Nonlinear Modeling of High-Rise Buildings Subject to Long-Period Ground Motion

Lauren M. Santullo, Ahmed E. Elbanna, & Setare Hajarolasvadi

Published August 15, 2018, SCEC Contribution #8632, 2018 SCEC Annual Meeting Poster #005

High rise buildings are particularly susceptible to long-period earthquake ground motion since the maximum displacement of the structure may approach or even exceed the peak ground displacement. Much of the currently used accelerometer data is of relatively lower magnitude earthquakes, with magnitudes of around 6 to 7 on the MMS. In contrast, large-magnitude earthquakes are expected in major metropolitan areas based on paleo-seismic records as well as numerical simulations. Areas such as Los Angeles, San Francisco, and Seattle have numerous high-rise buildings that might be affected. For an M8 earthquake, expected for example on San Andreas fault, the ground displacements may reach several meters. The response of tall structures, and in particular their structural stability, may be compromised in these cases due to complex nonlinear and second-order effects.

To simulate the effect of a large seismic event on a high-rise structure, time history analyses are performed on a 100-story, four-bay structure. The structure considered is a multi-story multi-bay steel frame with vertical loads computed based on representative concrete floors. The structure has a first natural period of about 6.7 seconds- above the common threshold for long-period structures- and used proportional damping values of 2% and 5% for a realistic scenario. A static pushover and elastic time history analyses were carried out. For the pushover, the top of the structure was displaced 6 meters to simulate a larger earthquake. Accelerometer data for the 1994 Northridge and 1992 Landers earthquakes were scaled so that the peak ground displacement was around 6 meters, a magnitude of displacement which is expected in a future San-Andreas earthquake. Preliminary results based on the elastic scaled time history analyses suggest an increase in the maximum top displacement, above the peak ground displacement, and a significant increase in the base moment pointing towards a possible loss of stability if the foundation is not properly designed. Preliminary results from the inelastic analysis suggest pervasive development of plastic hinges in the superstructure. Future work will focus on generating proper ground motion scenarios based on kinematic or dynamic earthquake models and nonlinear site response analysis. A variety of structural systems and layouts will also be considered to investigate the structural vulnerability landscape in a future mega-earthquake.

Key Words
High rise building, long period structure, mega earthquake, second order effects

Citation
Santullo, L. M., Elbanna, A. E., & Hajarolasvadi, S. (2018, 08). Nonlinear Modeling of High-Rise Buildings Subject to Long-Period Ground Motion. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Engineering Implementation Interface (EEII)