENT CONTINUOUS MEASURING DEVICE AND PERIODICAL REALIGNMENT SYSTEM DESIGNED TO MINIMIZE TRAFFIC INTERRUPTIONS

摘要

The paper presents the most recent developments on electronic bridge control applied to a bridge located along a southern Italian Motorway in an area where a landslip is in slow yet continuous motion. A previous bridge was closed for beam misalignment caused by the landslip action. A new bridge was recently designed with much sturdier foundations, but even during the initial construction phases it was evident that a static solution was undesirable, if not impossible. Jet, based on the observations of the last twenty years, the foreseen movements are relatively small, 20 cm being the maximum horizontal measured displa cement in that period. A further version of the bridge has thus been proposed, characterised by lighter and longer decks, in order to negotiate the section with fewer elements. Moreover, the monitoring and repositioning systems have been thoroughly redesigned, to allow an almost continuous adjustment of the bridge decks, severely limiting the realignment times, in order to reduce traffic interruptions. A reduced number of interferometric lasers have been used, using rotating drums with mirrors individually preset to sweep the entire measuring field. The lifters, in their present version, should substitute the props, being used as active connections between pillars and decks, thus being able to support all traffic induced dynamic stresses in the vertical direction. The lifters have also been made sturdier eliminating all ball bearings in favour of teflon sheets. In addition, computer controlled lateral supports have been added to the system, allowing to move the deck horizontally while transmitting traffic or hearth-quake shocks to the pillars. On the top of each lifter an elastic interface bearing strain gauges will enable the measurement of tangential stresses as well as uneven distribution of the load, providing further information on the need of beams realignment.