Collapse risk of tall buildings in the Los Angeles basin – Conventional vs. CyberShake

Nenad Bijelic, Ting Lin, & Gregory Deierlein

In Preparation 2018, SCEC Contribution #8039

Limited data on strong earthquakes and their effect on structures poses one of the main challenges of making reliable risk assessments of tall buildings. For instance, while the collapse safety of tall buildings is likely controlled by large magnitude earthquakes with long durations and high low-frequency content, there are few available recorded ground motions to evaluate these issues. The influence of geologic basins on amplifying ground motion effects raises additional questions. Absent recorded motions from past large magnitude earthquakes, physics-based ground motion simulations provide an attractive alternative. This paper examines collapse performance of an archetype tall building at sites in the Los Angeles basin utilizing ground motions simulated as part of the Southern California Earthquake Center’s (SCEC) CyberShake project. Seismic demands of an archetype 20-story tall building are obtained using large datasets (~500,000 ground motions per site) of unscaled, site-specific simulated seismograms. Seismic hazard and risk from direct analysis of CyberShake simulated motions is contrasted with risk estimates obtained using ‘conventional’ approaches relying on recorded motions coupled with probabilistic seismic hazard assessments from the U.S. Geological Survey. Site hazards are compared in terms of conditional spectra and significant durations; opportunities and challenges involved with estimation of intensity measure targets from simulations are discussed. In terms of seismic demands, the two approaches yield similar estimates for a site in Los Angeles downtown, while being drastically different at a site where basin depth is the largest. Extent and sources of these discrepancies are investigated. Further, deaggregation of collapse risk is used to identify the relative contributions of causal earthquakes, linking building responses with specific seismograms and contrasting collapse risk with hazard.

Citation
Bijelic, N., Lin, T., & Deierlein, G. (2018). Collapse risk of tall buildings in the Los Angeles basin – Conventional vs. CyberShake. Bulletin of the Seismological Society of America, (in preparation).


Related Projects & Working Groups
Ground Motion Simulation Validation (GMSV) Technical Activity Group (TAG), Earthquake Engineering Implementation Interface (EEII)