Pounding of an 18-Story Building during Recorded Earthquakes

During the San Fernando Earthquake (1971), two of the three triaxial recording instruments placed in an 18-story steel building in Los Angeles recorded the impact with an adjacent reinforced concrete parking structure. This provided an excellent opportunity to evaluate the modeling of such an event using current computer programs (time step, structure damping, impact damping, and use of a gap element) to evaluate the effect of the impact on the strength demands and evaluate the design implications (necessary separation). Although only the base recorder worked during the Northridge Earthquake, it was possible to evaluate the computer modeling using the San Fernando data, and then use the model to evaluate the building behavior under the stronger Northridge Earthquake (1994). Results of the numerical model indicate an agreement with the extensive cracking identified by the results of a damage investigation following the Northridge Earthquake in the two moment resistant transverse frames of the steel building. Much of this damage in the lower 10 floors of the transverse frames was probably because of the impact with the adjacent parking structure at the fifth floor level. Damage in the upper portion is thought to be because of the increase response in the higher modes of vibration caused by the impact and horizontal setback of the building at the fifth level. DOI: 10.1061/(ASCE)ST.1943541X.0000541. (C) 2012 American Society of Civil Engineers.