Monograph records
https://feeds.library.caltech.edu/people/Wang-L-J/monograph.rss
A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenTue, 16 Apr 2024 14:28:50 +0000Processing of near-field earthquake accelerograms
https://resolver.caltech.edu/CaltechEERL:1996.EERL-96-04
Authors: {'items': [{'id': 'Wang-L-J', 'name': {'family': 'Wang', 'given': 'Luo-Jia'}}]}
Year: 1996
The Near-Field pulse-like velocity and displacement time histories associated with a strong earthquake can greatly affect a wide range of different types of structures [I]. The important long period components in NEAR-FIELD earthquake accelerograms, however, are normally eliminated or distorted by conventional data processing which is based on band-pass filtering; for example, using an Ormsby filter with a low frequency cut-off of 0.2-0.4 Hz.
A new data processing technique has been proposed by Iwan and Chen [2] to recover the long period components from NEAR-FIELD earthquake accelerograms. This technique is based on the inverse of the data recording and retrieving procedure, which includes appropriate instrument correction according to the instrument type, and baseline correction without band-pass filtering. It may be briefly summarized by the following steps:
I .Apply a least-mean-square linear fit to the uncorrected accelerograms to eliminate any uncertainty in the instrument centering.
2.Apply instrument correction to compensate for the fact that the transfer function of the transducer is not flat over the entire frequency band.
3.Integrate the instrument corrected acceleration time history to obtain a raw velocity time history, assuming zero initial velocity. A trapezoidal integration rule and a central difference differentiation scheme are used herein.
4.Apply a segmented polynomial baseline fit to the raw velocity time history to remove any non-physical trends. Since the ground velocity physically begins at zero and ends at zero, the baseline is fitted to the initial and final portions of the raw velocity time history. These two polynomials are connected by the lowest order (smoothest) polynomial baseline connection that continuously connects the initial and final portions of the accelerogram. The objective of baseline correction is to diminish the long-period noise or drift introduced in the signal recording and playback process.
5.Integrate the baseline corrected velocity time history to obtain a displacement time history, assuming zero initial displacement. Differentiate the baseline corrected velocity time history to obtain the corrected acceleration time history.
A Matlab package has been written to fulfill this data processing procedure. The package is also able to plot acceleration, velocity, and displacement time histories, to plot horizontal displacement particle trajectories, and to compute and plot Response Spectra and Drift Demand Spectra [3]. There are a total of 15 Matlab routines (functions) in this package. Sample Matlab programs are contained in Appendix 1. SAMPLELM and SAMPLE2.M demonstrate the usage of the routines. Appendix 2 lists all routines. A floppy disk containing all routines is included with this report.https://authors.library.caltech.edu/records/e0wfb-mfb25A Collection of processed near-field earthquake accelerograms with response and drift spectra
https://resolver.caltech.edu/CaltechEERL:1996.EERL-96-05
Authors: {'items': [{'id': 'Wang-L-J', 'name': {'family': 'Wang', 'given': 'Luo-Jia'}}, {'id': 'Gu-Q', 'name': {'family': 'Gu', 'given': 'Qun'}}, {'id': 'Iwan-W-D', 'name': {'family': 'Iwan', 'given': 'Wilfred D.'}}]}
Year: 1996
A number of particularly important earthquake accelerograms were measured by instruments that were located in the Near-Field region of several recent earthquakes. For a strike-slip or a thrust fault earthquake, this region is taken to be the area within and immediately adjacent to the surface trace or the surface prediction of the fault rupture plane and its extension to the earth's surface. Such accelerograms are termed near-field earthquake accelerograms. They possess the following features that differ from other earthquake accelerograms:
distinctive pulse-like time histories,
high peak velocities, and
high ground displacements.
These features of nm-field ground motion have not yet been well documented and are generally not considered in seismic design. It has been shown, however, that they can place very serious demand on structures located in the near-field region of an earthquake [I].
This report presents uniformly processed data for 12 near-field earthquake accelerograms obtained from four recent earthquakes. The results are presented in the following format:
time histories of acceleration, velocity, and displacement rotated to east-west, north-south, and maximum velocity directions,
horizontal particle trajectories,
Response Spectra for the east-west, north-south, and maximum velocity directions, and
Drift Demand Spectra for the east-west, north-south, and maximum velocity directions.
Tables 1-4 summarize the relevant information for the earthquakes and near-field accelerograms in this report. Plots of time histories, horizontal particle trajectories, Response Spectra and Drift Demand Spectra are presented in the figures following Table 4.
All accelerograms were uniformly corrected using the processing scheme developed by Iwan and Chen [2]. This includes appropriate instrument correction according to the instrument type and baseline correction without band-pass filtering.
The time history, Response Spectrum and Drift Demand Spectrum for the north-south component of the El Centro (ELC) accelerogram obtained in the 1940 Imperial Valley earthquake are included in Appendix I for purposes of comparison. As shown by their response and Drift Demand Spectra, all 12 earthquake accelerograms featured in this report place much higher demands on the response and interstory drift of structures than does the standard ELC ground motion. This suggests that the widely used ELC accelerogram may be inadequate for some design purposes.
All data processing, response and Drift Demand Spectral computations, and plotting were performed using a Matlab-based package [4]https://authors.library.caltech.edu/records/72grz-zrp91Active interaction control for civil structures
https://resolver.caltech.edu/CaltechEERL:1997.EERL-97-04
Authors: {'items': [{'id': 'Wang-L-J', 'name': {'family': 'Wang', 'given': 'Luo-Jia'}}]}
Year: 1997
This thesis presents a civil engineering approach to active control for civil structures. The proposed control technique, termed Active Interaction Control (AIC), utilizes dynamic interactions between different structures, or components of the same structure, to reduce the resonance response of the controlled or primary structure under earthquake excitations. The primary control objective of AIC is to minimize the maximum story drift of the primary structure. This is accomplished by timing the controlled interactions so as to withdraw the maximum possible vibrational energy from the primary structure to an auxiliary structure, where the energy is stored and eventually dissipated as the external excitation decreases. One of the important advantages of AIC over most conventional active control approaches is the very low external power required.
In this thesis, the AIC concept is introduced and a new AIC algorithm, termed Optimal Connection Strategy (OCS) algorithm, is proposed. The efficiency of the OCS algorithm is demonstrated and compared with two previously existing AIC algorithms, the Active Interface Damping (AID) and Active Variable Stiffness (AVS) algorithms, through idealized examples and numerical simulations of Single- and Multi-Degree-of Freedom systems under earthquake excitations. It is found that the OCS algorithm is capable of significantly reducing the story drift response of the primary structure. The effects of the mass, damping, and stiffness of the auxiliary structure on the system performance are investigated in parametric studies. Practical issues such as the sampling interval and time delay are also examined. A simple but effective predictive time delay compensation scheme is developed.https://authors.library.caltech.edu/records/7tjsh-01n15