Ambient vibration tests of a seven-story reinforced concrete building in Van Nuys, California, damaged by the 1994 Northridge earthquake

被引:88
作者
Ivanovic, SS
Trifunac, MD [1 ]
Novikova, EI
Gladkov, AA
Todorovska, MI
机构
[1] Univ So Calif, Dept Civil Engn, Los Angeles, CA 90089 USA
[2] Univ Montenegro, Dept Civil Engn, YU-81000 Podgorica, Montenegro, Serbia Monteneg
[3] Geopex Ltd, Raleigh, NC 27603 USA
关键词
full-scale testing; ambient vibration surveys; ambient vibration testing; Northridge earthquake; modal analysis; earthquake damage;
D O I
10.1016/S0267-7261(00)00025-7
中图分类号
P5 [地质学];
学科分类号
0709 ; 081803 ;
摘要
Results of two detailed ambient vibration surveys of a 7-story reinforced concrete building in Van Nuys, California, are presented. Both surveys were conducted after the building was severely damaged by the 17 January 1994, Northridge earthquake (M-L = 5.3, epicenter 1.5 km west from the building site) and its early aftershocks. The first survey was conducted on 4 and 5 February 1994, and the second one on 19 and 20 April 1994, about one month after the 20 March aftershock (M-L = 5.3, epicenter 1.2 km north-west from the building site). The apparent frequencies and two- and three-dimensional mode shapes for longitudinal, transverse and vertical vibrations were calculated. The attempts to detect the highly localized damage by simple spectral analyses of the ambient noise data were not successful. It is suggested that very high spatial resolution of recording points is required to identify localized column and beam damage, due to the complex building behavior, with many interacting structural components. The loss of the axial capacity of the damaged columns could be seen in the vertical response of the columns, but similar moderate or weak damage typically would not be noticed in ambient vibration surveys. Previous analysis of the recorded response of this building to 12 earthquakes suggests that, during large response of the foundation and piles, the soil is pushed sideways and gaps form between the foundation and the soil. These gaps appear to be closing during "dynamic compaction" when the building site is shaken by many small aftershocks. The apparent frequencies of the soil-foundation-structure system appear to be influenced significantly by variations in the effective soil-foundation stiffness. These variations can be monitored by a sequence of specialized ambient vibration tests. (C) 2000 Elsevier Science Ltd. All rights reserved.
引用
收藏
页码:391 / 411
页数:21
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