Time-Variant Modal Parameters and Response Behavior of a Base-Isolated Building Tested on a Shake Table

This paper presents the identification of the instantaneous modal properties and the experimental response of a full-scale, five-story base-isolated RC building tested on a shake table. A suite of earthquake motions of various intensities was applied to the building to progressively increase the seismic demand. The deterministic-stochastic subspace identification method is employed to estimate the variations of the modal properties of the building by employing a short-time windowing approach. The changes of the modal parameters during the seismic motions are tracked and analyzed. Observed and measured responses of the structure are analyzed and correlated with the variation of the identified modal parameters. The nonlinear behavior of the isolators generates the variation of the identified natural frequencies and equivalent damping ratios of the building, which change in agreement with the input motion intensity. A high correlation between the effective stiffness of the isolators and the instantaneous frequency of the first mode is found. The effective damping ratio of the isolation system and the instantaneous damping ratio of the fundamental mode of the building are highly correlated.

[1]  Edward Cohen,et al.  Minimum Design Loads for Buildings and Other Structures , 1990 .

[2]  L. V. D. Einde,et al.  DEVELOPMENT OF THE GEORGE E. BROWN JR. NETWORK FOR EARTHQUAKE ENGINEERING SIMULATION (NEES) LARGE HIGH PERFORMANCE OUTDOOR SHAKE TABLE AT THE UNIVERSITY OF CALIFORNIA, SAN DIEGO , 2002 .

[3]  Heki Shibata,et al.  Construction of a three–dimensional, large–scale shaking table and development of core technology , 2001, Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences.

[4]  Jonathan P. Stewart,et al.  Observed Behavior of Seismically Isolated Buildings , 1999 .

[5]  Carlo Rainieri,et al.  Influence of model order and number of block rows on accuracy and precision of modal parameter estimates in stochastic subspace identification , 2014 .

[6]  Rodrigo Astroza.  Vibration-Based Health Monitoring and Mechanics-Based Nonlinear Finite Element Model Updating of Civil Structures , 2015 .

[7]  Atsuo Kakehi,et al.  Full‐scale shaking table test for examination of safety and functionality of base‐isolated medical facilities , 2011 .

[8]  Joel P. Conte,et al.  System identification of a full‐scale five‐story reinforced concrete building tested on the NEES‐UCSD shake table , 2016 .

[9]  Guido De Roeck,et al.  One-year monitoring of the Z24-Bridge : environmental effects versus damage events , 2001 .

[10]  Mohammad Noori,et al.  System Identification of Base-Isolated Building using Seismic Response Data , 2005 .

[11]  Yozo Fujino,et al.  Long‐term seismic monitoring of base‐isolated building with emphasis on serviceability assessment , 2015 .

[12]  Kung-Chun Lu,et al.  System identification of mid‐story isolation building using both ambient and earthquake response data , 2013 .

[13]  Masayoshi Nakashima,et al.  Full‐scale shaking table test of a base‐isolated medical facility subjected to vertical motions , 2013 .

[14]  Marina Schroder,et al.  Structural Control Past Present And Future , 2016 .

[15]  Randall J. Allemang,et al.  A Correlation Coefficient for Modal Vector Analysis , 1982 .

[16]  Joel P. Conte,et al.  Full-Scale Structural and Nonstructural Building System Performance during Earthquakes: Part I – Specimen Description, Test Protocol, and Structural Response , 2016 .

[17]  Babak Moaveni,et al.  Deterministic-stochastic subspace identification method for identification of nonlinear structures as time-varying linear systems , 2012 .

[18]  Jianghui Geng,et al.  Recovering coseismic point ground tilts from collocated high‐rate GPS and accelerometers , 2013 .

[19]  Bart De Moor,et al.  Subspace Identification for Linear Systems: Theory ― Implementation ― Applications , 2011 .

[20]  Joel P. Conte,et al.  Full-Scale Structural and Nonstructural Building System Performance during Earthquakes: Part II – NCS Damage States , 2016 .

[21]  Mehmet Çelebi,et al.  Successful performance of a base‐isolated hospital building during the 17 January 1994 Northridge earthquake , 1996 .

[22]  Joel P. Conte,et al.  Predominant period and equivalent viscous damping ratio identification for a full‐scale building shake table test , 2017 .

[23]  Chih-Chen Chang,et al.  Recursive Combined Subspace Identification Technique for Tracking Dynamic Characteristics of Structures under Earthquake Excitation , 2016 .

[24]  Kazuhiro Matsuda,et al.  Performance of Seismic Protection Technologies during the 2011 Tohoku-Oki Earthquake , 2013 .

[25]  Joel P. Conte,et al.  Landmark Data Set from the Building Nonstructural Components and Systems (BNCS) Project , 2016 .

[26]  Satish Nagarajaiah,et al.  Response of Base-Isolated USC Hospital Building in Northridge Earthquake , 2000 .