Concerning the 1994 Northridge earthquake…?
What was the main cause behind all the property damage (if the building were already supposed to be a resistant against earthquakes), and how were the buildings retrofitted to prevent such a tragedy in the future?
The main cause behind all the property damage to the buildings were the brittle failure in the welded connections. The beam to column connections were welded moment connections. Then as a result connections are being designed using yield line theory. I would imagine the use of just using angles and bolts added to the prior connections was used i order to retrofit the buildings.
http://nisee.berkeley.edu/northridge/mahin.html
HAITI EARTHQUAKE DAMAGE BUILDINGS.flv