Vertical Response of Twelve Structures Recorded during the Northridge Earthquake

This paper summarizes the results of a study on vertical response of twelve instrumented structures recorded during the Northridge earthquake. The selected structures include buildings ranging in height from 2 to 14 stories, located within a distance range of 8 to 71 km from the causative fault of the Northridge earthquake. They include four steel buildings, five concrete structures and three base-isolated buildings. The recorded peak vertical structural accelerations are found to be larger than those at the base by a factor of 1.1 to 6.4. The identified lowest vertical frequencies of the structural members and systems of all the twelve structures are within the frequency range of 3.9 to 13.3 Hz (period range of 0.075 to 0.26 sec). For the structures located in the near-source region, this period range may correspond to a range of high vertical spectral accelerations.