‘Earthquake’ Category

Base Isolator – Triple Pendulum Bearing

Photo Credit: Enrique Pasta

Description Credit: Nicole Paul

Seen here is an installed Triple Pendulum Bearing as designed and manufactured by Earthquake Protection Systems in Vallejo, CA for Acapulco City Hall in Guerrero, Mexico. The Triple Pendulum Bearing is a type of seismic isolation system that has curved sliding surfaces, which effectively act as three pendulums. These pendulums can be separately optimized for different level earthquakes – small, moderate and severe. The properties of each pendulum are based on the bearing geometry and typically chosen in order to dramatically reduce the peak accelerations and reduce shear forces acting on the seismically isolated structure and its contents during earthquakes. This allows for performance-based design, where the structure is not only designed not to collapse, but to be occupied and resume normal functionality soon after the earthquake takes place. Such design is most commonly used for hospitals, airports, LNG tanks, and other critical structures.

Reduced Moment Steel Connection

Photo Credit: Alex Mead

Seen here is a fully braced moment connection in a hybrid steel and wood structure. After the 1994 Northridge, California and 1995 Kobe, Japan earthquakes, however, fully braced moment connections were determined to be inadequate in resisting the forces generated by earthquakes due to many failures observed in building inspections after the event. Now days, as a result of work done at the University of California at Berkeley and elsewhere, reduced moment beam connections were determined to be a solution. The reduced beam can be seen just to the left of the beam column connection. See here for a brief explanation of how reduced moment connections work.

Collapsed Building Port-au-Prince, Haiti

Photo Credit: Andrew Sisson

Seen here is a collapsed building in the capital city Port-au-Prince of Haiti following the January 2010 earthquake. It appears to have been a soft story collapse seeing the entire roof structure is mostly intact. Possible explanations of this could be weak concrete used in the columns or possibly too little steel reinforcement. Seeing this building was built in Haiti, lower construction quality is likely compared to countries like the United States, and lower code requirements exist, which unfortunately lead to a weaker building more susceptible to collapse.

Earthquake Retrofit of Parking Garage

Photo Credit: Alex Mead

The parking structure above is a perfect example of earthquake retrofitting a structure. The crisscrossed red members on the front of the structure were added after the completion of the building to increase the strength in the event of an earthquake. If you look closely the connections of the frame to the ground are pin connections. These pin connections literally are large plates with simple holes connected by a rod. These pin connections allow for rotation of the joint, but do not allow the frame to move up, down, or side to side apart from ground motion.