SEISMIC RETROFIT OF A 50-YEAR OLD BRIDGE IN LIMA WITH ISOLATORS: OPPORTUNITIES AND DIFFICULTIES

Herrera J.; Sueldo E. · World Conference on Earthquake Engineering proceedings (2024)

Resumen

Lima, Perú is located in a high seismicity area (PGA=0.45g) and is currently under a seismic gap of more than 275 years. Consequently, the use of seismic devices has been promoted for the construction of new bridges in the city, searching for continuous operation after an earthquake. However, a large majority of bridges were built more than 20 years ago and designed considering the transmission of the seismic force from the deck to the substructure allowing certain damage, not guarantying the operation after a major event. One of these structures is Huascar Bridge, built in 1968 and located in a main access road to Lima, its continuous operation is of vital importance for the city. In this paper a retrofitting proposal for this bridge is discussed with emphasis in the reduction of the seismic force transmitted to the substructure and the difficulties encountered in the adaptation of very old bridges to the new movement requirements. Huascar Bridge has a variable depth box section and presents 5 continuous spans. The spectral and time history analysis performed concluded that in its current configuration the substructure would not stand the flexural-compression and shear stresses caused by a major earthquake. A conventional retrofitting would be extremely invasive and costly while the replacement of elastomeric bearings for seismic isolators presented as the optimal solution that avoided the substructure intervention.However, for the intervention the main problem was the reduced existing space for the devices (around 100mm) given that the bearings replacement was not considered in the original design, This issue was solved selecting low height double pendulum isolators which in most cases required even a small grout plinth to accommodate to the existing height. Replacing the elastomeric bearings with double pendulum isolators accomplished the optimization of the bridge’s dynamic properties with reduction of the superstructure accelerations and shear forces transmitted to the substructure.The increase in deck displacement required the evaluation of border conditions resulting in several modification to the original design and joint type change adapted to the new movement requirements. A unconventional anchorage system was also developed to fix the new devices. As a conclusion, the possibility to seismic retrofit +50 year old bridges in Lima, Peru raises as a good option to secure the continuous operation of the more important roads after a major earthquake.