Constructing and evaluating generalized models for a base‐isolated structure. Issue 11 (3rd September 2018)

• Record Type: Journal Article
• Authors: Brewick, Patrick T.; Johnson, Erik A.; Sato, Eiji; Sasaki, Tomohiro
• Is Part Of: Structural control and health monitoring. Volume 25:Issue 11(2018)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-09-03
• Subjects: base isolation -- dynamic testing -- full‐scale structures -- modal parameters -- seismic excitation -- subspace identification; Structural engineering -- Periodicals; Structural control (Engineering) -- Periodicals; Automatic data collection systems -- Periodicals; Detectors -- Periodicals; 624.17
• DOI: 10.1002/stc.2243
• Languages: English
• ISSNs: 1545-2255

Abstract

Summary: Full‐scale dynamic testing and earthquake engineering experiments are often costly, yet they are vital for advancing the understanding of the complex interactions between seismic protective systems and structural responses. E‐Defense (a part of the Japan's National Research Institute for Earth Science and Disaster Resilience) constructed and tested a four‐story reinforced‐concrete base‐isolated building to study, among other things, how different anti‐seismic devices in the isolation layer of a building improve its response. This structure was subjected in August 2013 to a series of tests, including random ground motions and simulated earthquakes. Analyzing the acceleration responses from these random excitations forms the first step in identifying the dynamic characteristics of this test structure. The advanced numerical algorithm for subspace state‐space system identification (N4SID), from the family of subspace identification methods, is used to estimate the nominal modal parameters of this structure for both input–output and output‐only models. These models are then evaluated for their generalizability by using them to predict the response of the structure to both random excitations and seismic inputs. Additional identification is performed using responses recorded during simulated earthquakes, and the recovered modal parameters are compared against the nominal parameters to analyze how the building's isolation system impacts its response. The results indicate that the interaction between seismic excitation and the base‐isolation layer has both local and global structural effects. Locally, the modes most directly associated with isolation layer displacements experience, as expected, significant decreases in frequency and increases in damping; globally, the modes with more substantial displacements across the superstructure also experience decreases in frequency and increases in damping but at a greatly reduced scale. Further, even in the presence of seismic forces large enough to induce nonlinear restoring forces in the isolation layer, the relative changes in identified modal parameters for the superstructure associated modes remained modest.