Effects of Near-Fault Ground Shaking on Sliding Systems
G. Gazetas, M.ASCE
1
; E. Garini
2
; I. Anastasopoulos
3
; and T. Georgarakos
4
Abstract: A numerical study is presented for a rigid block supported through a frictional contact surface on a horizontal or an inclined
plane, and subjected to horizontal or slope-parallel excitation. The latter is described with idealized pulses and near-fault seismic records
strongly influenced by forward-directivity or fling-step effects from Northridge, Kobe, Kocaeli, Chi-Chi, Aegion. In addition to the well
known dependence of the resulting block slippage on variables such as the peak base velocity, the peak base acceleration, and the critical
acceleration ratio, our study has consistently and repeatedly revealed a profound sensitivity of both maximum and residual slippage: 1
on the sequence and even the details of the pulses contained in the excitation and 2 on the direction + or - in which the shaking of
the inclined plane is imposed. By contrast, the slippage is not affected to any measurable degree by even the strongest vertical components
of the accelerograms. Moreover, the slippage from a specific record may often be poorly correlated with its Arias intensity. These findings
may contradict some of the prevailing beliefs that emanate from statistical correlation studies. The upper-bound sliding displacements
from near-fault excitations may substantially exceed the values obtained from some of the currently available design charts.
DOI: 10.1061/ASCEGT.1943-5606.0000174
CE Database subject headings: Sliding; Seismic effects; Ground motion; Symmetry; Asymmetry.
Introduction
Ground shaking in the close neighborhood of a rupturing seismic
fault may be affected by wave propagation effects known as “for-
ward directivity” and by tectonic deformations producing a per-
manent ground offset known as “fling step.” The former effect is
the outcome of the coherent arrival of seismic waves emitted
from a seismogenetic fault when its rupturing propagates toward
the site. It manifests itself with a single long-period high-
amplitude pulse occurring near the beginning of shaking, and ori-
ented perpendicularly to the fault Somerville 2000. The fling-
step effect is the outcome of the tectonic permanent deformation
of the earth in the proximity of the fault. It manifests itself in the
record with a static residual displacement, oriented parallel to the
fault strike with strike-slip earthquakes and perpendicular to the
fault with purely dip-slip normal or thrust earthquakes Abraha-
mson 2001.
Fig. 1a is a sketch, of a strike-slip event, portraying the ide-
alized “signatures” of the two phenomena on the fault-normal and
fault-parallel components of the displacement record. Fig. 1b
depicts two remarkable accelerograms, TCU-068 from Chi-Chi
1999 and Fukiai from Kobe 1995 exhibiting fling-step and
forward-directivity effects, respectively. The velocity time history
of TCU-068 contains a large pulse 2.6 m/s of huge duration
6.3 s, which is consistent with the permanent ground offset of
about 8 m that can be seen in the derived displacement record,
and which has actually been observed in the field. The derived
velocity time history of Fukiai contains several cycles with a
devastating maximum velocity step V 2.3 m / s. The destruc-
tive capacity of this quantity was first elaborated by Bertero et al.
1976.
A significant amount of research has been devoted to the two
phenomena, especially in the aftermath of the Northridge, Kobe,
Kocaeli, and Chi-Chi earthquakes. That research has so far fo-
cused: first, on identifying, interpreting, and mathematically rep-
resenting the effects of “directivity” and “fling” on the ground
motions Singh 1985; Somerville 2000,2003; Abrahamson 2001;
Makris and Roussos 2000; Mavroeidis and Papageorgiou 2003;
Hisada and Bielak 2003; Bray and Rodriguez-Marek 2004;
Haward et al. 2005; then, on developing empirical predictive
relationships for the parameter characterization of the directivity
or fling related pulses Somerville et al. 1997; Bray and
Rodriguez-Marek 2004; Xie et al. 2005; and finally, on assessing
the potential of directivity and fling pulses to inflict damage
in a variety of geotechnical and structural systems for example,
Bertero et al. 1978; Singh 1985; Hall et al. 1995; Gazetas 1996;
Kramer and Smith 1997; Iwan et al. 2000; Sasani and Bertero
2000; Makris and Roussos 2000; Alavi and Krawinkler 2000;
Jangid and Kelly 2001; Pavlou and Constantinou 2004; Shen
et al. 2004; Mavroeidis et al. 2004; Xu et al. 2006; Changhai et al.
2007.
The work presented here belongs in the latter category. It
summarizes studies on the effects of near-fault motions on two
idealized sliding systems: 1 a rigid block in contact with resting
on a horizontal base; 2 a rigid block resting on an inclined
plane, of angle Fig. 2. In both cases the contact between
structure and base is rigid-ideally plastic, obeying Coulomb’s fric-
tion law with a constant coefficient of friction, . The horizontal
or inclined base is subjected to parallel excitation, i.e., horizontal
motion in Case 1 and motion inclined at an angle in Case 2.
Furthermore, the effect of a simultaneous vertical acceleration
1
Professor, Laboratory of Soil Mechanics, National Technical Univ.,
Athens 15342, Greece corresponding author.
2
Ph.D. Student, Laboratory of Soil Mechanics, National Technical
Univ., Athens 15342, Greece.
3
Adjunct Lecturer, Laboratory of Soil Mechanics, National Technical
Univ., Athens 15342, Greece.
4
Ph.D. Student, Laboratory of Soil Mechanics, National Technical
Univ., Athens 15342, Greece.
Note. This manuscript was submitted on September 22, 2008; ap-
proved on June 10, 2009; published online on November 13, 2009. Dis-
cussion period open until May 1, 2010; separate discussions must be
submitted for individual papers. This paper is part of the Journal of
Geotechnical and Geoenvironmental Engineering, Vol. 135, No. 12,
December 1, 2009. ©ASCE, ISSN 1090-0241/2009/12-1906–1921/
$25.00.
1906 / JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING © ASCE / DECEMBER 2009
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