Type tests of the seismic isolators for Biobio bridge

Last week the type tests of the seismic isolators for the railway bridge at Biobio river in Chile were carried out. This bridge is being constructed by SACYR on behalf of EFE Trenes de Chile, and MC2 has been part of the modified design, proposing, among others, the isolation system. These tests were carried out at SISMALAB and our colleague Guillermo Blanco Fernández, in charge of the design of the isolation system, could attend. The 146 insulators of this bridge, type LRB, are being manufactured by SISMOTECH and tested at SISMALAB’s facilities in Italy.

Lead Rubber Bearings (LRB) are dynamic control devices consisting of a high-rise reinforced rubber bearing with a lead cylinder placed in its core. The isolation effect is achieved thanks to the low transverse stiffness of the rubber, which reduces the energy introduced by the earthquake by causing the structure to vibrate with higher periods. Additionally, the high initial stiffness of lead and its low yielding stress allow energy dissipation through hysteretic mechanisms, reaching very high damping ratios.

Tests performed are showing a good agreement between the real performance of the insulators and the theoretical values. Damping ratios of up to 28% are being achieved.

Many isolators are already on site, where the construction of the composite deck bridge is progressing at a good pace. All the substructure elements and almost half of its 62 spans have been completed. Our colleagues Miguel Rupérez Astarloa and Alberto Curbelo Diaz, after the development of the project, continue with the technical assistance to SACYR.
We want to thank SACYR for having placed their trust in MC2 and OPH for this project, and Paolo Scotti (SISMOTECH) and Ciro Caramia (SISMALAB) for having received so well our colleague Guillermo Blanco Fernandez in their facilities during these days.