LONG BEACH —Recording and evaluating how the new bridge responds during a seismic event is a critical part of ensuring its long-term safety and maintenance. To measure the impact of an earthquake, the new bridge will be a giant seismic sensor, fitted with 77 accelerographs to monitor and record its response during any ground motion. Information will pinpoint how the towers, columns, dampers, hinges and joints handle seismic energy.
Data from the accelerographs will be sent to the California Strong Motion Instrumentation Program in Sacramento where engineers and geologists around the world can analyze the new bridge’s performance to help improve earthquake resistance and recovery for other bridges, buildings and structures in active seismic zones across the globe.
When finished, the new bridge will offer seismic capabilities to withstand and quickly return to operation after large earthquakes, the types that occur once in a thousand years.
End Bents and Hinges
The point where the east and west approaches connect to the main span of the bridge is one of the bridges most intriguing areas. At these “end bents,” the column-supported approaches meet the cable-supported main span. These two types of structures will react different in an earthquake and flexible connections are a must .
Special joints designed in Germany, and built in the United States, will enable controlled-swivel movements in three directions (vertical, longitudinal, and lateral) at these junctions to compensate for movements between the adjacent structures. This will be the first application of this sophisticated joint for a bridge in California.
Additionally, between each section of the bridge road deck are expansion joints and hinges, allowing each section to move independently to avoid structural damage during major ground shaking.
Within the hinges are shear keys. Similar to an electrical fuse, shear keys are a sacrificial, replaceable element to absorb the bulk of seismic forces. At certain energy levels, they are designed to “trip” to release the force of the quake.
Atop each column are spherical bearings to enable a sliding movement between the superstructure (the bridge deck) and the substructure (the columns).